Optimization of Enzymatic Hydrolysis of Dilute Acid Pretreated Sugar Beet Pulp Using Response Surface Design

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.

Pretreatment of Sugar Beet Pulp with Dilute Sulfurous Acid is Effective for Multipurpose Usage of Carbohydrates

Sulfurous acid was used for pretreatment of sugar beet pulp (SBP) in order to achieve high efficiency of both extraction of carbohydrates and subsequent enzymatic hydrolysis of the remaining solids. The main advantage of sulfurous acid usage as pretreatment agent is the possibility of its regeneration. Application of sulfurous acid as hydrolyzing agent in relatively low concentrations (0.6-1.0 %) during a short period of time (10-20 min) and low solid to liquid ratio (1:3, 1:6) allowed effective extraction of carbohydrates from SBP and provided positive effect on subsequent enzymatic hydrolysis. The highest obtained concentration of reducing substances (RS) in hydrolysates was 8.5 %; up to 33.6 % of all carbohydrates present in SBP could be extracted. The major obtained monosaccharides were arabinose and glucose (9.4 and 7.3 g/l, respectively). Pretreatment of SBP with sulfurous acid increased 4.6 times the yield of glucose during subsequent enzymatic hydrolysis of remaining solids with cellulase cocktail, as compared to the untreated SBP. Total yield of glucose during SBP pretreatment and subsequent enzymatic hydrolysis amounted to 89.4 % of the theoretical yield. The approach can be applied directly to the wet SBP. Hydrolysis of sugar beet pulp with sulfurous acid is recommended for obtaining of individual monosaccharides, as well as nutritional media.