Isolation and characterization of L-valine-degrading Candida maltosa DLPU-zpb for D-valine preparation from DL-valine

Valorization of spent coffee grounds through integrated bioprocess of fermentable sugars, volatile fatty acids, yeast-based single-cell protein and biofuels production

Recovering nutrients from waste for biological processes aligns with sustainability principles. This study aimed to convert spent coffee grounds (SCG) into valuable products, including fermentable sugars, volatile fatty acids (VFAs), yeast-based single-cell protein and biofuels. Alkaline pretreatment was conducted before enzymatic hydrolysis, in which the pretreated SCG was hydrolyzed with varying enzyme loadings (20-60 filter paper units (FPU)/g-solid) and solid loadings (3-15 % w/v). The hydrolyzed slurry was utilized for VFAs and hydrogen production, yielding high values of 0.66 g/g-volatile solids (VS) and 109 mL/g-VS, respectively, using an enzyme loading of 50 FPU/g-solid and a solid loading of 3 % (w/v). The derived VFAs were used to cultivate a newly isolated yeast, Candida maltosa KKU-ARY2, resulting in an accumulated protein content of 43.7 % and a biomass concentration of 4.6 g/L. This study highlights the conversion of SCG into essential components, emphasizing the benefits of waste utilization through cascade bioprocesses.

Application and microbial preparation of D-valine

D-Valine is an important organic chiral source and has extensive industrial application, which is used as intermediate for the synthesis of agricultural pesticides, semi-synthetic veterinary antibiotics and pharmaceutical drugs. Its derivatives have shown great activity in clinical use, such as penicillamine for the treatment of immune-deficiency diseases, and actinomycin D for antitumor therapy. Fluvalinate, a pyrethroid pesticide made from D-valine, is a broad-spectrum insecticide with low mammalian toxicity. Valnemulin, a semi-synthetic pleuromutilin derivative synthesized from D-valine, is an antibiotic for animals. Moreover, D-valine is also used in cell culture for selectively inhibiting fibroblasts proliferation. Due to its widespread application, D-valine is gaining more and more attention and some approaches for D-valine preparation have been investigated. In comparison with other approaches, microbial preparation of D-valine is more competitive and promising because of its high stereo selectivity, mild reaction conditions and environmental friendly process. So far, microbial preparation of D-valine can be mainly classified into three categories: microbial asymmetric degradation of DL-valine, microbial stereoselective hydrolysis of N-acyl-DL-valine by D-aminoacylase, and microbial specific hydrolysis of DL-5-isopropylhydantoin by D-hydantoinase coupled with D-carbamoylase. In this paper, the industrial application of D-valine and its microbial preparation are reviewed.