Fermentation

Mechanical damage readily induces browning and flavor deterioration in fresh-cut shredded potatoes (FCSPs). This study applied mixed lactic acid bacteria (LAB) fermentation to improve the comprehensive quality of FCSP. A mixed fermentation system was established using Lactiplantibacillus plantarum ZYN-09 and Lacticaseibacillus rhamnosus ZYN-08, two strains isolated from naturally fermented shredded potatoes. Single-factor tests, Plackett–Burman screening, and central composite design (CCD) response surface methodology were combined to optimize the fermentation process. Under optimized conditions, antioxidant activity, key browning-related enzyme activities, and flavor components were determined to evaluate the quality changes induced by fermentation. The results showed that the optimal fermentation parameters were fermentation time of 42 h, temperature of 36 °C, inoculum size of 3.6% (v/v), strain ratio of 2:1 (v/v), and salt added amount of 2% (w/v). Under these conditions, the hardness of FCSP reached 4901.77 N with a sensory evaluation score of 92.08. Mixed LAB fermentation significantly enhanced the scavenging capacities against DPPH, ABTS⁺, and ·OH free radicals as well as Fe²⁺ chelating activity. It retarded browning by inhibiting polyphenol oxidase (PPO) and peroxidase (POD) activities and malondialdehyde (MDA) accumulation while increasing phenylalanine ammonialyase (PAL) activity. Meanwhile, it reconstructed the volatile flavor system and optimized flavor composition. In conclusion, this controlled mixed LAB fermentation technique can simultaneously improve texture, sensory attributes, antioxidant capacity, anti-browning performance and flavor quality of FCSP. This work provides technical support and theoretical basis for green preservation and quality regulation of fresh-cut potatoes.

Glutathione (GSH) is a crucial antioxidant tripeptide with extensive applications in pharmaceuticals, food, and cosmetics. Nevertheless, its microbial production is constrained by low yields, intracellular accumulation, and feedback inhibition. While Saccharomyces cerevisiae presents a promising host for GSH synthesis, the efficient secretion of GSH into the culture medium poses a significant challenge. In this study, we implemented a multi-stage bioengineering strategy aimed at maximizing extracellular GSH production by Saccharomyces cerevisiae. Statistical optimization of fermentation parameters and medium composition enhanced the extracellular glutathione (GSH) yield in shake-flask culture from 18.56 mg/L to 63.60 mg/L, representing a 3.43-fold increase. Furthermore, scaling up the fermentation process to a 30-L high-density fed-batch bioreactor resulted in a significant increase in GSH production, elevating the extracellular GSH concentration from 63.660 mg/L in the optimized shake-flask culture to 1033.33 mg/L. Moreover, the addition of 1% (v/v) ethanol during the later stages of cultivation enhanced both the biosynthesis and secretion of GSH by increasing membrane permeability. This treatment resulted in a 35.27% increase in total GSH content, reaching 94.80 mg/g, and redirected 76.76% of the total GSH into the extracellular fraction. Collectively, these strategies effectively addressed the cell-membrane transport barrier and significantly improved secretion efficiency. The integrated process offers a robust and scalable platform for industrial-scale extracellular GSH production.

This study demonstrated the potential of wild Bacillus strains isolated from Camelina sativa plants and rhizospheric soil for the bioconversion of camelina oilseed cake. Five selected strains (Z1, Z9, Z22, Z23, and Z26) exhibited promising enzymatic potential and the potential to improve the nutritional and functional properties of camelina cake. Both solid-state fermentation (SSF) and submerged fermentation (SF) increased the crude protein content and reduced the glucosinolate levels in ‘NS Slatka’ and ‘NS Zlatka’ camelina cake varieties, with the extent of these changes influenced by the bacterial strain, camelina variety, and fermentation mode. SSF generally showed a greater potential for improving the nutritional characteristics of the substrate, while fermentation also enhanced its antioxidant potential. Several wild isolates performed comparably to or better than the reference strain Bacillus subtilis ATCC 6051. Among the tested isolates, Z26 showed the most consistent overall performance, combining a broad enzymatic profile with favourable effects on the nutritional and functional properties of the fermented camelina cake under the investigated experimental conditions. MLSA (multilocus sequence analysis) putatively assigned Z26 to the B. amyloliquefaciens operational group, indicating a close relationship with B. amyloliquefaciens and B. velezensis. These findings highlight the potential of indigenous Bacillus strains as promising biocatalysts for the valorization of cold-pressed camelina oilseed cake and its conversion into a nutritionally improved feed ingredient.