The Effects Of Making Koji With Mixed Strains On Physicochemical Properties And Sensory Evaluation Of High-salt And Liquid-state Soy Sauce

The study investigated the effect on the qualities of soy sauce prepared with mixed-strainkoji to assess the improvement of Monascus on soy sauce fermentation. On the basis of the twokinds of Monascus (Monascus Ruber and Monascus purpureus) separated from red yeast rice, theoptimal culture conditions of making koji with mixed-strain were confirmed, and respectivelyapplied in the mixed system of soy sauce fermentation. Finally, the effects on the formation offlavor compounds as well as the essential aroma compounds were observed.On the basis of moisture, color value, glucoamylase activity and esterifying power of the redkoji produced by using Monascus Ruber (MS1) and Monascus purpureus (MS2) respectivly, theculture time was determined to be8days. With regard to the soy sauce prepared withmixed-strain koji, inoculation quantity of MS1and MS2were identified as1.0‰according to theprotease activity, glucoamylase activity as well as total nitrogen and amino nitrogen offermentation solution, insuring the optimal protein utilization and amino acids conversion. Whileas for the processings of kojis prepared respectively using A. oryzae3042and Monascus, theculture conditions of koji prepared using Monascus were identified as32℃、92h and30℃、68hrespectively for MS1and MS2. By adjusting the proportion of kojis prepared using A. oryzae3042and Monascus to balance the distribution of enzymes, the optimal ratio (w/w) of kojisparepared with A. oryzae3042and Monascus were1:2and1:1corresponding to MS1and MS2.Five kinds of soy sauces processing are the object of this dissertation. That is soy sauceprepared with A. oryzae3042(SS1), soy sauce prepared with mixed strain koji of MS1-A. oryzae3042(SS2), soy sauce prepared with mixed strain koji of MS2-A. oryzae3042(SS3), soy sauceprepared with mixture of MS1koji and A. oryzae3042koji (SS4), soy sauce prepared withmixture of MS2koji and A. oryzae3042koji (SS5). Result showed that non-salt soluble solid,reducing sugar, total acid, total nitrogen and amino nitrogen sharply increased in the earlierfermentation stage. Samples of SS2~SS5had higher content of non-salt soluble solid and totalacid. As for SS2and SS3, the total nitrogen and amino nitrogen content were significantlyimproved (P<0.05) compared to SS1, while SS4and SS5had higher content of reducing sugar ofall, and its reducing sugar content reached the maximum on10day of fermentation, earlier thanother kinds of soy sauce. In view of the higher quality and convenience of industrializedproduction, SS1, SS2and SS3were chosed for further study. It revealed that dark matter, red andyellow pigments all improved in SS2and SS3. Meanwhile, the peptides with molecular wight1～5kDa and flavor amino acids also improved, contributing to stronger taste. Besides, theQuantitative Description Analysis (QDA) showed that the salty taste was the strongest in SS2, while the umami and sweet taste were intense in SS3. Thus it could be seen that soy sauceprepared with mixed-strain koji efficiently improve the taste.According to analysis of GC-MS, there were65,69and71volatile compounds detected inSS1, SS2and SS3. Meanwhile, result of GC-O analysis showed that36,38and43aroma-activecompounds were detected respectively in SS1, SS2and SS3. Among these compounds, flavordilution factor (FD) higher than1024were listed as follows:3-(methylthio)-propanal,phenylacetaldehyde, ethanol,2,3-butanediol, phenethyl alcohol and4-hydroxy-5-ethyl-2-methyl-3(2H)-furanone (HEMF). The characteristic aroma compounds such as HEMF, HDMF andphenethyl alcohol were remarkably stronger in SS2and SS3. Combinating GC-MS/O analysisand QDA, the intense aroma of alcoholic and sour mainly depend on ethanol, acetic acid and3-methyl-butanoic acid, while the stronger sense of flowery, roasty, fruity and caramal-likedepend on the characteristic aroma in soy sauce which had higher FD in SS2and SS3.