Oil Uptake Lessening and Functionality Amelioration of Deep-Fried Fish Fillets Using Egg White Protein Edible Coating ^†

Abstract

This study aimed to develop an edible egg white protein coating to reduce fat uptake and mitigate protein oxidation in deep-fried Labeo rohita fillets. Fillets (4 × 4 × 2 cm) were coated with 2.5–25% egg white protein and analyzed for proximate composition, frying yield, coating pickup, protein solubility, water-holding capacity, carbonyls, sulfhydryl groups, texture, colour, and sensory attributes. Increasing coating concentration improved coating pickup (2.65–8.36%), frying yield (70.45–80.26%), and reduced fat uptake (9.67–48.66%), while offering partial oxidative protection. Sensory evaluation identified 15% egg white protein coating as most acceptable, and it also effectively lowered fat absorption while preserving protein quality, yielding a healthier fried fish product.

1. Introduction

Deep frying is the most popular method of cooking food products because it gives a crispy texture, an attractive golden colour, and a distinct flavour to the fried products. However, it also has several drawbacks, such as excessive oil absorption, protein denaturation, and the formation of thermally degraded products [1]. The rapid loss of moisture and sustained exposure to high temperature during frying promote protein unfolding, aggregation, and oxidative changes. For this reason, the structural integrity of muscle tissue becomes weak, leading to reduced juiciness, loss of texture, and decline in nutritional quality of fish and other protein-rich food products [2]. Due to these physicochemical changes, there is a need to develop effective strategies to stabilize muscle protein and reduce oil uptake during frying.

In the past few years, egg white protein (EWP) has gained considerable attention as an edible coating material to protect food during frying. It offers a wide range of functional properties including gelling, foaming, emulsifying, and film-forming, which make it effective in stabilizing muscle protein under high temperatures. Li et al. [3] noticed that heat-stable protein fractions such as ovalbumin and ovotransferrin help to maintain structural integrity and reduce protein denaturation. Similarly, Myers and Brannan [4] underlined the nutritional and techno-functional advantages of EWP, highlighted its suitability for improving the quality of fried food products. During frying, the interaction between EWP and lipids strengthens the protein network, forming a compact surface film that acts as a protective barrier [5]. Besides structural protection, EWP coating not only reduces moisture loss and oil absorption but also enhances the bioavailability of egg protein and supportsitscontribution in the development of healthier fried foods [1].

During frying, oil absorption in fried products is influenced by several factors especially the structural changes that occur due to rapid heating and cooling. When moisture rapidly evaporates, it creates small pores and channels that make it easier for oil to enter the product during the phase. To address this challenge, researchers have been investigating protein-based edible coatings as a potential way to reduce oil uptake in fried products. Cui et al. [6] showed that the addition of functional proteins (soy protein, egg white protein, and whey protein) to the batter system helped fried fish nuggets to retain more moisture and form a uniform crust layer which reduced oil absorption. Similarly, the coatings prepared from mineral-induced milk protein co-precipitates formed a smooth and uniform surface layer that restricted oil penetration in fried potato strips [7]. Xie et al. [1] also reported that protein-based coatings can reduce pore size, improve moisture retention, and modify crust formation that helps to minimize fat uptake during frying.

Despite notable advances in frying technology, the consistent reduction in oil absorption in fried products is still a challenge. During frying, the heat and mass transfer are influenced by multiple interacting factors, such as coating thickness, frying time, frying temperature, dehydration rate, and even the type of oil used. Furthermore, the use of edible protein coatings, especially EWP on fish fillet has received relatively little attention. This is because fish muscle protein is more delicate and contains more moisture than other processed fish products like fried fish nuggets [6]. Developing an effective method to reduce oil absorption requires a clear understanding of how EWP interacts with fish muscle tissue during dehydration, crust formation, and thecooling phase. Considering these aspects, the aim of the present study is to integrate EWP-based edible coating with optimized coating and frying conditions to produce fried Labeo rohita fillet with improved functionality, reduced oil absorption, and better nutritional profile.

2. Materials and Methods

Fresh Labeo rohita (2.02 ± 0.19 kg; 51.98 ± 0.92 cm) were purchased in live condition from a local fish market in Agartala, India, transported on ice (fish: ice = 1:1, w/w), and processed immediately upon arrival at the processing facility. After washing, beheading, and descaling, fish were manually filleted and cut into uniform strips (4 × 4 × 2 cm; 40 ± 1 g), ensuring removal of visible fat and irregular tips to maintain consistency across samples.

Egg white protein (Egg albumen protein, Madren healthcare, Pvt Ltd., Rajasthan, India) coating solution with different concentrations of 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 20%, and 25% was formulated with water (

Table 1. Codes assigned to different coating concentrations of egg white protein on fish fillets.

Code	Treatment
UN	Uncoated sample
EW1	2.5% aqueous egg white protein suspension
EW2	5% aqueous egg white protein suspension
EW3	7.5% aqueous egg white protein suspension
EW4	10% aqueous egg white protein suspension
EW5	12.5% aqueous egg white protein suspension
EW6	15% aqueous egg white protein suspension
EW7	20% aqueous egg white protein suspension
EW8	25% aqueous egg white protein suspension

). Rohu fillets were uniformly dipped, drained, and weighed to determine coating pick-up. Coating pickup (%) was quantified as described by Akdeniz et al. [8] using the percentage weight difference before and after coating.

Deep-fat frying was performed using a 2 L electric fryer (Inalsa Professional, 1700 W, Noida (Uttar Pradesh), India). Egg white protein (EWP) coated and uncoated fish fillets were fried at 180 °C for 5 min in fresh batches of refined soybean oil (Adani Wilmar Ltd., Haldia (West Bengal), India). Temperature was monitored using a calibrated metal thermometer. Post-frying, fillets were drained on absorbent paper and cooled to room temperature prior to analysis. Frying yield was calculated based on the weight difference between raw coated and fried samples following the method of Devatkal et al. [9]. Reduction in fat uptake (%) in coated fillets was computed using the equation proposed by Keller et al. [10].

The proximate composition was analyzed following the method of AOAC, 2016 [11]. For the analysis of protein content, a micro-Kjeldahl apparatus was used, while lipid was analyzed using Soxhlet extraction with petroleum ether (60–80 °C). All analyses were conducted in triplicate on a wet-weight basis.

Water-holding capacity (WHC) was measured following the method of Barrera et al. [12]. A 5 g sample was loaded onto Whatman No. 1 filter paper, centrifuged at 5000× g at 4 °C for 5 min (Eppendorf 5430R), and WHC was expressed as retained water percentage. Protein solubility was assessed according to Benjakul and Bauer [13] using homogenization in 0.6 M KCl, centrifugation, precipitation with TCA, and solubilization in NaOH, followed by Biuret protein estimation [14].

Oxidative stability indicators were analyzed through total carbonyl and sulfhydryl content estimation. Carbonyl content was measured following the method of Mercier et al. [15] using DNPH derivatization and absorbance at 370 nm. Total sulfhydryl groups were evaluated using Ellman’s reagent according to the method described by Eymard et al. [16].

Instrumental colours (L*, a*, b*) were measured using a Hunter LabScan XE Spectrocolorimeter standardized with black and white calibration tiles. Texture profile analysis (hardness, cohesiveness, springiness, chewiness) was conducted using a TA-XT Plus texture analyser with a 75 mm compression plate under standardized conditions (40% compression; pre-test speed 1 mm/s; post-test 5 mm/s; trigger force 5 g).

Sensory evaluation was performed by trained postgraduate and doctoral students as panellists, familiar with fish-based fried products. Samples were served and evaluated using a nine-point hedonic scale following the method of Morin et al. [17]. All analyses were conducted in controlled laboratory conditions to ensure reproducibility and minimize bias.

Statistical Analysis

Statistical analyses were performed using SPSS software (version 22.0; IBM SPSS, Armonk, NY, USA). Differences among the various coating treatments were evaluated using one-way analysis of variance (ANOVA). All experiments were carried out in triplicate (n = 3), and the results are expressed as mean values ± standard deviation (SD). When statistically significant differences were detected, Duncan’s multiple-range test was applied as a post hoc analysis at a significance level of p < 0.05 to compare the coated samples with the uncoated fried fish fillets used as the control.

3. Results and Discussion

The application of EWP coatings significantly improved the frying behaviour and sensory quality attributes of fresh Labeo rohita fillets during deep-frying. The moisture content of the fresh fish fillets was 78.46% that reduced to 65.55% in uncoated fish fillets after deep frying (

Table 2. Effect of protein coatings on proximate composition of fish fillets after frying.

Treatments	Parameters (% Wet Weight Basis)
	Moisture	Protein	Lipid	Mineral (Ash)
Fresh fish	78.46 ± 0.36 a	16.55 ± 0.39 e	1.71 ± 0.17 h	1.65 ± 0.24 c
UN	65.55 ± 0.39 e	19.51 ± 0.37 d	10.20 ± 0.14 a	2.52 ± 0.23 b
EW1	66.35 ± 0.05 d	19.68 ± 0.09 cd	9.21 ± 0.11 b	2.58 ± 0.07 b
EW2	66.75 ± 0.10 c	19.85 ± 0.12 cd	8.49 ± 0.09 c	2.60 ± 0.05 b
EW3	67.17 ± 0.06 c	20.26 ± 0.13 c	7.51 ± 0.12 d	2.65 ± 0.04 ab
EW4	67.83 ± 0.09 b	20.75 ± 0.15 ab	6.85 ± 0.12 fg	2.75 ± 0.04 ab
EW5	68.16 ± 0.08 bc	20.82 ± 0.13 ab	5.82 ± 0.09 f	2.76 ± 0.06 a
EW6	68.47 ± 0.09 c	21.17 ± 0.09 b	5.24 ± 0.13 e	2.65 ± 0.04 a
EW7	67.99 ± 0.06 c	22.13 ± 0.12 a	5.33 ± 0.08 fg	2.69 ± 0.06 a
EW8	67.83 ± 0.06 c	22.20 ± 0.15 a	5.43 ± 0.09 fg	2.69 ± 0.07 a

The values presented in the table are means ± SD, n = 3. Mean values bearing different superscripts (a, b, c, etc.) in a column are significantly different (p < 0.05).

). The fish fillet coated with 15% egg white protein (EW6) was shown to have the maximum protective effect on moisture (68.47%). During frying, the protective effect of egg white protein against moisture loss is due to the development of a cohesive, thermally induced protein film that slows down mass transfer by minimizing moisture loss and preventing pore enlargement. Gaurav et al. [18] reported that soy protein-based edible coatings undergo rapid denaturation to form dense surface matrices that slow moisture loss and structural collapse. Similar findings were also reported by Varidi et al. [19] in which the moisture content of the fried eggplant coated with Aloe vera gel rose from 41.06% to 60.52%.

The protein content of the fresh rohu fillet was found to be increased from 16.55% to 19.51% (uncoated fish fillets) after frying (Table 2). Hamad [20] reported that during pan frying, the protein content was increased significantly from 16.95% to 28.44% primarily due to moisture evaporation, which concentrates residual solids. The rohu fillet coated with egg white protein was found to increasefrom 19.68% (EW1) to 22.20% (EW8), attributable to the deposition and integration of protein coating into the surface crust during frying. Cui et al. [6] reported that in fish nuggets, protein coating (soy protein, egg white protein, and whey protein) contributes directly to the total measurable protein after frying. This effect results from the thermal behaviour of the protein coating, which unfolds and aggregates at frying temperatures to create a cohesive, compact surface layer that binds firmly to the food matrix and raises the solid mass of the crust [1]. Gaurav et al. [18] also demonstrated that soy protein isolate coatings increased the final protein (20.46–23.10%) in fried fish fillets by forming strong protein networks that bind to the crust, supporting the present observations.

The fat uptake reduction (%) was depicted in Figure 1, which was found to increase significantly from 9.67% (EW1) to 48.66% (EW6) with increasing the concentrations of egg white protein coating, but on further enhancement of coating concentration, the value decreased to 46.73% (EW8). The uncoated fried rohu fillets showed the highest fat due to rapid loss of moisture, pore enlargement, and capillary suction that formed during cooling after deep-frying. Meanwhile, the fish fillet coated with egg white protein enhanced fat uptake reduction by forming a compact surface barrier that reduces pore connectivity and oil penetration both during and after the frying process. During the frying process, the chemical interactions between oil and the food matrix initiate several changes including unfolding of proteins, breakdown and oxidation of frying oil, starch gelatinization, and development of various heat-derived compounds [21]. Gaurav et al. [18] reported that fish fillet coated with 15% soy protein isolate reduced fat uptake by 57.78%. Adrah et al. [22] also noticed that in a sweet potato starch-based battered sample, 5% chicken protein in edible coating reduced fat uptake by >52% in deep-fat-fried chicken. The reduction in fat uptake in protein-coated fried products is due to the protective effect of protein coating that restricts the migration of moisture and oil by forming a film throughout the food matrix [1]. Additionally, the rapid thermal-gelation effect of egg white protein above 70 °C makes the surface matrix stronger, which reduces the capillary pathways associated with fat uptake.

The frying yield (%) of egg white protein-coated samples wassignificantly increased from 70.45% (EW1) to 80.26% (EW6), as shown in

Table 3. Effect of protein coatings on coating parameters of fish fillets after frying.

Treatments	Coating Parameters
	Frying Yield (%)	Coating Pickup (%)	Water Holding Capacity (%)
UN	68.20 ± 0.16 h	0.00 ± 0.00 j	69.58 ± 1.14 f
EW1	70.45 ± 0.22 g	2.65 ± 0.34 i	72.45 ± 1.20 e
EW2	72.48 ± 0.25 f	3.53 ± 0.19 h	73.49 ± 1.23 de
EW3	73.71 ± 0.26 e	4.37 ± 0.18 g	74.72 ± 1.13 cd
EW4	76.25 ± 0.24 d	5.30 ± 0.17 f	75.44 ± 1.42 bcd
EW5	78.32 ± 0.29 b	7.47 ± 0.29 e	77.62 ± 1.34 ab
EW6	80.26 ± 0.26 a	8.36 ± 0.27 d	78.13 ± 1.56 a
EW7	77.37 ± 0.32 c	10.87 ± 0.33 b	76.57 ± 1.24 abc
EW8	76.46 ± 0.34 d	12.44 ± 0.25 a	76.43 ± 1.31 abc

The values presented in the table are means ± SD, n = 3. Mean values bearing different superscripts (a, b, c, etc.) in a column are significantly different (p < 0.05).

. However, with further increase in coating concentrations, the value was found to decrease. The higher frying yields directly reflect reduced moisture loss, enhanced crust formation, and minimized structural deformation during frying. The high viscosity of the egg white protein coating allows it to form a uniform film over the fish fillet which helps to retain its shape and prevent product loss during frying and leads to higher frying yield [6]. Coating pickup is defined as the amount of coating material that sticks to the surface of the product, and it is measured as the % increase in weight [23]. In the present study, the coating pickup (%) was found to be increased significantly (p < 0.05) from 2.65% (EW1) to 12.44% (EW8) as displayed in Table 3. The rise in coating pickup (%) may be explained by an increase in viscosity and solid content at higher coating concentration, which enhances film adherence to the rohu fillet.

Water-holding capacity (WHC) is the ability of fish muscles to retain water, which is a critical factor for juiciness, texture, and yield. It determines the functional and textural properties of fried products. It is also playing a major role in changing protein structure and water distribution [24]. In the present study, it was reported that the WHC of fresh rohu fillet was 75.88% that reduced significantly (p < 0.05) to 69.58% in uncoated rohu fillet after frying (Table 3). It was noticed that all the EWP-coated samples have more WHC than the uncoated samples after frying. The 15% EWP coating (EW6) showed the highest WHC (78.13%), followed by EW5(77.62%) and EW4 (75.44%). The highest WHC in the EWP-coated samples can be attributed to the formation of a cohesive protein gel network capable of entrapping moisture within the fish matrix during frying.

Sensory analysis is a critical parameter for quality evaluation of any food product. Among all the EWP-coated rohu fillet the highest overall acceptance was shown by EW4 and EW6 which have the same sensory score of 7.56 (Figure 2). However, based on fat uptake reduction, EW6 (48.66%) has shown better performance compared to EW4 (32.88%).

4. Conclusions

The present study demonstrates that egg white protein (EWP) edible coating markedly enhances the physicochemical, structural, and functional attributes of deep-fried Labeo rohita fillets, providing a viable strategy to develop healthier fried fish products without compromising sensory quality. Application of 15% EWP formed a cohesive thermo-gelated protein film that effectively limited moisture loss, restricted pore formation, improved water retention during frying, and reduced fat uptake by nearly 50% compared to uncoated fish fillets.Overall, the present findings reinforce contemporary evidence that protein-based edible coatings, especially EWP, offer superior film-forming and barrier properties that can significantly improve the quality of fried seafood. Considering the nutritional significance of Labeo rohita and the increasing consumer demand for lower-fat fried foods. Furthermore, EWP shows strong potential as an industry-compatible, clean-label coating material. Future research may integrate microstructural imaging (e.g., micro-CT), flavour–texture modelling, or antioxidant-enriched coatings to further optimize product performance.