Study On The Drying-Ripening Process Of Dry-Cured Fish And Its Proteolysis Rlue

Dry-cured fish as one of the favorite traditional dry-cured aquatic products have enter into the industrialized production age. Because fish is a kind of easy rotten seafoods, so the traditional processing usually tends to use high salt in order to prolong its preservation time. Therefore, the dry-cured products processed by the traditional workshop usually have the high salt content, which causes its flavour quality unstable. At present, dry-cured fish are generally processed using low-temperature salting and drying-ripening technologies. In order to prevent the products from rottenness, the drying-ripening temperature is usually no more than16±1℃. However, the lower drying-ripening temperature restrain the proteolysis, lipolysis and lipid oxidation and the flavour formation during processing. Furthermore, the material fish of traditional dry-cured fish processing used are mainly herring, carp, chub and bighead. In recent years, the high-temperature drying-ripening process has successfully used in the processing of dry-cured hams, dry-cured chicken, ducks and geese products, which effectively control the lipid oxidation and meantime, improve their flavour quality. Thus the main objective of this study was explore a new processing suitable for the processing of fish products by using the high-temperature drying-ripening process. In order to give out a theoretical basis for the industrialized production of dry-cured fish and its quality controlling, the proteolysis rule in fish muscle was also investigated during the processing of dry-cured fish.This research includes following three parts:1、Drying-ripening process of bream and its effects on proteolysisThe fresh bream were used as materials, studying the effects of dry-ripening temperature, relative humidity, processing time and the amount of salt on product quality, which were represented by moisture content、salt content and sensory evaluation, the results indicated that the processing parameter of bream products with the highest quality is temperature humidity:16-24℃/75-85%; time:3-4d; the amount of salt:4%, the moisture content is65%and the salt content is3.2%in the finally product. Study the proteolysis of bream during processing with TN (total nitrogen)、NTN(non-protein nitrogen)、∑FAA (total free amino acid) and SDS-PAGE technology, the results indicated that TN and NPN had a downturn in the curing process, TN maintain this trend but the NPN、the proteolysis index (P.I.%) and∑FAA had a significant increase in the first4d during the air-dried mature processing, increased32.19%and58.4%respectively. SDS-PAGE showed that the band of29KDa and44.3-97.2KDa nearby increased many small fragments which had a great contribution to the formation of flavor.2、Dry-ripening process of Japanese seabass and its effects on proteolysis and sensory qualityThe fresh Japanese seabass were used as materials of dry-cured fish products. The orthogonal test was designed to study the effects of the process conditions on proteolysis and sensory quality. The results showed that the P.I.%gradually increased with the rising of temperature, while the∑FAA showed an increase in early time and then decreased until the end of dry-ripening which may be the high temperature accelerated the degradation reaction of free amino acids strecker; The dry-ripening temperature had significant effects (p<0.01) on P.I.%and∑FAA; The optimum process obtained by regression optimizing using∑FAA as response were:dry-ripening temperature15-29℃, relative humidity70-82%, process time72h, the amount of added salt4.5%(%sample), the salt and moisture contents of dry-ripening products were2.84%and64.33%respectively, which were tally with the sensory evaluation results.3、Study on proteolysis and its porrelation during dry-ripening process of Japanese seabassStudy the proteolysis and its correlation during processing of Japanese seabass with the conditions of optimal parameters. The results showed that P.I.%and NTN had a decline trend during cured stage, but increased during dry-ripening process. P.I.%had a significant increase at96h during dry-ripening stage, the P.I.%peak attained5.65%, but it had a decline trend at108h, which may be the cause of high-temperature accelerated the degradation reaction of free amino acids. PI%and the temperature rise was positively correlated. The level of proteolysis was weak, the P.I.%of the ultimate product achieved16.85%. P.I.%and FAA daily increment reached the peak at96h during dry-ripening, comparing with traditional fish products, the∑FAA was5861.11mg/100g which increased one times, The mainly free amino acids in products were Glu、Ala、Lys and His, the content of Glu and Ala increased by2-4times than raw materials respectively, which can be considered as the taste characteristics of products.