A Research Of Identification And Degradation Characteristics On A Strain Degrading L-malic Acid And Citric Acid

L-malic acid or citric acid are flavor substances of fruit juice and wine, A quantity of L-malic acid is contained in apple juice and grape juice, citric acid is contained in lemon juice, pineapple juice and hawthorn juice in higher levels. Suitble organic acid can make the fruit juice and the wine taste mellow and refreshing, balance the bitter taste and inhibit bacterial activity. However, if the organic acid content is too high, it will make fruit juice or fruit wine too sour, too rough to drink, and even take on a phenomenon of losing optical turbidity. To solve this problem, this article studies strain S8 screened by our laboratory in 2008, which can both degrade L-malic acid and citric acid. The biological status of the strain S8 is determined through morphological observation, physiological and biochemical characteristics and homology analysis of rDNA-ITS (internal transcribed spcer)sequence. Its growth characteristics, tolerance and degradation characteristics are researched, the results are as follows:1. Through morphological observation, physiological and biochemical characteristics and homology analysis of rDNA-ITS sequence, the strain S8 is determined as Issatchenkia terricola which can degrade L-malic acid and critic acid.2. The growth curve of strain S8 shows that the period of the strain reaching the logarithmic phase is form 4 to 18 hours; After the growth characteristics of strain S8 has been studied, these are obtained that the optimum growth temperature of the strain is 28 to 30℃,the optimum initial pH is from 5.0 to 5.5, optimum rotation speed is 150 r/min; Having researched its tolerability, the following were found that the highest concentration of SO2 the strain could tolerate is 450 mg/L, the maximum concentration of alcohol is 5%(v/v) and the highest temperature is 70℃.3. After L-malic acid and citric acid having been taken as the sole carbon source and the degrading medium of strain S8 had been optimized, the next are made:yeast extract and peptone are the best nitrogen sources, the concentration of yeast extract is 0.6%, peptone is 0.4%, the rate of reducing L-malic acid reaches to 79.9%, and citric acid reaches to 73.1%.4. The optimal concentration on degrading acids is optimized and then these conclusions are made that the optimal degradation concentration of L-malic acid is 4 to 20g/L, the optimum degradation concentration of citric acid is 4 to 12g/L; Inoculation is optimized and these are written that the degradation time will be delayed if inoculation is 1%(v/v), the degradation time will be shorter if inoculation is more than 3%, so the best inoculation is 3%; The degrading time is optimized and these are conclued that the degrading rate of L-malic acid is up to 85.2% and citric acid is up to 80.6% when degrading time is 50th hours.