Valorization of Cabbage Waste as a Feedstock for Microbial Polyhydroxyalkanoate Production: Optimizing Hydrolysis Conditions and Polyhydroxyalkanoate Production.

Establishing a platform for the bioconversion of waste resources into value-added compounds is critical for achieving a sustainable and eco-friendly economy. Herein, we produced polyhydroxyalkanoate via microbial fermentation using cabbage waste as a feedstock and metabolically engineered Escherichia coli. For this, the hydrolysis conditions of cabbage waste were optimized by focusing on parameters such as substrate and enzyme concentrations to enhance the saccharification efficiency. The phaABC operon, which encodes key enzymes responsible for polyhydroxyalkanoate biosynthesis in Ralstonia eutropha H16, was overexpressed in E. coli. Using cabbage hydrolysate as the feedstock, this engineered E. coli strain could produce poly(3-hydroxybutyrate) with a polymer content of 26.0 wt % of dry cell weight. Moreover, malic acid in cabbage hydrolysate significantly enhanced poly(3-hydroxybutyrate) production; the addition of 0.5 g/L malic acid markedly increased poly(3-hydroxybutyrate) content by 59.9%. This study demonstrates the potential of cabbage waste as a promising raw material for the microbial production of polyhydroxyalkanoate.

Heterotypic stress-induced adaptive evolution enhances freeze-drying tolerance and storage stability of Leuconostoc mesenteroides WiKim33.

Lactic acid bacteria (LAB) are currently being investigated for their potential use as probiotics and starter cultures. Researchers have developed powdering processes for the commercialization of LAB. Previous studies have focused on identifying innovative cryoprotective agents and freeze-drying (FD) techniques to enhance the stability of LAB. In this study, adaptive laboratory evolution (ALE) was employed to develop a strain with high FD tolerance and enhanced storage stability. Leuconostoc mesenteroids WiKim33 was subjected to heterotypic shock (heat and osmosis shock) to induce the desired phenotype and genotype. An FD-tolerant enhanced Leu. mesenteroides WiKim33 strain (ALE50) was obtained, which harbored a modified fatty acid composition and cell envelope characteristics. Specifically, ALE50 showed a lower unsaturated fatty acid (UFA)/saturated fatty acid (SFA) ratio and a higher cyclic fatty acid (CFA) composition. Moreover, the exopolysaccharide (EPS) thickness increased significantly by 331% compared to that of the wild type (WT). FD tolerance, which was evaluated using viability testing after FD, was enhanced by 33.4%. Overall, we demonstrated the feasibility of ALE to achieve desirable characteristics and provided insights into the mechanisms underlying increased FD tolerance.

Utilization of coffee waste as a sustainable feedstock for high-yield lactic acid production through microbial fermentation.

Lactic acid is an important industrial precursor; however, high substrate costs are a major challenge in microbial fermentation-based lactic acid production. Coffee waste is a sustainable feedstock alternative for lactic acid production via microbial fermentation. Herein, the feasibility of coffee waste as a feedstock was explored by employing appropriate pretreatment methods and optimizing enzyme combinations. Coffee waste pretreatment with hydrogen peroxide and acetic acid along with a combination of Viscozyme L, Celluclast 1.5 L, and Pectinex Ultra SP-L achieved the 78.9 % sugar conversion rate at a substrate concentration of 4 % (w/v). Lactiplantibacillus plantarum WiKim0126-induced fermentation with a 4 % solid loading yielded a lactic acid concentration of 22.8 g/L (99.6 % of the theoretical maximum yield) and productivity of 0.95 g/L/h within 24 h. These findings highlight the viability of coffee waste as an eco-friendly resource for sustainable lactic acid production.

Sonochemical application reduces monosaccharide levels and improves cryoprotective effect of Jerusalem artichoke extract on Leuconostoc mesenteroides WiKim33 during freeze-drying.

Lactic acid bacteria (LAB) are being used for probiotic and starter cultures to prevent global damage to microbial cells. To retain the benefits of LAB in the commercially used powdered form, highly efficient cryoprotective agents are required during the manufacturing process. This study suggests a novel cryoprotective agent derived from Jerusalem artichoke (JA; Helianthus tuberous L.) and describes the mechanism of cryoprotective effect improvement by sonication treatment. The cryoprotective effect of JA extract was verified by examining the viability of Leuconostoc mesenteroides WiKim33 after freeze-drying (FD). Sonication of JA extract improved the cryoprotective effect. Sonication reduced fructose and glucose contents, which increased the induction of critical damage during FD by 15.84% and 46.81%, respectively. The cryoprotective effects of JA and sonication-treated JA extracts were determined using the viable cell count of Leu. mesenteroides WiKim33. Immediately after FD and storage for 24 weeks, the viability of Leu. mesenteroides WiKim33 with JA extract was 82.8% and 76.3%, respectively, while that of the sonication-treated JA extract was 95.2% and 88.8%, respectively. Our results show that reduction in specific monosaccharides was correlated with improved cryoprotective effect. This study adopted sonication as a novel treatment for improving the cryoprotective effect and verified its efficiency.