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

Abstract

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 24 h 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 Applications The 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.

Sprouts and Microgreens: Trends, Opportunities, and Horizons for Novel Research

“…In alfalfa and flax sprouts, freeze-drying minimized the chemical alteration of the product, resulting in a better preservation of antioxidants and an increase in phytosterol availability [173]. Conversely, air drying at 70 and 80 • C for 24 h, as opposed to freeze drying (below −50 • C and 0.3 mbar vacuum pressure, 36 h), increased total phenolic content and antioxidant capacity of mung bean sprouts [174]. Pan-roasting of cereal (barley, wheat) sprouts was shown a promising heat processing for tea production, based on higher total phenolics and flavonoid contents and antioxidative effects in-vitro compared to a steaming process [169].…”

Variability of phenolic and alkaloid content in different plant parts of Carissa edulis Vahl and Zanthoxylum chalybeum Engl.

“…The effect of thermal exposure on bioactive compounds has been investigated in a number of plant species and most of these have indicated a degradation of alkaloids on exposure to heat and an enhancement of phenols [ 15 , 18 , 42 – 44 ]. Enhancement of phenolic compounds has been associated with thermal destruction of cell walls and subcellular compartments that results in increased levels of free phenolic compounds, the formation of novel compounds or the inactivation of deteriorative enzymes such as polyphenol oxidases [ 15 ].…”

Effect of oven drying on antioxidant activity, phenolic compounds, fatty acid composition and tocopherol contents of pomegranate aril and oils

“…However, the increase appeared to be concentrated the antioxidants during drying. Similarly, Gan, Lui, Chan, and Corke () observed that hot air‐drying incresaed the phenolic content and antioxidant capacity of mung bean sprouts. In general, there was an important reduction in total phenolic content of both varieties, except the samples dried for 10 hr, when fruits were dried.…”