INFLUENCE OF THE AMINO ACID – DEXTROSE REACTION ON GROWTH OF LACTIC ACID BACTERIA

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Abstract
Growth of Lactobacillus arabinosus, L. casei, and Streptococcus faecalis (as measured by lactic acid production) was studied in relation to the effects of the products of the amino acid – reducing sugar (Maillard) reaction. Addition of preformed Maillard products to a medium had little or no effect. Medium that had been autoclaved after the addition of dextrose promoted more rapid growth (shorter lag phase) than medium for which the dextrose had been autoclaved separately. This effect could not be traced to the presence of Maillard products, but appeared to be a complex phenomenon depending in part on the Eh of the solution. Destruction of amino nitrogen occurred during autoclaving, and destruction of tryptophan was evident from a comparison of growth response curves. It is concluded that the Maillard reaction affects the growth of these organisms only when an essential amino acid (or other nutrient), present in limiting quantities, is destroyed by the reaction. A serious error may be introduced into microbiological assays for amino acids if the samples to be assayed contain dextrose.