Lactic acid production on molasses enriched potato stillage by Lactobacillus paracasei immobilized onto agro-industrial waste supports

Abstract

In this study, the production of lactic acid (LA) on sugar beet molasses enriched potato stillage by immobilized Lactobacillus paracasei NRRL B-4564 was examined. Three agro-industrial materials, such as sunflower seed hull (SSH), brewers' spent grain (BSG), and sugar beet pulp (SBP) were studied as carriers for cell immobilization. The carriers were physically characterized in terms of water adsorption index (WAI), critical humidity point (CHP) and porosity. Further, the stability and efficiency of the immobilized biocatalysts were evaluated in repeated batch fermentation of molasses enriched potato stillage and compared with free cell system. A strong cell attachment onto agro-industrial supports allowed easy separation from the fermentation media and efficient biocatalyst reuse in five successive batch cycles. The highest cell number attached on the support surface during the fermentation was detected for material with higher WAI and lower CHP. Porosimetry measurements showed that the attachment of L. paracasei cells to support materials and overall LA productivities achieved with different immobilized biocatalysts were not determined by the support porosity and surface morphology, but with the material characteristics such as electrostatic charge, chemical composition and hydrophilicity. LA productivity of 1.48 g/L h, maximal LA concentration of 80.10 g/L and average yield coefficient of 0.97 g/g were achieved in fermentation of molasses enriched potato stillage using SBP as a support material, followed by BSG and SSH. The studied approach showed to be an interesting alternative strategy for increasing the LA productivities on low-cost and abundant substrate.