Effects of pH and Sugar on Acetoin Production from Citrate by Leuconostoc lactis

Abstract

The relationship between acetoin production and citrate utilization in Leuconostoc lactis NCW1 was studied. In a complex medium the organism utilized citrate at neutral pH (initial pH, 6.3) and at acid pH (initial pH, 4.5) but produced nine times more acetoin at the latter pH. In resting cells the utilization of citrate was optimum at pH 5.3. Production of acetoin as a function of citrate utilization increased as the pH decreased, and at pH 4.3 all of the citrate utilized was recovered as acetoin. Glucose (10 mM) and lactose (10 mM) markedly stimulated citrate utilization but totally inhibited acetoin production in glucose- and lactose-grown cells. Addition of glucose to cells actively metabolizing citrate caused an immediate increase in citrate uptake and a reduction in the level of acetoin. The apparent K m values of lactic dehydrogenase for pyruvate were 1.05, 0.25, and 0.15 mM at pH 7.5, 6.5, and 5.0, respectively. Several heterofermentation intermediates inhibited α-acetolactate synthetase and decarboxylase activities. The implications of these results in regulating acetoin formatin are discussed.

Lactobacillus helveticus as a tool to change proteolysis and functionality in Swiss-type cheeses

“…β-Naphtylamide (β-Na) derivatives were used according to Goldbarg and Rutenburg (1958): Lysβ-Na for lysine aminopeptidase (PepN) and Phe-Proβ-Na for X-prolyl-dipeptidyl aminopeptidase (PepX). The total LDH activity was assayed using pyruvate as substrate, as previously described (Cogan et al, 1981).…”

Utilisation of a cell‐free extract of lactic acid bacteria entrapped in yeast to enhance flavour development in Cheddar cheese

“…Autolysis of starter cultures in cheese during ripening was monitored in triplicate by assaying for the release of the intracellular enzyme, lactate dehydrogenase (LDH) as described by (Cogan et al 1981). Both lactobacilli and lactococci contain the enzyme LDH.…”

Responses of lactic acid bacteria to oxygen

“…In general, when C4 compounds accumulate in growing cultures pyruvate, or an alternative source of pyruvate such as citrate, is available in addition to the fermentable sugar [54,78,[80][81][82][83]. Neverthe- less, C4 compounds have been observed occasionally in cultures of some streptococci growing in a sugar-based medium without additional pyruvate [41,73,79,84,85].…”