ABSTRACTThree commercial yogurt cultures and strains ofLactobacillus bulgaricusandStreptococcus thermophilusisolated therefrom were evaluated for their effect on aspartame degradation during and after fermentation. The rate of aspartame loss was related to growth of the organisms. Differences in losses due to strain type did not appear signficiant. Aspartame degradation rates were correlated to metabolic rate of the culture. As the rate decreased, loss of aspartame decreased. As a result, less than 10% aspartame was degraded during 6 wk refrigerated storage. Results indicate aspartame should remain stable in yogurt, provided it is added after fermentation.