IS L-LACTIC ACID A TRUE INDICATOR OF MICROBIAL INFECTION

Sugar loss due to microbial infection has always been a problem encoun tered by the industry and monitoring is very important. Conventional c ulture methods for estimates of microbes take at least 48 hours and th erefore chemical estimates of bacterial metabolites such as L-lactic a cid have been used for routine analysis. These chemical estimates will not hold true in all cases, and at one of American Crystal Sugar Comp any's factories, L-lactic acid numbers and microbial counts obtained b y 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 con ditions L-lactic acid is not a true indicator of microbial infection.