Pretreatment of Grape Stalks by Fungi: Effect on Bioactive Compounds, Fiber Composition, Saccharification Kinetics and Monosaccharides Ratio

Abstract

Grape stalks, an inedible lignocellulosic residue from winemaking and agro-industrial grape juice production, can be valorized as a source of bioactive compounds and as feedstock for the saccharification and bioconversion of soluble sugars. Solid-state fermentation (SSF) by six white-rot fungi was applied as pretreatment. Fiber composition, free radical scavenging activity, four ligninolytic, and three hydrolytic enzyme activities were determined. Saccharification kinetics, yield, and productivity were evaluated and complemented with scanning electron microscopy (SEM), high performance liquid chromatography (HPLC) quantification of monosaccharides, and principal component analysis (PCA). After SSF, the biomass exhibited a drastic free radical scavenging activity decrease and the main enzymes produced were manganese-dependent peroxidase and xylanase. Scanning electron microscopy revealed the erosion of cell walls, and PCA exhibited a negative correlation between saccharification, and neutral detergent fiber and acid detergent lignin. Phlebia rufa pretreated biomass gave the highest sugars yield and productivity, representing a nearly three-fold increase compared to untreated samples. Also, monosaccharides quantification revealed that the 1:1 ratio of glucose to the sum of xylose plus galactose changes to the value of 2:1 after pretreatment. In this work, and for the first time, P. rufa proved to be an effective pretreatment of grape stalks for the saccharification and further bioconversion into value-added chemicals. In addition, lignocellulolytic enzymes were also produced through SSF.

Solid-State Fermentation of Chestnut Shells and Effect of Explanatory Variables in Predictive Saccharification Models

“…In general, xylanase was a dominant fungal enzyme, being about three to eight times higher than the CMCase activity in all fungal strains except I. lacteus. Large differences within enzymatic activities detected in pretreated lignocellulosic substrates have been previously observed in several fungi, including all strains of this work [5,17,18,23]. As previously pointed out [36], this highlights the need to interpret the pattern of enzymatic activities detected as a function of interactions among fungal strains, substrates type and incubation periods.…”

“…WRF mediated degradation of recalcitrant lignin of plant cell walls, involves oxidation reactions catalyzed by laccase, LiP, MnP and VP enzymes. This group of enzymes, highly versatile in nature, are considered key factors in biomass pretreatment [5,[12][13][14][15][16][17][18][19]. Extracellular ligninolytic activities detected in WRF-fermented CNS are shown in Figure 1.…”

Improvement of Enzymatic Glucose Conversion from Chestnut Shells through Optimization of KOH Pretreatment

“…It is estimated that thermal water softens up the rigid structure of CNS. Various studies have reported that hot water pretreatment at high pressure and high temperature can enhance enzymatic hydrolysis of biomass without the addition of other chemicals [ 14 , 28 ]. The released glucose concentrations were found to be 8.7 g/L, 12.0 g/L and 15.3 g/L at KOH concentration of 1%, 2% and 3%, respectively, and were not significantly affected by KOH concentrations above 3%.…”

“…Pretreatment of biomass is a key process required to improve the recovery of fermentable sugars in enzymatic hydrolysis [ 13 ]. Various pretreatment (physical, chemical and biological) of lignocellulosic biomass have been conducted to remove the lignin, which inhibits the enzymatic hydrolysis, and to enhance the depolymerization and dissociation of fermentable sugar [ 14 ]. Chemical pretreatment has been widely used because of its advantages of low process cost and high sugar recovery [ 15 ].…”

Effects of Dietary Incorporation of Grape Stalks Untreated and Fungi-Treated in Growing Rabbits: A Preliminary Study

“…The generated by-products have been estimated to be around 25−30 kg/hL of produced wine, and on average, 4 kg of grape stalks are generated per each hL of produced wine, representing 10–15% of the total produced wastes [ 3 , 4 ]. Currently, grape stalks have been used as fertilizers, but most of the time they are disposed to landfills which, when not attended correctly, can cause environmental problems [ 5 , 6 ]. The nutritional content of grape stalks may not be appealing, limiting its use as a raw material for animal feeding, as they constitute a lignocellulosic fiber material composed mainly of cellulose (30–38%), hemicelluloses (14–21%), and lignin (17–33%) [ 4 , 7 , 8 , 9 ].…”