1. Introduction
Microbial contamination affects the safety and quality characteristics of foods, and may occur at any stage, during production, transport, processing, meal preparation, domestic storage, and retail trade [
1,
2]. Food-borne illnesses associated with pathogenic micro-organisms present a major community health concern throughout the world. Increased incidence of food borne illnesses (
Escherichia coli O157:H7 and
Listeria monocytogenes) has also spurred greater interest in finding innovative technologies to control infectious growth in foods. These technologies maintain quality, safety, and freshness [
3]. Antimicrobials are chemical mixtures, added or naturally originate in foods that inhibit or deactivate pathogenic and spoilage microorganisms [
4]. Spoilage may occur as an outcome of mishandling during the handling, commercialization, storage and distribution of the products [
5].
Antimicrobial edible coating is among the novel technologies to control the bacterial development and improves protection, while delays degeneration of essence, fish and pullet products [
6]. Essential oils (EOs) are fragrant and instable oily abstracts gathered from plant resources including buds, flowers, bark, roots, and verdures by revenue of appearance, fermentation, abstraction, or vapor concentration. EOs are usually applied as an additive mediator in products. These are likewise identified as a class of normal stabilizers, since their durable antimicrobial and antioxidant activity have been demonstrated in preceding inquiries [
7]. In horticulture products, coating plays an important role to maintain surface moisture and firmness, and prevents the weight loss of product during storage [
8]. The function of the coating is to reduce the metabolic actions in fresh food due to the reduction of respiration rate by serving as a moisture and oxygen barrier [
9]. Nowadays, there are different coating components that are used, in which some polysaccharides like chitosan and alginate have gained more attention [
10,
11].
Pomegranate (
Punica granatum) belongs to the
Punicaceae family and is commonly called ‘’ponus’’ and ‘’granatus’’ that is consequent from the Latin words. The wrapping of the pomegranate characterizes practically 26–30% of the fruit. The polyphenols including flavonoids (i.e., catechin and anthocyanins), hydrolysable tannins (i.e., ellagic acid, punicalagin, gallic acid, gallic penicillin, and pedunculagin), and total antioxidant capacity are high in this portion of pomegranate. These chemical compounds are present in the pomegranate peel and juice, and justify the 92% of the antioxidant activity related with the fruit [
12]. Forms of hydrolysable tannins are present in the pomegranate peel, and consist mainly of hexa-hydroxydiphenic acid and its products, as well as ellagic acid and its derivatives, penicillin, and punicalagin [
13]. The pomegranate peel and seed extracts are good sources of antioxidants and antimicrobials. The efficacy of pomegranate extract (PE) is considered to be high, in scavenging the hydroxyl and superoxide anion radicals. High concentration of PE could inhibit the growth of pathogens and spoilage bacteria. The addition of PE in chicken meat products enhances its shelf life by 2–3 weeks during refrigerated storage. PE is considered effective in controlling the oxidative rancidity in chicken products [
14].
Pomegranate peel holds about 40–50% of the total fruit weight [
13]. It is shaped as byproduct in huge quantities by the food industry and it is an important source of bioactive compounds [
15], such as hydrolysable tannins, ellagic acid, and gallic acid esters of fundamental polyol molecules [
16]. The hydrolysable tannins that are found in pomegranate peel contain hexa-hydroxydiphenic critical (HHDP) and its derivatives, ellagic acid and its products, penicillin, and punicalagin [
13].
Based on the aforementioned, chicken meat was used for the preparation of functional chicken nuggets using different edible coatings (SA and PPP) separately or in combination. At the 0th, 7th, 14th, and 21st days of storage intervals, DPPH, TPC, TBARS, POV, Hunter color values (L*, a*, and b*), and sensory analyses were carried out to investigate the functionality, quality, and oxidative stability of chicken nuggets.
3. Discussion
Different plant sources comprise a vital source of chemical compounds, including antimicrobials and antioxidants and total phenolic compounds. The peel of fruits contains these chemicals in abundant quantities. However, the pomegranate peel is a rich source of bioactive chemicals that play valuable role in the preservation of food products. In the current study sodium alginate and pomegranate peel powder were used separately and in combination as coating materials. Results showed the potential antimicrobial and antioxidant properties of the coating formulations used for the chicken nuggets. In another study, a natural antimicrobial and nontoxic substance called chitosan was used as a coating material, comprising however, a double practical component on the stability and shelf-life extension of foods. Chitosan plays also a significant role in the inhibition of fungus progression, by decreasing the fungus cell wall structure of protein inhibitors [
18].
Moosavi-Nasab et al. [
19] carried out a study on fish fillet quality and safety in which two types of the coating (chitosan coating and chitosan coating laterally with black pepper oil) were used during the storage of the product under refrigeration. The antimicrobial activity of chitosan was also shown in another study when applied to fresh fruit as an edible coating without additional antimicrobial agents [
20]. Previous studies have reported that chitosan antifungal properties are due to a motivation of defense enzymes [
21].
Green tea extracts (rich in antioxidants and polyphenols) were used in food to prevent the oxidation process in triglycerides [
22]. Lipid oxidation can be invented and improved by dissimilar appliances, comprising the invention of singlet oxygen, enzymatic and non-enzymatic formation of free radicals and active oxygen [
23]. The alginate based film layers on the shallow of the product may delay oxygen diffusion and, thus, might have undersized fat rancidities [
22].
GSE (grape seed extract) is labeled as a strong antiradical substance possessing scavenging actions beside free fundamental and Schiff-base metal complexes, as well as synergistic achievement with other antioxidants [
22]. Yingyuad et al. [
24] reported that chitosan coating could efficiently preserve refrigerated grilled pork in contradiction of lipid oxidation (which was totally expected) in agreement with the results of the present study. Yerramilli, [
25] compacted β-carotene by soybean protein isolate (SPI), sodium caseinate (SC), and whey protein isolate (WPI) by the homogenization-evaporation technique, and reported that that cellular antioxidant action of SC, WPI, and SPI nanoparticles was higher (60%) compared to β-carotene alone (45%) in CaCO
2 cells.
A previous study indicated that edible coating of cashews reduces lipid oxidation by protecting them from oxygen exposure during storage [
26]. During the storage, an additional protective effect against lipid oxidation of the studied samples treated with GSE is probably related to the development of phenolic aldehydes, due to squalor of some phenolic compounds [
27]. The results of our study (TBARS analysis) may be connected to those reported in a previous work for chicken breast meat [
28].
The current results of the POV showed that significant differences (
p < 0.05) were occurred in both coated and uncoated samples of chicken nuggets. The coated materials PPP and SA + PPP are vital sources of antioxidants that resulted in the lower POV in the coated chicken nuggets samples as compared to the uncoated ones. These results are in agreement with those of a previous study [
29]. During storage, the value of peroxides increased, but lower POV values were obtained for the coated chicken nuggets samples. This is probably related to the antioxidant mechanisms within the coated medium structure. Antioxidants lead to the construction of quality in the product by creating cross-linking pathways; antioxidants decrease the distribution of oxygen in the surface of the product [
30].
During refrigerated storage, similar findings were reported in previous studies for saline raw minced chicken meat and raw chicken meat [
29,
30]. In the current study, the antioxidants from the coated sources decreased the POV of chicken nuggets. These results are in line with those reported by Jeon et al. [
31], who used chitosan coatings in Atlantic cod samples. In another study, whey protein and soy protein coatings were applied on sausages and beef, respectively, during refrigerated storage to evaluate the products’ safety and quality. The results of this study [
32], are similar to the current findings. Topuz et al. [
33] reported that pomegranate juice has a high amount of phenolic compounds. In this context, the phenolic-rich coating including
Zataria multiflora essential oil and chitosan was used to delay/decline oxidation in pomegranate juice [
34].
Previous findings showed that fruits and vegetables are the sources of different phenolic compounds; these compounds are basically secondary metabolites that act as antioxidants during the process of oxidative stress [
33]. Phenolic compounds also play an important role in the auto-oxidation and chelation of metal ions that can modulate the activity of enzymes. In a previous study, in which alginate was mixed with carvacrol and methyl cinnamate, it was reported the preparation of relevant coating materials for fruits. Some other similar studies, in which some coating materials were used for various fruits like chitosan coating for strawberries; chitosan and alginate coating for blueberries and alginate coating for sweet cherry [
35,
36,
37] are in line with the present work.
The results of the present study are in agreement with those reported by Krishnamoorthy et al. [
38], who documented that coating can protect the total phenolic compounds in apple slices. Another study reported that standalone films have antioxidant activity. The test film was rich in natural volatile antioxidants that prevented oxidation [
39]. In addition, the present results are in agreement with Zhang et al. [
40], who added vinegar into the fatty portion of the studied product. The obtained peroxide values declined significantly in the treated samples. In fruits, there are different phytochemical profiles as reported by Kim et al. [
41], who showed that fruit scavenging activity was influenced by the flavonoid content. Mohammadian et al. [
42] conducted a study in which whey protein nanofibrils (WPNFs) were used. The results showed that WPNFs exhibited DPPH radical-scavenging activity. However, browning is well related to radical scavenging activity. Another study showed that WPNFs have a high radical-scavenging activity that inhibits the oxidation process in food products [
43].
The alginate-based coating chicken nuggets samples recorded higher color values as compared to the uncoated samples. This finding is probably related to the properties of polysaccharides, which are surface browning materials, the oxidative rancidity and dehydration. These observations are related to the results reported by Chidanandaiah and Sanyal [
44]. In the current study, the color values of the chicken nuggets decreased with the increase in storage time intervals. These variations in color are due to the beginning of oxidation and microbial population growth. Moreover, Garcia et al. [
45] reported that there were no variations in color when potatoes were stored under edible coatings. In another study [
6], fish fillets were stored under cinnamon coatings. The reported results indicated higher b* values (yellowness) in fish fillets, which is in agreement with the results of the present study. A previous study was carried out on poultry meat in which a mixture of thyme oil and chitosan were used as the coating agents. The results showed that there was no difference in b* values in all treatments [
46]. Keokamnerd et al. [
47] reported that a* values of ground chicken meat decreased during refrigerated storage. Correspondingly, the pepper color significantly decreased when the used coatings were made with a combination of chitosan and lemongrass oil [
48]. During processing, the meat pigment called myoglobin is oxidized and creates discoloration in meat [
49]. Feng et al. [
50] reported that during the storage of fish, some continuous changes occur including resilience, chewiness, hardness and springiness. These forms are due to protein, microbial activities, and endogenous enzymes activity in muscles and fat [
51].
In the current study, the pH values were slightly different for the uncoated and coated chicken nuggets during refrigerated storage. Moreover, the pH values of chicken nuggets were decreased. This finding may be probably due to the effect of coating material (sodium alginate). These findings are in agreement with the results reported in previous studies [
52,
53]. Duan et al. [
54], reported in an earlier study that the pH values of chicken meat were basically constant at different storage times when the products were coated with chitosan. Similar findings were reported in previous studies dealing with chicken bone [
55,
56], sausages, or chicken patties treated with chitosan and essential oil [
57].
Dashti et al. [
58] reported that with the addition of a natural source of antioxidants, the appearance of nuggets differentiated. This finding is in agreement with the results of the present study. In another study, dealing with beef patties, sodium alginate used as a coating material resulted in a decrease in the appearance score values [
59]. During the refrigerated storage of the coated and uncoated chicken nuggets, there were monitored differences in the texture of samples in agreement with the results reported in previous studies [
52,
60]. Horita et al. [
61] carried out a study on meat products in which the capacity of holding water and fat through the better development stage during different storage intervals resulted in the differentiation of the meat texture. In the current results, the decrease in the flavor score values of chicken nuggets during refrigerated storage may be probably related to the decrease in the unpredictable flavor segments, given the fat oxidation that takes place. Drake and Drake [
62] reported that refrigerated chicken patties had decreased taste score values. Similarly, Sarower et al. [
63] reported that the taste and flavor of nuggets diminished essentially with the development of storage time intervals. The authors clarified that this phenomenon might be due to the lipid peroxidation in the nuggets, which results in the decrease in the taste and flavor scores of the samples. In the results of odor, the obtained score values are related to the coating materials and storage time. Wood et al. [
64] reported that the shrinking in flavor scores might be due to the peroxidation of polyunsaturated fatty acids that leads to the development of rancid flavor and odor. Comparable results were also reported in previous studies dealing with food products [
52,
60,
65] stored under refrigeration. The overall acceptability score values of chicken nuggets changed significantly with respect to storage time and coatings. The general dullness scores of coating with PPP (1.5%) and SA + PPP preparation were rather lower than coating with SA (1.5%) formulation. Giatrakou et al. [
46] stated that chitosan coating applied on chicken resulted in differences in the acceptability score values of the product in relation to coated or uncoated samples. In another study, in agreement with the present results, the overall acceptability values of mutton patties were differentiated during storage time [
66,
67,
68].