Riboflavin application regulates sugar and energy metabolism in strawberries during cold storage

The commercial and nutritional value of strawberry fruit is drastically reduced due to its susceptibility to decay fungal diseases. In this study, we employed 40 μM riboflavin to delay senescence and decay of strawberry fruit during storage at 4 °C for 12 d. The findings showed that the treatment decreased strawberries mass loss, respiration rate, ROS level, and MDA content and maintained soluble sugars level. Riboflavin treatment maintained high levels of ATP content and energy charge, and activated the activities of succinate dehydrogenase (SDH), cytochrome C oxidase (CCO), H+-ATPase, Ca+-ATPase, glucokinase (GK), fructokinase (FRK), glucose-6-phosphate dehydrogenase (G6PDH), and 6-phosphogluconate dehydrogenase (6-P-GDH) and up-regulated the expression of their encoding genes. In addition, riboflavin-mediated NAD kinase (NADK) activation accelerated the conversion of NAD+ to DADP+ and the accumulation of DADPH. The respiratory pathway switched from the glycolytic (EMP)-tricarboxylic acid cycle (TCA) to the pentose phosphate pathway (PPP), reducing respiratory consumption. As a result, our findings suggest that riboflavin supplementation after harvest maintains a higher level of energy and delays senescence in strawberries.