| Pixian soybean paste(PSP)is known as the soul of Sichuan cuisine.It is popular with consumers because of its fresh,spicy and mellow flavor and rich flavor of soy esters.It is also a raw material for braised vegetables and hot pot base,and its products are exported overseas.At present,its research is mainly focused on the specific volatile flavor substances in the subsequent fermentation process,and there are few studies on its flavoring substances and flavor precursor substances.Therefore,because the special techniques for making,drying of PSP make it possible accumulation of biogenic amines such harmful substances.Based on the above problems,this subject took PSP in post-fermentation periods as the research object,and detected the differences in the types and contents of fatty acids,carbohydrate,biological amines compounds and microstructures by Gas chromatography(GC),High performance liquid chromatography(HPLC),Scanning electron microscope(SEM)and so on.With a view to providing a scientific basis for optimizing PSP flavor and improving the safety of food to realize the standardization and large-scale production of PSP.The specific research results are as follows:GC internal standard method was used to qualitatively and quantitatively analyze the fatty acids of PSP with eight different post-fermentation stages,which was extracted with petroleum ether and methylated with sulfuric acid-methanol.The results showed that the crude fat contents was 3.5%-4.5%,and the total fatty acid contents was 8.26-18.48 mg/g.There were nine fatty acids detected at different post-fermentation stages,which were linoleic acid(4.96-11.67 mg/g),oleic acid(1.18-2.71 mg/g),palmitic acid(0.75-1.65 mg/g),linoleic acid(0.40-0.89 mg/g),stearic acid(0.29-0.85 mg/g),myristic acid(0.13-0.30 mg/g),transoleic acid(0.12-0.23 mg/g),palmitoleic acid(0.05-0.14 mg/g)and lauric acid(0.03-0.11 mg/g).The results of principal component analysis showed that the contribution rates of the first and second principal components were 75.09% and 15.21% respectively,and the cumulative contribution rate was 90.3%,which could be better reflect the basic information of all fatty acid compositions.Moreover,the fatty acid changes in the post-fermentation period could be roughly divided into three stages(early stage,middle stage and late stage),and the changes of fatty acids in the early stage were far greater than those in the middle and late fermentation stage.And the correlation between fatty acids and microorganisms shows that during the post-fermentation process of PSP,fatty acids and microorganisms show a phased growth or inhibition relationship.Lactobacillus,Halomonas,Klebsiella,Cladosporium,Mucor and Penicillium can promote the formation of fatty acids.The changes of total sugar,reducing sugar and the types and contents of carbohydrate compounds in post-fermentation process of PSP were analyzed by the salicylic acid method and HPLC-RID.The results showed that during the post-fermentation stage of PSP,the total sugar content was 6.811%-12.257%(w/w)and the reducing sugar content was 4.426%-8.425%(w/w).A total of 7 kinds of sugars(fructose,glucose,sucrose,raffinose,stachyose,galactose,arabinose)were detected,the total sugar content is(17.801-39.291 mg/g).The glucose content gradually decreased;the fructose content decreased first and then increased,and the content was higher in the maturation period of 3 years;the sucrose content was higher in the late fermentation period,which may be a potential indicator to distinguish the deep ripening period from the previous stage.The lowest total sugar content in June was 17.801 mg / g.The changes of biogenic amines in post-fermentation process of PSP were analyzed by benzoyl chloride pre-column derivatization-HPLC.The results showed that a total of six biogenic amines(histamine,spermidine,?-phenylethylamine,putrescine,cadaverine,tryptamine)were detected in the post-fermentation stage,with a total biogenic amine content of 30.48-100.54 mg/kg.Spermidine,?-phenethylamine and histamine are the main biogenic amines;the content of histamine and ?-phenethylamine is relatively stable as the fermentation progresses;the content of other biogenic amines is low and the change during fermentation is not significant;putrescine(1.55 mg/kg)was only detected in 24 month sample.Analysis of the correlation between biogenic amines and microorganisms shows that during the entire post-fermentation stage,the relationship between the formation and degradation of microorganisms and biogenic amines is extremely complex,and the generation and degradation of microorganisms and biogenic amines are specific.None of microorganism has a relationship with the formation or degradation of all biogenic amines.SEM and CLSM can visually observe the distribution and changes of starch and protein during the post-fermentation period of PSP.The results showed that starch granules are gradually cleaved as the post-fermentation progresses,and the enzyme protein is always tightly surrounding the starch to hydrolyze the starch to provide energy for the growth and reproduction of microorganisms,so that PSP gradually matures under the action of time. |
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