Preliminary Study On The Acetaldehyde In The Yeast And Fermentation Process Of Chinese Rice Wine

Acetaldehyde, one of the main aldehydes in Chinese rice wine, is a by-product of Saccharomyces cerevisiae metabolism. Acetaldehyde has a low threshold but a high flavor intensity. The high content of acetaldehyde in Chinese rice wine will cause the spicy taste. At the same time, acetaldehyde is toxic. Drinking Chinese rice wine with high amount of acetaldehyde would cause strongly drunk, commonly known as “headache”. Therefore, the research of acetaldehyde in Chinese rice wine is of significant importance.The present study developed a new method using HS-SPME-GC-MS to detect acetaldehyde in Chinese rice wine.With this method, the study surved Chinese rice wine in local markets showed that the content of acetaldehyde ranged from 12.27 to 232.80 mg·L-1. The acetaldehyde varied in Chinese rice wine producer from different areas, with the generally higher content of acetaldehyde in Shaoxing area.The metabolism of acetaldehyde in the industrial Chinese rice wine yeast strain N85 was studied. The gene ADH2 encoding alcohol dehydrogenase; the gene ALD2 and ALD6 encoding aldehyde dehydrogenase, were disrupted seperately in Δura3 haploid yeast strain 2a(MATa ura3), using the disruption cassette “ADH2S-URA3-ADH2X”, “ALD2S-URA3-ALD2X” and “ALD6S-URA3-ALD6X” respectively. Lab-scale fermentation of Chinese rice wine was proceeded with 2a-A2(Δadh2), 2a-D2(Δald2), 2a-D6(Δald6) and the pyruvate decarboxylase gene deletion strains 2a-P1(Δpdc1), 2a-P5(Δpdc5), and 2a-P6(Δpdc6), which were constructed in our previous work, respectively. Compared with the parental haploid, the concentration of acetaldehyde in fermented liquor using 2a-P1, 2a-P5 and 2a-P6 was decreased by 25.26%, 32.68% and 20.46%, respectively. However the content of acetaldehyde was decreased by 7.14% with the engineered strain 2a-A2, which confirmed that the acetaldehyde was produced by the sugar metabolism in N85; and the pyruvate decarboxylase was the key enzyme. The generated ALD2 and ALD6 disruption mutants(2a-D2, 2a-D6) formed 144.91% and 88.87% more acetaldehyde than the parent haploid strain during fermentation, indicating that aldehyde dehydrogenase was the key enzymes for acetaldehyde degradation in N85, and the enzyme encoded by ALD2 gene played a more important role in converting acetaldehyde into acetic acidThe study inverstigated the effects of fermentation paraments on acetaldehyde formation in the Chinese rice wine. The factors including yeast strains, fermentation temperature, pitching rate of yeast, use of wheat Qu and ratio of rice to water were studied. The results showed that effect of wheat Qu varieties on the acetaldehyde content was not significant, while other factors could change the content of acetaldehyde obviously.The yeast strains Meyerozyma guilliermondii, Saccharomyces cerevisiae, Pichia guilliermondii, Saccharomycopsis fibuligera and Rhodotorula mucilaginosa preserved in our laboratory were fermented using the rice juice medium for acetaldehyde production analysis. The results showed that under the same fermentation condition, S. cerevisiae could produce the same amount of acetaldehyde as the industrial yeast strain N85, Rhodotorula mucilaginosa yielded less acetaldehyde, while variation of other strains produced little acetaldehyde.