Characteristics Of The Microflora, Physico-chemistry And Volatile Profile Of LaYu During Processing

LaYu is one of unique traditional aquatic products in China.It is popular in domestic and overseas because of its distinctive flavor,tangy,delicate,fishy and salty.But the production of LaYu has not been industrialized,mostly manufactured by extensively traditional handwork way.The system for quality evaluation has not been consummated. Little study about mechanism of forming flavor has been reported.Taking sliver carp as raw material,this paper investigated the effect of dry-salting conditions on microflora, physico-chemistry and volatile profile of LaYu.The aim was to expore the change law of microflora,physico-chemistry and volatile profile were investigated during salting and drying process.Additionally,the dominant microorganisms were identified and their fermentive properties were observed.It was anticipated to promoted technics and flavor evaluation method,and explained the role of microorganism in LaYu's flavor.The main results were summarized as follows:(1) Impact of salting condition on the qualities of LaYu.The amount of microbe in LaYu,at low salt and high temperature condition,were higher than others.TVB-N value decreased,but TBA value increased with increasing salt.TVB-N and TBA values increased with increasing temperature.Increasing temperature and decreasing salt were favorable to increase contents of most free amino acids,and prolong salting time could remarkedly enhance the contents of free Asp and Glu.The volatile compounds were no obvious trend at different salting conditions.The optimal salting parameters were adding 5%salt at 12℃for 4 days.(2) Changes of microflora,physico-chemistry and volatile profile in LaYu during processing.During processing,moisture declined but NaCl content increased gradually. All kinds of microorganism grew slowly,and contents of non-protein nitrogen and free amino acids show a decreasing trend during salting.The microbial amount significantly increased in earlier stage of drying,and the contents of non-protein nitrogen,free amino acids and TBA were significantly increased during the whole drying.Both salting and drying affected the composition of free amino acids in the muscle.The contents of Met, Glu,Val,Ser and Thr were higher in LaYu than those in raw muscle.The relative contents of hydrocarbons and alcohols' remarkedly deceased,however,the relative contents of aldehydes and ketones remarkedly increased,especially hexanal.These changes played an important role in the flavor of LaYu. (3) Dominant microorganisms and their fermentive properties.The dominant microbial groups in LaYu were lactic acid bacteria,Micrococcus and Staphylococcus and yeast.There were 75 dominant strains identified,which contained 9 Lactobacillus plantarum,4 L.alimentarius,2 L.curvatus,5 Pedicoccus acidilacticii,2 P pentosaceus, 10 Staphylococcus sciuri,9 S.epidermidis,9 S.simulans,6 S.warneri,3 S.xylosus,3 S. chromogenes and 2 S.saprophyticus.Lactic acid bacteria could grow at lower the 8% NaCl,and Staphylococcus could survive at lower the 11%NaCl concentration.All of the isolated strains could grow well above 15℃.The strains of lactic acid bacteria had the protease activity rather than lipase activity.The strains of S.sciuri,S.chromogenes and S. saprophyticus had protease activity,and all of the Staphylococcus had lipase activity except S.sciuri.(4) Characteristics of flavor in LaYu primarily.The dominant free amino acids in LaYu were His,Gly,Arg and Ala.The typical volatile compounds in LaYu were 1-limonene,sabinene,3-pinene,linalool,1-octen-3-ol,linalool,phenylethyl alcohol, hexanal,nonanal,heptanal,octanal,decanal,3,5-octadien-2-one,linalyl acetate and geranyl acetate.Hexanal could be used as an objective index for flavor evaluation of LaYu.