Effects of different natural preservative on catfish fillet quality during storage with combination of super-chilling and high-CO2 packaging

Abstract: In order to extend the shelf life and improve the safety of catfish (Clarias gariepinus) fillets, the fresh catfish fillets were treated with 5% natural preservatives of 3 different formulas respectively. Formula 1 (1# ) was composed of 0.5% chitosan, 0.1% propolis, 0.075% lysozyme, 0.075% nisin and 0.5% tea polyphenol, Formula 2 (2#) contained 5.6% cinnamon, 6% cloves, 19.12% ginger and 12.84% garlic, Formula 3 (3#) was the supernatant of pure lactic acid bacteria, and the samples treated with sterile distilled water were set as control. The catfish fillets were stored in modified atmosphere packaging (60% CO2 / 40% N2) at ?0.7 oC, and the influences of natural preservatives on the sensory quality, microbial index and physical-chemical properties and the protein oxidation of catfish fillets during 60 d storage were evaluated. The results proved that the preservatives effectively extended the shelf life of catfish fillets compared with control samples through the sensory analysis, which was carried out based on color, odor, texture, and springiness of raw catfish fillets and odor, taste, and soup clarification of cooked catfish fillets by the ten-point descriptive analysis test. The sensory shelf life (evaluated by the overall sensory scores) for 1#, 2#, and 3# samples was 40, 30 and 40 d, respectively, while the shelf-life for control samples was only 20 d. Total viable count (TVC) of control sample was always higher than 1#, 2# and 3# samples during the whole storage. TVC for control sample exceeded 6.00 log cfu/g after 30 d storage, whereas for 1#, 2# and 3# samples TVC exceeded the above number after 50, 40 and 50 d, respectively. In the chemical indicators of spoilage, total volatile base-nitrogen (TVB-N) values showed significant increases for all the samples (P<0.05), the value for control sample increased to 22.59 mg/100 g after 40 d storage, whereas the values for samples treated with preservatives were lower than 20.00 mg/100g during the same time of storage. The 2# preservative had excellent antioxidant activity, which was proved by the lower thiobarbituric acid resctive subastances (TBARS) values (0.09-0.14 mg/kg) in 2# samples during the whole storage. The initial potassium (K) value of fresh catfish fillets was 3.10%, and the value increased to 71.70% (for control sample after 40 d), 66.36% (for 1# sample after 60 d), 89.9% (for 2# sample after 60 d) and 61.28% (for 3# sample after 60 d) at the end of the storage. The study also investigated the effects of natural preservatives on protein oxidation of catfish fillets. The total sulphydryl contents of myofibrillar proteins decreased significantly (P<0.05) from 115.51 nmol/mg protein (0 d) to 54.53, 64.23, 81.15 and 55.38 nmol/mg protein on the 40th day of the storage for control, 1#, 2# and 3# samples, respectively. The results suggested significant inhibition of preservatives to disulfide bond formation in catfish protein. In addition, the carbonyl contents increased during the storage in a similar way as the total sulphydryl contents. The sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed that the preservatives reduced cross-linking polymerization and degradation of catfish myofibrillar protein during the storage. In conclusion, the 3 kinds of preservatives could inhibit microorganism growth, protein degradation, protein and lipid oxidation, and thus maintain the freshness and delay the deterioration of catfish fillets. The shelf-life extension efficiency of the 3 kinds of preservatives was in order of 3# > 1# > 2#, and the shelf-life of 1#, 2# and 3# samples was 40, 30 and 40 d respectively, while that of control sample was only 20 d. This result provides a reference for the application of natural preservatives in catfish meat during the storage.