Study On Isolation And Selection Of Yeast From Sichuan Pickle And Its Application

Based on the brewing characteristics of Sichuan pickles, the present work focusedon the improvement of aroma and fermentation process. Two yeasts were isolated andselected from the pickle juice of high quality. Furthermore, the constitution offermentation aids was meliorated on this basis so that the aroma of the productscan be improved and the fermentation can be speeded up. The results are as follows:The different temperature and culture media were chosen as the enrichmentconditions. 13 yeasts had been isolated from the pickle juice. The gas-producingability, acid-producing ability, ethanol producing ability, film-producing abilityand aroma-producing ability were used as primary selective conditions so yeasts whichwere not suitable as fermentation aids of pickles can be got rid of. Thesalt-tolerance, heat-resistance, acid-resistance and influence by the spice wereused as the secondary selective conditions. During the selection, sensory evaluationwas also emphasized. According to above requirements, two strains of yeast wereselected which canmeet the requirements of the brewing of Sichuan pickles and havegood fermentation ability. Two yeasts were identified as Candida-valida andCandida-parapsilosis and named as FA and YB respectively.The biological properties of the selected yeasts were studied in this paper.Growth of FA and FB which came from second selection changed slowly when salt densitywas lower than 7％; while it changed obviously when the salt density was higher than10％. Acid-resistance of FA and YB was good when the pH value was between 3 and 5.5.They had the best growth condition when PH value was 3.5 for FA and 4 for YB. Whenthe temperature was between 20℃and 30℃, growth condition of FA and YB was prettygood and had little change. But it obviously decreased when the temperature was higherthan 35℃. Studies on such characteristics also showed that FA anti YB are suitablefor the inoculation of pickles fermentation. Garlic had a fungistasis function onthe growth of FA and YB and it became more obvious along with the density of garlic juice became higher. Ginger also had a fungistasis function on YB but the yeastsnumber reduced little; while it had an obvious growth-promoting function on FA whenthe density was lower than 2％and the yeasts number had a great increase. But whenthe density was higher than 6％the yeast number had a decrease and the fungistasisfunction was showed. It had little influence on the growth of FA when the densityof chili juice was 4％, but when it was higher than that the growth of two yeastswas prohibited obviously. It was the same For YB when the density was higher than2％. Prickly ash had an obvious growth-promoting function on both FA and YB but acomparatively weaker function on the latter. In the experiment of the fermentableextract of Chinese cabbage, FA showed a good ability in ester-producing,acid-producing and utilizing sugar residue. While in this experiment YB showed agood ability in amino acid producing, acid producing and utilizing sugar residue.The mixed fermentation experiments of Sichuan pickles were carried out and improvedwhich based on the biological characteristics of the selected yeasts and combinedoriginal fermentation technology of Siehuan pickles. It is improved that thePhysicochemical index and sensory is much better when two yeasts and lactic acidbacteria work together in fermentation compared with one yeast and lactic acidbacteria work together or lactic acid bacteria work alone. Furthermore, the productspossess strong pickle aroma and taste.