The Kinetics Studies on Hydrolysis of Hemicellulose

The kinetics studies is of great importance for the understanding of the mechanism of hemicellulose pyrolysis and expanding the applications of hemicellulose. In the past years, rapid progress has been paid on the kinetics studies of hemicellulose hydrolysis. In this article, we first introduced the hydrolysis of hemicelluloses via various strategies such as autohydrolysis, dilute acid hydrolysis, catalytic hydrolysis, and enzymatic hydrolysis. Then, the history of kinetic models during hemicellulose hydrolysis was summarized. Special attention was paid to the oligosaccharides as intermediates or substrates, acid as catalyst, and thermogravimetric as analyzer method during the hemicellulose hydrolysis. Furthermore, the problems and suggestions of kinetic models during hemicellulose hydrolysis was provided. It expected that this article will favor the understanding of the mechanism of hemicellulose pyrolysis.

Valorisation of agroindustrial residues acid hydrolyzates as carbon sources for ethanol production by native yeast strains with different fermentative capabilities//Valorización de hidrolizados ácidos de residuos agroindustriales como fuente de carbono para la producción de etanol por levaduras nativas con capacidades fermentativas diferentes

A profitable, second-generation (2G) bioethanol production process requires the use of the maximum amountof sugars present in the lignocellulosic biomass; among them are those obtained from hemicellulose hydrolysis. An alternative is the search and kinetic characterization of yeasts capable of fermenting xylose to ethanol. In this study, 161 yeasts were isolated from agroindustrial residues, and selected according to best growth in glucose and xylose. Five strains belonging to the genera Candida (C. intermedia and C. parapsilosis), and Wickerhamomyces (W. anomalus) were molecularly identified. The kinetic parameters indicate that C. intermedia CBE002 had the best biomass yield in glucose and xylose (0.21 and 0.35 g/g of substrate), maximum specific growth rate (0.15 and 0.12 h-1) and metabolized both sugars simultaneously, desirable characteristics and rarely found together in other yeasts. Bioethanol production was made possible by C. intermedia (CBE002) from acid hydrolysates of corn stover and mango residues, with yields of 0.31 and 0.26 g/g of substrate, respectively. From the results obtained, this yeast is an attractive candidate to be used in bioethanol 2G production, and to take advantage of the large amount of agroindustrial residues available.RESUMENUn proceso de producción de bioetanol de segunda generación (2G) rentable, requiere el uso del máximo número de azúcares presentes en la biomasa lignocelulósica, como son los obtenidos por hidrólisis de hemicelulosa; para obtenerlo, una alternativa es encontrar levaduras capaces de fermentar eficientemente xilosa a etanol. En el presente trabajo se realizó el aislamiento de 161 levaduras a partir de residuos agroindustriales, se evaluó su capacidad de crecimiento en glucosa y xilosa. Se seleccionaron e identificaron molecularmente cinco de estas cepas pertenecientes a los géneros Candida (C. intermedia, C. parapsilosis) y Wickerhamomyces (W. anomalus). Los parámetros cinéticos demostraron que C. intermedia CBE002 obtuvo el mejor rendimiento de biomasa en glucosa y xilosa (0.21 y 0.35 g/g), la máxima velocidad específica de crecimiento (0.15 y 0.12 h-1) y fue capaz de metabolizar ambos azúcares simultáneamente, característica deseable y poco encontrada en otras levaduras. Fue posible la producción de bioetanol por C. intermedia CBE002 a partir de hidrolizados ácidos de rastrojo de maíz y residuos de mango, con rendimientos de 0.31 y 0.26 g/g de sustrato, respectivamente. Por lo anterior, esta levadura es atractiva para ser empleada en la producción de bioetanol 2G y aprovechar la gran cantidad de residuos agroindustriales disponibles.

Morphological aspects of starch and cell wall material mobilization in developing lupine cotyledons and the effect of kinetin on these processes

In the cotyledons of dry lupine seeds the presence of starch was not demonstrated. Its formation during seed imbibition in darkness is accompanied by a reduction in the thickness of cell walls containing hemicelluloses. It is believed that the products of hemicellulose hydrolysis, particullarily in isolated cotyledons, arę the main source of materials for the synthesis of starch, In the process of cell wall decomposition the invaginations of plasmalemma appear to be involved. Kinetin enhance the hydrolysis of cell walls and the mobilization of starch in isolated cotyledons.