IS L-LACTIC ACID A TRUE INDICATOR OF MICROBIAL INFECTION

Sugar loss due to microbial infection has always been a problem encountered by the industry and monitoring is very important. Conventional culture methods for estimates of microbes take at least 48 hours and therefore chemical estimates of bacterial metabolites such as L-lactic acid have been used for routine analysis. These chemical estimates will not hold true in all cases, and at one of American Crystal Sugar Company's factories, L-lactic acid numbers and microbial counts obtained by culturing methods gave conflicting results. In addition organic acid analysis by HPLC gave very high total lactic acid numbers (the sum of D and L-lactic acid). Additional investigation indicated the presence of Leuconostoc mesenteroides, a D-lactic acid producer. This unusual formation of D-lactic acid in preference to L-lactic acid is the first reported incidence to our knowledge, and shows that under unusual conditions L-lactic acid is not a true indicator of microbial infection.