Enzymatic modes of action on soybean hulls and corn distiller\'s dried grains with solubles considering substrates\' structures and variabilities

• Ano de defesa: 2022
• Autor(a) principal: Rosso, Diogo Filipe
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Casca de soja; DDGS; Enzima; Enzyme; Soybean hulls; Valorização; Valorization; Variabilidade; Variability
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/105/105131/tde-21032023-144734/

Valorization of agroindustrial residues through enzymatic upgrading is attractive because such feedstocks are inexpensive, available at industrial sites, and potentially synergistic with the production of food. Agroindustrial residues have been studied for applications such as the production of bio-renewable chemicals and alternative ingredients in animal production. However, their complex structural polysaccharides (cellulose, hemicelluloses, pectins, and others) represent a barrier to efficient valorization. In this Thesis, soybean hulls (SBH) and corn distiller\'s dried grains with solubles (DDGS), by-products of the industrial processing of soybean and corn, respectively, are investigated because of their importance in the South American landscape and the potential for valorization. For both types of substrates, the investigation covers compositional variability, substrate structure, and enzymatic reactions, but the emphasis of the investigation is tailored to the specificities of each type of substrate. The investigation of SBH privileged the understanding of the native hierarchical multiscale structure of the biomass, which is mostly preserved after the industrial separation of the hulls. SBH has been previously recognized as a substrate highly amenable to enzymatic conversion (i.e., low recalcitrance), which allows bioconversion without thermochemical pretreatment. This possibility is confirmed by this work. The multiscale characteristics of SBH shed light on the structural origins of the low recalcitrance. In aqueous media SBH have high nanoscale porosity, especially for pore sizes greater than enzyme sizes ∽5mm. Moreover, the contents of lignin are low and localized, and the relative purity of cellulose in SBH tissues also contributes to the low recalcitrance of SBH compared to other lignocellulosic feedstocks. These results provide a structural basis for understanding the low recalcitrance of SBH, paving the way for novel developments in SBH biotechnological valorization. As corn DDGS is concerned, this biomass is obtained from the corn ethanol production process and is composed mainly of the undigested fraction of corn grains. The experience from traditional production regions, chiefly the United States, has shown that variability is a key factor for DDGS valorization. With the emergence of the corn ethanol industry in South America, the variability of DDGS in this new production region becomes a timely question. This work investigates DDGS samples obtained by facilities from Brazil, Paraguay, and Argentina to learn about the variability of DDGS in South America and the consequences for enzymatic hydrolysis. The investigated samples presented higher compositional variability in comparison to previously reported data from other production regions. Yeast content in DDGS is shown to be a minor factor contributing to variability, whereas the content of extractives and the proportion between corn fiber and protein are major ones. Enzymatic hydrolysis with cocktails optimized for lignocellulose, corn fiber, and yeast revealed complementary and synergistic effects for the solubilization of DDGS structural components in a highly variable set of pre-extracted DDGS. Furthermore, the response to enzymes could be correlated to the main compositional variations of DDGS, establishing a basis for enzymatic strategies to upgrade DDGS with consideration of its patterns of variability. With these results, this Thesis contributes to the advancement of a robust knowledge base for the development of enzymatic upgrading strategies for SBH and corn DDGS.