Abstract
Sulforaphane (SFN) is a health-promoting compound occurring in broccoli. It is formed by action of myrosinase in a two-step reaction that also yields undesirable compounds such as nitriles and isothionitriles. Different techniques affecting enzyme activity and tissue integrity were proposed to increase SFN content in the edible parts and discards of broccoli. Ultrasound processing is an emerging technology that produces these effects in foods, but has been poorly explored in broccoli so far. The aim of this work was to study the effect of ultrasound-assisted blanching on myrosinase activity and SFN content in broccoli florets. Myrosinase showed first-order inactivation kinetics in blanching at different temperatures with and without ultrasound processing. The inactivation rate was faster using ultrasound, with kinetic constants two orders of magnitude higher than without ultrasound. The activation energy (Ea) in traditional blanching (57.3 kJ mol−1) was higher than in ultrasound-assisted blanching (15.8 kJ mol−1). Accordingly, ultrasound accelerates myrosinase inactivation. The blanching time and temperature significantly affected myrosinase activity and SFN content. At 60 °C and 4 min of ultrasound-assisted blanching, myrosinase activity was minimum and SFN content was the highest. These findings may help to design SFN enrichment processes and will contribute to the valorization of agro-industrial wastes.
Highlights
Sulforaphane (SFN) is an isothiocyanate widely recognized as a powerful anti-cancer and health-promoting compound [1]
The effect of time and temperature in ultrasound-assisted blanching on myrosinase activity and SFN content was studied through a multilevel factorial design
Significant differences appeared on myrosinase activity and sulforaphane content
Summary
Sulforaphane (SFN) is an isothiocyanate widely recognized as a powerful anti-cancer and health-promoting compound [1]. It occurs in cruciferous vegetables, mainly in broccoli. The conversion occurs through a two-step mechanism: hydrolysis of glucoraphanin by the action of myrosinase with the formation of an unstable intermediate (thiohydroxamate-O-sulfonate) and the release of an equimolar amount of glucose, followed by the spontaneous conversion of thiohydroxamate-O-sulfonate into sulforaphane or sulforaphane nitrile, depending on the chemical conditions. Acid pH together with the action of epithiospecifier protein (ESP) favor formation of sulforaphane nitrile, which is an undesirable product due to its potential toxicity. The hydrolysis final product is sulforaphane at neutral pH, and sulforaphane nitrile at acid pH together with the action of epithiospecifier protein [3]
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