Hot Air Drying Induces Browning and Enhances Phenolic Content and Antioxidant Capacity in Mung Bean (Vigna radiata L.) Sprouts

Hot air drying has been widely used for the processing and preservation of fresh fruits and vegetables. In this study, we investigated the browning of hot air dried mung bean (Vigna radiata L.) sprouts, as well as the antioxidant capacity and phenolic contents in their soluble and insoluble fractions. Hot air drying at 70 and 80C for 24h increased the browning of mung bean sprouts, and hot air dried samples generally had higher total phenolic content and antioxidant capacity compared to the freeze-dried sample. Rutin, caffeic acid and p-coumaric acid were identified in mung bean sprouts by LC-MS, and hot air drying at higher temperature (70 and 80C) reduced rutin and p-coumaric acid contents, while increasing the content of caffeic acid. Browning pigments and polyphenols may be the main contributors of antioxidant capacity in hot air dried mung bean sprouts. Practical ApplicationsThe mung bean sprout is a popular fresh vegetable in many Asian countries. We previously found that it had the highest antioxidant polyphenols among twelve cultivated edible bean sprouts, and this study further demonstrated that hot air drying was able to increase its antioxidant capacity and total phenolic conent compared to freeze-dried samples. Therefore, hot air dried mung bean sprout powders are good natural source of antioxidant polyphenols, and can be used as additives to fortify food antioxidant polyphenols or developed into novel functional foods with potential health benefits. This finding should be of interest to the public and experts in the field of food science and technology.