Isolation of yeast with high acetoin- producing ability from Liangzhou fumigated vinegar and optimization for its fermentation medium

Acetoin,a precursor of tetramethylpyrazine,is identified as a flavor component of Liangzhou fumigated vinegar. In the test,an acetoin-producing strain T8 was isolated from the fermented cultures of Liangzhou fumigated vinegar,which was identified as Hanseniaspora uvarum by classical identification methods and ITS gene sequence similarities. In order to further know the nutritional requirements of T8 growth and metabolism,the fermentation medium for producing acetoin with T8 was optimized,so that it could provide the better seed medium for flavoring yeast in modern vinegar brewing process.The key fermentation factors of affecting acetoin yield by H.uvarum were studied,including the carbon resource,the nitrogen resource,inorganic salts concentration. The results showed that the best fermentation medium component was: glucose 60 g/L,peptone 10 g/L,yeast extract10 g/L,( NH₄)_2HPO₄ 8 g/L,KH₂PO₄ 0.5 g/L,Mg SO₄·7H₂O 0.75 g/L,Mn SO₄ 0.6 g/L. Under the optimized conditions,the acetoin yield reached 15.236 g/L,which was increased by 20.65% in comparison with the initial fermentation medium,and the content of tetramethylpyrazine in vinegar cultures was increased by 22.1% in comparison with control in the artificial inoculation vinegar brewing test,it showed that T8 could help to improve the vinegar flavor.