Production of bioalcohols and antioxidant compounds by acid hydrolysis of lignocellulosic wastes and fermentation of hydrolysates with Hansenula polymorpha

Abstract

The effect of the H2SO4 concentration in the hydrolysis of sunflower‐stalk waste, at 95ºC and using a liquid/solid relation of 20, was studied. In a later stage, the hydrolysates were fermented at different temperatures with the aim of ethanol and xylitol production. A total conversion of the hemicellulose at the acid concentration of 0.5 mol/L was achieved; whereas an acid concentration of 2.5 mol/L was needed to reach the maximum value in the conversion of the cellulose fraction. The analysis of the hydrolysis kinetics has enabled to determine the apparent reaction order, which was 1.3. The hydrolysates from hydrolysis process with H2SO4 0.5 mol/L, once detoxified, were fermented at pH 5.5, temperatures 30, 40, and 50ºC with the yeast Hansenula polymorpha (ATCC 34438), resulting in a sequential uptake of sugars. In relation to ethanol and xylitol yields, the best results were observed at 50°C (YE/sO = 0.11 g/g; YXy/sO = 0.12 g/g). Instantaneous xylitol yields were higher than in ethanol, at the three temperatures essayed. Different phenolic compounds were analyzed in the hydrolysates; hydroxytyrosol was the most abundant (3.79 mg/L). The recovery of these compounds entails the elimination of inhibitors in the fermentation process and the production of high value‐added antioxidant products.

Fermentation of Sugar by Thermotolerant Hansenula polymorpha Yeast for Ethanol Production

“…The yeast biomass concentration (g•L −1 ) was measured spectrophotometrically using a standard calibration curve prepared using the optical density (OD) value (taken at 620 nm) and its biomass oven-dried (110 • C) weight (g). This method was previously reported by researchers for H. polymorpha [34,40]. Standard protocol by Bray (2003) [41] was used for scanning electron microscopy (SEM) analysis of yeast cells, which is briefly described as follows: A concentrated yeast cells suspension was dehydrated through gradual treatment with 30% (for 12 h) and then 70 to 100% (for 1 h) concentrations of ethanol in a PF17-Automatic Mini Tissue Processor (Lynx II, Aname, Madrid, Spain).…”

“…The maximum specific growth rate (µ m ) and biomass volumetric productivity (P b ) of the yeast were estimated using Equations ( 1) and (2) [34,40], respectively. In Equation (1), µ m = Maximum specific growth rate, h −1 ; x = cell concentration per volume; and x 0 = cell concentration at the initial time.…”

“…The uptake of substrates (glucose, fructose, or xylose) was assessed by determining the specific rate of substrate uptake ( q D S based on Equation (3) [34]. The q D S is the specific rate of substrate uptake by yeast with respect to time.…”

“…A preliminary study was carried out on different wild-type strains of H. polymorpha for the fermentation of glucose and xylose in tube cultivation for ethanol production [32]. The fermentation of sunflower-stalk hydrolysate (produced by acid hydrolysis) by H. polymorpha (ATCC 34438) was reported to produce ethanol and xylitol [33,34]. The fermentation of wheat straw hydrolysate (produced by enzymatic hydrolysis) by H. polymorpha (CBS 4732) was also reported to produce ethanol [35].…”

Mix and Match: Promoters and Terminators for Tuning Gene Expression in the Methylotrophic Yeast Ogataea polymorpha

“…The yeast can tolerate high temperatures of up to 50°C ( Cabeç-Silva and Madeira-Lopes, 1984 ), grows in a wide pH range from 2.5 to 6.5, is generally regarded as safe (GRAS status) and several Ogataea species have been sequenced ( Manfrão-Netto et al, 2019 ). O. polymorpha can not only grow on interesting carbon and nitrogen sources like xylose ( Ryabova et al, 2003 ; Martínez-Cartas et al, 2019 ) and glycerol ( de Koning et al, 1987 ) but it is also one of few yeasts that can utilize methanol as the sole carbon and energy source ( de Koning et al, 1987 ). Especially the latter, rare ability strengthens its upcoming role as an industrial workhorse.…”