Lactic acid production on liquid distillery stillage by Lactobacillus rhamnosus immobilized onto zeolite

In this study, lactic acid and biomass production on liquid distillery stillage from bioethanol production with Lactobacillus rhamnosus ATCC 7469 was studied. The cells were immobilized onto zeolite, a microporous aluminosilicate mineral and the lactic acid production with free and immobilized cells was compared. The immobilization allowed simple cell separation from the fermentation media and their reuse in repeated batch cycles. A number of viable cells of over 1010 CFU g−1 of zeolite was achieved at the end of fourth fermentation cycle. A maximal process productivity of 1.69 g L−1, maximal lactic acid concentration of 42.19 g L−1 and average yield coefficient of 0.96 g g−1 were achieved in repeated batch fermentation on the liquid stillage without mineral or nitrogen supplementation.