C2 feedstock-based biomanufacturing of value-added chemicals

Engineering microbes to produce value-added chemicals from C6/C5 sugars sometimes requires long biosynthetic pathways, which causes carbon loss due to involving multiple metabolic branch nodes, leading to a lower product yield. Using C2 feedstocks derived from gaseous, cellulosic, and plastic wastes could establish shorter biosynthetic pathways to produce some target chemicals, for example, acetyl-CoA-derived natural products. Utilizing these waste-derived feedstocks would also contribute to reducing the carbon footprint of the chemical industry. In this review, we highlighted the promising waste-processing technologies that could provide C2 feedstocks that are compatible with microbial fermentation. We also analyzed the recent metabolic engineering works in which the microorganisms/fermentation processes were modified/optimized to utilize acetate, ethanol, or ethylene glycol more efficiently.

Statistical Optimization of Alkali Pretreatment to Improve Sugars Recovery from Spent Coffee Grounds and Utilization in Lactic Acid Fermentation

Biorefinery, which utilizes carbon-neutral biomass as a resource, is attracting attention as a significant alternative in a modern society confronted with climate change. In this study, spent coffee grounds (SCGs) were used as the feedstock for lactic acid fermentation. In order to improve sugar conversion, alkali pretreatment was optimized by a statistical method, namely response surface methodology (RSM). The optimum conditions for the alkali pretreatment of SCGs were determined as follows: 75 °C, 3% potassium hydroxide (KOH) and a time of 2.8 h. The optimum conditions for enzymatic hydrolysis of pretreated SCGs were determined as follows: enzyme complex loading of 30-unit cellulase, 15-unit cellobiase and 50-unit mannanase per g biomass and a reaction time of 96 h. SCG hydrolysates were used as the carbon source for Lactobacillus cultivation, and the conversions of lactic acid by L. brevis ATCC 8287 and L. parabuchneri ATCC 49374 were 40.1% and 55.8%, respectively. Finally, the maximum lactic acid production by L. parabuchneri ATCC 49374 was estimated to be 101.2 g based on 1000 g of SCGs through the optimization of alkali pretreatment and enzymatic hydrolysis.