CO_2对啤酒发酵过程中酵母生长代谢及酯的形成影响

Effect of CO_2 on growth and ester formation of Saccharomyces cerevisiae during beer fermentation

啤酒加压发酵形成高浓度的CO2会使酿酒酵母生长受到抑制,导致主要风味物质酯的生成减少。CO2通过反馈抑制丙酮酸脱羧反应、降低基质和酵母胞内pH值、改变细胞膜的流动性和膜电势、抑制酵母的生长。乙酸酯类是乙酰辅酶和高级醇之间在醇酰基转移酶的催化作用下形成的。乙酰辅酶A、高级醇、醇酰基转移酶AATase活力是酯类形成的关键因素。发酵参数如温度和压力,特别是CO2对酯形成的研究是对酯形成机理的重要补充。然而,近年对CO2影响酯生成的研究并没有形成明确的机制理论。与乙酸酯相反,CO2可以刺激C6-C10中链脂肪酸乙酯(MCFA ethyl esters)的增加。CO2除了以底物形式参与酿酒酵母脂肪酸合成外,还能促进合成的进行,使脂肪酸积累,最终形成脂肪酸酯。

The increase top pressure in the beer fermentation inhibits yeast growth and reduces the synthesis of esters, following an increase of dissolved carbon dioxide in the fermenting medium. The effects of inhabitation of growth is feedback inhibition of the enzymic decarboxylation of pyru- vate （acetyl CoA precursor） and the drop in intracellular pH and the cell membrane fluidity, cell membrane potential. The increase in carbon dioxide pressure will thus give beer of less fruity character. Acetate ester is synthesized from higher alcohol and acetyl coenzyme A by alcohol acetyltrans- ferase （AATFase） in Saccharomyces cerevisiae. Acetyl coenzyme A, higher alcohol and AATFase were considered to be the most important factors during the ester forming. However, the parameters of fermentation such as temperature and pressure of CO2 which is especially play a key role on in- fluence the ester forming. The mechanism of CO2 work on ester is important to the ester forming theory have not been found clearly. Unlike the syn- thesis of acetate esters, the synthesis of MCFA ethyl esters is stimulated under conditions of CO2 pressure.