Co-fermentation of cassava waste pulp hydrolysate with molasses to ethanol for economic optimization

Microwave-assisted cassava pulp hydrolysis as food waste biorefinery for biodegradable polyhydroxybutyrate production

Cassava pulp is one of the most abundant agricultural residues that can cause serious disposal problems. This study aimed to apply a biorefinery approach by examining the feasibility of microwave-assisted cassava pulp hydrolysis to attain sustainable management and efficient use of natural resources. Four factors, namely, the liquid-to-solid ratio (20 mL/g, 10 mL/g, 7.5 mL/g, and 5 mL/g), types of acids (H2SO4 and H3PO4), watt power (600 W, 700 W, and 800 W) and time (3, 5 and 8 min), were carefully investigated. The highest fermentable sugar content of 88.1 g/L ± 0.7 g/L (0.88 g fermentable sugars/g dry cassava pulp) was achieved when 20 mL/g cassava pulp was hydrolyzed with 2.5% (v/v) H2SO4 under microwave irradiation at 800 W for 8 min. Glucose was a major product (82.0 g/L ± 5.2 g/L). The inhibitor concentration was 5.17 g/L ± 0.01 g/L, and the levulinic acid concentration was 5.15 g/L ± 0.01 g/L. The results indicated that the liquid-to-solid ratio, diluted acid concentration, irradiation watt power and time were important factors in producing fermentable sugars from acid hydrolysis under microwave irradiation. The crude hydrolysate was used for PHB production by Cupriavidus necator strain A-04. The hydrolysate to nutrients ratio of 30:70 (v/v) yielded a cell dry weight of 7.5 g/L ± 0.1 g/L containing PHB content of 66.8% ± 0.3% (w/w), resulting in a yieldY P / S (g-PHB/g-S P H B ) of 0.35 g/g. This study demonstrated that the microwave-assisted cassava pulp hydrolysate developed in this study provided a high amount of glucose (88.1% conversion) and resulted in a low concentration of inhibitors without xylose; this was successfully achieved without pregelatinization, alkaline pretreatment or detoxification.

Bioprospecting Kluyveromyces marxianus as a Robust Host for Industrial Biotechnology

Kluyveromyces marxianus is an emerging non-conventional food-grade yeast that is generally isolated from diverse habitats, like kefir grain, fermented dairy products, sugar industry sewage, plants, and sisal leaves. A unique set of beneficial traits, such as fastest growth, thermotolerance, and broad substrate spectrum (i.e., hemi-cellulose hydrolysates, xylose, l-arabinose, d-mannose, galactose, maltose, sugar syrup molasses, cellobiose, and dairy industry) makes this yeast a particularly attractive host for applications in a variety of food and biotechnology industries. In contrast to Saccharomyces cerevisiae, most of the K. marxianus strains are apparently Crabtree-negative or having aerobic-respiring characteristics, and unlikely to endure aerobic alcoholic fermentation. This is a desirable phenotype for the large-scale biosynthesis of products associated with biomass formation because the formation of ethanol as an undesirable byproduct can be evaded under aerobic conditions. Herein, we discuss the current insight into the potential applications of K. marxianus as a robust yeast cell factory to produce various industrially pertinent enzymes, bioethanol, cell proteins, probiotic, fructose, and fructo-oligosaccharides, and vaccines, with excellent natural features. Moreover, the biotechnological improvement and development of new biotechnological tools, particularly CRISPR-Cas9-assisted precise genome editing in K. marxianus are delineated. Lastly, the ongoing challenges, concluding remarks, and future prospects for expanding the scope of K. marxianus utilization in modern biotechnology, food, feed, and pharmaceutical industries are also thoroughly vetted. In conclusion, it is critical to apprehend knowledge gaps around genes, metabolic pathways, key enzymes, and regulation for gaining a complete insight into the mechanism for producing relevant metabolites by K. marxianus.

Production and development of vinegar fermentation from broken Riceberry rice using raw starch-degrading enzyme hydrolysis

Broken Riceberry rice was used as a substrate for sugar syrup production by the hydrolysis of raw starch-degrading enzyme as a low-temperature amylase (iKnowZyme^® LTAA, Thailand). Response surface methodology (RSM) with a central composite design (CCD) showed that an optimized substrate concentration of 250 g/L yielded 13°Brix of total soluble solid (TSS) content when incubated at 50 °C for 12 h. The major product from the broken Riceberry rice hydrolysis was glucose with lesser amounts of maltose and maltotriose. Maximum alcohol content (16% w/v) for broken Riceberry rice wine was obtained after fermentation with two mixed strains of Saccharomyces cerevisiae for 10 days. Scanning electron micrographs showed that yeast strains could grow on the solid residue of broken Riceberry rice that supported yeast cell survival under stress conditions. Broken Riceberry rice wine was used as the substrate for vinegar fermentation by Acetobacter aceti TISTR 354. Maximum acetic acid concentration was achieved at 5.4% when incubated at room temperature for 6 days, containing 10.92 mg/L and 965.53 ± 7.74 mL sample/g DPPH of anthocyanin content and antioxidant assay, respectively. Our finding revealed the feasibility of broken Riceberry rice substrate for sugar syrup, wine and vinegar production by raw starch-degrading enzyme hydrolysis which increased the value of low-cost agricultural crops through biotechnological processes.