Immobilization of lactic acid bacteria in a polymer matrix

Abstract

The sol-gel encapsulation has been proposed as a suitable model system for the study ofthe effects of crowding and confinement in a living cell.This work aimed to maximize the production of lactic acid (LA) by immobilizingLactobacillus plantarum (L.plantarum) genetically transformed to overexpressing the genof β-galactosidase (β-Gal). Bacteria were encapsulated, in a silicate matrix, by the sol?gelmethod using tetraethyl orthosilicate (TEOS), to generate an inorganic polymer expectingthat it would allow for higher survival rates and improved product yield. In free andimmobilized L.plantarum (either wild type or transformed) we determined the cell viabilityin sol-gel matrices, and also studied the effects of macromolecular crowding inL.plantarum through spectral confocal microscopy using ACDAN as a water polarizationsensitive probe.Fermentation with immobilized L. platarum was carried out in media containing 2% w/vlactose (Lac2%) as a carbon source. LA production was determined at differentfermentation temperatures (30°C, 35 °C, 37 °C and 40°C) and at 150 rpm agitation speedof the incubator. Viability d of the immobilized bacteria was determined at 0, 24, 48, 72,120, and 150 h. Every 36 hours, the fermentation broth was replaced with a freshmedium. All determinations were done in triplicate.For 36 hours the immobilized L. plantarum cells synthesized 20.5 g/L LA, a concentrationhigher than that produced by the free cells (16g/L). After a period of 150 h incubationperiod, minimum loss in bacterial count was observed, this showed the effectiveness ofcapsulation.