A biorefinery based on brewer`s spent grains: Arabinoxylans recovery by microwave assisted pretreatment integrated with butanol production

Abstract

This study proposes an integrated biorefinery of brewer's spent grain (BSG) based on the application of a microwave pretreatment to obtain bioproducts, such as arabinoxylans (AX) and an advanced biofuel, such as biobutanol. A prehydrolysate with 17 g/L AX was obtained at 172 °C and 0.38 M NaOH, which were subsequently precipitated using an organosolvent process, recovering 133 kg AX/t BSG. The subsequent enzymatic hydrolysis with endo-xylanases significantly increased the concentration of oligomers with 2-6 units of xylose. The presence of oligosaccharides with a degree of polymerization (DP) from 3 to 27 was confirmed by MALDI-TOF MS. On the other hand, the pretreated solid residue obtained in the microwave assisted alkaline pretreatment was enzymatically hydrolyzed with cellulases and fermented by Clostridium beijerinckii, producing 9.9 g/L butanol (28 kg butanol/t BSG and 37 kg ABE/t BSG). Thus, the potential for the efficient use of BSG in an integrated biorefinery was demonstrated. Microwave assisted sodium hydroxide pretreatment Arabinoxylans precipitation Endo-xylanases enzymatic hydrolysis ENRICHED ARABINOXYLANS SOLUTION LOW DEGREE OF POLIMERIZATION (DP2-DP6)

A bibliometric analysis on potential uses of brewer's spent grains in a biorefinery for the circular economy transition of the beer industry

“…91 Based on the literature, 1 ton of BSG can produce 133 kg of arabinoxylan, which means a yield of up to 50% of untreated BSG. 90 It is still possible to integrate the extraction of arabinoxylan and proteins because BSG presents up to 20% of crude proteins in its composition. For this technological route, after alkaline pretreatment, the arabinoxylans are recovered by precipitation with ethanol, and then protein-rich fractions can be obtained employing citric acid.…”

“…95 The butanol yield produced from BSG ranged from 7 to 11 g butanol L −1 , which means that 45 kg butanol ton −1 BSG can be produced. 90,95,96 In an experiment with an acid pretreatment, xylose was the main sugar obtained from BSG, with an extraction efficiency of up to 90%. 31 Xylose can also be converted into xylitol by Candida guilliermondii yeast, a technological route to upgrade the economic indicators of a biorefinery.…”

“…As Fig. 8 shows, different pretreatments were applied in the BSG, such as acid, 31 alkali, 93 acid‐alkali, 100 chemical, 96 supercritical, 70 pulsed electric, 89 hydrothermal, 29 and enzymatic hydrolysis 90 . Most of them can be promising approaches to upgrade the sugar yield.…”

Microwave-assisted enzymatic hydrolysis to produce xylooligosaccharides from rice husk alkali-soluble arabinoxylan

“…Microwave-assisted pretreatment of lignocellulosic biomass immersed in alkaline glycerol showed increased enzyme hydrolysis of corn straw and rice husk to sugar production 48 . The AX concentration in spent grains from the brewing process was maximized under pretreatment conditions of microwave heating at 172 °C and 0.38 M sodium hydroxide 49 . Microwave processing at 140 °C for 5 min provided the highest AX content but the A/X ratio was high, as shown in Table 1 .…”

Developing thermoplastic corn starch composites filled with brewer's spent grain for applications in biodegradable films

“…[26] Among other attempts to explore its economical uses are: the extraction of simple compounds such as sugars and proteins; the production of value-added compounds such as lactic acid; as growth media for culture of microorganisms; the production of enzymes; the extraction of cellulose nanocrystals; and energy production. [27][28][29][30][31] However, industrial-scale use of BSG is still in its initial steps. [27] Another recent option for sustainable use of BSG is as a filler or reinforcement in polymer composites, as summarized in Table 1.…”