Acetoin and Diacetyl Production by Lactobacillus plantarum Able to Use Citrate

Abstract

Whole-cell suspensions of Lactobacillus plantarum grown on lactose in the presence of citrate did not produce acetoin and diacetyl (AD) (D) from citrate in succinate buffer, pH 4.4 unless both a source of energy and nitrogen was present, but did from pyruvate. The total AD and the amount of D, produced by citrate-grown cells, from citrate were about two times the amounts formed from pyruvate, calculated on a molar basis. It appears, that AD are formed not only from pyruvate resulting from cleavage of citrate but also from acetyl-coenzyme A arising during a probable breakdown of citrate in a reversible reaction of citrate synthetase. Neither acetate nor acetaldehyde had any effect on the total AD or the amount of D produced from pyruvate by pyruvate-grown cells. The rates of AD production from pyruvate by whole-cell suspensions of pyruvate-grown L. plantarum and Streptococcus subsp. diacetylactis represented only 69.7 and 6.6%, respectively, of that produced by Lactobacillus casei. These were 0.075 μmoles/mg dry wt−1 ml−1 min−1 for L. casei, 0.053 for L. plantarum and 0.005 for S. lactis subsp. diacetylactis.

13C nuclear magnetic resonance analysis of glucose and citrate end products in an ldhL-ldhD double-knockout strain of Lactobacillus plantarum

“…1). Oxalacetate is usually decarboxylated to pyruvate, which is further dissipated into by-products, such as C 4 compounds (9,30,31). However, these metabolites were not observed with the wild-type strain in our experiments.…”

“…Glucose and citrate degradation pathways proposed for the L. plantarum wild-type strain (NCIMB8826) and LDH-defective strain (TF103). [1], LDH; [2], pyruvate formate-lyase; [3], acetaldehyde dehydrogenase; [4], alcohol dehydrogenase; [5], phosphotransacetylase; [6], acetate kinase; [7], pyruvate oxidase; [8], pyruvate decarboxylase; [9], ␣-acetolactate synthase; [10], ␣-acetolactate decarboxylase; [11], 2,3-butanediol dehydrogenase; [12], nonenzymatic decarboxylation; [13], pyruvate carboxylase; [14], malate dehydrogenase; [15], fumarase; [16], fumarate reductase; [17], malolactic enzyme; [18], citrate lyase; [19], oxalacetate decarboxylase; [20], mannitol-1-phosphate dehydrogenase; [21] (28), and the authors hypothesized the involvement of hydroxyisocaproate dehydrogenase activities. However, we did not detect any hydroxyisocaproate dehydrogenase activity in TF103 cell extracts using several ␣-keto acids as substrates.…”

High-Efficiency Conversion of Pyruvate to Acetoin by Lactobacillus plantarum during pH-Controlled and Fed-Batch Fermentations

“…Lactobacillus plantarum is a homofermentative bacterium that ferments lactose and glucose almost entirely to lactic acid, but also produces trace (parts per million) quantities of acetoin, diacetyl, and 2,3-butanediol (13,14). Relative insensitivity to bacteriophage attack; tolerance to low pH, heat, and salt; generally recognized as safe status in foods (3); and the ability to ferment more than 20 different sugars (4) recommend this species for use in biotechnological processes.…”

“…The addition of citrate enhances diacetyl synthesis by inducing citrase and acetate synthetase (24) and increases acetoin synthesis in L. plantarum, but it is inhibitory to growth and cell mass synthesis (27). Pyruvate also stimulates diacetyl and acetoin synthesis (13,15,27). Lactobacillic starter cultures form acetoin and diacetyl in proportion to the concentration of pyruvate added (1).…”