Avaliação do potencial biotecnológico de leveduras em cultivos com pectina e açúcares pécticos

Abstract

The large-scale production of orange juice results in large volumes of waste, mainly fruit peels, which are inappropriately discarded, causing environmental and economic problems. To solve this dilemma, it is proposed to use these residues in second-generation biorefineries, where microorganisms can metabolize the sugars present in this residual biomass, producing valuable compounds, such as ethanol. This integrated approach between sustainability and technology shows promise for optimizing industrial processes and reducing environmental impacts. Therefore, the present work aimed to analyze the biotechnological potential of yeasts isolated from decaying oranges and their capabilities concerning cell growth and enzymatic activity. Furthermore, through Central Composite Rotatable Design (CCRD), the possibility of ethanol production in media rich in pectin or pectin hydrolyzate was evaluated. To this end, 38 yeast strains were initially screened in microscale experiments in minimal media containing 6.7 g/L of yeast nitrogen base, with 20 g/L of the following monosaccharides added alternately: glucose, xylose, fructose, galactose, or galacturonic acid. All yeasts were able to grow using glucose, xylose, fructose, or galactose as carbon sources. In the medium containing galacturonic acid, only 13 strains grew. Through these microscale experiments, the maximum specific growth rate of yeasts was determined. The highest rates were observed in glucose, fructose, and galactose (0.93 0.98 h-1). In galacturonic acid, the maximum specific growth rate found was 0.29 h-1. For the agitated-flask cultures we carried out afterwards, 21 of these strains were chosen. In this case, the yeasts were subjected to YP media (1% yeast extract, 2% peptone, pH 7.0) containing, alternately, 1% crude pectin (obtained from orange peels in the present work PB), 1% purified pectin (Sigma-Aldrich PS) or 1% dehydrated and crushed orange peel (CT), with or without 50 mg/L of Aspergillus niger pectinase (Sigma-Aldrich). As a control, yeasts were also grown in 1% galactose (GAL) or 1% glucose (GLI). In these cultures, growth curves were analyzed, and pectinase activity assays were performed after 90 h of incubation. Through these experiments, it was possible to observe that two strains had pectinolytic activity >40 U/mL and that two others stood out regarding cell growth. Next, to optimize the conditions for fermentative performance, two CCRD-type designs were carried out using the two strains that grew best (CHAP-070 and CHAP-074). For the first CCRD, the strains were cultivated in YPGAL medium (1% yeast extract, 2% peptone, and 0.5% galactose) with varying pH and varying concentrations of commercial pectin and A. niger pectinase. In the other CCRD, the strains were grown in YPGAL with varying pH and varying concentrations of pectin hydrolyzate. For this study, small ethanol concentrations were produced by the tested yeast strains; however, the results indicated that the tested parameters did not influence ethanol production.