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.
Highlights
The human dependence on non-renewable resources, fossil fuels depletion, and climate issues [1]have influenced an increasing trend in the adoption of decarbonization policies [2], mainly in critical areas such as the transport sector, which accounts for about 23% of total CO2 emissions [3]
Total polyphenols (TPP) of aqueous fractions in untreated and fungal treated samples were quantified by the Folin–Ciocalteau method [22] at 750 nm, using gallic acid as the standard
total polyphenols (TPP) content was expressed as mg gallic acid equivalent (GAE) per gram of sample dry weight
Summary
Have influenced an increasing trend in the adoption of decarbonization policies [2], mainly in critical areas such as the transport sector, which accounts for about 23% of total CO2 emissions [3]. In this context, the European Union is committed to a 25% increase in biofuels production for the transport sector by 2030 in order to reach a substantial reduction in greenhouse gas emissions [4]. Concerning lignocellulosic biomass, the content of cellulose, hemicellulose, and lignin may range between 30–50%, 20–40%, and 10–30%, respectively [5]. Public Health 2020, 17, 5900; doi:10.3390/ijerph17165900 www.mdpi.com/journal/ijerph
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