Production of lactic acid from whey lactose by Lactiplantibacillus plantarum cells entrapped in a mesoporous silicate matrix

Abstract

In this study, a sol-gel silica matrix was used in repeated batch fermentations for Lactic acid (LA) production, as a carrier of confined Lactiplantibacillus plantarum, previously transformed by incorporating a plasmid containing the gene encoding for E.coli ?-galactosidase (?-Gal). The overexpression of ?-Gal and the increased LA production in transformed L.plantarum, compared with the wild-type bacteria, was confirmed. The parameters involved in lactose fermentation, such as agitation, pH, and temperature involved in the fermentation process, were optimized to improve lactose conversion, reduce fermentation rates, and achieve higher LA productivity by entrapped cells compared to the free cells. LA concentration, yield, and productivity were compared in terms of LA output. The effect of confinement on the cell viability was studied after seven cycles, and minimal loss in bacterial count was observed. Entrapped t-bacteria could be kept preferably at 4ºC for at least 3 months. Immobilized cells reached an LA yield up to 20.7g/L while the free cells reached 18g/L under the same optimized conditions. LA yield depended on the nutrient level of the culture media: broth > whey > lactose solution.