| The soaking and cooking step during traditional xiaoqu liquor manufacture is energyconsuming,labor-consuming and environmentally unfriendly.As a continuous mixing,kneading and heating technology,extrusion has the advantages of convenient operation,low energy consumption,high gelatinization degree and no waste water pollution,therefore,it is used to replace traditional soaking and cooking step during liquor manufacture.However,high viscosity of extrudates may affect the progress of saccharification and maillard reaction products will reduce the quality of liquor.In this context,we use enzymatic extrusion to change the properties of sorghum extrudates,and apply it to the fermentation of xiaoqu liquor.The volatile compounds of traditional and novel liquor samples are also compared?Physical and chemical properties of traditional cooking sorghum(TCS),no-enzymatic extrusion sorghum(NEES)and enzymatic extrusion sorghum(EES)was compared by SEM,RVA,DSC and XRD.Results showed that sorghum starch granules were completely destroyed and 38.71% of the starch was hydrolyzed,so the water solubility index of EES increased to 30.74%.Bulk density of EES(1.12 g/cm3)was much higher than NEES(0.74 g/cm3)as the degree of swelling decreased.RVA showed that the peak viscosity of EES was 163 cp,enzymatic extrusion effectively solved the problem of high viscosity of NEES(3503 cp).GE of EES improved by 53.30% at the similar processing temperature of TCS and avoided the maillard reaction occurrence.The relative crystallinity of EES was 6.96% and the setback was only 4 cp,indicated that the starch of EES is stable and not easy to retrogradate.Results of fermentation experiment showed semi-solid fermentation(SSF)exhibited the highest fermentation efficiency comparing with solid-state fermentation(SF)and liquid-state fermentation(LF).The ethanol yield in solid-state saccharification was twice than that of liquidstate saccharification,indicated that solid-state saccharification was effective in yeast proliferation.The product inhibition in SF(EES)was obvious in the third day,which affected the alcohol metabolism of yeast and ended the fermentation progress.Product inhibition was not exist in LF,but its fermentation efficiency was only 72.17% of SF.SSF could effectively solve the problem of product inhibition in SF,meanwhile,its fermentation efficiency was 89.80%(EES)as a result of solid-state saccharification.Based on Response surface methodology(RSM),the optimum extrusion conditions to obtain maximum fermentation efficiency of 93.73% were at the BT of 98.40°C,MC of 33.28% and AC of 1.62‰.The formation of volatiles of enzymatic extrusion sorghum xiaoqu liquor(EESL)and traditional cooking sorghum xiaoqu liquor(TCSL)was compared by GC-MS,a total of 35 main volatile compounds were identified.Results showed that the compositions of EESL and TCSL were similar,the main alcohols were 3-methylbutanol,2-methylpropanol and 2-phenylethanol,the main acid was acetic acid and the main esters were ethyl acetate and ethyl lactate.However,total alcohol content in EESL was 196.62 mg/L,much higher than that in TCSL(135.62 mg/L).Total esters content(20.32 mg/L)and total acids content(25.30 mg/L)in EESL was slightly lower than that of TCSL.Difference in volatile compounds indicated that enzymatic extrusion might have some effect on the quality of xiaoqu liquor.In order to adjust the fermentation process of EES and improve the flavor quality of EESL,a study on the effect of Proanthocyanidins on the volatiles content of EESL was carried out.Results showed that the retention rate of Proanthocyanidins after enzymatic extrusion was 79.71%,and the increase of water solubility index of EES could accelerate the diffusion of Proanthocyanidins in fermented grains.20% addition of sorghum episperm could observably reduce the enzyme activities of glucoamylase and acidprotease at the beginning of fermentation,meanwhile,the total alcohol content was reduced by 22.83%,the total ester content was increased by 47.59% and the total acid content was almost unchanged. |
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