Brewer’s spent grain biotransformation to produce lignocellulolytic enzymes and polyhydroxyalkanoates in a two-stage valorization scheme

Abstract

Lignocellulolytic enzymes from low-cost sources are gaining attention as a tool to reduce production costs. Such enzymes can be obtained sustainably by diverse fungal strains via solid-state fermentation (SSF) of lignocellulosic-derived residues as substrates. Besides, these enzymes allow hydrolyzing the same residue, releasing fermentable sugars that can be transformed into valueadded products. This study shows a two-stage valorization approach for the lignocellulosic leftover brewer's spent grain (BSG): first, by producing lignocellulolytic enzymes through the SSF of BSG using three fungal strains and, second, by using the selfproduced enzymes to hydrolyze the same BSG and obtaining sugar-rich hydrolysates that serve as an alternative carbon source for polyhydroxyalkanoates (PHA) production. From the evaluated set, Aspergillus niger and Thermoascus aurantiacus produced the highest xylanase activities compared with Trichoderma reesei (268 ± 24, 241 ± 10, and 150 ± 24 U per gram of dry BSG, respectively). Also, A. niger extracts resulted in the most effective for releasing sugars from BSG, obtaining up to 0.56 g per gram of dry BSG after 24 h without any pretreatment needed. Thus, the sugar-rich hydrolysate obtained with A. niger was used as a source for producing PHA by using two bacterial strains, namely, Burkholderia cepacia and Cupriavidus necator. Maximum PHA yield was achieved by using C. necator after 48 h with 9.0 ± 0.44 mg PHA•g −1 dry BSG. These results show the significant potential of BSG as raw material for obtaining value-added bioproducts and the importance of multiple valorization schemes to improve the feasibility of similar residue-based systems.

Production of polyhydroxybutyrate and polyhydroxybutyrate-co-MCL copolymers from brewer’s spent grains by recombinant Escherichia coli LSBJ

“…The fermentation of agro-industrial residue hydrolysates in batch shake flask production can result in PHA titers between 0.1 and 15 g/L [12,40,[56][57][58][59][60]. In this work, the production titers of PHB and PHB-co-MCL by E. coli LSBJ from BSG hydrolysate are observed to be higher here than what has been previously reported with native producers B. cepacia (1.01 g/L) and C. necator (1.19 g/L) using the same substrate [30]. This can be explained by the different nutrients and PHA metabolism of E. coli LSBJ as compared to the native producers.…”

“…A recent paper by Llimós et al showed the conversion of BSG without pretreatment into PHB using native PHBproducing organisms Burkholderia cepacia and Cupriavidus necator, with corresponding PHB titers from 1.0 to 1.2 g/L, respectively [30]. The objective of the present study is to establish a comprehensive process for conversion of BSG into PHB with higher final polymer titers that are commonly observed and would be feasible for further optimizations, as well as to demonstrate for the first-time production of PHB-co-MCL copolymers using BSG substrate.…”

Integrated solid-state enzymatic hydrolysis and solid-state fermentation for producing sustainable polyhydroxyalkanoates from low-cost agro-industrial residues

“…Self-produced enzymatic extracts used in the hydrolysis experiments were obtained starting from BSG, as suggested by Llimós et al (2020). Briefly, the BSG was fermented in solid-state using A. niger as inoculum (10% w/w).…”

“…Nevertheless, one of the most interesting traits of SSF is its versatility to process a wide variety of solid wastes to obtain different value-added products through an extensive range of microorganisms (Soccol et al, 2017;Yazid et al, 2017). Accordingly, SSF has been successfully used in combination with several wastes for producing marketable bioproducts such as enzymes (Llimós et al, 2020;Melikoglu et al, 2015), base chemicals (Martínez-Avila et al, 2020), phenolic compounds (Santos da Silveira et al, 2019, among others. Oliveira et al, (2004) first tested the PHA production via SSF using soy cake supplemented with molasses.…”

Sustainable Production of Lignocellulolytic Enzymes in Solid-State Fermentation of Agro-Industrial Waste: Application in Pumpkin (Cucurbita maxima) Juice Clarification

“…Previously, many studies failed to address the efficiency of enzyme extracts in SSF [12][13][14]. For instance, a recent study by Llimós, et al [16] investigated biotransformation of brewer's spent grain to produce lignocellulolytic enzymes and polyhydroxyalkanoates in a two-stage valorization. Moreover, most of these studies in this area are limited to the production with only a few studies focusing on application of the produced enzymes.…”