l‐Glutamate maintains the quality of apple fruit by mediating carotenoid, sorbitol and sucrose metabolisms.

Background: l‐Glutamate is involved in many important chemical reactions in horticultural products and improves postharvest disease resistance. Quality decline of apple fruit caused by senescence and fungus invasion often leads to tremendous losses during logistics. This study was performed to evaluate the variations of quality attributes, carotenoid, sorbitol and sucrose metabolisms in apples (cv. Qiujin) after l‐glutamate dipping treatment. RESUITS: l‐Glutamate immersion maintained high values of L*, a* and b*, flesh firmness, titratable acidity, as well as the total soluble solids, soluble sugar, reducing sugar and ascorbic acid contents in apples. l‐Glutamate also decreased mass loss, respiratory rate and ethylene release, enhanced sucrose synthase‐cleavage, acid invertase and neutral invertase activities, whereas reduced sorbitol dehydrogenase, sucrose phosphate synthase, sucrose synthase synthesis and sorbitol oxidase activities in apples. Moreover, l‐glutamate inhibited lutein, β‐carotene and lycopene accumulation, and down‐regulated phytoene synthase, lycopene β‐cyclase, ζ‐carotene desaturase, phytoene desaturase, carotenoid isomerase, ζ‐carotene isomerase and carotenoids cleavage dioxygenase gene expressions, but up‐regulated 9‐cis‐epoxycarotenoid dioxygenase gene expression in apples. Conclusion: Postharvest l‐glutamate dipping treatment can keep apple quality by modulating key enzyme activity and gene expression in sorbitol, sucrose and carotenoid metabolisms. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]