Effect of sugar addition and oxygen presence on the metabolism of lactic acid bacteria: soybean and culture medium

Abstract

Studies in soybean pastes (PS) without added sugar and low moisture concentration, showed that Lacticaseibacillus paracasei subsp. paracasei CRL 207 produced mainly acetic acid and, to a lesser extent, lactic acid and ethanol, presenting a change in its normal metabolic pathway. The strain did not use the main carbohydrates present, so a limiting substrate condition could be generated with changes in the use of pyruvate. Oxygen is an important factor in the metabolism and fate of pyruvate and it is present in solid substrates, mainly those with lower water content. In order to understand the behavior presented by the strain in the PS, in this work we studied the growth, consumption of substrate and production of organic acids by the strain in PS with 65% moisture added with sucrose, glucose or fructose, using basal PS as control. In addition, studies were carried out in a liquid medium added with the same sugars, under agitation to evaluate the influence of oxygen. The results obtained demonstrated a change in the metabolism of the strain under the studied conditions (different carbon sources and oxygen availability) due to the low moisture of the solid soybean substrate.