RESUMO
Prebiotics are non-digestible compounds that promote intestinal microbiota growth and/or activity. Xylooligosaccharides (XOS) are new prebiotics derived from the hemicellulose fraction of lignocellulosic materials. Challenges in using those materials as sources for prebiotic compounds lie in the hemicellulose extraction efficiency and the safety of those ingredients. In this sense, this work aims to optimize hemicellulose extraction and XOS production through direct enzymatic hydrolysis of alkali pre-treated wheat straw without undesired byproducts. By increasing the temperature of the enzymatic step from 40⯰C to 65⯰C we achieved an improvement in the extraction yield from 55â¯% to 80â¯%. Products with different degrees of polymerization were also noticed: while XOSâ¯≤â¯X6 where the main products at 40⯰C, a mixture of long arabinoxylan derived polymers (ADPo) and XOSâ¯≤â¯X6 was obtained at 65⯰C, irrespective of the extraction yield. Thus, a modulatory effect of temperature on the product profile is suggested here. Among the XOSâ¯≤â¯X6 produced, X2-X3 were the main products, and X4 was the minor one. At the end of the hydrolysis, 146.7â¯mg XOS per gram of pre-treated wheat straw were obtained.
RESUMO
BACKGROUND: Grapes after harvesting are air dried and pressed in order to concentrate sugars, acids and flavour compounds to produce vino tostado (toasted wine), a wine with intense aroma and flavour notes and high residual sugar concentration. In order to get a better knowledge of the difficulties involved, several fermentations were conducted at 12 and 28 degrees C using 0, 15 and 30 g hL(-1) ammonium sulfate and 0, 25 and 50 g hL(-1) exogenous commercial yeast (Saccharomyces cerevisiae var. bayanus) to study the kinetics of sugar consumption and ethanol, acetic acid and glycerol production. RESULTS: Fermentation kinetic parameters were calculated and metal concentrations and antioxidant activity were analysed. CONCLUSION: The spontaneous fermentation at 12 degrees C and all fermentations conducted with the commercial yeast gave vino tostado of adequate quality, while the spontaneous fermentation at 28 degrees C was sluggish. High-temperature fermentations led to sweeter wines with higher volumetric productivities, although low-temperature fermentations produced better wines in terms of higher glycerol and lower acetic acid levels. Fructose was the only sugar to be consumed during spontaneous fermentations, while both glucose and fructose were consumed during fermentations of the inoculated musts, with preference for each monosaccharide depending on temperature.