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In this study, the lycopene β-cyclase (LCYb) and lycopene ε-cyclase (LCYe) genes were cloned from maize, and the encoded products were analyzed by bioinformatics methods. After expression in Escherichia coli, the catalytic properties of LCYb and LCYe from maize were explored by color complementation and product analysis experiments. The results of sequence analysis showed that the full-length cDNA of maize LCYb and LCYe were 1 470 and 1 611 bp, respectively, which were more than 90% homologous to those of sorghum and millet. LCYe and LCYb proteins were successfully purified by fusion expression with glutathione thiotransferase tags. The results of color complementation test and high performance liquid chromatography (HPLC) analysis showed that maize LCYb had catalytic activity on β-ring, could cyclize both ends of lycopene to form β-carotene, and had very weak ε-ring catalytic activity, which could form α-carotene through the intermediate γ-carotene. Maize LCYe was also found to able to catalyze both ends of lycopene to form ε-carotene. This study can lay a foundation for exploring the molecular mechanism of the regulation of maize carotenoid.

Abstract Background Xanthophylls are a large class of carotenoids that are found in a variety of organisms and play particularly important roles in the light-harvesting and photoprotection processes of plants and algae. Violaxanthin is an important plant-derived xanthophyll with wide potential applications in medicines, foods, and cosmetics because of its antioxidant activity and bright yellow color. To date, however, violaxanthins have not been produced using metabolically engineered microbes on a commercial scale. Metabolic engineering for microbial production of violaxanthin is hindered by inefficient synthesis pathway in the heterologous host. We systematically optimized the carotenoid chassis and improved the functional expression of key enzymes of violaxanthin biosynthesis in Escherichia coli. Results Co-overexpression of crtY (encoding lycopene β-cyclase), crtZ (encoding β-carotene 3-hydroxylase), and ZEP (encoding zeaxanthin epoxidase) had a notable impact on their functions, resulting in the accumulation of intermediate products, specifically lycopene and β-carotene. A chassis strain that did not accumulate the intermediate was optimized by several approaches. A promoter library was used to optimize the expression of crtY and crtZ. The resulting strain DZ12 produced zeaxanthin without intermediates. The expression of ZEP was further systematically optimized by using DZ12 as the chassis host. By using a low copy number plasmid and a modified dithiol/disulfide system, and by co-expressing a full electron transport chain, we generated a strain producing violaxanthin at about 25.28 ± 3.94 mg/g dry cell weight with decreased byproduct accumulation. Conclusion We developed an efficient metabolically engineered Escherichia coli strain capable of producing a large amount of violaxanthin. This is the first report of a metabolically engineered microbial platform that could be used for the commercial production of violaxanthin.

BACKGROUND: The food industry has begun to develop foods fortified with unsaturated fatty acids; however, the susceptibility of pine nut oil to oxidation and other properties limits its use in food production. Researchers often inhibit the oxidation of oil by adding antioxidants. After the combination of polyphenols and proteins, the complex formed can improve or enhance the performance of the emulsion when it stabilizes the emulsion. Encapsulating, protecting, and controlling the release behavior of vitamin D (VD) during digestion through an emulsion delivery system can effectively overcome limitations such as easy degradation during processing and storage. This research uses tannic acid, gallic acid, tea polyphenol, and vanillic acid to prepare Pickering emulsions, and the type of phenolic compound is explored by multi‐dimensional characterization and the amount of emulsion. RESULTS: The influence of traits, microstructure, stability, VD load application, and effect on the emulsion matrix's encapsulation rate and bioaccessibility is studied. A method was investigated to enhance the oxidative stability of whey protein isolate‐stabilized emulsions by introducing phenol. Pickering emulsions could be obtained in the presence of phenol, while the type of phenol played a relatively important role, probably because the mechanism involved interactions between particles. Viscosity and creaming stability of emulsions increased with crosslinking of phenol in emulsions. In addition, the presence of phenol in emulsions significantly increased the bioaccessibility of encapsulated VD after in vitro digestion. CONCLUSION: The method presented in this study was important for improving the oxidative stability of pine nut oil emulsions, expanding the application of pine nut oil in the food industry, and providing the theoretical and application basis of application and active substance emulsion delivery systems. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]