Effect of Several Pretreatments on the Lactic Acid Production from Exhausted Sugar Beet Pulp.

Exhausted sugar beet pulp (ESBP), a by-product of the sugar industry, has been used as a substrate to produce lactic acid (LA). Due to the fact that ESBP contains a high percentage of pectin and hemicellulose, different pretreatments were studied to solubilize them and to facilitate the access to cellulose in the subsequent enzymatic hydrolysis. Several pretreatments were studied, specifically biological, oxidant with alkaline hydrogen peroxide (AHP), and thermochemical with acid (0.25, 0.5, or 1% w/v of H2SO4). Pretreated ESBP was enzymatically hydrolysed and fermented with the strain Lactiplantibacillus plantarum for LA production. The hydrolysis was carried out with the commercial enzymes Celluclast®, pectinase, and xylanase, for 48 h. After that, the hydrolysate was supplemented with yeast extract and calcium carbonate before the bacteria inoculation. Results showed that all the pretreatments caused a modification of the fibre composition of ESBP. In most cases, the cellulose content increased, rising from 25% to 68% when ESBP was pretreated thermochemically at 1% w/v H2SO4. The production of LA was enhanced when ESBP was pretreated thermochemically. However, it was reduced when biological and AHP pretreatments were applied. In conclusion, thermochemical pretreatment with 1% w/v H2SO4 had a positive impact on the production of LA, increasing its concentration from 27 g/L to 50 g/L.

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. © 2020 Society of Chemical Industry.

Feasibility of exhausted sugar beet pulp as raw material for lactic acid production.

BACKGROUND: Exhausted sugar beet pulp pellets (ESBPP), a sugar industry by-product generated after sugar extraction in the sugar production process, have been used as a raw material for lactic acid (LA) production via hydrolysis and fermentation by Lactobacillus casei. To design a more cost-effective process, simultaneous saccharification and fermentation (SSF) of ESBPP is proposed in the present study. The effects of pH control, nutrient supplementation and solid addition in fed-batch SSF on lactic acid production were investigated. RESULTS: The highest LA concentration (26.88 g L-1 ) was reached in fed-batch SSF at a solid/liquid loading of 0.2 g mL-1 , with pH control (by adding 30 g L-1 CaCO3 to the medium) and nutrient supplementation (by adding 20 mL of MRS medium per 100 mL of buffer). Under these conditions, a maximum productivity of 0.63 g L-1 h-1 was achieved, which is 2.7 times higher than that attained in the control experiment (SSF inoculated at time 0 h). However, a slightly lower LA yield was obtained, revealing the need of an increasing dose of enzymes at high solid loading SSF. CONCLUSION: An efficient fed-batch SSF strategy with pH control and MRS supplementation is described in the present study, attaining higher LA productivity compared to separate hydrolysis and fermentation and SSF. © 2020 Society of Chemical Industry.