| Congresso Brasileiro de Microbiologia 2023 | Resumo: 1227-1 | ||||
Resumo:The reuse of the waste generated by agro-industrial activities is necessary due to the challenges faced in recent decades to achieve a circular and sustainable economy. Brewer’s spent grain (BSG), formed by the solid part obtained from the filtration of the brewing wort before boiling, and consisting mainly of remains of malt husk and pulp, represents up to 85% of the total waste generated by the brewing process. Currently, despite having interesting physicochemical characteristics, this biomass is poorly applied to achieve biotechnological applications. This lignocellulosic residue contains important amounts of carbohydrates from the holocellulosic portion that can be accessed through pretreatments and subsequently processed to obtain value-added byproducts such as second-generation ethanol, xylitol, (xylo)oligosaccharides, furfural and, recently, volatile organic compounds (VOCs). VOCs are aliphatic and aromatic compounds with low molecular weights, low boiling points, and the ability to interact with olfactory receptors. They are extremely important in food and beverage processing, being responsible for the typical flavors desired in the final product. Yeasts are well-known VOC producers during their primary and secondary metabolism. In this study, a hemicellulosic hydrolysate containing xylose, arabinose, and glucose, derived from the pretreatment of BSG with 4,5% of oxalic acid and supplemented with yeast extract and peptone, was subjected to fermentation by three strains of Saccharomyces cerevisiae (PE-2, MP-P5 and JDY-01) in pre-defined conditions of temperature (15,9 – 20,0 – 30,0 – 40,0 – 44,1 °C) and pH (1,8 – 3,0 – 6,0 – 9,0 – 10,2), to evaluate the production of VOCs and consumption of carbohydrates by the yeasts. The pretreatment with 4,5% of oxalic acid, despite providing >99% of the hemicellulose present in the biomass in the form of xylose and arabinose monomers, proved to be inadequate for the fermentation step of the hydrolysate. To reach the pH levels of the experiments, a high amount of 2 M NaOH was added to the medium due to the two buffering points that this organic acid has between pH 1.0 and 5.0, which led to the dissociation of a large amount of its conjugate base, oxalate, and consequently compromising the performance of the yeasts due to the osmotic stress. Even so, some VOCs were produced, probably because of the nutrient sources added to the culture medium, since little or no carbohydrates were consumed at the end of the 48 h of fermentation. The main compound identified by GC/MS after dichloromethane extraction was 4-hydroxy-2-methylacetophenone, with a peak area of ~40% in all experiments, indicating recovery potential. In smaller amounts (<5%) phenylethyl alcohol, pantolactone, 1-propanol, 3-(methylthio)-ethanol, 2-(pentyloxy)-linoleic acid, stearic acid, and 2,4-di-tert-butylphenol were also detected. The production of VOCs from the fermentation of lignocellulosic biomass is a promising field of study, and BSG proved to be suitable for this purpose, since, even under non-ideal conditions, the tested yeasts were able to produce very interesting compounds with well-established applications in the industry. Palavras-chave: Brewer´s spent grain, volatile organic compounds, oxalic acid, fermentation, circular economy Agência de fomento:INCT Leveduras: Biodiversidade, preservação e inovações biotecnológicas (Processo CNPq nº. 406564/2022-1); CAPES e CNPq | |||||