Study On The Flavor Formation And Quality Changes Of Silver Carp During Cured-ripening Process

Silver carp is one of the major freshwater fish in our country, its meat is nutritious, cheap and readily available. Drying-cured freshwater fish become large consumer’s favorite traditional salted products because of its rich flavor. Since the fish products are vulnerable to spoilage, so the drying-cured fish has a high salt content, low security, flavor instability and other problems by the traditional method. In the ordinary way we would utilize low temperature salted-ripening technology to produce drying-cured fish, in order to ensure the product’s quality, the ripening temperature is generally lower, but the lower ripening temperature limits proteolysis and lipolysis-oxidation, affecting the flavor formation and safety quality of the final product. In this paper, the main aim is to figure out the impact on physical and chemical, biochemical and microbiological changes, flavor and safety by inoculating mixed starter cultures into silver carp during fementation and ripening process, to provide some technical supports and theoretical bases for traditional cured-ripening fish products.The main contents of this paper include the following aspects: 1. The effect of mixed starter cultures on silver carp during fermentation processingFermented silver carp were processed using silver carp as raw material, by utilizing the microorgainsm isolated from the traditional salted fish. The variations of microorgainsm(Aerobic bacteria, Lactic acid bacteria, yeast, Staphylococcus, Enterobacteriaceae and Pseudomonas), physical and chemical parameters( pH, total acidity, TVBN, ANN and TBARS) and volatile components were determined to study the effect on cured-ripening fish products by inoculating mixed starter cultures. The results showed that: the mixed starter cultures can shorten the fermentation time and improve the volatile components; compared with the NS, the esters, ketones and acids in inoculated samples increased more obviously; the main volatile flavor compounds include acetic acid, hexanol, 1-octene-3-ol, 3,5-Octadien-2-one, 3-methyl butanal; during fermentation, the lactic acid bacteria were subject to rapid growing in the samples inoculated with mixed starter cultures, pH declined to 4.5 within 48 h, effectively inhibited the growth and reproduction of spoilage bacteria and pathogens,and slowed the accumulation of volatile basic nitrogen(TVBN) and thiobarbituric acid(TBARS). 2. The effect of mixed starter cultures on silver carp protein during ripeningThe changes of the total nitrogen(TN), non-protein nitrogen(NPN), total free amino acids(FAA) and protease were determined during processing in order to investigate the effect of mixed starter cultures on silver carp proteolysis. The results showed that, water cotent showed a significant decrease, salt content increased, compared with NS, inoculated samples had lower salt content. During ripening process,TN content and NPN content increased, the change in the inoculated group was obvious; FAA content increased initially then decreased, the highest content reached 3.05 mg / 100 g; the protease activity in the inoculated samples increased in the first then decreased, while the protease activity in the NS showed a decreasing trend in the whole ripening process, the protease activity in the inoculated samples was significantly higher than NS. Thus, the mixed starter cultures affect proteolysis significantly, and improve the flavor formation of ripening silver carp. 3. Effect of mixed starter cultures on silver carp lipid during ripeningThe change of total fat, peroxide value(POV), acid value(AV), TBARS, lipase, lipoxygenase(LOX) and free fatty acid(FFA) were determined to study the effect of mixed starter cultures on lipid oxidation and lipolysis. The results showed that: the content of total fat and POV reduced significantly(P <0.05), TBARS and AV values increased, but TBARS in NS was significantly higher than inoculated samples; LOX and lipase activity decreased, but the lipase and LOX activity in inoculated samples still showed higher activity. The total free fatty acid of the samples with mixed starter cultures was slightly lower than NS, but the EPA(eicosapentaenoic acid) and DHA(docosahexaenoic acid) were higher in inoculated samples, it indicated that the mixed starter cultures play a important role on lipid oxidation and lipolysis. 4. Effect of mixed starter cultures on cured ripening silver carpThe difference of volatile flavor compounds, biogenic amines and texture between samples with mixed starter cultures and NS were studied to analyze the effect of mixed starter cultures on finished products. 66 volatile compounds were isolated and identified of inoculated samples, obiviously higher than the control group(54 volatile compounds). The volatile flavor compounds in inoculated samples was higher compared to those in the NS after cured-ripening. The effects of mixed starter cultures on the biogenic amines(BA) and texture were investigated. The results showed that the mixed starter cultures lowed the accumulation of BA; meanwhile, increased the hardness, elasticity and chewiness of the samples with mixed starter cultures. Thus, the microorgainsm isolated from traditional cured fish can improve the flavor, increase safety, improve product quality of cured-ripening silver carp.