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Title: Identification of some microorganisms isolated from poi and characterization of the biological properties of one lactic acid bacteria 
Author: He, Lijun
Date: 2003-12
Publisher: University of Hawaii at Manoa
Abstract: Lactic acid producing microorganisms from poi and the biological properties of one lactic acid bacteria are studied in this work. Based on phenotypical analysis, five bacterial strains isolated from fresh poi are identified as Lactobacillus acidophilus, Lactobacillus delbrueckii, Lactococcus lactis lactis, Leuconostoc citreum and Leuconostoc lactis individually. The gas-producing bacterial strain first identified as Lactobacillus acidophilus is finally identified as Weissella confusa by combining the results of phenotypical analysis and genotypical analysis. Acid tolerance of Weisselfa confusa is examined by exposing the bacterial cells to MRS broth at different pH with/without adaptation. When exposed to acid stress, the bacterial strain can survive at pH 3.70 with a decreased growth rate. No bacteria are detected at pH 3.0. However, the survival rate of the bacterial cells at pH 3.0 increases by adapting the cells at pH 4.46. Results suggest that the bacteria can grow in acidic condition and the acid tolerance is adaptable. The effect of the taro base on the growth of Weissella confusa is investigated by examining the growth of the bacteria in four kinds of taro/sucrose mixture (10% taro, 3% taro, 3% taro plus 1.3% sucrose, 3% taro plus 3.2 sucrose). All four media supported the fast growth of the bacteria during the incubation period and the pH of the taro base dropped fast, ranging from 3.39 to 3.73 after three-day incubation. The growth curves of W. confusa in taro/sucrose base (3% taro plus 1.3%sucrose) and acid/heat treated poi were established with the bacterial count and the pH of the sample every day. The bacteria grew rapidly in both of the medium. These preliminary results seem to indicate that a taro-based fermented food is feasibly produced by monoculture with W. confusa as starter culture. In addition, a different pH change was observed in these two taro-based media. These results suggest that the acid/heat treatment and solid content had some effect on the pH change of the taro medium. Based on genotypical analysis, the bacterial strain isolated from sour poi is identified as Lactobacillus p/antarum and the yeast-like microorganism isolated from sour poi is identified as Candida tropicalis. Candida trapicalis can ferment glucose, fructose, sucrose, and starch. Their existence may explain the acid production at the late stage of the fermentation and the consumption of starch. This work helps to elucidate the fermentation process of poi and improve the production by identifying pure cultures of starters. In addition, this work suggests Weisselfa confusa may be a potential bacterial strain in food fermentation.
Description: xii, 79 leaves
Rights: All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.

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