Brewing Rich β-Phenylethanol Beer From Cassava And Its Producing Metabolisms In Yeast

As one of the three tubers,cassava has rich nutritional value and is the main food and energy source for more than 800 million people in Africa and other tropical regions.However,due to the low added value of existing cassava deep processing products and excess production capacity,cassava industry develops slowly.Therefore,it is urgent to develop new uses of cassava,increase the added value of products and break the development dilemma of cassava industry.Beer is the most consumed alcoholic beverage in the world,and malt is one of the main raw materials of beer.However,due to the influence of international trade in recent years,the price of malt has been soaring continuously,so the development of new raw materials for beer is conducive to the benign development of beer industry.Since the price of cassava is much lower than that of malt,it is of great scientific significance and economic value to explore the possibility of cassava as an auxiliary material in beer brewing,and to study its key technology,flavor characteristics and biochemical mechanism.Cassava itself contains high levels of hydrocyanic acid and starch,these characteristics will bring bad taste and adverse effects on quality of beer.In this study,a set of innovative cassava beer brewing technology was developed through raw material ratio,improvement of preparation technology and yeast strains optimization.The specific technologies were as follows: heating the cassava homogenate to 50 ℃,holding for 10 minutes,adding 180-200 U/g high temperature resistant amylase and0.5g/kg calcium chloride,heating to 70 ℃,holding for 30 minutes,and then heating to95 ℃.The cassava paste was obtained after 30 minutes of heat and boiling for 10 minutes.Afterwards,cassava beer was fermented by mashing,filtration,boiling,cycloprecipitation and fermentation.The technology eliminated the negative effect of cassava,and the quality of the finished cassava beer was excellent,the content of hydrocyanate in beer was less than 0.1 mg/kg.Meanwhile,the physical and chemical indexes,sensory evaluation,flavor substances and nutritional elements of cassava beer and wheat beer were systematically studied and compared.The results showed that compared with wheat beer,cassava beer had balanced nutrition and harmonious flavor.Specially,the content of β-phenylethanol in cassava beer increased significantly,which made it have delicate and elegant rose aroma.In addition,it was found that the activities of L-phenylalanine aminotransferase,phenylpyruvate decarboxylase and phenylacetaldehyde dehydrogenase in Ehrlich pathway of β-phenylethanol synthesis in cassava beer fermentation process were generally higher than those in wheat beer.aro9 encoding L-phenylalanine aminotransferase and aro10 encoding phenylpyruvate decarboxylase were up-regulated at the later fermentation stage,indicating that they are the main regulatory genes in the Ehrlich pathway of β-phenylethanol production from phenylalanine as substrate during the production of cassava beer.This study not only provides a new product and application of cassava processing,but also lays a theoretical foundation for further understanding the biosynthesis pathway and mechanism of β-phenylethanol,which plays an important role in food industry.