Changes in Quality Features of Pork Burgers Prepared with Chokeberry Pomace During Storage

Featured Application

The work fits into the idea of sustainable development by utilizing by-products from the production of plant-based food. The obtained results prove the possibility of using “raw” (i.e., unprocessed, shredded only) fruit pomace in the production of processed products from ground meat from the category of convenience food, which can be used to create more sustainable meat products. However, the use of raw fruit pomace, which is a perishable raw material, requires very efficient cooperation between the supplier and the recipient of this by-product.

Abstract

This study aimed to evaluate the effect of adding shredded black chokeberry (Aronia melanocarpa) pomace on the quality of heat-treated and vacuum-packed pork burgers stored for 14 days at +4 °C. Four burger treatments—Control (BC) and products with 2%, 3.5%, and 5% chokeberry pomace (B2, B3.5, and B5, respectively)—were analyzed for physicochemical properties (thermal loss, shrinkage, content of selected chemical components, pH, color parameters, and shear force) and microbial quality (aerobic mesophilic microorganisms, psychrotrophic bacteria, lactic acid bacteria, Enterobacteriaceae, Pseudomonas spp., Brochothrix thermosphacta, and yeasts and molds). The addition of chokeberry pomace increased (p < 0.05) the thermal loss of pork burgers from 23.5% (BC) to 30.8% (B5) and decreased (p < 0.05) the pH from 6.93 (BC, day 1) to 6.74 (B5, day 14). The introduction of pomace into the pork burgers also significantly (p < 0.05) affected the content of chemical components. However, the nutritional value of pork burgers remained high, with a protein content not lower than 26.68% (BC) and a fat content not exceeding 13.96% (B5). The most affected quality feature of the pork burgers was color. Products B2, B3.5, and B5 exhibited lower L* and b* parameters (p < 0.05) while showing higher a* values. The b* parameter had negative values for products B3.5 and B5 on days 7 and 14. The use of chokeberry pomace did not deteriorate the microbial quality of pork burgers, as indicated by the maximum total count of aerobic mesophilic microorganisms, which reached 4.4 × 10³ cfu/g (B3.5). Moreover, on the final day of storage, moderate antimicrobial properties of chokeberry pomace were observed, with a lower (p < 0.05) number of lactic acid bacteria and Pseudomonas spp. in products B2–B5 compared to BC. The results indicate that incorporating shredded chokeberry pomace into burger-type ground pork products does not present major technological difficulties. However, raw shredded fruit pomace is a perishable microbiological material and requires rapid processing. Further research on the use of chokeberry pomace in burger-type meat products is recommended due to its nutritional value and health-promoting properties. However, this research should include a comprehensive sensory evaluation of the finished product.

1. Introduction

In the European food industry, the implementation of sustainable production and processing methods, referred to as “less waste” or “zero waste,” is increasingly evident [1,2,3]. These changes in food production and consumption patterns stem from climate policy and environmental concerns related to excessive food raw material production [4,5,6,7,8]. In response to the challenges of promoting a sustainable food production and consumption strategy, research is being conducted to improve the management of waste products from the fruit and vegetable industry by incorporating them into meat products [9].

Most by-products from plant food processing consist of parts not utilized in producing juices, pulps, or jams, such as pomace, peels, and fruit pits [9,10]. These by-products constitute approximately 10–35% of the mass of processed plant raw material, with pomace from traditional fruit pressing averaging 20% to 25% of the raw material mass [10]. Since fruit and vegetable pomace is a source of many bioactive compounds, it is reasonable to use it to enrich food with these valuable ingredients [11,12].

Review articles comprehensively describe the latest trends in managing pomace from plant raw materials for food production. The most promising applications for these by-products include products made from fruits, vegetables, cereals, and milk, as well as sweets and snacks. Additionally, pomace can enhance some quality attributes of meat products [11,12]. Strategies for using fruit and vegetable pomace in meat processing aim to increase the health value of meat products and extend their shelf life. Pomace has been successfully incorporated into minced meat products such as patties, burgers, and sausages [12,13,14,15,16]. In meat products, pomace is typically used in dried form or as water or alcohol extracts [16,17,18,19]. This is due to the high water content in these waste products, which makes them unstable. Therefore, pomace is often subjected to “valorization,” which may involve the extraction of bioactive components [12].

One of the fruits with significant health benefits is the black chokeberry (Aronia melanocarpa). Originally introduced to Europe from North America, black chokeberry bushes are relatively easy to cultivate on the continent [20]. Poland is one of the top producers of black chokeberries in Europe [21]. The health benefits of consuming Aronia melanocarpa fruits are widely documented, including antioxidant, hypoglycemic, hypolipidemic, hepatoprotective, cardioprotective, and antimutagenic effects [22]. Due to their tart taste, black chokeberry fruits are rarely eaten fresh and are primarily processed [20,23,24]. When black chokeberry fruit is processed into juice, pomace is obtained as a by-product. This pomace is rich in health-beneficial components, including polyphenols, anthocyanins, and dietary fiber [20,22,24,25]. Comparative studies of fourteen chokeberry products—including fruits, dried fruits, juices, jams, syrups, and pomace—showed that pomace contained the highest total levels of polyphenols and anthocyanins [26]. Polyphenolic compounds in chokeberry pomace have demonstrated antioxidant and antibacterial effects in ground meat products [14]. However, studies [24] indicate that chokeberry pomace should be regarded as a heterogeneous raw material. For example, processing should consider separating the seeds, which are a valuable source of fat, protein and minerals. Raw chokeberry pomace is highly perishable and requires rapid processing or freezing. This has led researchers to develop various methods of chokeberry pomace valorization in order to expand the possibilities of using this by-product. The term valorization refers to increasing the availability and functionality of specific components found in pomace, e.g., antioxidants and dyes. The main strategies for valorization include drying, freeze-drying, and the extraction of bioactive compounds. However, the large-scale implementation of these methods will likely require additional investments, which could result in increased costs [12,19]. Therefore, it seemed justified to attempt to use black chokeberry pomace in a minimally processed form as an ingredient of minced meat products.

The literature provides limited information on the potential use of raw, shredded black chokeberry pomace in meat products. Previous studies examined its application in ground meat products, such as pork burgers [27]. Findings revealed that incorporating chokeberry pomace in the form of shredded paste was feasible. However, the quantity of added plant material significantly impacted the quality characteristics of pork burgers, including organoleptic attributes. It is important to note that this study was preliminary, with no storage tests or microbiological quality assessments. The promising results led to further research.

Thus, the aim of this study was to assess selected physical, chemical, and microbiological quality characteristics of pork burgers containing black chokeberry (Aronia melanocarpa) pomace. Pomace was added to the meat batter in shredded form in amounts ranging from 2.0% to 5.0% relative to the weight of meat and fat raw materials. After thermal treatment, the burgers were vacuum-packed and stored under refrigeration for 14 days.

2. Materials and Methods

2.1. Materials

The raw materials (pork ham and pork jowl) were purchased at the Makro Cash and Carry wholesale store on the day of burger production. The pomace from black chokeberry (Aronia melanocarpa) was prepared at the Department of Fruit, Vegetable and Cereal Technology of the Warsaw University of Life Sciences (WULS).

2.2. Preparation of Black Chokeberry Pomace and Determination of Dry Matter in Fresh Pomace

The black chokeberry fruits (Aronia melanocarpa) of the Nero variety originated from a conventional plantation in eastern Poland (Lublin Voivodeship), with a high degree of fertilization, and were harvested in mid-September 2024. The pomace was delivered to the laboratory the next day after harvesting and transported in a refrigerated vehicle. Before production, fresh chokeberries were washed and pressed using a laboratory hydraulic press (BUCHER Unipektin AG HPL 14; Bucher Unipektin AG, Niederweningen, Switzerland) equipped with a drainage filter recommended for pressing berries and pome fruits. Approximately 10 kg of chokeberries underwent a three-cycle juice pressing process at a pressure of 5 bar. Between cycles, the material was loosened to improve yield and reduce water content in the pomace. The appearance of fresh black chokeberry pomace is shown in Figure S1. After production, the pomace was vacuum-packed in 0.070 mm thick PA/PE bags using a Multivac C200 packaging machine (Multivac, Natalin, Poland) in two portions, each weighing approximately 0.5 kg, then frozen and stored at −60 ± 1 °C. On the day of burger production, the required amount of frozen pomace was defrosted in a microwave oven (4 min, 900 W) and shredded into a “paste” consistency using a Thermomix^® device (Vorwerk, Warsaw, Poland) at a knife speed of 4000/min for 5 min at a maximum temperature of 37 °C.

The dry matter content of the pomace was determined gravimetrically. A 0.05 g (±0.001 g) sample was dried stepwise at 70 °C for 40 min, 90 °C for 40 min, and 95 °C for 30 min, with cooling intervals in a desiccator. Drying continued until weight differences between successive measurements were no greater than 0.001 g.

2.3. Pork Burgers Formulation and Production and Experiment Design

The following basic recipe was used in burger production: 80% pork ham (skinless and boneless), 20% pork jowl (de-skinned), and 1.8% salt (relative to the weight of meat and fat raw materials). Based on this formulation, four burger treatments were prepared: control product (BC) without the addition of black chokeberry pomace and B2, B3.5, and B5 products with the addition of pomace at levels of 2.0%, 3.5%, and 5.0%, respectively. The amounts of added pomace were set at a maximum level that did not impair the organoleptic quality of the products [27].

Pork ham and pork jowl were ground separately in a laboratory grinder (Mesko WN40; Mesko AGD Sp. z o.o., Skarżysko-Kamienna, Poland) using a 4.5 mm hole diameter mesh. The meat batter was prepared in a laboratory mixer (Kenwood Major KM800; Kenwood Ltd., Havant, UK) by introducing the ingredients into the mixing bowl in the following order: first meat with table salt, then pork jowl, and finally, in the case of B2, B3.5, and B5 treatments, shredded chokeberry pomace. The mixture was blended until all ingredients were evenly distributed (approx. 10 min). Burgers weighing approximately 110 g were formed using a hand molder (Hendi BV, Rhenen, The Netherlands) and baked in the air at 180 °C (relative air humidity 10%) in a convection-steam oven (Rational SCC WE61; Rational AG, Landsberg am Lech, Germany). Thermal treatment continued until the temperature at the geometric center of the burgers reached 80 °C. The appearance of pork burgers after heat treatment is shown in Figure S2. After cooling, the burgers were vacuum-packed in 0.070 mm thick PA/PE bags using a Multivac C200 packaging machine (Multivac, Natalin, Poland) and stored under cooling conditions (+4 ± 1) °C in the absence of light for 1, 7, and 14 days. Burgers intended for microbiological analysis were packed separately. The experiment was conducted in two independent series.

On the day of production, culinary quality characteristics, including thermal loss and shrinkage (change in burger diameter after baking), were determined, along with selected chemical components. Other quality characteristics, such as pH, color parameters, texture, and microbiological quality, were assessed 1 day after production and after 7 and 14 days of storage at (+4 ± 1) °C. On each of these days, one package containing 10 burgers was retrieved from cold storage for each treatment. The experimental design was determined by logistical considerations regarding laboratory access.

2.4. Methods

2.4.1. Culinary Quality Characteristics and Chemical Properties of Pork Burgers—Production Day

Thermal Loss

The thermal loss of burgers was determined using the weight method. Three randomly selected burgers from each treatment were weighed with an accuracy of 0.01 g before and after baking (and cooling), and the result was expressed as a percentage of the weight of the product before baking.

Shrinkage

Shrinkage was calculated by measuring the diameter of three randomly selected burgers from each treatment before and after baking (and cooling). Measurements were taken using an electronic caliper with an accuracy of 0.01 mm, and the result was expressed as a percentage of the diameter before baking.

Chemical Properties

The content of selected chemical components in burgers, including water, protein, fat, and sodium chloride, was determined following the PN-A-82109:2010 standard [28] using a near-infrared spectrometer (FoodScan™2, Foss Analytical A/S, Hillerød, Denmark). The device operated in the wavelength range of 850–1500 nm and utilized calibration based on an artificial neural network model. Measurements were performed on heat-treated (baked and cooled) burger samples. Before measurement, approximately 300 g of each product treatment (three randomly selected burgers) was ground twice in a laboratory meat grinder (Diana 886.8, Zelmer, Rzeszów, Poland) using a 2 mm mesh and mixed thoroughly. The prepared samples were placed on a measuring cuvette in the device’s measuring station, where the measurement was performed automatically. The results were displayed on a computer monitor. Each burger treatment was measured in duplicate per experimental series, and the mean values were used as the final results.

2.4.2. Quality Characteristics of Pork Burgers—During Storage

pH

The pH of the burgers was measured using a Testo 206-pH2 pH meter (Testo SE and Co. KGaA, Titisee-Neustadt, Germany). The measurement was performed by inserting the pH meter electrode into the product sample. Three randomly selected burgers from each treatment were separately ground in a laboratory grinder equipped with a 2 mm mesh (Diana 886.8, Zelmer, Rzeszów, Poland). A 10 g (± 0.01 g) sample of ground burger was mixed with 30 mL of distilled water in a beaker, and the measurement was performed in duplicate per experimental series. The mean values were taken as final results.

L*, a* and b* Color Parameters

The MINOLTA^® CR-400 colorimeter (Minolta, Tokyo, Japan; light source D65, observer 10°, a measuring head hole of 8 mm) was used for color measurements of burgers. Before measurement, the device was calibrated on a white standard (Y: 95.2 x: 0.3159, y: 0.3326). Two randomly selected burgers of each product treatment were analyzed for color parameters: L* (lightness), a* (redness and b* (yellowness). Each experimental series included six repetitions per treatment, with the mean values used as the final results.

The total color difference (ΔE) between the control product and burgers with added black chokeberry pomace (for each storage time individually) was calculated using Equation (1) [29]:

$$∆E=\sqrt{{{(∆L}^{*})}^2+{{(∆a}^{*})}^2+{{(∆b}^{*})}^2}$$

(1)

where ΔL*, Δa*, and Δb* represent the differences in color parameters between the control product (BC) and the burgers with added black chokeberry pomace (B2, B3.5 and B5).

Texture—Shear Force

Shear force was measured using the Zwicki 1120^® universal testing machine (Zwick GmbH and Co., Ulm, Germany) equipped with a flat-blade knife measuring head. Six randomly selected burgers from each product treatment were prepared in cuboid shapes (approx. 10 cm long, 3 cm wide, 0.8 cm thick). The test was performed at a blade speed of 50 mm/min, with an initial force of 0.5 N and a force deactivation threshold of 50% of the maximum force recorded. The highest force recorded during the cut was taken as the shear force measurement. Six repetitions were performed per experimental series, with mean values used as the final results.

Microbiological Analyses

On analysis days, burger packages were opened under sterile conditions. Samples were prepared according to Polish Standard PN-EN ISO 6887–2:2017 [30]. Microbiological assessments included determining the total count of aerobic mesophilic microorganisms [31], as well as the number of psychrotrophic bacteria [32], lactic acid bacteria (LAB) [33], Enterobacteriaceae [34], Pseudomonas spp. [35], Brochothrix thermosphacta [36], and yeasts and molds (YAM) [37]. Bacterial counts were expressed as colony-forming units per gram of product (cfu/g). Methods for microbiological quality assessment were based on previous studies by Chmiel et al. [38] and Cegiełka et al. [39]. Each burger treatment in a given experimental series was analyzed in duplicate. The microbiological quality of chokeberry pomace was also assessed for the same groups of microorganisms.

Statistical Analysis

The data were presented as means ± standard deviation (SD). Statistical analyses were performed using Statistica^® v. 13.0 software (StatSoft Inc., Tulsa, OK, USA). One-Way Analysis of Variance (One-Way ANOVA) was applied to determine the effect of black chokeberry pomace addition on culinary quality characteristics assessed only on the production day (thermal loss, shrinkage, and selected chemical components). Tukey’s HSD test was used as a post hoc test at a significance level of α = 0.05. The normality of data was verified using the Shapiro–Wilk test, while the homogeneity of variances was assessed using the Levene test.

The effects of treatment (BC, B2, B3.5, B5), storage time (1, 7, and 14 days), and their interaction (Treatment × Storage Time) on other quality characteristics, including pH, shear force, L*, a*, and b* color parameters, and microbiological quality, were analyzed using Two-Way Analysis of Variance (Two-Way ANOVA). Fixed terms included burger treatments and storage intervals, while experimental series were treated as random terms. Tukey’s multiple range test (α = 0.05) was used to determine the significance of treatment, storage time, and their interaction.

The number of measurement results “n” used in statistical calculations was determined based on the product of the number of measurements performed (repetitions), two experimental series, and the number of storage days on which measurements were conducted.

3. Results and Discussion

3.1. Culinary Quality Characteristics and Chemical Properties of Pork Burgers

Thermal loss in burgers after baking ranged from 23.5% in the BC product to 30.8% in the B5 product and varied significantly (p < 0.05) depending on changes in the raw material composition of the burgers (

Table 1. Thermal loss (n = 6), shrinkage (n = 6), and the content of selected chemical components (n = 4) in pork burgers with added black chokeberry pomace (mean value ± standard deviation).

Feature	BC *	B2 *	B3.5 *	B5 *
Thermal loss [%]	23.5 a ± 1.58	27.4 b ± 0.85	27.7 b ± 1.52	30.8 c ± 0.80
Shrinkage [%]	16.9 a ± 1.92	17.5 a ± 2.07	18.7 a ± 1.68	21.1 a ± 0.90
Water content [%]	59.3 d ± 0.06	57.74 c ± 0.03	57.08 b ± 0.11	55.97 a ± 0.11
Protein content [%]	26.68 a ± 0.08	27.89 b ± 0.10	27.71 b ± 0.11	28.47 c ± 0.06
Fat content [%]	12.47 a ± 0.01	12.84 b ± 0.00	13.77 c ± 0.12	13.96 c ± 0.06
Sodium chloride content [%]	1.94 b ± 0.03	1.71 a ± 0.04	1.64 a ± 0.03	1.63 a ± 0.02

* Treatments: BC—pork burgers without chokeberry pomace; B2—pork burgers with 2.0% chokeberry pomace; B3.5—pork burgers with 3.5% chokeberry pomace; B5—pork burgers with 5.0% chokeberry pomace; a–d—mean values in the same row marked with different letters are significantly different at p < 0.05.

). Compared to the control product (BC), burgers with a lower concentration of chokeberry pomace, i.e., B2 and B3.5, exhibited a greater (p < 0.05) weight loss. Burgers with the highest amount of chokeberry pomace (B5) showed the highest (p < 0.05) thermal loss among all meat product treatments.

The change in the diameter of burgers after baking referred to as “shrinkage”, ranged on average from 16.9% in the BC product to 21.1% in the B5 product and increased with the proportion of pomace in the raw material composition (Table 1). However, the differences between the burger treatments were insignificant (p > 0.05).

The results of this study indicate that incorporating a plant-based ingredient into the raw material composition of a minced meat product can affect some aspects of its culinary quality. Similarly, other researchers [40,41] found that the production yield of burgers after heat treatment—measured as the ratio of the finished product weight to meat batter weight—may depend on the inclusion of a plant-based ingredient. However, the results are not conclusive. For example, the production yield of grilled mixed beef and pork burgers significantly decreased (p < 0.05) when 6.0% oat fiber preparation was added to the meat batter [41]. Unlike the present study, López-Vargas et al. [42] demonstrated that the cooking characteristics of pork burgers improved (p < 0.05) with the addition of passion fruit albedo at concentrations of 2.5% and 5%. The authors attributed the increased cooking yield to the dietary fiber in the fruit albedo, which has a high capacity for retaining moisture and fat. Additionally, burgers containing passion fruit albedo exhibited a smaller reduction in diameter after cooking than control burgers. In beef burgers, adding 5% dried Sicilian sumac fruit resulted in reduced cooking loss compared to the control product, though the differences were not statistically significant [43].

Limited literature is available on using raw fruit pomace in minced meat products. Most research has focused on the possible applications of dried fruit or vegetable pomace and fruit pomace extracts in meat processing [13,15,16,44,45].

Peiretti et al. [13] found that adding 1% or 2% dried berry pomace resulted in a relatively small, insignificant (p > 0.05) increase in pork patty yield after heat treatment. According to the authors, dried fruit pomace is rich in dietary fiber, which helps retain moisture and fat within the product matrix, preventing weight loss. However, in contrast to the present study, there was a tendency to decrease “shrinkage” in meat products containing fruit pomace, which was seen as a positive aspect of culinary quality. The authors concluded that dimensional changes occurring in pork patties during baking were primarily due to the denaturation of meat proteins, the predominant ingredient in the product.

Tarasevičienė et al. [16] investigated the impact of berry pomace (from raspberries and blackberries) at levels of 1%, 3%, and 5% on the quality of beef patties during 9 days of storage at 4 °C. The highest weight loss was observed in the control patties (without added pomace) while adding pomace from both raspberries and blackberries resulted in a slight reduction in weight loss.

In this study, the observed tendency of increasing thermal loss in burgers with higher amounts of chokeberry pomace may have been due to introducing a low-acid ingredient. This observation aligns with findings by Tyburcy et al. [46], who added prunes to pork burgers.

The use of chokeberry pomace in pork burgers resulted in relatively small but significant (p < 0.05) differences in the content of chemical components (Table 1). The water content ranged from 55.97% in the B5 product to 59.31% in the BC product, with a decrease (p < 0.05) noted as the concentration of chokeberry pomace increased. This reduction in water content in burgers containing chokeberry pomace can most likely be attributed to higher thermal loss (Table 1). In contrast to the water content, both protein and fat levels in the burgers increased with higher amounts of pomace. The B5 product had significantly (p < 0.05) the highest protein content (28.47%), while the BC product had the lowest (26.68%). The B2 and B3.5 products formed a homogeneous group, exhibiting lower (p < 0.05) protein levels than those in the B5 product but higher (p < 0.05) than in the BC product. Regarding fat content, the most significant difference (p < 0.05) was observed between the BC product (12.47%) and both the B5 and B3.5 products (19.96% and 13.77%, respectively). The sodium chloride content in pork burgers ranged from 1.63% in the B5 product to 1.94% in the BC product, being significantly higher (p < 0.05) in the burgers without chokeberry pomace (BC) compared to those containing added pomace (B2–B5). The difference in the sodium chloride content between the control product (BC) and products containing chokeberry pomace (B2–B5) could be because the amount of this ingredient added was calculated with the total pork ham and pork jowl without taking into account the relatively small weight of pomace. Therefore, the initial concentration of sodium chloride in the B2–B5 products was slightly lower than in the product without pomace. Moreover, the reduction in the sodium chloride content in burgers containing chokeberry pomace was most likely caused by differences in the amount of thermal loss between BC–B5 burgers. The greater the thermal loss, the higher the amount of pomace added. The quantitatively dominant component of thermal loss from a meat product is water [42], but it also contains sodium chloride [47].

To sum up, the differences in the chemical composition of pork burgers can be attributed to the different proportions of raw materials used for production: meat, fat, and chokeberry pomace. The dry matter content of fresh chokeberry pomace used in this study was 26.5%, which indicates a high water content in this raw material. However, the results regarding the water content in burgers containing this plant component indicate that the water introduced with the pomace was not retained in the matrix of the meat product. As reported by other researchers [10,20,23], the quantitatively dominant components of the dry matter of chokeberry pomace are carbohydrates and fiber, and therefore, pomace differs from meat and fat raw materials. According to the data in the review article [12], the dry matter of chokeberry pomace contains 5.9–10.8% protein, 3.6–5.2% fat, 28.9% carbohydrates and 21.8–95.8% total dietary fiber. The dietary fiber of chokeberry pomace is characterized by a significant content of cellulose, hemicellulose and pectin [24]. The contents of these components were not determined in this work, which may be considered its limitation.

The content of chemical components such as water, protein, and fat in burgers is important because it primarily determines nutritional value [48]. The results of other studies [40,41] have also demonstrated that the levels of chemical components—such as protein, fat, and water—found in burger-type meat products primarily depend on the type of meat used as the raw material. Likewise, these studies confirmed that adding plant components to the meat filling can alter the chemical composition of the final meat product.

In studies on the use of valorized, i.e., dried fruit and vegetable pomace [15,44,49], no clear effect of these plant ingredients on the content of chemical components in meat products was demonstrated. Skwarek and Karwowska [15], who examined the effect of freeze-dried tomato pomace (0.5%, 1%, and 1.5%) on the quality of fermented sausages with reduced nitrite content, found significant differences (p ≤ 0.05) in protein, fat, and water content among the sausage treatments. Only the table salt content was similar in the experimental sausages. Dried tomato pomace was also used in beef frankfurters [44]. The study revealed that increasing the concentration of tomato pomace from 1 kg to 3, 5, and 7 kg per 100 kg of meat batter significantly (p ≤ 0.05) influenced the fat, protein, ash, and water content in the sausages, depending on the proportion of vegetable pomace in the recipe. With higher amounts of pomace, there was a tendency to increase carbohydrates, protein, and ash in the sausages while decreasing water and fat content. Another study [49] showed that the addition of 4% and 6% dried pomace from Citrus reticulata fruit, a hybrid variety of mandarin, resulted in a significant (p < 0.05) reduction in protein and fat content in ground pork products compared to the control product.

3.2. pH Value of Pork Burgers During Storage

The average pH value of the pork burgers varied from 6.73 in the B5 product on day 7 to 6.93 in the BC product on day 1 (

Table 2. Changes in pH value (n = 12) in pork burgers with added black chokeberry pomace during storage (mean value ± standard deviation).

Storage Time [Days]	BC *	B2 *	B3.5 *	B5 *
1 7 14	6.93 e ± 0.02 6.91 e ± 0.01 6.90 e ± 0.01	6.82 d ± 0.01 6.80 cd ± 0.00 6.79 bcd ± 0.01	6.77 abc ± 0.01 6.76 ab ± 0.01 6.76 ab ± 0.01	6.75 ab ± 0.01 6.73 a ± 0.00 6.74 a ± 0.01
p-value	Treatment: p = 0.0000	Storage time: p = 0.039	Treatment × Storage time: p = 0.6872

* Treatments: BC—pork burgers without chokeberry pomace; B2—pork burgers with 2.0% chokeberry pomace; B3.5—pork burgers with 3.5% chokeberry pomace; B5—pork burgers with 5.0% chokeberry pomace; a–e—mean values marked with different letters are significantly different at p < 0.05.

). It was found that both product treatment (i.e., the addition level of black chokeberry pomace) and storage time significantly affected (p < 0.05) the pH value of pork burgers. However, no interaction (p > 0.05) was observed between the treatment and storage time (Table 2).

It was found that incorporating chokeberry pomace into burgers resulted in a significant (p < 0.05) reduction in pH, regardless of storage time. The product without chokeberry pomace (BC) had the highest pH (p < 0.05) across all storage times, measuring 6.93 on day 1 and 6.90 on day 14. The results indicated that even the smallest amount of chokeberry pomace (B2) led to a relatively small but significant (p < 0.05) pH decrease compared to the BC product. Pork burgers (B2) with 2% chokeberry pomace had a significantly lower pH than the control product (BC) throughout the storage period. Increasing the addition of chokeberry pomace to 3.5% and 5% (B3.5 and B5, respectively) further reduced the pH. The lowest pH was recorded in the B5 product, ranging from 6.75 on day 1 to 6.74 on day 14. The B5 product had a significantly (p < 0.05) lower pH than the BC and B2 products, regardless of storage time.

During the 14-day storage period, pH decreased only slightly in each product treatment, with the observed changes being insignificant (p > 0.05; Table 1). The variations in pH during storage were minimal, reaching a maximum of 0.03 units for BC and B2 products.

The pH values of pork burgers with different levels of added chokeberry pomace were likely influenced by the active acidity of the raw materials and their proportions in the recipe. The average pH of the raw materials used in burger production was 6.03 for pork ham, 6.08 for pork jowl, and 3.36 for chokeberry pomace. Based on this, incorporating chokeberry pomace into the meat batter is expected to lower the burger’s pH. Additionally, the slight pH decrease observed on day 14 of storage may be attributed to lactic acid bacteria growth, which will be discussed later in the article.

The results of this study align with those of other researchers [14,16,45], who demonstrated that including a plant ingredient, even in processed form, in a meat product formulation can reduce active acidity.

In contrast, other researchers [17,44] reported that fruit or vegetable pomace in processed forms did not significantly alter the pH of meat products. For instance, raw pork burgers containing an alcoholic extract from red grape pomace (0.06 g per 100 g final product) and stored under aerobic conditions showed no significant difference (p > 0.05) in active acidity compared to the control product over six days [17]. Similarly, dried tomato pomace at levels ranging from 0% to 7% (w/w) had no effect (p > 0.05) on the pH of beef sausages [44].

3.3. L*, a*, and b* Color Parameters of Pork Burgers During Storage

Table 3. Changes in color parameters (L*, a*, and b*) (n = 36) in pork burgers with added black chokeberry pomace during storage (mean value ± standard deviation).

Storage Time [Days]	BC *	B2 *	B3.5 *	B5 *
	L* (Lightness)
1 7 14	64.42 e ± 1.85 63.13 e ± 1.87 62.07 e ± 1.55	55.95 d ± 1.77 55.23 d ± 2.46 54.38 d ± 2.02	51.02 c ± 2.85 50.23 bc ± 3.00 49.28 abc ± 2.38	49.73 abc ± 1.83 47 76 ab ± 2.25 46.98 a ± 2.85
p-value	Treatment: p = 0.0000	Storage time: p = 0.0001	Treatment × Storage time: p = 0.9588
	+a* (redness)
1 7 14	+5.77 a ± 1.17 +5.70 a ± 0.85 +5.44 a ± 1.42	+7.30 b ± 1.05 +6.48 ab ± 0.55 +6.38 ab ± 0.61	+8.99 c ± 0.97 +9.00 c ± 0.60 +9.27 c ± 0.94	+9.44 c ± 0.77 +9.59 c ± 0.47 +9.61 c ± 0.76
p-value	Treatment: p = 0.0000	Storage time: p = 0.4558	Treatment × Storage time: p = 0.2024
	+b*/−b* (yellowness/blueness)
1 7 14	+8.08 f ± 0.80 +10.53 g ± 0.88 +10.58 g ± 0.57	+4.46 e ± 0.98 +3.47 e ± 0.85 +1.87 d ± 0.45	+0.85 cd ± 0.52 −0.74 b ± 1.40 −2.00 a ± 0.66	+0.44 c ± 0.65 −2.00 a ± 0.62 −2.77 a ± 0.74
p-value	Treatment: p = 0.0000	Storage time: p = 0.0005	Treatment × Storage time: p = 0.0005

* Treatments: BC—pork burgers without chokeberry pomace; B2—pork burgers with 2.0% chokeberry pomace; B3.5—pork burgers with 3.5% chokeberry pomace; B5—pork burgers with 5.0% chokeberry pomace; a–g—mean values regarding a given color parameter marked with different letters are significantly different at p < 0.05.

presents the results of instrumental measurement of color parameters (L*, a*, and b*) of pork burgers differing in the amount of black chokeberry pomace added.

A significant effect (p < 0.05) was observed for both burger treatment and storage time on the L* parameter; however, there was no interaction between these factors was found (p > 0.05; Table 3). The L* values ranged from 46.98 (B5 product, day 14) to 64.42 (BC product, day 1). The BC product consistently exhibited the lightest color (p < 0.05), regardless of storage time. The addition of 2% chokeberry pomace (B2 product) significantly darkened the burgers. Increasing the chokeberry pomace content to 3.5% and 5% (B3.5 and B5, respectively) further decreased the L* value; however, the differences between the B3.5 and B5 products were not significant.

All burger treatments tended to darken during storage, as indicated by a slight decrease (p > 0.05) in the L* value (Table 3).

For the a* parameter, a significant effect (p < 0.05) was observed only for burger treatment; neither storage time (p > 0.05) nor the interaction between treatment and storage time (p > 0.05) had an effect (Table 3). The a* value ranged from +5.44 (BC product, day 14) to +9.61 (B5 product, day 14; Table 3). Redness increased with higher chokeberry pomace content. Regardless of storage time, the BC product exhibited lower (p < 0.05) redness than the pomace-containing products (B2–B5). The addition of 2% chokeberry pomace (B2) resulted in a higher a* value than the BC product; however, this difference was significant only on day 1. The B3.5 and B5 products had significantly higher a* values than the BC and B2 products, forming a distinct homogeneous group.

For all burger treatments, only minor (p > 0.05) changes in the a* parameter were observed during storage (Table 3).

Yellowness (b* parameter) was the color characteristic most affected by chokeberry pomace addition (Table 3). Both treatment and storage time significantly influenced (p < 0.05) the b* value, and an interaction between these factors was also observed (p < 0.05). The b* value ranged from –2.77 (B5 product, day 14) to +10.58 (BC product, day 14). Regardless of storage time, the BC product exhibited the highest b* value. As the level of pomace increased, the b* value gradually decreased. On day 1, the b* value was lower (p < 0.05) in the B2 product than in the BC product. Increasing the pomace content to 3.5% and 5% (B3.5 and B5, respectively) further reduced (p < 0.05) the yellowness. On days 7 and 14, the B3.5 and B5 products exhibited negative b* values, indicating a predominance of blue over yellow in the burgers’ overall tone.

Significant changes (p < 0.05) in the b* values were observed during storage across all burger treatments. In BC burgers, the b* value increased over time, whereas burgers containing chokeberry pomace (B2–B5) showed a decrease in the b* parameter.

Black chokeberry pomace is a rich source of water-soluble anthocyanin pigments, which give it a dark purple color [20]. Therefore, the observed color differences between the pork burgers in this study were most likely due to the dark hue of the chokeberry pomace. The effect of black chokeberry pomace on pork burger color was confirmed by the total color difference (ΔE) between the control product (BC) and the burgers with varying amounts of chokeberry pomace (Table S1). The ΔE values were quite high, ranging from 9.42 (BC vs. B2 on day 1) to 20.57 (BC vs. B5 on day 14), indicating that burgers containing chokeberry pomace differed so distinctly from the control product that an ordinary observer might perceive them as having two different colors [29].

Previous studies [13,14,17,45] suggest that the effect of fruit pomace on the color of comminuted meat products varies, depending on factors such as the form of pomace used as an ingredient.

Similar to the present work, Tamkutė et al. [45] found that adding 2% ethanol extract from defatted black chokeberry pomace to minced pork burgers significantly (p < 0.05) reduced the L* value and increased (p < 0.05) the a* value compared to control burgers without pomace. However, unlike our findings, the increase in the b* value in burgers with chokeberry pomace extract was insignificant (p > 0.05). Furthermore, the study observed that color differences between control burgers and those with added chokeberry pomace extract were most pronounced immediately after production and diminished over the 16-day refrigerated storage period.

3.4. Texture (Shear Force) of Pork Burgers During Storage

The shear force values for pork burgers ranged from 20.83 N in the BC product on day 1 to 27.99 N in the B5 product on day 14 (

Table 4. Changes in shear force value [N] (n = 36) in pork burgers with added black chokeberry pomace during storage (mean value ± standard deviation).

Storage Time [Days]	BC *	B2 *	B3.5 *	B5 *
1 7 14	20.83 a ± 3.40 21.55 abc ± 21.55 24.17 abcd ± 2.04	21.01 ab ± 1.80 21.67 abc ± 1.64 24.64 bcde ± 2.48	21.03 ab ± 3.77 23.28 abcd ± 2.04 24.82 cde ± 2.46	24.43 abcde ± 2.52 25.88 de ± 3.41 27.99 e ± 2.88
p-value	Treatment: p = 0.0000	Storage time: p = 0.0000	Treatment × Storage time: p = 0.9568

* Treatments: BC—pork burgers without chokeberry pomace; B2—pork burgers with 2.0% chokeberry pomace; B3.5 pork burgers with 3.5% chokeberry pomace; B5—pork burgers with 5.0% chokeberry pomace; a–e—mean values marked with different letters are significantly different at p < 0.05.

). Both burger treatment and storage time significantly affected (p < 0.05) shear force, and an interaction between these factors was observed. Adding black chokeberry pomace to pork burgers gradually increased shear force, with the greatest differences noted between the BC product (without pomace) and the B5 product (highest pomace level). On day 1, the shear force values for BC and B5 products were 20.83 N and 24.43 N, respectively, though the difference was not significant (p > 0.05). However, significant differences (p < 0.05) in shear force between the BC and B5 products emerged on days 7 and 14. By day 14, shear force values were highest, ranging from 24.17 N in the BC product to 27.99 N in the B5 product.

Regardless of treatment, burgers tended to become ”harder” during storage, as indicated by progressively higher shear force values (Table 4).

The incorporation of shredded chokeberry pomace in pork burgers was expected to influence their textural properties. Previous studies have shown that the texture of burger-type meat products can be significantly affected by the composition of raw materials, particularly when nonmeat ingredients are introduced [40,41]. Changes in the texture parameters of minced meat products due to plant ingredient additions may be attributed to their impact on the meat batter matrix. The observed increase in the “hardness” of pork burgers as the amount of chokeberry pomace increased is likely related to greater thermal loss and shrinkage compared to the control product (Table 1). Moreover, the shear force of burgers could have been affected by components such as dietary fiber in chokeberry pomace; however, the quantity of pomace added to the meat batter was relatively minor.

Limited research exists on the impact of crushed fruit pomace on the textural properties of meat products. Therefore, this discussion focuses on how valorized forms of pomace influence meat texture. Martín-Sánchez et al. [50] examined the effect of fresh date palm by-products at levels of 0%, 5%, 10%, and 15% on the texture of a champagne-type pork pâté using texture profile analysis (TPA). The authors suggested that date palm by-products, being rich in dietary fiber, could affect the protein–water and protein–protein gel network, thereby influencing pâté consistency. However, significant (p < 0.05) increases in hardness and gumminess were observed only in the product with the lowest level of date paste addition. Meanwhile, measurements of texture parameters such as springiness, cohesiveness, and resilience indicated that date “paste” did not significantly alter the deformation properties or recovery after compression.

Instrumental texture parameters of meat products can also be influenced by the addition of dried fruit and vegetable pomace [44,49]. In a TPA test of pork patties where dried kinnow pomace powder was used to replace lean meat at levels of 0%, 2%, 4%, and 6%, hardness significantly increased (p < 0.05) with the addition of 4% and 6% of the plant ingredient compared to the control product [49]. The increase in hardness was attributed to improved binding properties of the meat batter after heat treatment, likely due to the higher fiber content.

3.5. Microbiological Quality of Pork Burgers During Storage

The black chokeberry pomace used in the burgers exhibited good microbiological quality. In the pomace samples, only aerobic mesophilic microorganisms and bacteria from the Enterobacteriaceae family were detected, both at a level of 1 × 10² cfu/g. No lactic acid bacteria, yeasts, or molds were found in the pomace samples.

The microbial quality results for pork burgers are presented in

Table 5. Changes in microbial quality [cfu/g] (n = 12) of pork burgers with added black chokeberry pomace during storage (mean value standard deviation).

Storage Time [Days]	BC *	B2 *	B3.5 *	B5 *
	Total Count of Aerobic Mesophilic Microorganisms
1 7 14	2.2 × 101 a ± 7.6 × 100 2.7 × 102 a ± 3.5 ×102 1.5 × 103 b ± 2.2 × 103	1.2 × 101 a ± 5.8 × 100 3.2 × 101 a ± 2.6 × 101 9.0 × 102 ab ± 7.0 × 101	1.1 × 101 a ± 1.2 × 100 1.0 × 103 a ± 1.6 × 103 4.2 × 103 ab ± 9.5 × 102	3.5 × 101 a ± 5.0 × 100 4.5 × 101 a ± 5.0 × 100 1.9 × 103 b ± 2.0 × 103
p-value	Treatment: p = 0.1049	Storage time: p = 0.0000		Treatment × Storage time: p = 0.0921
	Psychotropic bacteria
1 7 14	2.3 × 101 a ± 2.5 × 100 1.4 × 101 a ± 4.0 × 100 3.6 × 102 d ± 4.0 × 101	2.1 × 101 a ± 2.0 × 100 2.0 × 101 a ± 1.0 × 101 1.6 × 102 bc ± 5.3 × 101	1.0 × 101 a ± 5.8 × 100 6.0 × 101 ab ± 1.7 × 101 2.7 × 102 cd ± 7.6 × 101	1.1 × 101 a ± 2.0 × 100 2.2 × 101 a ± 1.0 × 101 2.0 × 102 cd ± 1.5 × 101
p-value	Treatment: p = 0.0040	Storage time: p = 0.0000		Treatment × Storage time: p = 0.0027
	Lactic acid bacteria (LAB)
1 7 14	1.2 × 101 a ± 1.5 × 100 2.9 × 101 a ± 1.0 × 101 9.1 × 103 c ± 1.7 × 102	1.7 × 101 a ± 6.0 × 101 1.8 × 101 a ± 4.4 × 100 5.7 × 103 b ± 1.9 × 103	1.7 × 101 a ± 1.1 × 101 3.6 × 101 a ± 5.3 × 100 5.2 × 103 b ± 3.4 × 103	3.3 × 101 a ± 2.1 × 101 2.7 × 101 a ± 2.1 × 101 2.5 × 103 ab ± 5.6 × 102
p-value	Treatment: p = 0.0040	Storage time: p = 0.0000		Treatment × Storage time: p = 0.0007
	Bacteria from the Enterobacteriaceae family
1	ND **	ND **	ND **	ND **
7	ND **	ND **	ND **	ND **
14	ND **	ND **	ND **	ND **
	Pseudomonas spp.
1	1.5 × 102 a ± 5.0 × 101	1.5 × 102 a ± 7.0 × 101	2.7 × 102 a ± 2.1 × 102	1.1 × 102 a ± 1.5 × 101
7	1.9 × 102 a ± 6.0 × 101	1.4 × 102 a ± 4.0 × 101	2.8 × 102 a ± 1.9 × 102	5.3 × 102 a ± 2.8 × 102
14	8.9 × 103 c ± 6.3 × 102	2.5 × 103 b ± 1.4 × 103	1.3 × 103 ab ± 2.1 × 102	2.7 × 103 b ± 1.2 × 103
p-value	Treatment: p = 0.0000	Storage time: p = 0.0000		Treatment × Storage time: p = 0.0000
	Brochothrix thermosphacta
1	ND **	ND **	ND **	ND **
7	1.3 × 102 a ± 5.8 × 101	1.1 × 102 a ± 1.0 × 101	1.0 × 102 a ± 6.0 × 100	1.6 × 102 a ± 3.6 × 101
14	7.5 × 103 b ± 1.3 × 103	5.7 × 103 b ± 1.1 × 103	6.9 × 103 b ± 2.5 × 103	5.2 × 103 b ± 2.0 × 103
p-value	Treatment: p = 0.4225	Storage time: p = 0.0000		Treatment × Storage time: p = 0.4491
	Yeast and molds
1	ND **	ND **	ND **	ND **
7	ND **	ND **	ND **	ND **
14	ND **	ND **	ND **	ND **

* Treatments: BC—pork burgers without chokeberry pomace; B2—pork burgers with 2.0% chokeberry pomace; B3.5—pork burgers with 3.5% chokeberry pomace; B5—pork burgers with 5.0% chokeberry pomace; a–d—mean values regarding a given microbial group marked with different letters are significantly different at p < 0.05. ** not detected in 0.1 g of sample.

.

Aerobic mesophilic microorganisms were detected in all burger treatments, with counts ranging from 1.1 × 10¹ cfu/g in the B3.5 product on day 1 to 4.2 × 10³ cfu/g in the same product on day 14 (Table 5).

Only storage time significantly affected (p < 0.05) the total number of mesophilic microorganisms in pork burgers; product treatment had no significant effect (p > 0.05), nor was there an interaction between treatment and storage time (p > 0.05). These findings suggest that aerobic mesophilic microorganisms introduced into the B2–B5 products via chokeberry pomace did not significantly (p > 0.05) increase burger contamination compared to the control product (BC). Conversely, the addition of chokeberry pomace did not significantly inhibit the growth of aerobic mesophilic microorganisms. The microbiological quality of the burgers was likely influenced by heat treatment, which reduced the initial microbial load in the meat product.

Regarding the effect of storage time, no significant differences (p > 0.05) were observed in the number of aerobic mesophilic microorganisms among burger treatments (BC–B5) on any of the testing days (Table 5). Regardless of the amount of chokeberry pomace added, the number of aerobic mesophilic microorganisms increased over the 14-day storage period. However, a significant increase (p < 0.05) from day 1 to day 14 was observed only in the BC and B5 products.

Psychrotrophic bacteria were present in all burger treatments (Table 5), and both product treatment and storage time significantly influenced (p < 0.05) their counts. An interaction between these factors was also observed.

On day 1, psychrotrophic bacteria counts ranged from 1.0 × 10¹ cfu/g in the B3.5 and B5 products to 2.3 × 10¹ cfu/g in the BC product (Table 5). Similar to aerobic mesophilic microorganisms, psychrotrophic bacteria increased in all burger treatments (BC–B5) during storage. In the first seven days, the growth of these bacteria was insignificant (p > 0.05), regardless of the amount of pomace added. On days 1 and 7, no significant differences (p > 0.05) were observed in psychrotrophic bacteria counts between the control burger (BC) and those containing chokeberry pomace (B2–B5). However, by day 14, a significant increase (p < 0.05) was observed in all treatments. On the final storage day, a significant (p < 0.05) difference in psychrotrophic bacterial contamination was noted between the B2 product, which had the lowest count (1.6 × 10² cfu/g), and the BC product, which had the highest count (3.6 × 10² cfu/g).

Lactic acid bacteria (LAB) were detected in all pork burger treatments (Table 5). LAB counts ranged from 1.2 × 10¹ cfu/g in the BC product on day 1 to 9.1 × 10³ cfu/g in the same product on day 14. Both product treatment and storage time significantly affected (p < 0.05) LAB counts, and an interaction between these factors was observed.

Regardless of the amount of chokeberry pomace added, LAB counts increased during storage (Table 5). From day 1 to day 7, the increase in LAB was insignificant (p > 0.05) across all burger treatments. Additionally, no significant differences (p > 0.05) in LAB counts were found between the control product (BC) and burgers containing chokeberry pomace (B2–B5) on these days. However, on day 14, a significant (p < 0.05) increase in LAB was observed in the BC product and products with lower amounts of chokeberry pomace (B2 and B3.5). In contrast, the increase in LAB during storage was not significant (p > 0.05) in the B5 product, which contained the highest proportion of pomace. Notably, on day 14, LAB counts in burgers with chokeberry pomace (B2–B5) were significantly lower (p < 0.05) than in the control product (BC).

The number of Pseudomonas bacteria in pork burgers ranged from 1.5 × 10² cfu/g (B5 product, day 1) to 8.9 × 10³ cfu/g (BC product, day 14; Table 5). Statistical analysis indicated that both product treatment and storage time significantly affected (p < 0.05) Pseudomonas spp. counts, and an interaction between these factors was observed.

From day 1 to day 7, Pseudomonas counts did not differ significantly (p > 0.05) across pork burger treatments, regardless of chokeberry pomace content (Table 5). However, on day 14, a significant increase in Pseudomonas contamination was observed in all pork burgers except for the B3.5 product. The highest Pseudomonas growth was recorded in the BC product, while products containing chokeberry pomace (B2–B5) exhibited lower bacterial counts. On day 14, Pseudomonas counts in products B2–B5 were significantly lower (p < 0.05) than in the BC product.

After burger production (day 1), no B. thermosphacta was detected in any pork burger treatments (Table 5). Only storage time significantly affected (p < 0.05) B. thermosphacta counts, while product treatment and the interaction between these factors had no significant effect.

The results indicate that adding chokeberry pomace did not significantly (p > 0.05) influence B. thermosphacta counts in pork burgers on any storage day (Table 5). However, the number of these bacteria increased over time, with significant growth (p < 0.05) observed between days 7 and 14 across all treatments (BC–B5). On day 7, B. thermosphacta counts ranged from 1.0 × 10² cfu/g (B3.5 product) to 1.6 × 10² cfu/g (B5 product). By day 14, counts increased to between 5.2 × 10³ cfu/g (B5 product) and 7.5 × 10³ cfu/g (BC product).

Throughout the 14-day refrigerated storage period, no Enterobacteriaceae family bacteria, yeasts, or molds were detected in any of the products, regardless of the amount of chokeberry pomace added (Table 5).

The findings suggest that all pork burger treatments in this study maintained good microbiological quality, as Enterobacteriaceae bacteria are considered indicators of food microbiological quality and production hygiene [51]. On days 1 and 7, the addition of chokeberry pomace, regardless of concentration, did not significantly reduce the growth of aerobic mesophilic microorganisms, psychrotrophic bacteria, LAB, Pseudomonas spp., or B. thermosphacta. However, by day 14, chokeberry pomace had a beneficial effect on microbiological quality, as products containing pomace (B2, B3.5, and B5) exhibited significantly lower LAB and Pseudomonas counts than the control product (BC). Importantly, incorporating chokeberry pomace did not negatively impact microbiological quality or compromise the health safety of the burgers. Given that raw, unprocessed chokeberry pomace is a potential source of microflora and is susceptible to microbiological spoilage [10], the results obtained are satisfactory. While these findings are preliminary, they provide a foundation for designing improved meat products incorporating plant by-products.

The available literature provides no information on the direct application of unprocessed chokeberry pomace in meat products. However, research has focused on using dried fruit or vegetable pomace and extracts derived from pomace [14,15,17,45].

Black chokeberry fruits and their by-products, such as pomace, are rich in polyphenolic compounds, with anthocyanins being the dominant group [20,24]. These compounds are known for their antioxidant and antimicrobial properties [22]. According to Diez-Sánchez et al. [12], the antimicrobial effect of pomace is believed to result from both the presence of many bioactive compounds and the low pH value.

Minced meat products, such as burgers stored at refrigerated temperatures, provide an ideal environment for microbial growth, leading to quality deterioration and reduced shelf life. While no legal limit exists for the maximum number of aerobic mesophilic bacteria in meat products, it is generally accepted that they become unfit for consumption when bacterial counts reach 7–8 log cfu/g [52]. Additionally, LAB, Pseudomonas, Enterobacteriaceae, and B. thermosphacta can proliferate under refrigerated conditions [51,53,54].

Babaoğlu et al. [14] investigated the antibacterial properties of water extracts from various fruit pomaces, including black chokeberry, blackberry, red currant, and blueberry (60 g/800 g of meat batter), as potential ingredients in minced beef patties stored under refrigeration for 9 days. On the first day after production, the total number of aerobic mesophilic bacteria was significantly (p < 0.05) lower in products containing extracts from chokeberry, blackberry, and blueberry pomace compared to the control. This trend persisted until day 6 of storage. The observed reduction in the antibacterial activity of berry pomace extracts was attributed to the gradual degradation of bioactive compounds, including polyphenols. A similar decline in antibacterial activity was observed for psychrotrophic bacteria, LAB, and Staphylococcus bacteria. Unlike in the present study, Babaoğlu et al. [14] found that none of the berry pomace extracts significantly inhibited LAB growth during beef patty storage. However, the authors concluded that water extract from black chokeberry pomace was the most promising natural preservative among the tested berry pomace extracts.

Tamkutė et al. [45] evaluated the effects of different concentrations of water and ethanol extracts from defatted chokeberry pomace on the growth of selected pathogenic and spoilage bacteria. Based on results obtained from pork slurries, ethanol extract from chokeberry pomace was selected for further testing in pork meat products. One of these products was minced meat burgers, which, according to the authors, provide a particularly favorable environment for microbial growth due to significant cell damage, high free water content, and suitable pH. Spoilage of such refrigerated meat products is largely attributed to the growth of B. thermosphacta, LAB, Pseudomonas spp., and Enterobacteriaceae. While heat treatment can stabilize the microbiological quality of burgers, it may also weaken the antimicrobial properties of plant extracts due to the degradation of temperature-sensitive bioactive compounds. It was found that adding 2% ethanol extract from chokeberry pomace inhibited the growth of B. thermosphacta in pork burgers during 16 days of refrigerated storage. In samples without extract, B. thermosphacta counts increased to 7 log cfu/g, while in samples containing the extract, bacterial counts remained significantly lower at 3.87 log cfu/g. Additionally, chokeberry pomace extract effectively inhibited the growth of aerobic mesophilic bacteria, Pseudomonas putida, and LAB during storage. On day 16, the number of these microorganisms in burgers with the extract was significantly lower than in the control product.

Garrido et al. [17] examined the effect of two types of red grape pomace extracts on the microbiological quality of pork burgers packed under aerobic conditions and stored at +4 °C for 6 days, simulating retail conditions. The authors found no significant effect of grape pomace extracts on total viable count, psychrophilic bacteria, or coliforms. Instead, the primary factor influencing microbial growth was storage duration. By day 6, regardless of raw material modifications, bacterial counts in all burgers exceeded the spoilage threshold (10⁶–10⁷ cfu/g). The authors attributed this to the relatively low dose of added extracts (0.06 g per 100 g of final product), which may have been insufficient to exert a strong antimicrobial effect.

Skwarek and Karwowska [15] investigated the effect of freeze-dried tomato pomace (0.5%, 1%, 1.5%) on the quality of dry fermented sausages with reduced nitrite content. Their findings demonstrated a significant reduction in Enterobacteriaceae counts with increasing levels of tomato pomace powder.

Koskar et al. [55] compared the antimicrobial properties of plant-based powder preparations, including chokeberry pomace, in both raw and cooked minced pork. The study concluded that plant preparations have a strong potential for developing meat products with satisfactory microbiological quality. However, the highest antimicrobial effectiveness was observed in combinations of various plant powders rather than individual components.

4. Conclusions

The incorporation of chokeberry pomace into the meat batter for pork burgers was expected to influence the quality of the final product, and the results of this study confirmed this hypothesis.

This study demonstrated that using black chokeberry pomace in a minimally processed raw form for pork burgers does not pose technological challenges but significantly affects multiple quality parameters. The addition of chokeberry pomace influenced the culinary quality characteristics of pork burgers, which may impact consumer acceptance. As the level of pomace increased, thermal loss also increased (p < 0.05), ranging from 23.5% (BC) to 30.8% (B5). Additionally, the addition of chokeberry pomace lowered (p < 0.05) the pH of the burgers, from 6.93 (BC, day 1) to 6.74 (B5, day 14), and influenced (p < 0.05) the composition of water, protein, fat, and sodium chloride. The increased thermal losses associated with higher pomace concentrations likely contributed to these differences. The pork burgers contained at least 26.68% protein (BC), no more than 13.96% fat (B5), and no more than 1.94% sodium chloride.

Chokeberry pomace significantly affected the color quality of pork burgers. Burgers containing chokeberry pomace (B2–B5) were significantly (p < 0.05) darker, redder, and less yellow compared to the control product (BC). The color parameter values varied as follows: lightness (L*) ranged from 46.98 (B5, day 14) to 64.42 (BC, day 1); redness (a*) varied from +5.44 (BC, day 14) to +9.61 (B5, day 14); and yellowness (b*) ranged from –2.77 (B5, day 14) to +10.58 (BC, day 1). The observed color differences were likely due to the anthocyanin pigments found in chokeberry pomace. The addition of chokeberry pomace resulted in a gradual increase in shear force, which ranged from 20.83 N to 27.99 N over 14 days of storage.

The addition of chokeberry pomace (2–5%, B2–B5) did not cause significant (p < 0.05) differences between the control product (BC) and pomace-containing products in terms of microbial counts on days 1 and 7. The satisfactory microbiological quality of the burgers was demonstrated by the absence of Enterobacteriaceae, yeasts, and molds in all treatments throughout the 14-day storage period. However, on the final day of storage, the chokeberry pomace exhibited moderate antimicrobial properties, as indicated by significantly lower (p < 0.05) counts of LAB and Pseudomonas spp. in B2–B5 products compared to BC.

In conclusion, raw, unprocessed chokeberry pomace is a perishable material susceptible to microbiological changes, which limits its industrial application despite its potential, as demonstrated in this work. The use of raw chokeberry pomace in meat products would likely require pretreatment to reduce microbial contamination, which would increase production costs. Nevertheless, these findings contribute to the development of more sustainable meat products in the convenience food category, incorporating plant by-products. However, for such innovative products to be commercially viable, they must meet consumer acceptance criteria. Therefore, a thorough evaluation of chokeberry pomace’s impact on pork burger quality should include sensory analysis, considering attributes such as color, taste, flavor, and texture. The sensory quality of burgers containing chokeberry pomace will be the focus of future research.