Effects of Hot Air Drying on the Nutritional and Phytochemical Composition of Radish (Raphanus sativus L.) Microgreens

ABSTRACT: Cruciferous microgreens are recognized for their high content of phytochemicals, particularly glucosinolates. Their high moisture content and water activity make them highly perishable after harvest and highlight the need for effective preservation methods that maintain their nutritional quality. This study evaluated the impact of hot air drying at 45°C, 65°C, or 95°C compared to freeze-drying on the content and bioaccessibility of nutrients and phytochemicals in radish microgreens. Total phenolic content (TPC) and glucoraphenin (GE) exhibited opposite responses to heat: TPC decreased at 45°C (by 9%) and 65°C (21%), but did not change at 95°C, whereas GE decreased only at 95°C (by 21%). Vitamins B₁ and B₉ were stable across drying treatments, whereas vitamins B₂, B₃, and C were reduced by up to 35%, 36%, and 63%, respectively, with the exposure to the three temperatures. The in vitro bioaccessibility of TPC and vitamins B₁, B₃, B₉, and C ranged from 13% to 68% and did not differ between drying treatments. The bioaccessibility of vitamin B₂ was higher in samples dried at 65°C compared to the other treatments. GE and monomeric anthocyanin content (MAC) could not be quantified following in vitro digestion. The overall metabolomes of the samples were compared by liquid chromatography–mass spectrometry. Partial least squares-discriminant analysis (PLS-DA) showed separation by drying treatment, with glucosinolates and flavonoids driving the separation. Overall, this research indicates that hot air drying represents an effective approach for postharvest nutrient preservation in radish microgreens and may facilitate the use of radish microgreen powder in formulated foods.