Shelf Life Extension of Grouper Fish Fillet (Epinephelus coioides) Using Biodegradable Chitosan/Chia Mucilage Coating Containing Rubia tinctorum L. Plant Extract

IntroductionFish supplies a type of nutrients containing protein and long-chain omega-3 polyunsaturated fatty acids (n-3 PUFAs) and micronutrients such as selenium, iodine, potassium, D and B-vitamins. Groupers are one of the best fishes in the south of Iran that are extensively distributed in tropical and warm waters all over the world. The perishability is considered as one of the main problems for fish with high nutritional value in food supply chains during the shelf life. The use of edible coatings indicates a novel method to extend the shelf life. The aim of present research was to apply biodegradable chitosan/ chia mucilage coating containing Rubia tinctorum L. plant extract (0, 0.5, 1 and 2 % as T1, T2, T3 and also T4) on the surface of grouper fillet fish to maintain qualitative and microbial attributes during the shelf life (1, 15, 30 and 45 days).Materials and MethodsThe qualitative and qualitative assays (peroxide index (meq O2/kg sample), thiobarbituric acid (mg MA/kg), total volatile nitrogen (mg /100 g) and trimethylamine (mg /100 g)), microbial counts (aerobic mesophilic and lactic acid bacteria, total coliforms, mold and also yeast), texture (hardness, adhesion, flexibility, cohesiveness and gumminess), sensory attributes (taste, smell, color, texture and overall evaluation) and measurement of identified biogenic amines were carried out during the shelf life.Results and DiscussionThe results illustrated that oxidation parameters of treatments such as peroxide index, trimethylamine, total volatile nitrogen components and thiobarbituric acid were declined by increasing the extract concentration in a fixed time period (p ≥ 0.05). The highest and lowest microbial loads were obtained in T1 and T4 during the storage, respectively. The microbial counts increased significantly (p < 0.05) by extending the storage time of treatments and on the other hand, this decreased significantly (p < 0.05) by increasing the concentration of Rubia tinctorum L. extract in a fixed period of time. The utilization of Rubia tinctorum L. extract and chia mucilage in a coating of chitosan created a synergistic effect and led to a lower microbial load in treatments. On the other hand, a reduction was occurred in textural attributes particularly cohesiveness and hardness through moisture loss and drying of coating surface in fillets during storage (p < 0.05). The softening tissue could be related to the higher microbial activities during storage, although intensity of these changes was lower in T3 and T4 treatments due to the lower microbial load, which indicated the positive effect of Rubia tinctorum L. extract on maintaining tissue quality. All examined factors changed and most of the mentioned parameters in T1 and T2 exceeded the permissible limit during storage, but T3 and T4 had better conditions during storage. Finally, fish fillet coated with 1 % Rubia tinctorum L. extract (T3) compared to others demonstrated better sensory evaluation at the end of shelf life, which was selected as the superior treatment. The type and amount of biogenic amines in control and T3 (superior sample) illustrated that the highest amine compound was recorded for histamine at 79.87 (mg/kg) on the 15th day and the lowest level in tyramine at 0.79 (mg/kg) on the 1st day of storage. The concentration of amines increased significantly during storage time (p < 0.05).ConclusionThe results shown that applying chitosan/ chia mucilage coating including Rubia tinctorum L. extract has significant effect on extending the shelf life of fish fillets.