Valorisation of fungal hydrolysates of exhausted sugar beet pulp for lactic acid production

BACKGROUND Exhausted sugar beet pulp pellets (ESBPP) were used as raw material for lactic acid (LA) fermentation. The enzymatic hydrolysis of ESBPP was performed with the solid obtained after the fungal solid-state fermentation of ESBPP as a source of hydrolytic enzymes. Subsequently, a medium rich in glucose and arabinose was obtained, which was used to produce LA by fermentation. For LA production, two Lactobacillus strains were assayed and the effects of the supplementation of the hydrolysate with a nitrogen source and the mode of pH regulation of the fermentation were investigated. Moreover, a kinetic model for LA fermentation by Lactobacillus plantarum of ESBPP hydrolysates was developed. RESULTS L. plantarum produced a LA concentration 34% higher than that produced by L. casei. The highest LA concentration (30 g L-1) was obtained with L. plantarum when the hydrolysate was supplemented with 5 g L-1 yeast extract and the pH was controlled with CaCO3. The concentration of acetic acid differed depending on the concentration of CaCO3 added, producing its maximum value with 27 g L-1 CaCO3. The proposed kinetic model was able to predict the evolution of substrates and products depending on the variation of the pH in the hydrolysate, according to the amount of CaCO3 added. CONCLUSIONS ESBPP can be revalorised to produce LA. A pure LA stream or a mixture of LA and acetic acid, depending on the pH control method of the fermentation, can be produced. Thus, this control is of great interest depending on the destination of the effluent. (c) 2020 Society of Chemical Industry

Automated summary

Exhausted sugar beet pulp pellets were utilized for lactic acid fermentation. Lactobacillus plantarum showed higher lactic acid production compared to Lactobacillus casei, with the highest concentration achieved with the addition of yeast extract and pH control with CaCO3. A kinetic model was developed to predict substrate and product evolution based on pH variation in the hydrolysate with CaCO3 addition.