Part of the xanthophyll (or violaxanthin) cycle for controlling the concentration of zeaxanthin in chloroplasts. Catalyzes the two-step mono de-epoxidation reaction. Stereospecific for all-trans xanthophylls. Zeaxanthin induces the dissipation of excitation energy in the chlorophyll of the light-harvesting protein complex of photosystem II. all-trans-violaxanthin + 2 L-ascorbate = all-trans-zeaxanthin + 2 H2O + 2 L-dehydroascorbate Activity limited by low ascorbate availability. Feedback inhibition by zeaxanthin. Requires the presence of micelle-forming lipids such as monogalactosyldiacylglyceride (MGDG). Low concentration of bilayer forming lipids, such as digalactosyldiacylglyceride (DGDG) or phosphatidylcholine, supports a slower but nearly complete activity (PubMed:11891252, PubMed:14749490, PubMed:16532316). 80% of the specific activity in lumenal chloroplast fractions is lost in vitro in the presence of reduced thioredoxin (PubMed:20049866). Interacts in vitro with LTO1. The cysteine rich N-terminal region is required for activity. The amount of VDE in vivo is estimated to be 1 molecule per 20-100 electron transport chains. Belongs to the calycin superfamily. Lipocalin family.