| Higher alcohols are by-products producing when yeast synthesise cell proteins during the fermentation of Chinese rice wine. According to some relevant literatures, appropriate content of higher alcohols could make wine with rich and enjoyable taste, coordinate the overall flavor and improve the quality. But excess higher alcohols would cause strongly drunk, known as "headache", and generate unpleasant odor in the rice wine. Therefore many people has paid attention to how to control the content of higher alcohols effectively.This paper fermented the rice wine by immobilized yeast depending on jel embedding technique. On this basis, tha author studyed the generation of higher alcohols during the rice wine fermentation, in order to provide feasible methods producing rice wine with low higher alcohols content. The results were as fellows.According to the study and production experience of beer and grape wine fermentation by immobilized yeast at home and abroad, this paper choosed calcium alginate as embedding medium to make immobilized yesat, then fermented Chinese rice wine with it. The reasult showed that107个/mL yeast concentration,2%sodium alginate and4%calcium chloride could guarantee the paricles with sufficient machanical strength and fermentation activity. This paricles used twelve times for the rice wine primary fennentation. The results were that alcohol degree maintained at about9.4%vol, physical and chemical indexes stayed stable, which indicated that immobilization technology was useful to guide the continuous production of rice wine.The fermentation performance of free yeast was compared with those of three batches of immobilized yeast. Results showed that the speed of fermentation by immobilized yeast was slower in intial stage, but final alcohol degree of free yeast fennentation and immobilized yeast fennentation were both around14.0%vol, residual sugars close to7.4g/L, and other physical and chemical indexes had no significant difference. GC-2014C gas chromatograph was used to detect the content of higher alcohols in the distillate. The results were that the total content in the wine fermented by immobilized yeast (545.86±8.26mg/L) was significantly lower than that of wine fermented by free yeast (688.82mg/L), which indicated that immobilization technology was helpful to reduce the higher alcohols content. On the basis of immobilization technology, this paper continued to study the influence of initial glucose content, yeast inoculation, primary fermentation temperature and initial ammonia nitrogen content on the higher alcohols content during the fermentation process.Studied the influence of initial glucose content on the higher alcohols content and the results showed alcohol degree rised with the increase of glucose content. When the initial glucose content was set as120g/L,140g/L,160g/L,180g/L and200g/L, the final total higher alcohol contents in the wine distillate were297.17mg/L,355.43mg/L,447.82mg/L,335.82mg/L and365.59mg/L, respectively. Fermented wih glucose content180g/L could ensure the wine with low higher alcohols content and ideal alcohol degree, so it was a good choice.Studied the influence of yeast inoculation on the higher alcohols content and the results indicated that inoculation should be set in the suitable range in order to guarantee the final rice wine with desirable alcohol degree. When yeast inoculation was set as0.2×107个/mL,0.6×107个/mL,1×107个/mL,1.4×107个/mL and1.8×107个/mL, the final total higher alcohol contents in the wine distillate were347.12mg/L,342.33mg/L,327.81mg/L,336.49mg/L and360.24mg/L, respectively. There were difference between the value-added amplitude of different kinds of higher alcohols during the fermentation process, so was the final proportion of every higher alcohols. Studied the influence of primary fermentation temperature on the higher alcohols content and the results revealed that if the temperature was too high, the yeast quantity would be fewer, alcohol degree lower, the total acid content higher so that the wine seemed to be rancidity. On the other hand, the low temperature would influence the generation of alcohol. When primary fermentation temperature was set as26℃,28℃,30℃,32℃and34℃, the final total higher alcohol contents in the wine distillate were325.00mg/L,348.13mg/L,386.49mg/L,320.92mg/L and304.54mg/L, respectively. And the higher alcohols content was positively correlated with yeast quantitiy in the rice wine sample.This paper added protein hydrolyzate into the fermentation liquor in order to study the influence of initial ammonia nitrogen content on the higher alcohols content. The results revealed that appropriate content (0.4g/L～0.8g/L) was helpful to yeast alcoholic fermentation. When initial ammonia nitrogen content was set as0.1g/L.0.2g/L,0.4g/L,0.6g/L,0.8g/L and1.0g/L, the final total higher alcohol contents in the wine distillate were346.75mg/L,342.27mg/L,297.60mg/L,255.27mg/L,272.57mg/L and359.22mg/L, respectively. The difference was significant.The single factor experiment result showed that initial glucose content, primary fermentation temperature and initial ammonia nitrogen content had more significant influence on higher alcohols content than yeast inoculation, so them were choosed to do the response surface optimization. The result indicated that the influence of initial glucose content and primary fermentation temperature on the higher alcohols content were extremely significant, and that of initial ammonia nitrogen content was significant. The optimal conditions were as fellows:initial glucose content was183.09g/L, primary fermentation temperature was27.63℃, initial ammonia nitrogen content was0.58g/L, under this conditions, the theoreical higher alcohols content was260.05mg/L. Three batches of rice wine fermentation tests were taken to verify the result, the practical higher alcohols content was265.65±7.64mg/L... |
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