关键词: 自絮凝酵母, 锌离子, 乙酸胁迫, 乙醇发酵

Abstract: Acetic acid is one of the major inhibitory compounds for cell growth and ethanol fermentation of Saccharomyces cerevisiae, and is present in cellulosic hydrolysate as well as in industrial culture broth contaminated by acetic-acid producing bacteria. Therefore, improvement of acetic acid tolerance plays important role for efficient ethanol production. Although adjustment of pH to 5 or 6 was proved to be effective against acetic acid toxicity, it is impractical for large scale industrial production due to the cost and increased risk of contamination. Zinc is an essential metal for yeast cell growth and metabolism, however, the important role of zinc is often neglected due to its status as a trace element. Previous studies showed that zinc has protective effect on yeast ethanol tolerance and thermal tolerance of self-flocculating yeast SPSC01. In this study, the effect of different concentrations of zinc sulfate on ethanol production of self-flocculating yeast SPSC01 in presence of high concentration of acetic acid was studied in batch fermentation in the 3L bioreactor using 100 g?L-1 glucose. The results showed that zinc exhibits protective effect against acetic acid toxicity. Of the different concentrations of zinc sulfate tested in this work, 0.03 g?L-1 zinc sulfate showed the best protective effect. Addition of 0.03 g?L-1 zinc sulfate shortened the lag phase time of cell growth of the self-flocculating yeast in presence of 10 g?L-1 and 15 g?L-1 acetic acid, and the fermentation time was also subsequently reduced. The lag phase time was shortened nearly 30 h, with a 27.8% increase in the biomass yield and a 66.7% increase in the ethanol productivity comparing with the non-addition control. The by-products lactic acid and propionic acid were repressed by zinc addition, and significant reduction of propionic acid production was observed upon zinc addition, while no apparent effect was observed on succinic acid and citric acid biosynthesis. The results from this study showed the important role of zinc in cell growth and ethanol fermentation when subject to acetic acid stress, and demonstrated that adjusting the concentration of zinc in the culture medium is a simple and effective method to improve ethanol fermentation performance in presence of high concentration of acetic acid.

Key words: self-flocculating yeast, zinc ion, acetic acid toxicity, ethanol fermentation