Interdependence between lignocellulosic biomasses, enzymatic hydrolysis and yeast cell factories in biorefineries

Abstract

Biorefineries have a pivotal role in the bioeconomy scenario for the transition from fossil-based processes towards more sustainable ones relying on renewable resources. Lignocellulose is a prominent feedstock since its abundance and relatively low cost. Microorganisms are often protagonists of biorefineries, as they contribute both to the enzymatic degradation of lignocellulose complex polymers and to the fermentative conversion of the hydrolyzed biomasses into fine and bulk chemicals. Enzymes have therefore become crucial for the development of sustainable biorefineries, being able to provide nutrients to cells from lignocellulose. Enzymatic hydrolysis can be performed by a portfolio of natural enzymes that degrade lignocellulose, often combined into cocktails. As enzymes can be deployed in different operative settings, such as separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF), their characteristics need to be combined with microbial ones to maximize the process. We therefore reviewed how the optimization of lignocellulose enzymatic hydrolysis can ameliorate bioethanol production when Saccharomyces cerevisiae is used as cell factory. Expanding beyond biofuels, enzymatic cocktail optimization can also be pivotal to unlock the potential of non-Saccharomyces yeasts, which, thanks to broader substrate utilization, inhibitor resistance and peculiar metabolism, can widen the array of feedstocks and products of biorefineries.

Optimization of Carotenoids Production from Camelina sativa Meal Hydrolysate by Rhodosporidium toruloides

“…To release sugars from lignocellulosic biomasses, either acid or enzymatic hydrolysis is generally performed, with the latter the preferred method because of the broad enzymatic portfolio available and its mild reaction conditions, which are often more compatible with the subsequent growth of chosen microbial cell factories [24,34]. In addition, acid hydrolysis releases several inhibitory compounds that might impair microbial growth [24]. Nevertheless, glycosidic enzymes need to be evaluated as cost items; therefore, reducing the loading of enzymatic cocktails can be crucial to the economics of a bioprocess.…”

“…Nevertheless, even when starting from 5.95% and decreasing to a value of 0.56% w/w Camelina meal of enzyme loading, no significant difference could be observed, as the lowest dose also resulted in the release of approximately 15 g/L of total sugar. hydrolysis releases several inhibitory compounds that might impair microbial growth [24]. Nevertheless, glycosidic enzymes need to be evaluated as cost items; therefore, reducing the loading of enzymatic cocktails can be crucial to the economics of a bioprocess.…”

“…This possible application permits the use of SSF to produce intracellular products such as carotenoids, that, in general, are hardly separated from the cells mixed with WIS. In addition, SSF-like processes are, generally speaking, more desirable than SHF from the industrial point of view, because of the reduction in operative steps [24]. Nevertheless, in this work we focused more on SHF due to the possibility of collecting data regarding cell growth (in terms of OD or CDW).…”

“…Enzymatic cocktails are a valuable ally in the hydrolysis of LCBs and in the release of fermentable sugars for the development of microbial-based bioprocesses [24]. Nevertheless, enzymes have costs that decisively impact second generation biorefineries, since the amount needed for the maximum hydrolysis yield is often not at an economically optimum level [25][26][27][28][29].…”

Subcritical Water Pretreatment for the Efficient Valorization of Sorghum Distillery Residue for the Biorefinery Platform

“…Sustainable bioprocessing is essential for commercial reasons, as biomass can be transformed into a wide range of products and by-products that include food, feed, materials, chemicals, and energies (fuel, power, heat). Sustainable bioprocessing technology represents an essential aspect of biorefinery [4]. Integrated biorefinery develops a broad range of value-added products with simultaneous generation of major products.…”