Sugar addition and oxygen presence affect the metabolism of L. paracasei on MRS medium and soy paste

BORQUEZ, J; RODRÍGUEZ DE OLMOS, A; GARRO, MS

San Miguel de Tucumán

Simposio; V Simposio Internacional de Bacterias Lácticas; 2016

CERELA-CONICET

It is well known that lactic acid bacteria (LAB) may change their metabolism in response to different conditions, resulting in a diverse end-product pattern than seen with glucose fermentation under anaerobic conditions. In previous work we have optimized the main fermentation parameters of L. paracasei subsp. paracasei CRL 207 on soybean paste without added sugar and low moisture conditions (65%). This strain was able to grow without viability loss but the pH showed little change from paste control. Oxygen transfer is an important factor in solid substrate fermentation that could have an effect on the use of pyruvate by LAB, changing the produced organic acids. In order to understand the behavior of the strain in soy paste, the aim of the present work was to analyze the effect of sugar addition on the production of organic acids by L. paracasei in soy paste. The effect of oxygen was also investigated in MRS broth. Sucrose is the main sugar in soybean and glucose is present only in low amount. Because of that, sucrose and its hydrolysis products (glucose, fructose) were selected for the following studies. Soybean paste and MRS (with 2% each sugar) were inoculated with L. paracasei and incubated at 37 °C for 24h. The effect of oxygen was analyzed on MRS with each added sugar under agitation conditions. The strain growth was followed by plate count or OD600, and pH measures. Carbohydrate consumption and organic acids production were determined by HPLC. In MRS without sugar and with added sucrose showed low OD without differences between both conditions. However an increase of biomass and pH was found in agitation condition for all sugars assayed. Despite that in soy paste was observed scarce use of sucrose compared to glucose or fructose, the cell count was similar in all condition assayed. The differences were observed in the pH values. In soybean pastes, the profile of organic acids obtained was different when the strain grew in the presence of sucrose and without addition of sugar compared to the other conditions assayed. Acetic acid was the main end product in presence of sucrose, while in glucose or fructose was lactic acid. Soybean paste is a complex substrate that could present other energy sources to explain the behavior of L. paracasei in the paste without added sugar by solid state fermentation. These results demonstrated a change in the strain metabolism under different carbon source and oxygen availability by low moisture of soy solid substrate.