Effect of Light Irradiation on Sugar, Phenolics, and GABA Metabolism on Postharvest Grape (Vitis vinifera L.) During Storage

The impact of red and blue light-emitting diodes (LEDs) irradiation on the sugar metabolism and gamma-aminobutyric acid in postharvest table grapes stored at 4 degrees C for 21 days after harvest were explored. Grape clusters were exposed to red and blue light irradiation at the same intensity (500 lx). The findings revealed that red and blue light treatments enhanced total soluble solids (TSS) and total acidity (TA) content. Furthermore, red-light irradiation retained higher phenolic compound during storage than blue light and control. Red-light radiation sustained higher levels of phenolic biosynthesis-related enzymes, including phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL), cinnamate 4-hydroxylase (C4H), and p-coumarate ligase (4CL), than blue light irradiation and control. The results showed that red light increased glucose, fructose, and sucrose levels, which were 32.19, 33.18, and 2.95 mg g(-1), compared with those in blue light and control at the end of storage and enhancing the sucrose synthase synthesis (SS-synthesis) and acid invertase (AI), while blue light enhanced sucrose synthase cleavage (SS-cleavage). In addition, red light irradiation increased glutamic acid decarboxylase (GAD) activity while red and blue light irradiation inhibited gamma-aminobutyric acid transaminase (GABA-T) activity by 22.14 and 20.71 U g(-1) at 21 days of storage, compared to control, leading to gamma-aminobutyric acid (GABA) accumulation. These findings suggest that red and blue light will help in maintaining the quality of grape during postharvest storage.