Study On Collagen Change And Quality Control Of Grass Carp(Ctenopharyngodon Idella) Fillets During Chilling Storage

Grass carp(Ctenopharyngodon idella) is an important freshwater economic fish in China with delicious taste and large production. With the development of the cold chain technology and the improvement of living standards, small packages of fresh aquatic products in the low temperature have gradually become the trend of aquatic industry’s development. With high content of water and endogenous enzyme, freshwater fish is perishable. Therefore, it’s crucial to use timely and effective preservation to ensure the aquatic product’s quality and safety during storage, transportation and sales process. Ice-storage and superchilling both can delay the degradation of fish quality effectively in a short period of time. Collagen is an essential component of connective tissue and it also plays an important role in the maintenance of muscle structure. The effect of collagen and related enzymes on fish quality during the process of storage has drawed high attention of scholars both at home and abroad. But most of the existing research focus on the seawater fish. It’s not known exactly how collagen and collagenase affect the freshwater fish quality and collagen. The living environment and body composition are different between freshwater fish and ocean fish. Therefore, the effect of collagen on freshwater fish’ quailty cannot be ignored. This research use the grass carp as research object to study the impact of collagen and collagenase on quality change of grass carp fillets stored under superchilled and ice storage, and then a quality control technology based on the collagenase activity have been further put forward. The results have guiding significance for the quality improvement of freshwater fish at low temperature preservation, and also provide certain theory basis for the mechanism of freshwater fish quality change in the process of preservation.By determining the texture, microscopic structure and the content, type, degradation degree of collagen as well as the collagenase activity, we have studied the relationship between the collagen change and fillet quality during ice-storage and superchilling condition. The results showed that with the increase of storage time, fillets’ quality were declined to different extents. After 21 d of storage, fillet’s firmness was reduced by 61.20%(superchilling) and 61.73%(icestorage) respectively. From microscopical perspective of grass carp fillet, detachments between muscle cells as well as cracks inside the cells were evident after storage. It was also noticed that the superchilled fillets showed the myofibrillar breakages after 21 days. Masson stained picture showed that collagen degradation was more obvious during ice-storage. At the same time, the total collagen content tended to decline, and this declining trend was significantly associated with the changes of firmness(ice-storage: r = 0.990; superchilling: r = 0.971). And the compositions of collagen have changed dramatically. Amino acids and SDS-PAGE analysis showed that superchilling had less impact on degradation bands as compared to the ice-stored samples. The activity of collagenase decreased sharply during the first 3 d, and then increased slowly in both stored samples.Through determining the fillet texture, content of collagen and activity of collagenase, we studied the inhibitory effects of catechin, tea polyphenols, gallic acid and Na-citrate on the collagenase activity, collagen degradation and texture change of grass carp by in vitro test and storage test. Collagenase activity measurement and SDS-PAGE analysis in vitro text showed that four additives all have certain inhibition effects on collagenase and could delay the degradation of collagen. Among them, catechin was the most effective inhibitor and the residual activity of collagenase was only 10.80% to 21.78%. Adding four edible inhibitors to fillet by injections and soaking,all additives were able to suppress the softening of chilled fillets to varying degrees and catechin was the most effective one to retard the degradation of collagen and softening of grass carp fillets under both conditions.In order to improve the preservation of fresh fish, we added catechin, allicin and chitosan to the fillet and studied the effect of compound fresh-preserving agent on grass carp muscle by measure the texture, p H, total number of colonies, TCA peptide content, TBA value and TVBN value of fillet. Results show that during the first 3 d, the firmness of the blank control fillet droped fast, while the firmness of compound preserved group only fell by 15%(superchilling) and 7%(ice-storage) which were significantly lower than the blank control group. Compared with the blank control group, changing scale of p H value was smaller in compound preserved fillet. Total number of colonies and psychrophilic bacteria results also showed that the compound preservation had strong antimicrobial activity. TCA peptide content, TBA value, TVB-N value and activities of endogenous enzymes results showed that the compound preservation could prevent the deterioration in the aspects of protein degradation and fat oxidation. The quality of compound preserved fillet was better than single preserved fillet through different coordination mechanism.