Effects of ultrasonication on germination and bioactive content of red rambo radish microgreens (Raphanus sativus)

Abstract

Radish microgreens are a high-value commodity due in part to their rapid growth and nutrientdensity. Ultrasonication, the application of sound waves, has been shown to improve the germination rates, but it is not clear how it impacts nutritional quality. The aim of this study was to evaluate the effects of ultrasonication (0, 3, 6, 9, 12, 15 min, 20 kHz) on germination and bioactive content (carotenoids and polyphenols) in Red Rambo radish microgreens. The effects of ultrasonication on Red Rambo radish microgreens were assessed pre-harvest by treating seeds prior to germination and post-harvest by treating the microgreen plant. The percent of seeds that germinated was recorded every eight hours over a 128-hour period. Bioactive compounds were extracted with 0.1% BHT in hexane and acetone. Carotenoids were quantified using high- performance liquid chromatography equipped with a diode array detector and a spectrophotometric method. The total polyphenolic and anthocyanin compounds were quantified through the Folin-Ciocalteu method and pH differential method, respectively. Results showed a significant increase (P < 0.05) of germination percentage in the ultrasonicated samples compared to the control group. Differences were not observed (P > 0.05) in the carotenoid profile for radish microgreens treated pre-harvest and post-harvest. Ultrasonication did not have a significant impact (P > 0.05) on the total monomeric anthocyanin content for microgreens for both pre- and post-harvest treatments. Ultrasonication can potentially stimulate the production of secondary metabolites and induce oxidative stress but has not been shown to be stimulated in Red Rambo radish microgreens. Overall, findings indicate that ultrasonication improves germination and but not health promoting compounds of Red Rambo radish microgreens. Conducting research in this area can potentially add value to existing crops and improve growth efficiency. This exploration can expand to include various types of microgreens and their mature counterparts.