Sugar addition and oxygen presence affect the production of organic acids of L. paracasei on soy paste

RODRIGUEZ DE OLMOS A; BORQUEZ J; GARRO M S

Tucuman

Simposio; SIBAL2016 V International Symposium on Lactic Acid Bacteria; 2016

CERELA-CONICET

It is well known that lactic acid bacteria (LAB)may change their metabolism in response to different conditions, resulting in adiverse end-product pattern than seen with glucose fermentation under anaerobicconditions. In previous work we have optimized the main fermentation parametersof L. paracasei subsp. paracasei CRL 207 on soybean pastewithout added sugar and low moisture conditions (65%). This strain was able togrow without viability loss but the pH showed little change from paste control.Oxygentransfer is an important factor in solid substrate fermentation that could havean effect on the use of pyruvate by LAB, changing the produced organic acids. Inorder to understand the behavior of the strain in soy paste, the aim of thepresent work was to analyze the effect of sugar addition on the production oforganic acids by L. paracasei in soypaste. The effect of oxygen was also investigated in MRS broth. Sucrose is themain sugar in soybean and glucose is present only in low amount. Because ofthat, sucrose and its hydrolysis products (glucose, fructose) were selected forthe following studies. Soybean paste and MRS (with 2% each sugar) wereinoculated with L. paracasei andincubated at 37ºC for 24h. The effect of oxygen was analyzed on MRS with each addedsugar under agitation conditions. The strain growth was followed by plate countor OD600, and pH measures. Carbohydrate consumption and organicacids production were determined by HPLC. In MRS without sugar and with addedsucrose showed low OD without differences between both conditions. However anincrease of biomass and pH was found in agitation condition for all sugarsassayed. Despite that in soy paste was observed scarce use of sucrose comparedto glucose or fructose, the cell count was similar in all condition assayed.The differences were observed in the pH values. In soybean pastes, the profileof organic acids obtained was different when the strain grew in the presence ofsucrose and without addition of sugar compared to the other conditions assayed.Acetic acid was the main end product in presence of sucrose, while in glucoseor fructose was lactic acid. Soybean paste is a complex substrate that couldpresent other energy sources to explain the behavior of L. paracasei in the paste withoutadded sugar by solid state fermentation. Theseresults demonstrated a change in the strain metabolism under different carbonsource and oxygen availability bylow moisture of soy solid substrate.