The Nutritional Quality,flavor Characteristics And Preservation Of Air-drying Bream

In this paper,we compared the nutritional quality and of air-drying bream with the fresh bream.The physical and chemical properties of the bream in the whole process of fermentation were researched.Besides,the flavor compounds in the fresh bream,air-drying bream and cooked air-drying bream were investigated.At last,the pickling process of air-drying bream was optimized.These results could provide an important theoretical basis for improving the stability and safety of air-drying bream and its commercial production.Firstly,the nutritional components of air-drying were compared with fresh bream.The percentage of moisture in air-drying bream decreased(57.78%)while that of protein(33.17%),crude fat(3.64%)and ash went up(4.52%),by contrast with fresh bream.During the pickling process,the content of sodium chloride in air-drying bream went up to 2.85% and it proved that air-drying bream is a kind of low-salt food.The contents of free amino acids increased by 2.5 times and that of umami amino acid rose up significantly also.Compared to fresh bream,the percentage of saturated fatty acid increased while the percentage of unsaturated fatty acid decreased,especially the content of mono unsaturated fatty acid declined significantly.The content of mineral substance and microelement are abundant,such as Na,P,Mg,Fe,Zn,Ga,etc.Secondly,the changes of physical and chemical properties from air-drying bream in the whole process of fermentation and food safety were researched.The content of TVB-N in air-drying bream reached the standard of slight corruption in the 5th day of pickling.Oxidative rancidity happened on the fat in air-drying bream during curing so that its quality declined,but this is acceptable.The results indicated that the texture characteristics of air-drying bream in the process of curing were significantly changed.Hardness,adhesion,chewiness were increased,and flexibility,springness and recovery was reduced.At the same time,amino nitrogen content increased,which indicated that the umami substances augment.The pH value decreased at first and increased later.The water activity in air-drying bream declined during curing at first and then tended to balance.After 96 hours of pickling,the water activity value is 0.8,which can restrain the growth of bacteria effectively.During the period of curing air-drying bream,the contents of nitrite increased gradually to 23.95 mg/kg,which is within safe levels.Biogenic amines contents were also increased,but were lower than national standards.Thirdly,volatiles in air-drying breams,fresh breams and steamed air-drying breams and the bacon stuffed in breams were analyzed by gas chromatography–mass spectrometry(GC–MS).A total of 94 volatile compounds,consisting mainly of aldehydes,alcohols,sulphur compounds,and aromatic compounds etc.were quantified.In air-drying breams,aldehydes(29.56%),alcohols(15.96%)and sulfur compounds(13.77%)were the most prevalent groups of volatiles.Odor activity values(OAV)were determined to identify aroma-active compounds.A major 16 odor-active compounds were distinguished to contribute as key aroma compounds(OAV >10)in breams.Results showed that decanal contributed the major proportion and might impart special fishy flavour to air-drying breams.To sum up,through fermentation and air-drying,the “fishy,fatty,grassy” odor became weaker,while the “waxy,citrus,floral” odor turned to be stronger.Bacon stuffed in air-drying breams mainly contributed to the “oily,fruity,cheesy,fatty” aroma.This may be an important complement to the particular aroma of air-drying breams.Finally,the change in microoganism of air-drying bream in the curing process were investigated,and then Nisin and tea polyphenols were chosen as natural preservatives to extend the shelf-life of air-drying bream on room temperature.Lactic acid bacteria,Micrococcus,Staphylococcus and yeast were detected in air-drying bream during curing,and the dominant microbial groups were Lactic acid bacteria.The total count of bacteria colonies,TVB-N value,TBA value,K value was lower in these samples with Nisin or tea polyphenols treatment than the blank test group.The preservative term of Air-drying bream could be prolonged remarkably both by using Nisin and tea polyphenols,for the bacterial growth was inhibited significantly during cold storage.The effect of Nisin on air-drying bream on room temperature was better than the tea polyphenols.