ReviewAn overview of preharvest factors affecting vitamin C content of citrus fruit

•Vitamin C is an important nutritional quality indicator of citrus fruit and products.•Ascorbic acid (AsA) in citrus fruit can be influenced by numerous preharvest factors.•L-galactose pathway is the predominant route for AsA biosynthesis in citrus fruit.•AsA in citrus is determined by the balance of biosynthesis, oxidation, and recycling.

Citrus fruits are an important diet for human health by providing some nutritional and antioxidant components, especially ascorbic acid (AsA). As the major antioxidant compound, the concentration of AsA is an important nutritional quality indicator for citrus fruit and its derivative products. Although the emphasis is on vitamin C content of harvested citrus fruit, this review of literature focuses on preharvest factors affecting this nutritional quality variable. The literature reviewed in this study showed that the content of AsA in citrus fruits is influenced by numerous preharvest factors including genotype, cultural practices, climatic conditions, fruit maturity and postharvest management. To better understand the mechanism underlying the vitamin C content of different citrus fruits, the introduction of this paper will first provide an overview of major proposed biosynthetic pathways and genes encoding for enzymes involved in AsA biosynthesis and oxidation. The review will then concentrate on the current state of knowledge regarding inherent genetic, environmental, fertilization, maturity and harvesting factors affecting AsA of citrus fruits. Some suggestions for future research are also highlighted.