Ultrasounds and a Postharvest Photoperiod to Enhance the Synthesis of Sulforaphane and Antioxidants in Rocket Sprouts

Abstract

Ultrasounds (US) and LED illumination are being studied to optimize yield and quality. Evaluate the effect of a pre-sowing US treatment combined with a postharvest photoperiod including LEDs on rocket sprouts’ quality and phytochemicals during shelf life. A US treatment (35 kHz; 30 min) applied to seeds and a postharvest photoperiod of 14 h fluorescent light (FL) + 10 h White (W), Blue (B), Red (R) LEDs or Darkness (D) were assayed. Antioxidants as phenolics and sulfur compounds (glucosinolates and isothiocyanates) were periodically monitored over 14 days at 5 °C. The US treatment increased the sulforaphane content by ~4-fold compared to CTRL seeds and sprouts. The phenolic acids and the flavonoid biosynthesis were enhanced by ~25%, ~30%, and ~55% under photoperiods with W, B, and R, respectively, compared to darkness. The total glucosinolate content was increased by >25% (W) and >45% (B and R) compared to darkness, which also reported increases of ~2.7-fold (W), ~3.6-fold (B), and ~8-fold (R) of the sulforaphane content as a main isothiocyanate. Postharvest lighting is an interesting tool to stimulate the secondary metabolism, while a US treatment was able to increase the sulforaphane content in seeds and sprouts, although no synergistic effect was reported.

Effect of Ultrasound and High Hydrostatic Pressure Processing on Quality and Bioactive Compounds during the Shelf Life of a Broccoli and Carrot By-Products Beverage

“…For the determination of glucosinolates, myrosinase inactivation, desulfated step, purification, identification, and quantification were carried out in triplicate according to Martínez-Zamora et al [37] based on the method previously described by Kiddle et al [38]. The glucosinolate content (ds-glucoraphanin, ds-4-methoxy-glucobrassicin, and ds-neoglucobrassicin) was expressed as mg per L of sample, and glucoraphanin (Phy-toLab GmbH & Co. KG, Vestenbergsgreuth, Germany) was used as standard.…”

“…Each sample was analyzed in triplicate. A UPLC instrument (Shimadzu, Kyoto, Japan) equipped with a C18 column, DGU-20A degasser, LC-30AD quaternary pump, SIL-30AC autosampler, CTO-10AS column heater, and SPDM-20A photodiode array detector was used as previously described [37] for both analysis.…”