Regulation Mechanism Of The Saccharomyces Cerevisiae Ydcs101on Acetic Acid Metabolism During Litchi Wine Fermentation

In allusion to the problem which volatile acid easily exceeded during litchi wine fermentation caused by the raw material, Saccharomyces cerevisiae, which have strong abilities to metabolize acetate and to produce alcohol, was choosed as original strain. To preliminary reveal the control law of acetic acid metabolism by Saccharomyces cerevisiae, ultraviolet spectrophotometer method and high performance liquid chromatography (HPLC) method were adopted to analysis acetic acid metabolism-related enzyme activity and several intermediate metabolite changes during litchi wine fermentation by Saccharomyces cerevisiae strain DCCS101.The effect of different initial concentrations of acetic acid on the metabolish of acetic acid by Saccharomyces cerevisiae was studied.The results indicated that the amount of acetic acid metabolized by Yds101increased with initial acetic acid concentration increasing and then decreased. While litchi juice supplemented with1.5g/L acetic acid before fermentation, at the end of fermentation, the content of acetic acid was0.78g/L and decreased by48.0%. The effects of acetic acid on the metabolic products of yeast were that: there were less glycerin and more acetaldehyde and ethanol than these unsupplemented with acetic acid during the fermentation.In order to study effects of temperature changes on key enzyme activity and metabolism of acetic acid, when initial concentration of acetic acid was1.5g/L, setting the fermentation temperature were20℃,24℃,28℃,32℃,36℃. The results show that: the low temperature can effectively control the content of volatile acids. At20℃, when fermentation was finished, acetic acid content was0.53g/L, the percentage of acetic acid metabolism by S.cerevisiae was relatively high, up to48%, and alcohol content was11.4%(v/v). With fermentation temperature increasing, the content of acetic acid increased at the end of fermentation, but the content of alcohol increased first and then reduced. The specific activity variation of PDC increased and then decreased, but the activity of ACS gradually increased with temperature increasing. The activity of ADH and ALDH decreased while fermentation temperature increasing, when the temperature exceeds28℃, ADH activity weakened rapidly, but the activity of ALDH weakened relatively slow. When the fermentation temperature increaseed, the content of succinic acid increased, but the content of L-malic acid, lactic acid and citric acid were reduced.Single factor experiment was carried out to investigate the pyruvate transport protein inhibitor of a-cyano-4-hydroxy cinnamic acid (a-CCA) and the effect of TCA cycle intermediate metabolites such as oxaloacetate (OAA) on the activities of key enzymes and acid metabolism. The results indicate that:when the initial concentration of acetic acid was 1.5g/L in the fermentation medium, with the a-CCA and OAA concentration increasing, the content of acetic acid reduced first and then increased. Supplemented with0.5mM a-CCA, the content of acetic acid reduced to0.38g/L at the end of the fermentation.a-CCA could promote the activity ADH, ALDH and ACS, however, inhibit the activity of PDC. When the inhibitor concentration increaseed, the contents of L-malic acid and lactic acid increased, but the content of succinic acid and citric acid were reduced. When addding0.8g/L OAA, low levels of acetic acid exist at the end of litchi wine fermentation, only0.47g/L. OAA had a promoting effect on enhance the activities of PDC, ALDH and ACS, but has a certain extent inhibition to the activity of ADH. When the OAA concentration increased, the contents of L-malic acid and succinic acid increased, but the content of lactic acid and citric acid were reduced.To examine how the metal ions influnce acetic acid metabolism and key enzyme activity, when the initial concentration of acetic acid was1.5g/L, litchi juice supplemented with different contents of K+, Mg2+, Ca2+and Cu2+serve as fermentation medium. The results showed that:K+and Mg2+can promote cell metabolism of acetic acid, but Ca2+and Cu2+are not conducive to the metabolism of acetic acid by S.cerevisiae. With the concentrations of K+and Mg2+increasing, at the end of the fermentation, the concentration of acetic acid reduced first and then increased. When addding6mmol/L K+and4mmol/L Mg2+, the minimum concentration of acetic acid exist in litchi wine,0.44g/L and0.39g/L, respectively. K+can significantly improve the activity of ALDH and ACS, however, has little effect on the activities of PDC and ADH; Mg2+can improve the activities of PDC, ALDH and ACS,and inhibit the activity of ADH. Ca2+can inhibit the activities of ADH and ACS, and increased the activity of ALDH, and has little influence on the activity of PDC, so there is higher levels of acetic acid at the end of fermentation, up to1.03g/L, which is far greater than the absence of Ca2+of0.53g/L. Copper stress severely inhibited the yeast growth, the lag phase and yeast number were dependent on its ion concentration.0.05mmol/L and0.25mmol/L copper stress did not signifi cantly affect the survival of yeast.0.25mmol/L copper is largely suppressed fermentation process of yeast, and the finished sample with lower alcohol and higher residual sugar, signifi cant difference compared with control. Copper stress over0.05mmol/L, decreased the ability of metabolism acetic acid and ACS activity of yeast.