Effect Of Fatty Acids On Formation Of Aroma Of Fish Sauce During Fast Fermentation

The process of fast-fermented of fish sauce can significantly improve the fermentation speed,but serious shortages of key aromatic substances in quantity and content and its weak aroma are always a large problem.In order to clarify aromatic compositions of fast-fermented fish sauce made of freshwater fish,analytic methods of volatile compounds and composition of key aromatic substances were established and optimized.In addition,the relationship between aroma compounds and precursor substances were analyzed based on composition of raw materials and fatty acids.Furthermore,effect of fatty acids on formation of critical aromatic substances in fish sauce was explored,which could be a theoretical foundation for solving the problem of weak aroma of fast-fermented fish sauce.The main results are summarized as follows.(1)Gas Chromatography-Mass Spectrometry(GC-MS)was used to investigate the separation effect of DB-5 MS column and DB-WAX column.DB-WAX and dual columns were selected for quantitative and qualitative analysis after weighing their pros and cons.Further comparison was performed for other factors for Solid-Phase Micro Extraction(SPME),including fiber,extraction temperature,extraction time and Na Cl concentration.The best extraction condition was obtained via these optimizations: Na Cl was added to the 10 m L sample to a concentration of 270 g/L in a 30 m L sample tube,and then inserted into a 75 ?m CAR/PDMS(black color)extraction head for 40 min after a constant temperature water bath at 50 ? for 30 min.Finally,aroma of Fish Sauce Quick Fermentation extracted by SPME and Solvent-Assisted Flavor Evaporation(SAFE)were compared.The results showed that SAFE lost more volatile aldehydes and alcohols and could not be used for quantitative analysis of fatty acid metabolites.(2)The basic composition and fatty acid of three types of freshwater fish raw materials(Culter alburnus,Carassius auratus and Ietalurus Punetaus)with significant differences in protein and crude fat content(P <0.05)were determined.The results showed that the crude fat content of Culter alburnus was 5.98±0.17%,and its unsaturated fatty acid consisted of 37.02% oleic acid(C18:1),20.34% linoleic acid(C18:2),4.18% palmitoleic acid(C16:1),4.11% docosahexaenoic acid(DHA,C22:6),2.33% linolenic acid(a-C18:3n6)and 1.35% arachidonic acid(C20:1).The crude fat content of Carassius auratus was 8.03±0.21%,and its unsaturated fatty acid consisted of 34.86% oleic acid(C18:1),19.72% linoleic acid(C18:2),3.47% palmitoleic acid(C16:1),3.14% docosahexaenoic acid(DHA,C22:6),2.90% linolenic acid(a-C18:3n6)and 2.79% arachidonic acid(AA,C20:4).The crude fat content of Ietalurus Punetaus was 10.83±0.16%,and its unsaturated fatty acids consisted of 49.33% oleic acid(C18:1),20.95% linoleic acid(C18:2),2.61% linolenic acid(a-C18:3n6),2.08% peanut monoenoic acid(C20:1),1.61% palmitoleic acid(C16:1)and 1.08% docosahexaenoic acid(DHA,C22:6).(3)Three types of freshwater fish raw materials(Culter alburnus,Carassius auratus and Ietalurus Punetaus)were used to made fish sauce quick fermentation.The results of electronic nose analysis showed that there were significantly different(P <0.05)in the aroma of the three kinds of fish sauce quick fermentation,which could be clearly distinguished and reproduced;HS-SPME-GC/MS analysis results showed that a totally 71 kinds of volatile compounds were identified in the three types of fish sauce quick fermentation,and the content of compound was ranked as acid> alcohol> aldehydes> furan> sulfur> Ester> Others.(4)Critical aromatic substances of three kinds of fish sauce quick fermentation were selected,and there were nine types of key aroma substances among them.The highest OAV value was isovaleraldehyde(OAVCulter alburnus = 232.87,OAVCarassius auratus = 142.57,OAVIetalurus Punetaus = 721.32),followed by isoamyl alcohol(18.56,21.9,37.18)and 3-methylthiopropanal(14.74,10.86,25.81),then 1-octen-3-ol,phenylacetaldehyde,nonanal,dimethyl trisulfide,decanal and n-hexanol.(5)Correlation analysis of three major fatty acids and two key aroma substances and derivatives showed that the precursor substance of the key aromatic compound nonanal in fish sauce quick fermentation was oleic acid,and the correlation coefficient was 0.9755;The precursor of the key aromatic compound 1-octen-3-ol was linoleic acid instead of arachidonic acid,and the correlation coefficient was 0.9967.Aiming to study the effect of nine key aromatic compositions on the aroma of fish sauce,the aroma reorganization and loss experiments will be adopted in the next step.Also,further expanding the scale of fermentation for production verification will be carry out soon.