Development of Gluten-Free Coated Chicken Liver, Examination of the Effects of Spices and Cooking Methods on Product Quality Characteristics and Heterocyclic Aromatic Amine (HCA) Compounds

Abstract

The objectives of this study were to develop a coated gluten-free chicken liver product that could be consumed by a wide range of consumer groups and to investigate the quality characteristics and heterocyclic aromatic amine (HCA) compounds. The effects of three different formulations (thyme, turmeric, and control) and two different cooking methods (deep-frying and oven cooking) on the physical, chemical, microbiological, and sensorial characteristics and HCA compounds of samples, which were stored at −20 °C for 60 days, were investigated. TBARS values were lower in the oven-cooked samples than in the deep-fried samples at the end of the storage, with turmeric proving most effective (p < 0.05). TMAB and total HCA were lower in thyme and turmeric-added samples than in the control samples (p < 0.05). The total HCA content of the deep-fried and oven-cooked samples decreased by 14.42% and 13.20% with the addition of thyme and by 18.75% and 23.35% with the addition of turmeric, respectively. The oven-cooked sample with turmeric was stored for 60 days without any significant changes in the color, flavor, and overall acceptance according to the beginning of the storage (p > 0.05). In conclusion, gluten-free oven-cooked turmeric-added coated chicken liver can be a healthy food alternative in the market.

1. Introduction

Chicken liver is one of the most consumed and nutritious offal meats and edible chicken by-products. It has a similar protein content as that of muscle meat and is also a rich source of vitamins A, B12, and minerals [1]. It is notable that high levels of highly bioavailable iron (15–25%) are found in chicken liver. Nevertheless, it is important to consider that chicken liver has a relatively short shelf life due to rapid oxidation as a result of the presence of endogenous enzymes and metals [2]. In traditional cuisines worldwide, chicken liver is cooked with other ingredients such as fried liver and liver pate [3], but often discarded of as waste [4]. The global production of chicken liver exceeds 4.56 million metric tons per annum, thereby contributing to disposal issues that are associated with this [4]. The development of food products containing offal could be part of the solution to the upcoming demand for animal protein. It is evident that the utilization of edible animal by-products for human consumption has diminished throughout the 21st century [5]. Therefore, considering the high nutritional value of chicken liver, there is a need to evaluate it by offering it for sale in different forms that can be consumed with pleasure by more consumer groups, especially young people who are accustomed to fast food.

Coated meat products are a popular and widely consumed fast food and are also offered for sale as ready-to-eat products in the markets. Nevertheless, the deep-fat-frying process is applied to coated meat products. It is unfortunate that substantial quantities of oil are absorbed by the products during the process of deep-frying, with the range being between 10 and 40%, leading to accelerated lipid oxidation. This process can lead to an increase in calorie intake and potentially detrimental health effects [6,7]. Oz and Yuzer [8] reported that the total HCA content was significantly higher in deep-fried turkey breast (52.34 ng/g), compared to that of oven-cooked turkey breast (44.74 ng/g).

HCAs, a type of contaminant from cooking, have strong carcinogenic and mutagenic properties and are widely present in protein-containing food products [9]. As a result of studies, it is emphasized that the concentrations of HCA compounds depend upon the type and quantity of meat, the fat content, precursors in the meat, cooking time, the duration and temperature of the cooking process, type of oil used for cooking, and the pre-treatments applied [10]. Since HCAs have been conclusively proven to be hazardous to human health, research is ongoing to develop methods that can prevent or reduce the formation of these compounds during the cooking of meat and meat products [11,12]. The formation of HCA is a redox reaction, and the presence of antioxidants has been demonstrated to have the capacity to reduce the number of HCAs formed [13]. Antioxidant substances have recently been incorporated into a growing number of food products, including meat, as a means of mitigating human exposure to detrimental compounds generated during cooking processes [14,15]. Natural antioxidants contained in spices and herbs have received major consideration as possible inhibitors against the mutagenic HCAs formed in heat-treated meats [16].

Celiac disease is a specific immune response that is caused after the consumption of gluten present in wheat, rye, barley, and related grains from genetically predisposed patients [17]. Celiac patients or individuals with a gluten intolerance should avoid the consumption of foods containing gluten. Nevertheless, gluten is a protein that is widely used in many areas of the food industry, including the production of meat products, because of its properties. The contemporary market offers celiac patients a variety of gluten-free products [18]. Given that approximately one-third of American consumers avoid gluten, it is estimated that the market for gluten-free products was valued at 6.4 billion USD in 2020 and is projected to reach 11 billion USD by 2026 [19]. These data are considerably higher than those coming from the purchases of individuals who have been clinically diagnosed with celiac disease, which accounts for only 1% of the global population. This indicates that a large number of people are following a gluten-free diet of their own volition, believing that it is a healthier option. According to a survey, 30% of adult Americans consider gluten to be a risky ingredient. Consequently, individuals are actively trying to limit or avoid gluten in their diets [20]. Furthermore, of new product introductions in 2020, 6.5% bore the gluten-free claim, which is the third most popular claim behind ‘kosher’ and ‘low allergen’ or ‘no/reduced allergen’ [19]. According to the Market Data Forecast 2024 [21], the global market for gluten-free meat substitutes is projected to reach USD 4.97 billion by 2029. However, it is observed that gluten-free meat products with high nutritional value offered for sale are very limited.

The demand for gluten-free but tasty and easy-to-prepare healthy meat products and the possibility of increasing the consumption of chicken liver with high nutritional value by processing it into different products constituted the starting point of this research. It has been observed that there is a gap in the literature concerning the development of gluten-free meat products with high nutritional value and the detailed examination of the properties and HCA compounds contents of these products together with the effects of the cooking methods applied. Therefore, based on the above-mentioned issues, the aim of this study was to develop chicken liver, one of the by-products of the chicken processing industry with high nutritional value, as a coated gluten-free product that will be consumed more by consumers, and also, to investigate the effects of thyme, turmeric, and cooking methods (deep-frying and oven cooking) on the quality characteristics and HCA compounds of this new product in order to maintain its characteristic of being a healthy product.

2. Materials and Methods

2.1. Materials

The fresh raw chicken livers (Banvit A.S.), salt, spices (black pepper, cumin, thyme, and turmeric), sunflower oil, eggs, buckwheat, and corn flour were purchased from a supermarket in Izmir, Turkiye. In this study, a single chicken liver was divided into two pieces and 600 half livers were used; these livers were obtained from 300 chickens. Chicken livers were brought to the Ege University Food Engineering Department in the cold chain.

2.2. Coated Chicken Liver Production

During the preparation of the raw material, chicken livers were separated from the fat tissues and a single chicken liver was divided into two pieces. Within the scope of the developed product formulation, all chicken liver samples were thoroughly mixed with salt (1.5%), black pepper and cumin (3.5%) based on liver weight. Then, the samples were divided into three groups, i.e., sample groups containing thyme or turmeric (1–2%) and a control group without thyme or turmeric (

Table 1. Experimental design of coated chicken liver production.

Sample	Cooking Methods		Formulations
	Deep-Fat Frying	Oven	Salt	Black Pepper	Cumin	Thyme	Turmeric
FC	✓		✓	✓	✓
FTH	✓		✓	✓	✓	✓
FTU	✓		✓	✓	✓		✓
OC		✓	✓	✓	✓
OTH		✓	✓	✓	✓	✓
OTU		✓	✓	✓	✓		✓

FC: deep-fried sample group containing salt, pepper, and cumin, FTH: deep-fried sample group containing salt, pepper, cumin, and thyme, FTU: deep-fried sample group containing salt, pepper, cumin, and turmeric, OC: oven-cooked sample group containing salt, pepper and cumin, OTH: oven-cooked sample group containing salt, pepper, cumin, and thyme, OTU: oven-cooked sample group containing salt, pepper, cumin, and turmeric.

). Chicken livers mixed with the spice blends prepared according to the experimental design were kept at 4 °C for 20 min. No synthetic additives were used in the production of coated chicken livers. Considering the color and the flavor of the products, two types of gluten free flours, buckwheat and corn flours, were selected for the coating process of the samples. Buckwheat flour was chosen for the pre-dusting due to its high nutritional value, widespread availability, and low cost. Corn flour was used on the outside, as it was thought to create a texture similar to that of rusk and to give the yellowish color expected in coated products. According to the coating processing technique, first of all, chicken liver samples were coated with buckwheat flour (predusting—3 s), then dipped in a beaten whole egg (battering—3 s), and finally coated with corn flour (breading—5 s), respectively. After the breading was completed, the chicken livers were kept for 15 min at 4 °C for better adhesion of the coating. The combination of various formulations in the blend is divided into two groups based on the distinct cooking methods (3 × 2 = 6).

2.3. Methods of Cooking and Experimental Setup

In this study, two different cooking methods were applied to the coated chicken liver samples, including deep-fat frying and oven cooking. The cooking parameters for the samples were determined by pre-tests based on a minimum internal temperature of 75 °C and sensorial properties in terms of appearance and flavor. Coated chicken liver samples were fried by immersing in sunflower oil in a programmable deep fat fryer (Felix chips, Model FL 269, Type ZG-01A, 1200 watts, China) set at 180 °C for 1.5 min or cooked in a preheated electrical oven (Arçelik-MD 1300, Bolu, Turkey) at 180 °C for 25 min (Table 1). After the cooking processes, end product samples were cooled to room temperature and filled into polypropylene packaging. Then, they had been stored at −20 °C for 60 days. The samples were thawed at 4 °C for 16 h before periodic storage analysis.

2.4. Analysis

The proximate composition, total iron analysis, and pH measurements were performed on the raw chicken liver used in the production of coated chicken liver samples. During the production of coated chicken liver samples, temperature measurements were performed. The proximate composition, pH, cooking loss, coating pickup, color measurement, texture profile, DPPH free radical scavenging activity, thiobarbituric acid reactive substances (TBARSs), total mesophilic aerobic bacteria (TMAB), HCA analysis, and sensory evaluation were performed on cooked coated chicken livers. During storage at −20 °C for 60 days, pH, color measurement, texture profile, TBARS, TMAB, and sensory analyses were performed on samples.

2.4.1. Proximate Composition

The proximate composition analysis was performed on raw chicken liver and coated liver samples. The moisture and ash content of chicken liver samples were measured in accordance with AOAC [22] procedures. The fat content was determined by using the soxhlet extraction method, as suggested by AOAC [23]. The protein content was determined by the Kjehdal method, according to [24].

2.4.2. Total Iron

The total iron of raw liver samples were detected according to [25,26] using atomic absorption spectroscopy (Analytik Jena AG 07745, Jena, Germany).

2.4.3. pH

A total of 10 g of the raw chicken liver sample was homogenized with 100 mL of distilled water using an Ultraturrax (IKA, T18 basic, Wilmington, NC, USA). The pH value of the samples were determined using a pH meter (Inolab, WTW Series pH 7110, Weilheim, Germany) equipped with an electrode (WTW SenTix^® 81, Weilheim, Germany) [27].

2.4.4. Temperature Measurements

After the cooking processes were completed with the determined parameters, surface and internal temperature measurements of 5 different coated chicken liver samples were taken from each sample group. Surface temperature measurements of the coated chicken liver samples at two different points on both surfaces were made with the Testo 830-T1 infrared thermometer (Testo SE & Co. KGaA, Titisee-Neustatd, Germany). Internal temperature measurements of samples were controlled by a Testo 175-T3 temperature recorder (Testo SE & Co., KGaA, Titisee-Neustatd, Germany) and the Testo probe directly into the sample. After the probe was inserted into the samples, a response time of 10 s was allowed for the temperature to reach a constant value.

2.4.5. Cooking Loss

The percentage of cooking loss was determined by calculating the weight differences of the samples before and after cooking. In the coated samples, the post-cooking weight includes the sum of the meat and coating material [28].

2.4.6. Coating Pickup

The coating pickup of samples was evaluated using the following equation [29].

[(weight after battering − weight before battering)/weight before battering] × 100

(1)

2.4.7. Color Measurement

The color measurement of the coated chicken liver samples was carried out via HunterLab Colorflex (CFLX 45–2 Model Colorimeter, HunterLab, Reston, VA, USA). The instrument was calibrated each time with black glass and a white tile for correction prior to measurement. Color measurements were taken on the outer surfaces of the cooked coated samples. Four readings were recorded for each sample, and three samples were examined for each sample group [30]. The color values of the samples were obtained in accordance with the CIE L*, a*, and b* values. Among these values, L* represents brightness, a* represents green/red, and b* represents blue/yellowness.

2.4.8. Texture Profile Analysis

The texture profile analysis of cooked coated chicken liver samples was conducted using a texture analyzer (TA-XT2 Plus, Stable Micro Systems, Surrey, UK). A cylindrical plate (20 cm diameter) and 5 kg load cell were utilized for this purpose.

The sample was compressed twice, with a 5 s delay between landings, and a distance of 5 mm. (Pre-test speed: 1.0 mm s⁻¹; test speed: 5.0 mm s⁻¹; post-test speed: 5.0 mm s⁻¹). The results were presented as the mean of 10 repeated runs for each of the applications. The sample’s hardness, cohesiveness, springiness, gumminess, chewiness, and resilience characteristics were analyzed.

2.4.9. DPPH Free Radical Scavenging Activity

The antiradical activity of the cooked coated chicken liver samples was determined by the DPPH (2,2-diphenyl-1-picrylhydrazil) method, according to [31]. Measurements were made at the 517 nm wavelength of the spectrophotometer (Cary 60, UV-Vis Spectrophotometer, Agilent Technologies, Penang, Malaysia).

2.4.10. TBARS

The fat oxidation of cooked coated chicken liver samples was measured according to the method described by [32]. Sample absorbances were measured spectrophotometrically (Cary 60-UV-Vis Spectrophotometer, Agilent Technologies, Penang, Malaysia). Results were expressed as 2-thiobarbituric acid reactive substances (TBARSs) as mg malonaldehyde (MDA)/kg sample.

2.4.11. Total Mesophilic Aerobic Bacteria (TMAB)

A total of 10 g of cooked coated chicken liver samples were homogenized for 1 min at a standard speed with 90 mL of peptone water (PW, 0.1% (w/v), pH 6.3–6.7, Merck KGaA, Darmstadt, Germany). Plate Count Agar (pH 7.0 ± 0.2, Merck KGaA, Darmstadt, Germany) was inoculated according to the pour plate method and the petri dishes were incubated for 48 h at 35 °C for the total mesophilic aerobic bacteria count [33].

2.4.12. Heterocyclic Aromatic Amine (HCA) Analysis

Chemicals

The following HCA standards were purchased from Toronto Research Chemical (Toronto, ON, Canada): IQ (2-amino-3-methylimidazo[4,5-f]quinoline), MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline), 4,8-DiMeIQx (2-amino-3,4,8-trimethylimi-dazo[4,5-f]-quinoxaline), PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine), and harman (1-methyl-9H-pyrido[3,4-b]indole). Norharman (9H-pyrido[3,4-b]indole) was purchased from Sigma (Switzerland). Methanol, acetonitrile, acetic acid, and ammonium hydroxide were purchased from Merck (Germany), high-performance liquid chromatography (HPLC) grade. Purified water was obtained from a water purification system, Zeneer Power I (Water Purification System, Human Corporation, Seoul, Republic of Korea, 0.2 µm Capsule Filter HMC-DPL-S).

Extraction of Heterocyclic Aromatic Amines

The extraction and purification of HCAs were determined according to [34]. A total of 4 g of cooked coated chicken liver sample was used. The extraction and analyses were determined in duplicate.

Chromatographic Conditions

The extract was analyzed with a Diode Array Detector (DAD), Fluorescence detector, and colon (Poroshell 120 EC-C18 4.6 × 150 mm, 4 μm). MeIQx, 4,8DiMeIQx, and IQ compounds were detected by DAD detector (Agilent Serial No: DEAC612736). The IQ was studied at 254 nm; MeIQx and 4,8-DiMeIQx were measured at 263 nm. The mixture of acetic acid/methanol/acetonitrile/water/ (2/8/14/76 v/v/v/v) at pH 5.0 (adjusted with ammonium hydroxide 25%) was used as mobile phase A, while acetonitrile (100%) was used as mobile phase B. The flow rate was 0.3 mL/min for the first 35 min and was then changed to 1 mL/min. The flow rate was again 0.3 mL/min at the 49th minute and was constant until the end of the analysis. The injection volume was 20 µL. The run time analysis was 55 min. A gradient program (0–20 min 100% A, 20–34 min 70% A, 34–49 min 0%A, and 49–55 min 100% A) was used. Harman, norharman, and PhIP compounds were detected by fluorescence detectors at 340 nm and 370 nm as excitation and emission wavelengths, respectively. A total of 0.5 M ammonium acetate was used as mobile phase A, while methanol (100%) was used as mobile phase B at a flow rate of 0.5 mL/min. The injection volume was 15 μL. The run time analysis was 30 min. A gradient program (0–10 min 90% A, 10–15 min 75% A, 15–20 min 50% A, 20–22 min 0% A, and 25–30 min 90%A) was used. The retention time of unknown peaks in the sample chromatogram was determined by comparison with reference standards used to identify HCAs. The number of HCAs were calculated as ng/g cooked coated chicken liver samples.

LOD, LOQ, and Recovery of HCAs

The analysis methods for the HCAs were validated in terms of limits of detection (LOD), limit of quantification (LOQ), correlation coefficients (R²), and recovery (%). The LOD and LOQ were calculated based on signal to noise ratios of 3 and 10, respectively. The quantification of the HCAs was based on external calibration. The calibration curves were established from the known concentrations. Recovery rates for the different HCAs in the samples were determined by the standard addition method [35]. The regression coefficients (R²) for the standard curves were greater than 0.99 for all the HCAs identified in this study.

2.4.13. Sensory Evaluation

The sensory evaluation of the coated chicken liver samples was carried out by at least 10 untrained panelists, consisting of graduate students at the sensory evaluation laboratory equipped with individual ceiling lighting in individualized booths, in accordance with the International Organization for Standardization [36] at the Ege University Food Engineering Department. A nine-point hedonic scale was used (9—extremely likeable, 1—extremely dislikeable). After the cooking processes, coded samples with 3-digit randomized numbers were provided to each panelist in plates immediately with bread and water. The samples were presented to the panelists in a random order and evaluated in terms of appearance, color, flavor, texture, and overall acceptance [37]. During storage, thawed samples were presented to the panelists after being heated in an electric pan (King A.Ş., Model No: K 5026 Type ZG-01A, 1500 watts, Istanbul, Turkey) for 2 min on each side.

2.4.14. Statistical Analysis

The effect of different spices and different cooking methods on physical, chemical, and sensory characteristics and HCA compounds were determined using a one-way ANOVA. Differences among the means were compared using Duncan’s Multiple Range test. A significance level of p < 0.05 was used for all evaluations. The data were analyzed using the “Scientific Package for Social Sciences” IBM SPSS software version 26 package program [38]. The paired T-Test method was applied in paired comparisons. The values were given in terms of mean values and standard error in tables. The interaction effects of spice type, cooking method, and storage period on color, texture profile analysis, TBARS, TMAB, HCA, and sensory evaluation were determined via a significance level of p < 0.05. The entire trial was replicated twice.

3. Results and Discussion

3.1. Proximate Composition, pH Value, and Iron Content of Raw Chicken Liver

The proximate composition of raw chicken liver has been determined as follows; moisture content 73.70 ± 0.25%, protein content 20.52 ± 0.63%, fat content 3.55 ± 0.51%, and ash content 1.45 ± 0.06%. In accordance with these results, the moisture content of raw chicken liver was determined to be 75.72% [39] and the ash content was detected to be 1.17% [40]. Abu-Salem and About Arab [41] reported the moisture, protein, fat, and ash contents of raw chicken liver as 66.80%, 24.60%, 6.00%, and 1.40%, respectively.

The pH value of raw chicken liver was determined to be 6.64 ± 0.07. In a study, the pH of normally colored chicken livers (6.38) was significantly higher than that of abnormally colored chicken livers (6.18). The researchers reported that this was due to the fact that the chickens from which abnormally colored chicken livers were obtained were exposed to more stress, which caused glycolysis to accelerate, leading to a further decrease in pH [40]. It was observed that the pH values measured in normal-colored chicken livers in this study were closer to the pH values in the present study.

The iron content of raw chicken liver was detected to be 47.03 ± 4.43 μg/g. The liver is a major systemic store of iron. Iron is bound by ferritin as a ferric complex in a protein shell. Ferritin is the major intracellular storage protein found in all cells, with the highest concentrations in liver, spleen, and bone marrow [42]. One study reported that the iron content of chicken liver was 69.933 μg/g [40]. The reason why the iron content of chicken liver in this study was higher than that found in the present study is predicted to be due to differences in the feeding regimes of chickens.

3.2. Proximate Composition and pH Values of Coated Chicken Liver Samples

The effects of spices and cooking methods on the proximate composition and pH values of the coated chicken liver samples are presented in

Table 2. Proximate composition and pH values of coated chicken liver samples.

Sample	Moisture (%)	Protein (%)	Fat (%)	Ash (%)	pH
FC	58.89 ± 0.40 c	20.54 ± 0.28 a	15.51 ± 0.19 b	2.17 ± 0.07	6.67 ± 0.04 c
FTH	58.35 ± 0.57 bc	20.58 ± 0.30 a	15.98 ± 0.41 b	2.21 ± 0.09	6.53 ± 0.02 a
FTU	59.15 ± 0.34 c	20.71 ± 0.16 a	15.59 ± 0.29 b	2.22 ± 0.03	6.76 ± 0.02 d
OC	56.53 ± 0.23 a	21.50 ± 0.18 b	4.51 ± 0.05 a	2.29 ± 0.03	6.61 ± 0.01 b
OTH	57.50 ± 0.45 ab	21.59 ± 0.13 b	4.68 ± 0.06 a	2.32 ± 0.03	6.55 ± 0.02 a
OTU	58.53 ± 0.51 bc	21.73 ± 0.21 b	4.56 ± 0.04 a	2.33 ± 0.01	6.65 ± 0.01 bc

Results are given as mean ± standard error. a–d: Different letters used in the same column indicate that the difference between the mean values is statistically significant (p < 0.05). FC: deep-fried sample group containing salt, pepper, and cumin, FTH: deep-fried sample group containing salt, pepper, cumin, and thyme, FTU: deep-fried sample group containing salt, pepper, cumin, and turmeric, OC: oven-cooked sample group containing salt, pepper, and cumin, OTH: oven-cooked sample group containing salt, pepper, cumin, and thyme, OTU: oven-cooked sample group containing salt, pepper, cumin, and turmeric.

. The incorporation of thyme and turmeric into the formulation of the samples did not demonstrate a significant impact on the moisture content among the deep-fried samples (p > 0.05). However, the addition of turmeric caused an increase in the moisture content of the oven-cooked samples (p < 0.05). Studies have reported that turmeric powder protects membrane integrity, increases the water retention of muscle tissue, and reduces cooking loss due to its strong antioxidant activity [43].

The moisture content of the oven-cooked control sample was found to be lower than that of the deep-fried samples (p < 0.05). Similarly, in a study, it was reported that deep-fried chicken nuggets had the highest moisture content as compared to those cooked in a conventional oven and microwave oven [44]. In the present study, during oven cooking, contact of the sample surfaces with air and a longer cooking time compared to deep-fat frying resulted in dry crust formation and a lower moisture content in the samples. As reported by Varela et al. [44], the moisture loss was more pronounced in the outer layers and crust formation is influenced by a combination of water migration and other physical and chemical phenomena that occur during the cooking process.

The addition of thyme and turmeric to the sample formulations did not cause a significant difference in protein, fat, and ash contents of the samples (p < 0.05) (Table 2). Moreover, the cooking method was detected as significant on the protein and ash contents of the samples. it was observed that while the protein content of oven-cooked samples was found to be statistically higher than those of the deep-fried samples, the fat content of the oven-cooked samples was detected as lower than that of the deep-fried samples (p < 0.05). One of the reasons for this situation is that the oven-cooked samples lost more moisture than the deep-fried samples; therefore, the proportional protein value of the oven-cooked samples is higher. The second reason is attributed to the absorption of oil by the samples during the process of deep-fat frying. Oroszv́ari et al. [45] and Rahimi et al. [46] stated that due to simultaneous heat and mass transfer, some of the oil used during frying is absorbed and diffused by the product. Additionally, Bhosale et al. [47] reported that moisture loss resulted in increased fat absorption during the deep-frying of chicken nugget samples.

In consideration of the elevated level of oil absorption, the resultant cooking loss value is not numerically high. In the present study, higher oxidation levels were detected in the deep-fried samples compared to the oven-cooked samples due to the higher fat content of the deep-fried samples.

Coated chicken liver samples had a pH value ranging from 6.53 to 6.76. Similarly, in a study, the initial pH of cooked minced chicken liver was reported as 6.13 [39]. It was observed that the pH value of samples that were cooked using both methods decreased with the inclusion of thyme in comparison to those of the control samples (p < 0.05). Additionally, the highest pH value was detected in the deep-fried turmeric-added sample. Similar to the present study, Milon et al. [48] detected that the pH value of the turmeric-added beef meatball sample was higher compared to the control sample and the sample containing BHA, a synthetic antioxidant. In addition, a study found that the pH of cooked chicken meatballs was not significantly affected by the different levels of turmeric [49].

3.3. Temperature Measurements and Cooking Loss of Coated Chicken Liver Samples

It is imperative that chicken liver is cooked correctly to ensure a microbiologically safe product [1]. The USDA Food Safety and Inspection Service (FSIS) recommends cooking poultry livers to an internal temperature of 73.9 °C to mitigate the food-safety risks [50]. The results of sample internal and surface temperatures measured at the end of the cooking processes and cooking loss values are shown in

Table 3. Internal and surface temperatures and cooking loss values of coated chicken liver samples.

Sample	Internal Temperature (°C)	Surface Temperature (°C)	Cooking Loss (%)
FC	78.31 ± 0.73 a	99.55 ± 1.32 b	8.61 ± 0.35 a
FTH	77.48 ± 0.95 a	97.58 ± 1.64 b	8.03 ± 0.44 a
FTU	77.23 ± 0.63 a	98.62 ± 1.91 b	7.75 ±0.31 a
OC	81.07 ± 0.79 b	86.61 ± 1.34 a	20.23 ± 0.43 b
OTH	82.75 ± 0.85 b	90.07 ± 1.17 a	20.20 ± 0.32 b
OTU	81.32 ± 0.74 b	90.29 ± 1.33 a	19.51 ± 0.43 b

Results are given as mean ± standard error. a–b: Different letters used in the same column indicate that the difference between the mean values is statistically significant (p < 0.05). FC: deep-fried sample group containing salt, pepper, and cumin, FTH: deep-fried sample group containing salt, pepper, cumin, and thyme, FTU: deep-fried sample group containing salt, pepper, cumin, and turmeric, OC: oven-cooked sample group containing salt, pepper, and cumin, OTH: oven-cooked sample group containing salt, pepper, cumin, and thyme, OTU: oven-cooked sample group containing salt, pepper, cumin, and turmeric.

. As the internal temperature values of the samples in this study range from 77.23 to 82.75 °C, they are in compliance with the specified temperature value in terms of food safety.

While the cooking method applied to the samples had a significant effect on the internal and external surface temperature values of the samples (p < 0.05), the effect of the sample formulation was insignificant (p > 0.05). The internal temperatures of the oven-cooked samples were higher, and the surface temperatures were lower compared to those of the deep-fried samples (p < 0.05). In an oven, heat is transmitted directly via infrared radiation emitted by the heated oven walls, as well as via hot air circulated by convection and conduction through the cooking container. The food absorbs the infrared radiation emitted from the oven walls, and this is converted to heat. In the case of frying, heat is transferred from the frying medium to the product surface by convection and from the surface to the interior of the food by conduction [51]. Therefore, in the present study, the external surface temperatures of the fried samples were measured to be higher than those of the samples cooked in the oven. The interaction effect of CMxF on internal and surface temperatures was determined as insignificant (p > 0.05).

At higher cooking temperatures, the increased water loss and more extensive destruction of cell structure lead to a substantial cooking loss [1]. The cooking loss in cooked chicken livers is mainly caused by the loss of moisture, melting of fat, and denaturation of protein [52]. The cooking loss values of the samples were significantly affected by the cooking method applied (p < 0.05). The cooking loss values of all oven-cooked samples were significantly higher than those of the deep-fried samples (p < 0.05). During deep-frying, the sample absorbs some of the frying oil. Therefore, this weight gain results in lower cooking loss values for deep-fried samples compared to samples cooked in the oven. In addition, the frying oil surrounding the sample acts as a barrier during deep-frying, reducing the cooking loss. The interaction effect of CMxF on cooking loss was determined as insignificant (p > 0.05). In a study conducted by Hadi [53], as a result of different cooking processes applied to fresh liver, the highest cooking loss was determined in samples cooked using the grilling method (32%), followed by samples cooked with the frying method (28%) and boiling method (26%). Additionally, the cooking loss was detected in liver samples that were stir-fried and varied between 23.2 and 32.1% [54]; further, the cooking loss of samples packaged in plastic bags and heated in a water bath at 80 °C for 30 min was 13% [52]. Although not statistically significant, it was observed that the cooking loss values of the samples containing turmeric were lower than the other samples. Studies have reported that turmeric powder protects membrane integrity, increases the water retention ability of muscle tissue, and reduces cooking loss due to its strong antioxidant activity [43].

3.4. Coating Pickup of Coated Chicken Liver Samples

The application of coating materials can form a layer on the food surface, reducing its porosity and altering its hydrophobicity. This can lead to a reduction in mass transfer, water loss, and oil uptake [55]. Higher viscosity coating solutions exhibit superior adhesion properties, leading to enhanced pickup [56,57]. According to the research, the coating layer thickness is important, as it has a direct impact on customers’ sensory approval. A larger amount of flour is often found in thicker dough, which results in a higher coating uptake. Additionally, batter consistency is a significant quality characteristic of coatings, affecting their performance during frying [58]. The coating pickup values of samples are shown in

Table 4. Coating pickup values of coated chicken liver samples.

Sample	Coating Pickup (%)
C	30.19 ± 0.76
THS	31.13 ± 0.60
TUS	30.88 ± 0.79

C: Control, THS: Thyme-added sample, TUS: Turmeric-added sample.

.

The differences in the coating pickup values of the samples were detected as statistically insignificant (p > 0.05). Gökçe et al. [59] investigated the effects of wheat, corn, rye, and soy on the quality characteristics of deep-fried chicken nuggets. The coating pickup was detected as varying between 11.53 and 14.28%, with the highest value being achieved in samples prepared using rye flour. However, in the present study, it is thought that the use of buckwheat flour and corn flour, which were selected as gluten-free flour, in the coating stages and the different structure of the chicken liver surface facilitated the adhesion of the coating material; so, the coating pickup values were higher compared to the values determined in the specified study.

3.5. Color Characteristics of Coated Chicken Liver Samples

The Maillard reactions, along with the associated protein and sugar contents, play an important role in the color of coated products. Furthermore, it has been demonstrated that the concentrations of proteins, amino acids, and reducing sugars, in addition to the cooking temperature and frying time, have a significant impact on the color development of fried products [60].

The effects of the incorporation of spices to the formulations and applied cooking methods on L*, a*, and b* color characteristics of gluten-free coated chicken liver samples are presented in Figure 1. The interaction effects of the cooking method, formulation, and storage period on the color characteristics of samples are given in

Table 5. The interaction effects of cooking method, formulation, and storage period on the color values of coated chicken livers.

Dependent Variables	Independent Variables
	CM	F	SP	CMxF	FxSP	CMxSP	CMxFxSP
L*	<0.000	<0.144	<0.169	<0.000	<0.004	<0.000	<0.043
a*	<0.000	<0.000	<0.730	<0.000	<0.000	<0.000	<0.037
b*	<0.000	<0.000	<0.000	<0.000	<0.000	<0.000	<0.000

CM: cooking method, F: formulation, SP: storage period, CMxF: cooking method x formulation, FxSP: formulation x storage period, CMxSP: cooking method x storage period, CMxFxSP: cooking method x formulation x storage period.

.

The usage of thyme and turmeric additives in oven-cooked sample formulations resulted in an increase in the L* values of the products at the beginning of the storage period (p < 0.05). At the end of the storage period, the impact of spices on the L* values of the samples were determined to be non-significant (p > 0.05). The frying method eliminated the brightness–darkness differences in the colors of the samples and the L* value difference between the deep-fried samples was found to be insignificant (p > 0.05). All of the oven-cooked samples exhibited higher L* values and a brighter appearance in comparison to the deep-fried samples, as expected (p < 0.05). In a manner consistent with the present study, it was determined that the L* value of chia-added chicken nugget samples subjected to oven cooking was significantly higher than that of the samples that underwent deep-frying [61]. The Maillard reaction plays a particularly critical role in determining the color properties of deep-fried foods. Studies have shown that an increased incidence of the Maillard reaction during deep-frying results in a darker appearance of the fried products, leading to lower L* (lightness) values [62]. The storage period affected the L* values of the samples differently, depending on the applied cooking method. During storage, the L* values of the deep-fried samples increased, while those of the samples cooked in the oven decreased (p < 0.05).

It was determined that the spices added to the samples caused a decrement according to the control samples and the deep-frying method caused an increase according to the oven cooking method of the a* values of the samples at the beginning of the storage period (p < 0.05). Furthermore, it was observed that the a* values of the thyme-added sample groups increased during storage (p < 0.05), suggesting that the antioxidant effect of the thyme additive was responsible for preserving the red color (a* value) of the samples during this period. A study reported that rabbit burgers with turmeric powder stored for seven days had a* values similar to those of burgers with ascorbic acid, and higher than those of the control group [63].

The distinctive yellow color of turmeric is due to the presence of the result of its three main pigments: curcumin, demethoxy curcumin, and bisdemethoxy curcumin [64]. Curcumin, a hydrophobic polyphenol, is the critical coloring agent in turmeric that can be extracted and is valuable as a natural food colorant [65]. In the present study, the highest b* value was recorded among the deep-fried and oven-cooked samples in those containing turmeric at the onset of storage due to its strong yellow color (p < 0.05). A comparable study conducted by Arshad et al. [66] revealed that the b* values in chicken meat samples increased with the addition of turmeric powder. In current study, the highest b* value among the deep-fried and oven-cooked samples was observed in those containing turmeric at the beginning of the storage period, due to its strong yellow color (p < 0.05). Similarly, Arshad et al. [66] revealed that the b* values in chicken meat samples increased with the addition of turmeric powder. While the b* values of the oven-cooked samples at the beginning of the storage period were significantly higher than those of the deep-fried samples (p < 0.05), this effect of the cooking methods disappeared at the end of the storage period. It was determined that the b* value of all samples, except OTU, increased in a statistically significant way with storage (p < 0.05). The interaction effect of CMxF, FxSP, CMxSP, and CMxFxSP on the L*, a*, and b* values of the samples was detected as significant (p < 0.05) (Table 5).

3.6. Texture Profile of Coated Chicken Liver Samples

The texture profile results of gluten-free coated chicken liver samples are given in

Table 6. Texture profile of coated chicken liver samples.

Day 0
Sample	Hardness (N)	Springiness (mm)	Cohesiveness	Gumminess (N)	Chewiness (N·mm)	Resilience
FC	9.65 ± 0.83 aB	0.32 ± 0.02 B	0.34 ± 0.02 B	1.62 ± 0.12 ab	0.28 ± 0.03 B	0.14 ± 0.01 B
FTH	9.49 ± 0.83 aB	0.32 ± 0.02 B	0.37 ± 0.01 B	1.51 ± 0.09 ab	0.29 ± 0.04 B	0.14 ± 0.01 B
FTU	9.15 ± 0.87 aB	0.34 ± 0.02 B	0.36 ± 0.01 B	1.29 ± 0.15 a	0.29 ± 0.07	0.14 ± 0.01 B
OC	13.42 ± 1.18 bB	0.36 ± 0.02 B	0.37 ± 0.01 B	2.84 ± 0.38 dB	0.34 ± 0.03	0.14 ± 0.01 B
OTH	12.83 ± 1.08 bB	0.34 ± 0.02 B	0.37 ± 0.02 B	2.54 ± 0.22 cB	0.32 ± 0.03	0.15 ± 0.01 B
OTU	12.64 ± 0.19 bB	0.34 ± 0.01 B	0.35 ± 0.01 B	2.15 ± 0.24 bc	0.38 ± 0.13	0.14 ± 0.01 B
Day 60
Sample	Hardness (N)	Springiness (mm)	Cohesiveness	Gumminess (N)	Chewiness (N·mm)	Resilience
FC	3.30 ± 0.28 aA	0.25 ± 0.01 bA	0.30 ± 0.01 bA	1.43 ± 0.08 a	0.19 ± 0.01 aA	0.10 ± 0.01 A
FTH	3.92 ± 0.38 aA	0.26 ± 0.02 bA	0.31 ± 0.01 bA	1.27 ± 0.11 a	0.19 ± 0.01 aA	0.09 ± 0.01 A
FTU	3.78 ± 0.41 aA	0.29 ± 0.01 bA	0.31 ± 0.02 bA	1.26 ± 0.15 a	0.18 ± 0.01 a	0.09 ± 0.01 A
OC	5.00 ± 0.18 bA	0.19 ± 0.01 aA	0.25 ± 0.01 aA	1.96 ± 0.11 bA	0.27 ± 0.02 b	0.11 ± 0.01 A
OTH	5.27 ± 0.29 bA	0.18 ± 0.02 aA	0.26 ± 0.01 aA	2.01 ± 0.10 bA	0.24 ± 0.02 b	0.09 ± 0.01 A
OTU	5.04 ± 0.33 bA	0.20 ± 0.02 aA	0.23 ± 0.02 aA	2.11 ± 0.10 b	0.26 ± 0.01 b	0.09 ± 0.01 A

Results are given as mean ± standard error. a–d: different letters used in the same column indicate that the difference between the mean values is statistically significant (p < 0.05). A–B: different letters used in the same column indicate that the difference between the mean values is statistically significant (p < 0.05). FC: deep-fried sample group containing salt, pepper, and cumin, FTH: deep-fried sample group containing salt, pepper, cumin, and thyme, FTU: deep-fried sample group containing salt, pepper, cumin, and turmeric, OC: oven-cooked sample group containing salt, pepper and cumin, OTH: Oven-cooked sample group containing salt, pepper, cumin, and thyme, OTU: oven-cooked sample group containing salt, pepper, cumin, and turmeric.

. The texture of cooked meat is often associated with heat-induced changes in connective tissue, soluble proteins, and myofibrillar proteins [67]. Ensuring the desired texture in coated products is contingent on the properties of the coating components [59,68,69]. In addition, moisture loss, protein denaturation, starch gelatinization, and the degree of oil hydrogenation during the frying process affect the product texture [70].

In formulations comprising turmeric and thyme, oven-cooked samples demonstrated significantly reduced gumminess values compared to those exhibited by the control sample. The turmeric-added oven-cooked sample at the onset of storage was found to show the lowest gumminess value (p < 0.05).

Diverse cooking methods caused significant differences only in the hardness and gumminess values of the samples at the beginning of the storage (p < 0.05). Additionally, at the end of the storage, in addition to these properties mentioned, springiness, cohesiveness, and chewiness properties were also significantly affected by different cooking methods (p < 0.05). In a study conducted by Pathera et al. [71], the hardness values of chicken nuggets cooked in the oven and steamed were significantly higher than those cooked in the microwave. It has been hypothesized that the moisture and fat contents of fried samples have a significant impact on the resultant hardness [7]. In the current study, while the hardness, gumminess, and chewiness values of the oven-cooked samples were detected as higher, springiness and cohesiveness values were detected as lower compared to deep-fried samples (p < 0.05). The low moisture content and high cooking loss of oven-cooked samples, due to the longer cooking time in the oven compared to deep-frying, is thought to increase the hardness value of the samples. It was determined that different formulations and cooking methods had no statistically significant effect on the resilience values of the samples during storage (p > 0.05).

Compared to the beginning of storage, it was seen that there is a decrease in the hardness, springiness, cohesiveness, and resilience values of the samples (p < 0.05). The gumminess values of OC and OTH oven-cooked samples decreased significantly during storage (p < 0.05). Only FC and FTH samples showed a significant decrease in chewiness values during storage (p < 0.05). Myofibrillar and cytoskeletal proteins are degraded by proteolytic enzymes [72,73,74]. In this study, it is assumed that the samples undergo a reduction in hardness due to the action of proteolytic enzymes (calpains, cathepsins, and caspases) during storage.

While the interaction effect of CMxSP on the hardness, springiness, and cohesiveness values of samples was detected as significant (p < 0.05), CMxF, FxSP, and CMxFxSP were determined as insignificant (p > 0.05). The interaction effect of CMxF, FxSP, CMxSP, and CMxFxSP on the gumminess, chewiness, and resilience values of the samples was determined as insignificant (p > 0.05) (

Table 7. The interaction effects of cooking method, formulation, and storage period on TPA values of coated chicken livers.

Dependent Variables	Independent Variables
	CM	F	SP	CMxF	FxSP	CMxSP	CMxFxSP
Hardness	<0.007	<0.603	<0.000	<0.925	<0.829	<0.000	<0.964
Springiness	<0.003	<0.434	<0.000	<0.250	<0.610	<0.000	<0.967
Cohesiveness	<0.000	<0.369	<0.000	<0.236	<0.812	<0.000	<0.673
Gumminess	<0.000	<0.116	<0.002	<0.993	<0.114	<0.101	<0.396
Chewiness	<0.017	<0.898	<0.001	<0.749	<0.868	<0.839	<0.954
Resilience	<0.244	<0.207	<0.000	<0.906	<0.054	<0.560	<0.551

CM: cooking method, F: formulation, SP: storage period, CMxF: cooking method x formulation, FxSP: formulation x storage period, CMxSP: cooking method x storage period, CMxFxSP: cooking method x formulation x storage period.

).

3.7. DPPH Values

The stable radical 2-Diphenyl 2-Piperylhydrazyl (DPPH) exhibits its maximum absorption at approximately 517 nm and can be rapidly inactivated by an antioxidant. This method is extensively used to measure the degree of the free radical inhibition of various compounds [75]. The values of DPPH obtained from the coatings of the chicken liver samples can be seen in

Table 8. DPPH values of coatings obtained from coated chicken liver.

Sample	DPPH Value (%)
FC	79.93 ± 0.34 a
FTH	86.18 ± 0.29 b
FTU	88.83 ± 0.60 c
OC	85.85 ± 0.19 b
OTH	88.40 ± 0.29 c
OTU	90.82 ± 0.13 d

Results are given as mean ± standard error. a–d: different letters used in the same column indicate that the difference between the mean values is statistically significant (p < 0.05). FC: deep-fried sample group containing salt, pepper, and cumin, FTH: deep-fried sample group containing salt, pepper, cumin, and thyme, FTU: deep-fried sample group containing salt, pepper, cumin, and turmeric, OC: oven-cooked sample group containing salt, pepper, and cumin, OTH: oven-cooked sample group containing salt, pepper, cumin, and thyme, OTU: oven-cooked sample group containing salt, pepper, cumin, and turmeric.

.

The DPPH values of the samples demonstrated statistically significant differences with regard to both formulations and cooking methods (p < 0.05). It was determined that the DPPH values of samples increased with the addition of thyme and turmeric compared to those of the control samples in both deep-fried and oven-cooked samples (p < 0.05). The highest DPPH values were observed in turmeric-added samples cooked with both cooking methods. It was detected that the oven-cooked samples had significantly higher DPPH values than those of the deep-fried samples (p < 0.05). During deep-frying, the sample reaches high temperatures in a much shorter period of time compared to oven cooking. There is a difference in the heat transfer mechanism between deep-frying and oven-cooking methods. In addition, oxidation develops more rapidly during deep-frying. For these reasons, there is a possibility that the antioxidant activity may decrease more in deep-fried samples compared to oven-cooked samples. In addition, in the present study, the cooking loss of the samples cooked in the oven was found to be higher than deep-fried samples, and accordingly, the protein value was found to be higher. Studies have shown that proteins have a potent antioxidant property due to free radical scavenging and metals have chelating potential [76]. Therefore, the high protein content of the oven-cooked samples compared to the deep-fried samples also contributed to the high antioxidant activity.

The interaction effect of CMxF on the DPPH value was detected to be significant (p < 0.05). A study revealed that turmeric has a significantly higher DPPH value than thyme due to its phytochemical composition, including curcuminoids [77]. Curcuminoids, a prominent phytochemical in turmeric, possess substantial antioxidant potential and demonstrate heat resistance [78]. In the study by Mahmud et al. [62], the DPPH radical scavenging activity of curcumin was evaluated at various concentrations (0.5–3 g/dm³), with activity values ranging from 62.16% to 88.18%. It was observed that the DPPH activity exhibited a positive correlation with the increase in curcumin concentration. The basis of the DPPH assay is the reaction of the DPPH radical with hydrogen-donor molecules from curcumin.

In the present study, the DPPH values of the samples to which thyme was added were assessed to be lower than those of the samples to which turmeric was added, but higher than the control sample. A study was conducted to investigate the antioxidant effects of aqueous extracts of thyme varieties. The study concluded that they possessed significant antioxidant activity and potent anti-inflammatory activity [79]. This result is in accordance with the fact that thyme is abundant in total polyphenols and flavonoids [80]. In another study, in line with these findings, thyme was found to have higher antioxidant activity compared to the synthetic antioxidant BHT [81].

3.8. TBARS Values of Coated Chicken Liver Samples

Deep-fat-fried foods are popular, known for their delicious taste and affordability. Nevertheless, it is well-documented that these foods frequently absorb excessive amounts of oil during the frying process, resulting in accelerated lipid oxidation and a consequent reduction in shelf life [7].

Table 9. TBARS values of coated chicken liver samples.

Sample	TBARS (mg Malonaldehyde/kg)
	Storage (Days)
	Day 0	Day 15	Day 30	Day 45	Day 60
FC	0.27 ± 0.01 cA	0.44 ± 0.03 bB	0.52 ± 0.01 cC	0.75 ± 0.01 eD	1.82 ± 0.01 fE
FTH	0.30 ± 0.01 dA	0.35 ± 0.01 aB	0.46 ± 0.01 bC	0.66 ± 0.03 dD	1.56 ± 0.01 dE
FTU	0.23 ± 0.01 bA	0.36 ± 0.01 aB	0.51 ± 0.01 cC	0.55 ± 0.01 bcD	0.77 ± 0.01 bE
OC	0.26 ± 0.01 cA	0.35 ± 0.01 aB	0.44 ± 0.01 bC	0.59 ± 0.02 cD	1.61 ± 0.01 eE
OTH	0.21 ± 0.01 aA	0.35 ± 0.01 aB	0.40 ± 0.01 aC	0.49 ± 0.01 aD	1.48 ± 0.02 cE
OTU	0.26 ± 0.01 bcA	0.32 ± 0.01 aB	0.40 ± 0.01 aC	0.54 ± 0.01 bD	0.63 ± 0.02 aE

Results are given as mean ± standard error. a–e: different letters used in the same column indicate that the difference between the mean values is statistically significant (p < 0.05). A–E: different letters used in the same row indicate that the difference between the mean values is statistically significant (p < 0.05). FC: deep-fried sample group containing salt, pepper, and cumin, FTH: deep-fried sample group containing salt, pepper, cumin, and thyme, FTU: deep-fried sample group containing salt, pepper, cumin, and turmeric, OC: oven-cooked sample group containing salt, pepper, and cumin, OTH: oven-cooked sample group containing salt, pepper, cumin, and thyme, OTU: oven-cooked sample group containing salt, pepper, cumin, and turmeric.

shows the TBARS values of the coated chicken liver samples during storage.

TBARS values of the samples were in the range between 0.21 and 1.82 during 60 days of storage. The range of 2–2.5 mg MDA/kg has been determined as the acceptable limit value at which consumers do not perceive any rancidity in meat and meat products [82,83,84]. The addition of thyme to the sample when it was cooked in the oven at the beginning of the storage process had a significantly lower TBARS value compared to all the other samples (p < 0.05). It was determined that the impact of thyme and turmeric on TBARS exhibited variation in accordance with the cooking method. While thyme and turmeric significantly decreased TBARS values in deep-fried samples (p < 0.05) on the 15th day of storage, this effect was not significantly determined in oven-cooked samples (p > 0.05). On the 30th day of storage, it was determined that the addition of thyme to the fried samples and the addition of thyme and turmeric to the oven-cooked samples resulted in lower TBARS values in the samples compared to the control sample (p < 0.05). Zhang et al. [85] determined that turmeric powder inclusion significantly reduced lipid peroxide formation and increased antioxidant activity in hamburger patties during cooking.

The study revealed that deep-frying resulted in statistically higher TBARS values compared to oven cooking for all samples during the storage period of 30 and 60 days (p < 0.05). This result is due to the increased oxidation occurring in the deep-fried samples in comparison to those cooked in an oven, a phenomenon attributable to the integration of the frying oil within the structure of the deep-fried samples. Oxidation is a common reaction in the frying process. The presence of oxidized and rancid fats and oils in the frying medium has been shown to result in the penetration of these substances into the surface of the food, leading to the deterioration in quality [86].

As demonstrated in

Table 10. The interaction effects of cooking method, formulation, and storage period on the TBARS values of coated chicken livers.

Dependent Variables	Independent Variables
	CM	F	SP	CMxF	FxSP	CMxSP	CMxFxSP
TBARS	<0.000	<0.000	<0.000	<0.000	<0.000	<0.000	<0.00

CM: cooking method, F: formulation, SP: storage period, CMxF: cooking method x formulation, FxSP: formulation x storage period, CMxSP: cooking method x storage period, CMxFxSP: cooking method x formulation x storage period.

, on the 45th and 60th days of storage, turmeric and thyme additives significantly inhibited oxidation in samples cooked with both methods of cooking (p < 0.05). As storage progressed, the antioxidant effect of the thyme and turmeric on the samples became more pronounced. The lowest TBARS values among both deep-fried and oven-cooked groups were found in the turmeric-containing samples at the end of the storage period. In a similar manner, Arshad et al. [66] reported a decrease in the TBARS value of chicken meat with the addition of 3% turmeric powder. Curcumin is the major active component isolated from turmeric [85]. In a study, different concentrations of curcumin were added to the oleogels and incorporated into chicken nuggets fried with carnauba wax and canola oil. A significant reduction in fat absorption and lipid oxidation was observed in the fried chicken nuggets compared to the control samples [62]. Manju et al. [87] verified that a synthetic curcumin analogue salicylcurcumin was effective for preventing the formation of lipid peroxidation products and TBARS in the liver of Anabas testudineus under both in vitro and in vivo conditions.

During the storage period, all samples TBARS values increased statistically significantly (p < 0.05). Estevez and Cava [88] reported that the TBARS values of liver pates from Iberian and white pigs increased with storage periods. The interaction effects of CMxF, FxSP, CMxSP, and CMxFxSP on the TBARS values of the samples were detected as significant (Table 10).

3.9. TMAB Count of Coated Chicken Liver Samples

TMAB is considered as an important criterion in determining the microbiological quality of cooked meat products [89,90]. TMAB counts of coated chicken liver samples are given in

Table 11. TMAB counts of coated chicken liver samples.

Sample	TMAB (Log CFU/g)
	Storage Period (Days)
	Day 0	Day 15	Day 30	Day 45	Day 60
FC	3.53 ± 0.01 A	3.72 ± 0.01 bB	4.24 ± 0.01 abC	4.47 ± 0.01 cD	4.99 ± 0.02 bE
FTH	3.49 ± 0.01 A	3.64 ± 0.02 aB	4.19 ± 0.04 abC	4.30 ± 0.03 bD	4.82 ± 0.02 aE
FTU	3.54 ± 0.03 A	3.60 ± 0.01 aA	4.12 ± 0.01 abB	4.17 ± 0.03 aB	4.84 ± 0.02 aC
OC	3.55 ± 0.02 A	3.73 ± 0.02 bA	4.30 ± 0.12 bB	4.46 ± 0.01 cB	5.07 ± 0.02 cC
OTH	3.56 ± 0.03 A	3.65 ± 0.03 aA	4.10 ± 0.01 aB	4.25 ± 0.06 abC	4.83 ± 0.01 aD
OTU	3.51 ± 0.03 A	3.63 ± 0.02 aB	4.10 ± 0.04 aC	4.17 ± 0.01 aC	4.85 ± 0.04 aD

Results are given as mean ± standard error. a–c: different letters used in the same column indicate that the difference between the mean values is statistically significant (p < 0.05). A–E: different letters used in the same row indicate that the difference between the mean values is statistically significant (p < 0.05). FC: deep-fried sample group containing salt, pepper, and cumin, FTH: deep-fried sample group containing salt, pepper, cumin, and thyme, FTU: deep-fried sample group containing salt, pepper, cumin, and turmeric, OC: oven-cooked sample group containing salt, pepper, and cumin, OTH: oven-cooked sample group containing salt, pepper, cumin, and thyme, OTU: oven-cooked sample group containing salt, pepper, cumin, and turmeric.

. The initial TMAB count of samples was between 3.49 and 3.56 log cfu/g at the beginning of the storage and there was no statistically significant difference between samples (p > 0.05). As demonstrated by Hasapidou and Savvaidis [91], the initial mesophilic total viable counts of chicken liver samples were 5.4 log cfu/g, likely attributable to product cross-contamination during manual processing. These values increased to 7 log cfu/g (which is regarded as the upper acceptable limit) on day 3.

On the 15th, 45th, and 60th days of storage, turmeric and thyme additives exhibited an antimicrobial effect, resulting in a significant reduction in TMAB counts compared to the control samples (p < 0.05). Nevertheless, on the 30th day of storage, it was determined that only the oven-cooked samples with thyme and turmeric had lower TMAB counts compared to those of the control sample (p < 0.05). The shelf life of buffalo liver stored under aerobic conditions was studied by Devatkal and Mendiratta [92]. The results of that study indicated that the mean values of aerobic plate counts at 37 °C were 4.96, 5.76, 6.53, and 7.15 log10 cfu/g on days 0, 2, 4, and 6, respectively, and the authors revealed that the microbiological and sensory quality of buffalo liver remained acceptable up to the third day of storage. It is thought that in the present study, the application of thyme and turmeric in conjunction with the coating process to the livers provides enhanced protection of the microbial quality of the product during storage. The difference in cooking method applied to the samples until the 60th day of storage did not cause a significant difference in the TMAB count of the samples. Additionally, on the 60th day, the TMAB count of the oven-cooked control sample was determined to be significantly lower than the TMAB count of the deep-fried sample. The TMAB count of all the samples showed a statistically significant increase during the storage period (p < 0.05). While the sample with the lowest TMAB count among the deep-fried cooked samples on the 45th day of storage was the turmeric-added sample, no significant difference was determined between the samples containing turmeric and thyme on the 60th day of storage. According to the International Commission on Microbiological Specifications for Foods [93] (ICMSF Standards), the acceptable limit value for TMAB is set as 1 × 106 cfu/g. In the present study, it was determined that the samples did not exceed this limit value and were microbiologically safe during the 60-day storage period.

Table 12. The interaction effects of cooking method, formulation, and storage period on the TMAB values of coated chicken livers.

Dependent Variables	Independent Variables
	CM	F	SP	CMxF	FxSP	CMxSP	CMxFxSP
TMAB	<0.502	<0.000	<0.000	<0.317	<0.000	<0.486	<0.401

CM: cooking method, F: formulation, SP: storage period, CMxF: cooking method x formulation, FxSP: formulation x storage period, CMxSP: cooking method x storage period, CMxFxSP: cooking method x formulation x storage period.

shows the interaction effects of the cooking method, formulation, and storage period on the TMAB values of coated chicken liver samples. The interaction effect of FxSP on the TMAB values of samples was determined as significant, while CMxF, CMxSP, and CMxFxSP were determined as insignificant.

3.10. HCA Content of Coated Chicken Liver Samples

Heterocyclic aromatic amines (HCAs), a type of cooking-induced contaminant with strong carcinogenic and mutagenic properties, are commonly found in high-protein food products [9]. According to studies, it has been concluded that when meat and fish marinated with antioxidant-containing substances are cooked at high temperatures, antioxidants suppress free radical formation and reduce the formation of HCAs. Thus, the formation of HCAs was shown to be inhibited by various natural substances [94]. Free radical intermediates generated in the Maillard reaction were involved in the formation of heterocyclic amines. It was suggested that antioxidants could scavenge free radicals and inhibit radical reactions during HCA formation, thus effectively inhibiting the formation of heterocyclic amines [10,95].

The recoveries for IQ, MeIQx, 4,8-DiMeIQx, harman, norharman, and PhIP were found between 61.25 and 81.18%. Limit of detection (LOD) and limit of quantification (LOQ) values were found to be 0.0036 and 0.0120 ng/g for IQ, 0.0048 and 0.0160 ng/g for MeIQx, 0.0024, and 0.0080 ng/g for 4,8-DiMeIQx, 0.0003 and 0.0010 ng/g for PhIP, 0.0021 and 0.0070 ng/g for harman, and 0.0007 and 0.0023 ng/g for norharman, respectively. A representative chromatogram from the HPLC analysis of one of the samples of FTH is given in Figure 2. IQ, MeIQx, 4,8-DiMeIQx, PhIP, norharman, and harman contents and total HCA (MeIQx, 4.8-DiMeIQx, IQ, harman, norharman, and PhIP) amounts of coated chicken liver samples are given in

Table 13. HCA contents of coated chicken liver samples (ng/g).

Sample	IQ	MeIQx	4,8-DiMeIQx	PhIP	Norharman	Harman	Total HCA
FC	5.22 ± 0.03 d	3.59 ± 0.06 e	4.52 ± 0.01 d	0.27 ± 0.01 ab	4.17 ± 0.03 c	1.47 ± 0.01 ab	19.25 ± 0.07 e
FTH	4.29 ± 0.08 a	3.09 ± 0.02 c	3.42 ± 0.02 b	0.26 ± 0.01 ab	4.03 ± 0.02 bc	1.46 ± 0.02 a	16.54 ± 0.05 b
FTU	4.83 ± 0.03 c	2.58 ± 0.01 a	3.08 ± 0.02 a	0.25 ± 0.01 a	3.54 ± 0.13 a	1.46 ± 0.01 a	15.73 ± 0.11 a
OC	5.34 ± 0.01 d	3.70 ± 0.01 f	5.50 ± 0.02 f	0.28 ± 0.01 b	4.23 ± 0.05 c	1.53 ± 0.04 b	20.57 ± 0.06 f
OTH	4.48 ± 0.05 b	3.19 ± 0.01 d	5.31 ± 0.05 e	0.27 ± 0.01 ab	3.87 ± 0.16 b	1.44 ± 0.01 a	18.54 ± 0.16 d
OTU	4.80 ± 0.01 c	2.69 ± 0.03 b	4.39 ± 0.03 c	0.26 ± 0.02 ab	3.99 ± 0.05 bc	1.48 ± 0.02 ab	17.60 ± 0.09 c

Results are given as mean ± standard error. a–f; different letters used in the same column indicate that the difference between the mean values is statistically significant (p < 0.05). FC: deep-fried sample group containing salt, pepper, and cumin, FTH: deep-fried sample group containing salt, pepper, cumin, and thyme, FTU: deep-fried sample group containing salt, pepper, cumin, and turmeric, OC: oven-cooked sample group containing salt, pepper, and cumin, OTH: oven-cooked sample group containing salt, pepper, cumin, and thyme, OTU: oven-cooked sample group containing salt, pepper, cumin, and turmeric.

.

The addition of thyme and turmeric to the formulation of coated chicken liver samples, which were both deep-fried and cooked in the oven, significantly decreased the IQ, MeIQx, 4.8-DiMeIQx, and total HCA content compared to the control group (p < 0.05). Results have shown that cooking methods affected the HCA contents of the samples, except the PhIP and harman contents. Thyme and turmeric additives had a significant reducing effect on the IQ contents of the samples, with the thyme effect being stronger (p < 0.05). The cooking method was only effective on the samples containing thyme, and the IQ value of the thyme-added deep-fried sample was found to be lower than that of the sample cooked in the oven (p < 0.05). Similarly, in the study by Keşkekoğlu and Uren [96], a significantly lower amount of IQ compound was determined in deep-fried (7.97 ng/g) compared to oven-cooked (57.97 ng/g) chicken meatballs containing a pomegranate seed extract.

The highest MeIQx and 4.8-DiMeIQx content in the deep-fried and oven-cooked sample groups were found in the control group, followed by the sample groups containing thyme and turmeric, respectively (p < 0.05). The PhIP content of samples was not affected significantly by thyme and turmeric in different formulations and applied cooking methods (p > 0.05). While turmeric decreased the norharman content of deep-fried samples significantly compared to the control group, thyme was more effective in reducing the norharman content of the oven-cooked samples (p < 0.05). Similarly, the harman content of thyme-added oven-cooked samples were lower than that of the control (p < 0.05). Thyme and turmeric demonstrated an inhibitory effect on the formation of different HCAs in samples and this result was reflected in the total HCA contents of the samples. Turmeric demonstrated the highest inhibitory effect on the total HCA content of samples cooked with both of the cooking methods. As a result of deep-frying or oven cooking, a decrease of 14.42% and 13.20% in the case of adding thyme and 18.75% and 23.35% in the case of adding turmeric was determined in the total HCA amount, respectively. It was concluded that the most appropriate spice and cooking method combination to achieve the lowest total HCA levels in coated chicken liver samples was turmeric and oven cooking. The addition of turmeric to chicken meatballs [49], black pepper to beef meatballs [97], and red chili, paprika, ginger, and black pepper to beef and chicken meatballs [98] were reported to have inhibitory effects on HCAs.

Spice antioxidants may inhibit the formation of HCA by donating hydrogen atoms and transferring single electrons to decrease or quench active radicals [98]. It was determined that the total HCA content of the thyme-containing deep-fried samples was 12.09% less than the oven-cooked samples. The total HCA, MeIQx, and 4.8-DiMeIQx contents of the oven-cooked samples were found to be higher than those of the deep-fried samples (p < 0.05). The number of HCAs increases significantly with frying time [99]. HCA formation increases due to cooking above 150 °C and for more than 2 min [100]. Because the deep-fat-frying time in the current investigation was restricted to 1.5 min, it is thought that the HCA content of the samples is lower compared to the oven-cooked samples. Another factor affecting HCA formation is related to cooking loss. It has been established that an increase in cooking loss results in an increase in HCA formation, due to an increase in dry weight. The present study revealed that the cooking loss of the oven-cooked samples was higher than that of the deep-fried samples. It is hypothesized that this increased cooking loss of the oven-cooked samples led to an increase in the HCA content.

3.11. Sensory Evaluation of Coated Chicken Liver Samples

The texture, juiciness, aroma, and color of meat products are the main characteristics that influence the overall quality perception of consumers. These characteristics can be influenced by different production factors and techniques [101]. Sensory evaluation is of great importance, especially in the context of newly developed products. The sensory evaluations of coated chicken liver samples are shown in

Table 14. Sensory evaluation scores of coated chicken liver samples.

Sample	APPEARANCE
	Storage Period (Days)
	Day 0	Day 15	Day 30	Day 45	Day 60
FC	8.40 ± 0.17 bB	8.05 ± 0.18 bB	8.25 ± 0.18 cB	8.15 ± 0.17 cB	7.15 ± 0.24 bA
FTH	8.60 ± 0.13 bC	8.20 ± 0.17 bBC	7.95 ± 0.20 bcB	8.10 ± 0.19 cBC	7.10 ± 0.23 bA
FTU	8.60 ± 0.11 bC	8.20 ± 0.19 bBC	8.25 ± 0.16 cBC	7.90 ± 0.18 cB	7.30 ± 0.19 bA
OC	7.85 ± 0.25 aC	7.00 ± 0.18 aB	7.05 ± 0.23 aB	6.45 ± 0.22 aAB	6.30 ± 0.22 aA
OTH	7.60 ± 0.23 aB	7.20 ± 0.25 aB	7.50 ± 0.26 abB	7.20 ± 0.16 bB	6.30 ± 0.29 aA
OTU	7.75 ± 0.23 aC	7.35 ± 0.22 aBC	7.25 ± 0.26 aBC	6.90 ± 0.22 abB	6.05 ± 0.21 aA
Sample	COLOR
	Storage Period (Days)
	Day 0	Day 15	Day 30	Day 45	Day 60
FC	8.25 ± 0.16 cB	8.00 ± 0.19 bB	8.05 ± 0.17 bB	8.30 ± 0.16 bB	7.50 ± 0.31 bA
FTH	8.20 ± 0.16 c	8.35 ± 0.17 b	8.10 ± 0.23 b	8.50 ± 0.11 b	8.25 ± 0.16 b
FTU	8.10 ± 0.14 c	8.05 ± 0.18 b	8.10 ± 0.19 b	8.35 ± 0.15 b	8.00 ± 0.18 b
OC	7.00 ± 0.24 aB	7.20 ± 0.20 aB	7.15 ± 0.22 aB	6.60 ± 0.18 aAB	6.20 ± 0.32 aA
OTH	7.75 ± 0.10 bcC	7.10 ± 0.31 aBC	7.25 ± 0.26 aBC	6.95 ± 0.22 aB	6.15 ± 0.31 aA
OTU	7.30 ± 0.21 abB	7.15 ± 0.20 aB	7.10 ± 0.19 aAB	6.90 ± 0.19 aAB	6.50 ± 0.27 aA
Sample	TEXTURE
	Storage Period (Days)
	Day 0	Day 15	Day 30	Day 45	Day 60
FC	8.25 ± 0.16 abcC	8.25 ± 0.19 abC	7.30 ± 0.31 B	7.15 ± 0.15 AB	6.50 ± 0.34 A
FTH	8.45 ± 0.15 bcC	8.45 ± 0.14 bC	7.65 ± 0.20 BC	7.20 ± 0.39 AB	6.60 ± 0.49 A
FTU	8.55 ± 0.11 cB	8.05 ± 0.18 abB	7.10 ± 0.20 A	7.05 ± 0.37 A	6.85 ± 0.33 A
OC	7.80 ± 0.16 aB	8.05 ± 0.18 abB	7.85 ± 0.18 B	6.70 ± 0.44 A	6.60 ± 0.28 A
OTH	8.05 ± 0.21 abcB	7.65 ± 0.29 aAB	7.60 ± 0.26 AB	7.15 ± 0.33 A	6.95 ± 0.29 A
OTU	7.90 ± 0.27 abB	7.65 ± 0.21 aB	7.55 ± 0.28 B	6.65 ± 0.31 A	6.55 ± 0.42 A
Sample	FLAVOR
	Storage Period (Days)
	Day 0	Day 15	Day 30	Day 45	Day 60
FC	7.40 ± 0.28 B	7.30 ± 0.24 B	7.35 ± 0.33 B	6.20 ± 0.29 aA	6.10 ± 0.27 abA
FTH	7.80 ± 0.12 C	7.75 ± 0.20 C	7.30 ± 0.30 BC	6.65 ± 0.27 abAB	6.45 ± 0.34 bA
FTU	7.55 ± 0.29 B	7.05 ± 0.20 AB	7.00 ± 0.27 AB	7.00 ± 0.28 abAB	6.50 ± 0.25 bA
OC	7.20 ± 0.30 B	7.10 ± 0.27 B	6.60 ± 0.37 B	6.85 ± 0.30 abB	5.40 ± 0.24 aA
OTH	7.50 ± 0.38 B	7.70 ± 0.21 B	7.35 ± 0.22 AB	7.35 ± 0.30 bAB	6.60 ± 0.29 bA
OTU	7.40 ± 0.15 B	7.10 ± 0.29 AB	7.10 ± 0.23 AB	6.95 ± 0.27 abAB	6.40 ± 0.21 bA
Sample	OVERALL ACCEPTANCE
	Storage Period (Days)
	Day 0	Day 15	Day 30	Day 45	Day 60
FC	8.20 ± 0.16 bcB	7.75 ± 0.20 abAB	7.55 ± 0.18 bcA	7.40 ± 0.23 bA	7.30 ± 0.27 bA
FTH	8.10 ± 0.16 bcC	8.05 ± 0.17 bBC	7.75 ± 0.23 cABC	7.50 ± 0.22 bAB	7.25 ± 0.19 bA
FTU	8.30 ± 0.15 cB	7.75 ± 0.14 abA	7.60 ± 0.19 bcA	7.50 ± 0.21 bA	7.35 ± 0.21 bA
OC	7.70 ± 0.18 abC	7.40 ± 0.21 aBC	6.80 ± 0.28 aAB	6.65 ± 0.26 aAB	6.25 ± 0.34 aA
OTH	7.30 ± 0.22 aB	7.25 ± 0.26 aB	7.10 ± 0.14 abcAB	6.90 ± 0.22 abAB	6.55 ± 0.23 abA
OTU	7.45 ± 0.20 aB	7.35 ± 0.24 aAB	7.00 ± 0.27 abAB	6.95 ± 0.26 abAB	6.65 ± 0.28 abA

Results are given as mean ± standard error. a–c; different letters used in the same column indicate that the difference between the mean values is statistically significant (p < 0.05). A–C; different letters used in the same row indicate that the difference between the mean values is statistically significant (p < 0.05). FC: deep-fried sample group containing salt, pepper, and cumin, FTH: deep-fried sample group containing salt, pepper, cumin, and thyme, FTU: deep-fried sample group containing salt, pepper, cumin, and turmeric, OC: oven-cooked sample group containing salt, pepper, and cumin, OTH: oven-cooked sample group containing salt, pepper, cumin, and thyme, OTU: oven-cooked sample group containing salt, pepper, cumin, and turmeric.

.

All of the appearance and color scores of the deep-fried samples were significantly higher than those of the oven-cooked samples (p < 0.05). The main reason for this was the fact that the oven-cooked samples have a floury and lighter appearance. This result is expected, considering that coated products are usually fried, and consumers are accustomed to a yellowish fried color; so, their preferences are in this direction.

Color scores at the beginning of the storage and appearance scores on the 45th day of storage of the oven-cooked samples with thyme were higher than those of the control samples (p < 0.05). While the appearance scores of the oven-cooked samples with thyme did not show any significant change during the 45-day storage period, those of the control sample showed a significant decrease on the 15th day (p < 0.05). The interaction effect of CMxF, FxSP, CMxSP, and CMxFxSP on the appearance scores of the samples was determined as insignificant (

Table 15. The interaction effects of cooking method, formulation, and storage period on the sensory evaluation values of coated chicken livers.

Independent Variables
Dependent Variables	CM	F	SP	CMxF	FxSP	CMxSP	CMxFxSP
Appearance	<0.000	<0.452	<0.000	<0.422	<0.907	<0.543	<0.342
Color	<0.000	<0.045	<0.000	<0.843	<0.901	<0.001	<0.352
Texture	<0.077	<0.312	<0.000	<0.790	<0.922	<0.048	<0.828
Flavor	<0.590	<0.000	<0.000	<0.349	<0.522	<0.175	<0.618
OverallAcceptance	<0.000	<0.623	<0.000	<0.899	<0.867	<0.830	<0.939

CM: cooking method, F: formulation, SP: storage period, CMxF: cooking method x formulation, FxSP: formulation x storage period, CMxSP: cooking method x storage period, CMxFxSP: cooking method x formulation x storage period.

).

The incorporation of diverse spices into the formulation of the samples did not result in a difference in the texture scores determined during the storage period. However, the effect of different cooking methods on texture scores was observed. At the onset of storage, the texture score of the deep-fried sample with turmeric was determined to be higher than those cooked in the oven (p < 0.05). Additionally, on day 15, the deep-fried sample containing thyme received significantly higher texture scores than those of the oven-cooked sample (p < 0.05). It was observed that deep-fried samples containing thyme and all oven-cooked samples maintained their high texture scores for up to 45 days, while this period was 30 days for the other deep-fried samples (p < 0.05). The decline in texture scores of all samples during storage is attributable to the reduction in hardness of the samples, as evidenced by the texture profile results. It is hypothesized that the texture scores of oven-cooked samples decreased later during storage than those of the fried samples due to the fact that the coating layers were harder and drier, which is desirable for this type of coated product. While the interaction effect of CMxSP on the color and texture scores of samples was detected as significant, CMxF, FxSP, and CMxFxSP were determined as insignificant (Table 15).

The addition of spices to the samples did not cause a significant change in flavor scores until the 45th day of storage (p > 0.05). At the end of storage, the thyme and turmeric-added samples cooked in the oven had higher flavor scores compared to those of the control (p < 0.05) The reason why this positive effect of thyme and turmeric, which increased flavor scores, becomes especially evident at the end of storage and only in oven-cooked samples, may be due to their oxidation-inhibiting properties. As seen in the TBARS values determined at the end of storage, oxidation was lower in oven-cooked samples compared to deep-fried samples and spice-added samples compared to the control sample. It was shown that there was no statistically significant difference in the flavor scores of the samples cooked with different cooking methods (p > 0.05). All of the oven-cooked samples’ flavor scores were preserved and did not change significantly until the 45th day of storage. The interaction effect of CMxF, FxSP, CMxSP, and CMxFxSP on the flavor scores of the samples was determined as insignificant (p > 0.05) (Table 15).

It was observed that the overall acceptance scores of the samples on a 9-point evaluation scale were between 7.30 and 8.30 at the onset of storage, and during storage, all the overall acceptance scores of the samples were above 6.25. The samples containing thyme and turmeric were found to have similar overall acceptability scores to the control samples during storage (p > 0.05). The cooking method was detected as effective and the overall acceptance of the deep-fried samples with thyme and turmeric was higher than that of the oven-cooked samples at the beginning of storage. The overall acceptance scores of the oven-cooked samples with thyme and turmeric did not change significantly until the last day of storage (p < 0.05). On the other hand, the overall acceptance scores of the deep-fried samples with thyme and turmeric remained unchanged until the 45th and 15th day of storage, respectively. This situation reveals that thyme and turmeric can better preserve the sensory properties during storage especially in samples cooked in the oven. Oyom et al. [7] developed edible coatings from oleogels loaded with thyme essential oil at varying concentrations for deep-fried chicken nuggets and showed that adding thyme essential oil to the coating did not affect the overall sensory quality of the fried products. The interaction effect of CMxF, FxSP, CMxSP, and CMxFxSP on the overall acceptance scores of the samples was determined as insignificant (p > 0.05) (Table 15).

4. Conclusions

The results obtained from this study indicated that oxidation development was lower in oven-cooked turmeric-added samples compared to thyme-added samples and all deep-fried samples at the end of the storage. Deep-frying resulted in higher oxidation development compared to oven cooking for all samples during the storage period of 30 and 60 days. Turmeric and thyme additives exhibited an antimicrobial effect, resulting in a significant reduction in TMAB counts compared to the control samples during the storage period. The addition of thyme and turmeric to the formulation of coated chicken liver samples, which were then subjected to either deep-frying or oven cooking, resulted in a substantial reduction in the carcinogenic IQ, MeIQx, and 4.8-DiMeIQx compounds and total HCA content. For the total HCA content of the deep-fried and oven-cooked samples, the addition of thyme resulted in a decrease of 14.42% and 13.20%, and the addition of turmeric resulted in a decrease of 18.75% and 23.35%, respectively. The sensory properties of all the samples were evaluated with high scores by the panelists during storage (ranging from 6.10 to 8.60 on a 9-point scale) While the appearance and color scores of the deep-fried samples were significantly higher than those of the oven-cooked samples, formulation differences did not cause any significant differences in the texture, flavor, and overall acceptance scores of samples. However, the fact that the oxidation development is higher in deep-fried samples compared to oven-cooked samples is a limitation due to the shorter shelf life of deep-fried samples. In the light of the data obtained, it was concluded that turmeric-added gluten-free coated chicken liver cooked in the oven can be stored at −20 °C for up to 60 days while maintaining its microbiological, oxidative, and sensorial quality in terms of texture, flavor, and overall acceptance, and can take its place in the food market as a pre-cooked frozen healthy offal product. Further studies could focus on designing new, healthier, ready-to-eat gluten-free pre-cooked offal products prepared with different spices and with a longer shelf-life. In order to maintain the healthy properties of these products, studies can be carried out on the application of alternative cooking methods.