The physicochemical pretreatment is an important step to reduce biomass recalcitrance and facilitate further processing of plant lignocellulose into bioproducts. This process results in soluble and insoluble biomass fractions, and both may contain by-products that inhibit enzymatic biocatalysts and microbial fermentation. These fermentation inhibitory compounds (ICs) are produced during the degradation of lignin and sugars, resulting in phenolic and furanic compounds, and carboxylic acids. Therefore, detoxification steps may be required to improve lignocellulose conversion by microoganisms. Several physical and chemical methods, such as neutralization, use of activated charcoal and organic solvents, have been developed and recommended for removal of ICs. However, biological processes, especially enzyme-based, have been shown to efficiently remove ICs with the advantage of minimizing environmental issues since they are biogenic catalysts and used in low quantities. This review focuses on describing several enzymatic approaches to promote detoxification of lignocellulosic hydrolysates and improve the performance of microbial fermentation for the generation of bioproducts. Novel strategies using classical carbohydrate active enzymes (CAZymes), such as laccases (AA1) and peroxidases (AA2), as well as more advanced strategies using prooxidant, antioxidant and detoxification enzymes (dubbed as PADs), i.e. superoxide dismutases, are discussed as perspectives in the field.
Studies have been conducted on detoxification of hemicellulose hydrolysates, but an effective detoxification method remains to be developed. The use of layered double hydroxides (LDHs) as adsorbents may be a solution to this problem. In this study, LDHs composed of 30, 63, or 70% MgO were used in their uncalcined and calcined states to adsorb acetic acid, formic acid, hydroxymethylfurfural, and furfural from a synthetic hemicellulose hydrolysate. Kinetic studies revealed that calcined LDH composed of 70% MgO (MG70c) had the best performance: it was able to remove 73% of acetic acid and 90% of formic acid in 6 h of incubation at 50 °C. Hydroxymethylfurfural and furfural were not adsorbed (C/C 0 ≈ 1) by calcined or uncalcined LDHs under the studied conditions. The adsorption equilibrium was determined at different temperatures. Adsorption isotherms were best described by the Langmuir−Freundlich model. These results show the potential of MG70c to remove acetic and formic acids from hemicellulose hydrolysates, thereby increasing their suitability as fermentation substrates.
Acetic acid (AA) and formic acid (FA) are two of the major fermentation inhibitors found in hemicellulosic hydrolysates. Their removal, which is necessary for the use of hydrolysates as fermentation substrates, can be achieved by adsorption on hydrotalcites. This study aimed to assess the efficiency of hydrotalcites in removing AA and FA from aqueous solution. Kinetic, thermodynamic, and equilibrium experiments were conducted using hydrotalcites composed of 30, 63, or 70% MgO. Calcined hydrotalcites composed of 70 and 63% MgO (MG70c and MG63c) had the best kinetic performance, removing 97% of FA and 91% of AA. The adsorption process followed pseudo-first-order kinetics. The Boyd model showed that external mass transfer or a combination of intraparticle diffusion and external mass transfer controls the process. Adsorption equilibrium was evaluated at different temperatures (30, 40, 50, and 60 °C) using MG70c as an adsorbent. The Freundlich model provided the best fit to adsorption isotherms. Thermodynamic studies indicated that adsorption was spontaneous and endothermic in nature. The results confirmed the efficiency of MG70c in removing AA and FA from aqueous solution.
Resumo O tamarindo é uma fruta com alto potencial a ser explorado pelo mercado brasileiro e o seu processamento em forma de geleia promove o aumento da vida útil, oferece um derivado em qualquer época do ano e coloca no mercado um alimento diferenciado pelo seu sabor agridoce. Neste sentido, o presente trabalho objetivou processar geleia a partir da polpa de tamarindo sem o acréscimo de aditivos, realizar análises físico-químicas e microbiológicas e, finalmente, verificar sua aceitação sensorial. Em relação aos parâmetros físico-químicos, foi observado que a atividade de água foi coerente com o valor estipulado para geleias. Os resultados de pH 2,4 e acidez 44,44% da geleia indicam que a elevada acidez da matéria-prima foram conservadas no produto após o tratamento térmico e as análises microbiológicas estavam dentro dos limites estabelecidos pela Revista GEINTEC
A novel “green” Aspergillus niger lipase, obtained from the fermentation of pumpkin seeds, was used in a free form and encapsulated in sol-gel matri x in butyl butyrate (pineapple flavor) synthesis. Esterification reactions were performed with varying substrate molar ratio (butanol: butyric acid) ranging between 1:1 and 5:1; temperature between 30 and 60°C and biocatalyst mass between 0 and 1g, respectively, according to experimental design 23 with 6 axial and 3 central points. Maximum butyl butyrate production was obtained when substrate molar ratio (butanol:butyric acid) 3:1, temperature at 60°C and 0.5 g free or encapsulated lipase as biocatalyst, were used. Temperature was the most significant parameter for production with the two biocatalysts, indicating that higher rates mean greater compound synthesis. Response surface plots showed that higher butyl butyrate production may be obtained with higher temperature and molar ratio rates (butanol:butyric acid) and with lower rates of biocatalyst mass in reactions catalyzed by free or encapsulated lipase. Aspergillus niger lipase obtained from agro-industrial waste could be employed as biocatalyst in esterification reactions in the production of natural aroma as butyl butyrate.
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