Co-metabolism of citrate and maltose byLactobacillus brevis subsp.lindneri CB1 citrate-negative strain: effect on growth, end-products and sourdough fermentation

Abstract

Growth, substrates and end-product formation of the maltose and citrate co-metabolization byLactobacillus brevis subsp.lindneri CB1 citrate-negative strain were initially studied in synthetic medium. Compared to maltose (19 g/l) fermentation, the co-metabolization of maltose (10 g/l) plus citrate (9 g/l) caused faster cell growth, increased the concentrations of lactic acid and especially of acetic acid (from 0.7 g/l to 2.9 g/l), produced succinic acid (0.5 g/l) and reduced ethanol synthesis. Highest activities of acetate kinase, the same of lactate dehydrogenase and a reduced alcohol dehydrogenase activity were detected in cytoplasmic extracts of cells growing on maltose plus citrate. The breakdown of citrate depended upon the continuous presence of maltose in the growth medium. Upon depletion of citrate, the cells continued through the normal maltose fermentation, having a diauxic metabolic curve as shown by impedance measurements. Concentrations of citrate from 3 g/l to 15 g/l led to increases of acetic acid from 1.25 g/l to 5.55 g/l. Since maltose was naturally present during sourdough fermentation, the addition of 9 g citrate per kg wheat dough enabled the co-metabolization of maltose and citrate byL. brevis subsp.lindneri CB1. Compared with traditional sourdough fermentation, faster cell growth, a higher acetic acid concentration and a reduced quotient of fermentation were obtained by co-metabolism.