Glycine betaine inhibits postharvest softening and quality decline of winter jujube fruit by regulating energy and antioxidant metabolism

Winter jujube fruit easily softens after harvest. To investigate the effects of glycine betaine (N,N,N-trimethylglycine; GB) treatment on the quality of postharvest jujubes, fresh winter jujubes (Zizyphus jujuba Mill. cv. Dongzao) were immersed in 20 mmol·L^-1 GB for 20 min. The results showed that GB application can effectively maintain cell wall component content by restraining gene expression and enzyme activities, including PG, CX, PME and β-Glu. Meanwhile, the activities of antioxidant enzymes (APX, CAT, SOD, POD) and the contents of nonenzymatic antioxidants (MDA, H₂O₂, ASA, GSH) were enhanced in treated jujubes, thereby reducing the content of ROS. In addition, energy metabolism enzyme activities (H⁺-ATPase, Ca²⁺-ATPase, SDH and CCO) and gene expression were also significantly increased, thus maintaining higher energy levels (ATP, ADP, AMP and EC). In summary, GB enhances ATP biosynthesis by increasing energy metabolism. It offers essential energy for the antioxidant metabolism, thus retarding the softening of postharvest jujubes.