Effects Of Aquaculture Environment And Fermentation On The Quality Of Freshwater Fish

In this paper,the Cyprinus carpio cultured in paddy fields and ponds in Qingtian,Zhejiang Province was taken as the research object.Sensory analysis,taste nucleotides,amino acids,and volatile odorants were used as indicators,combined with the analysis of electronic tongue,monosodium glutamate equivalent and key odorant substances,two kinds of odorants were measured and analyzed.Differences in C.carpio flavor in culture mode.Secondly,using Hypophthalmichthy nobilis as raw material and Saccharomyces cerevisiae as starter,the effect of adding S.cerevisiae on the flavor,quality and biosafety of H.nobilis was studied.1.There were significant differences in the flavor of C.carpio cultured in paddy fields and in ponds.In order to explore the effect of rice field culture on the muscle flavor of C.carpio,traditional pond culture was used as the control group,and C.carpio from two culture environments were randomly collected to determine their free amino acids,nucleotides and volatile substances.The composition and content of nucleotides and volatile substances were compared and analyzed.The results of sensory analysis showed that the C.carpio muscles in the two breeding environments had obvious differences in odor in October.The types of amino acids and nucleotides in the muscle of C.carpio cultured in the two breeding environments were the same,and the content of umami amino acids such as glutamic acid in the muscle of C.carpio cultured in paddy field was significantly higher than that in pond culture(P < 0.05);the maximum of EUC reached5.68 MSG g/100 g,which was significantly higher than the EUC of 4.61 MSG g/100 g in pond culture.At the same time,there were earthy and grassy substances in the muscles of C.carpio cultured in paddy fields,the highest content of hexanal and nonanal were 21.75%and 6.42%,which were significantly lower than 39.76% and 12.76% under pond culture,indicating that the unpleasant odors in the muscles of C.carpio cultured in paddy fields,such as hexanal,1-octene-3-ol;the C.carpio cultured in paddy field tastes more delicious,and the content of substances with earthy smell is less.2.The addition of S.cerevisiae had a significant effect on the sensory properties and taste of H.nobilis muscle.In this chapter,the 0-day fish meat was used as the control group(K),the added S.cerevisiae was group(Y)and the non-added was group(Z)to study and analyze the sensory characteristics,texture,color difference,and free amino acids of H.nobilis muscle.The results showed that there was no significant difference in the color and texture of H.nobilis muscle between the group Y and group Z.The rancid smell of group Z was obvious;however,the sweet smell of group Y was strong,and the Y7 sample had a higher acceptability on the whole.During the fermentation process,the content of aspartic acid,glutamic acid,glycine and alanine approached or exceeded their respective taste thresholds,and they were the main components affecting the taste of the samples.Free amino acid umami synergy analysis showed that the umami equivalent concentration of H.nobilis muscle in group K was 3.62 mg MSG/100g;group Z was15.46-47.47 mg MSG/100 g,and group Y was 20.11-48.99 mg MSG/100 g,much higher than group K and group Z.That is,the highest umami effect produced by free amino acids(glutamic acid and glycine)in fish meat of 100 g dry weight group Z and group Y was the same as the umami effect produced by 47.47 and 48.89 mg of sodium glutamate(MSG).The MSG threshold is 30 mg/100 g,so the highest EUC of taste activity values(TAV)of the group Z and group Y are 1.58 and 1.63,indicating that the synergistic effect of glutamic acid and glycine in enhancing freshness is significant,and the addition of S.cerevisiae can enhance the umami intensity of H.nobilis muscle.3.The addition of S.cerevisiae had an important effect on the degradation of muscle protein in H.nobilis.This chapter analyzes the non-protein nitrogen(NPN),TCA-soluble peptides,protease activity,protein composition and sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE)patterns of H.nobilis muscle in group Y and group Z.The results showed that during the fermentation process of H.nobilis muscle,the activities of NPN,TCA-soluble peptide and protease all increased,and the contents of sarcoplasmic protein and myofibrillar protein were significantly decreased.SDS-PAGE showed that sarcoplasmic protein and myofibrillar protein were denatured and hydrolyzed,and the degradation degree of group Y was higher than that of group Z,indicating that adding S.cerevisiae can promote the decomposition of protein,thereby improving the taste of the product.4.The addition of S.cerevisiae ensures the quality and enriches the flavor of the H.nobilis muscle.In this paper,the microbial characteristics,biogenic amine content and odor of H.nobilis muscle of group Y and group Z were analyzed.The results of microbial analysis showed that the growth of S.aureus in group Y was inhibited,which was related to the decrease of anaerobic and p H during fermentation.In acidic and anaerobic environments,S.aureus was relatively less competitive and increased acidity inhibited its growth.The number of Escherichia coli showed a trend of increasing first and then decreasing,which because the early stage was rich in nutrients,and Escherichia coli grew in large quantities.With the progress of fermentation,S.cerevisiae became the dominant bacteria,and its growth was inhibited.5 biogenic amines were detected in group Y and group Z,namely cadaverine(CAD),putrescine(PUT),histamine(HIS),tyramine(TYR)and phenylethylamine(PHE).With the progress of fermentation time,CAD,PUT,HIS and PHE all increased obviously.The contents of PUT,CAD and HIS of group Y were lower than those in group Z.Among them,the HIS content of group Y was lower than that of group Z,probably because S.cerevisiae has a certain ability to degrade histamine.The analysis of volatile substances showed that the volatile substances in the group Y and group Z mainly included aldehydes and ketones,alcohols,esters,hydrocarbons and other compounds,which the alcohols in group Z accounted for a higher proportion;the esters in group Y was relatively high.There were 28,30,and 25 kinds of volatile compounds in Y3,Y5 and Y7 respectively,which were more than those in Z3,Z5 and Z7,indicating that the addition of S.cerevisiae could enrich the odor of H.nobilis muscle.