Trehalose delays postharvest browning of litchi fruit by regulating antioxidant capacity, anthocyanin synthesis and energy status

Abstract

Litchi fruit is extremely vulnerable to postharvest browning due to its perishable physiological characteristics, which seriously restricts the shelf-life and industrial development of products. Trehalose is a natural product with excellent biological activity and safety. In this work, the ability of trehalose to mitigate the browning of ‘Feizixiao’ litchi fruit stored at 25 °C and its physio-biochemical mechanisms were evaluated. The application of trehalose at 2.5 g L⁻¹ to litchi fruit delayed browning and redness loss. Trehalose treatment alleviated oxidative stress-induced impairment of membrane system, as indicated by reduced generation of O₂^-., H₂O₂ and malondialdehyde (MDA) and lowered relative electrolyte leakage (REL), which was a result of increased activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR). Compared to control fruit, repressed activities of polyphenol oxidase (PPO) and peroxidase (POD) coincident with higher contents of total phenolics, flavonoids, anthocyanins, procyanidin B2 and cyanidin-3-O-glucoside were observed in fruit receiving trehalose, indicating an amelioration of enzymatic browning by trehalose treatment. Furthermore, trehalose treatment stimulated the expression of anthocyanin biosynthetic genes (LcPAL, Lc4CL, LcCHS, LcCHI, LcANS, LcDFR and LcUFGT) and their transcriptional activator genes (LcMYB43435, LcMYB18362, LcMYB30086 and LcMYB2539), while suppressing the transcription of microRNAs (miR159, miR319, miR828 and miR858) that mediate MYB degradation. Additionally, trehalose treatment increased content of adenosine triphosphate (ATP) and expression of LcPGK and LcCa²⁺-ATPase, while repressing the transcription of miR2118 that can target and negatively regulate LcPGK and LcCa²⁺-ATPase, which facilitated the synthesis and utilization of energy. These findings suggest that trehalose could retard postharvest browning in litchi fruit by enhancing antioxidant capacity, promoting anthocyanin synthesis and maintaining energy homeostasis.