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The effect of adaptation of Lactobacillus amylovorus to increasing concentrations of sweet potato starch on the production of lactic acid for its potential use in the treatment of cannery waste

Abstract Lactobacillus amylovorus, an amylolytic species, was cultured in increasing concentrations of sweet potato starch to test the effect of this progressive acclimation on lactic acid production. This research is part of a project on the use of the waste stream from a sweet potato cannery to produce lactic acid. The media used for this acclimation was a modified version of the de Man, Rogosa and Sharpe medium, in which glucose was partially or totally substituted with sweet potato starch. The process was done in five steps, starting with 100% glucose in the first step and ending with 100% sweet potato starch in the last one. At each step, the effectiveness of the acclimation was tested by running fermentations with and without pH control for 62 h. The effect of the overall adaptation process was tested by comparing the growth and activity of the acclimated vs non-acclimated bacteria using sweet potato starch as the only source of carbohydrates. Growth and activity assessments indicated that L. amylovorus was able to ferment sweet potato starch into lactic acid. In most cases, pH control resulted in better substrate utilisation and larger amounts of lactic acid. In the comparison study, however, the adaptation process had a major influence on lactic acid production than the effect of pH. For 20 g L–1 sweet potato starch media, adapted L. amylovorus under no pH control yielded 11.20 g L–1 versus the non-adapted bacteria, which yielded 7.10 g L–1. Under controlled pH conditions, 14.80 and 4.20 g L–1 lactic acid were produced by adapted and non-adapted bacteria respectively.