Mg-modified zeolite as a carrier for Lactobacillus rhamnosus in L(+) lactic acid production on distillery wastewater

• Simple method for modification of zeolite molecular sieves by Mg ions.
• Efficient immobilization of L. rhamnosus ATCC 7469 onto Mg-modified zeolite.
• Higher lactic acid productivity and yield in Mg-modified system than in Na system.
• Improved stability of L. rhamnosus biofilm with Mg(OH)2 as a neutralizing agent.

Biorefinery concept in lactic acid (LA) fermentation based on parallel production of LA and biomass enriched feed on a waste substrate was investigated. In this study, nitrogen opulent liquid stillage was used as a media for repeated batch L(+) LA fermentation by probiotic strain Lactobacillus rhamnosus ATCC 7469 immobilized onto non-modified and Mg-modified zeolite. The highest LA concentration of 47.60 g/L, overall productivity of 1.41 g/L/h, a yield of 0.86 g/g and yield coefficient of 0.96 g/g were obtained in fermentation with utilization of immobilized biocatalyst onto Mg-modified zeolite and Mg(OH)2 as a neutralizing agent. Very high number of 8 × 1010 CFU/g cells immobilized onto Mg-modified zeolite, proven beneficial effect of zeolite in animal health and probiotic characteristics of L. rhamnosus qualify solid remains after the fermentation as a high quality probiotic feed additive. High productivity of LA in the fermentation and valorization of the remains in animal nutrition could recommend this process which employs a simple modification of zeolite as a promising one for bio-based renewable LA production.

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