Supplementation Of Cooked Broccoli By Exogenous Myrosinase To Enhance Formation Of Isothiocyanates

Broccoli and brassica vegetables have health benefits such as anti-cancer activity,which are attributed to isothiocyanates(ITC),a product of glucosinolate hydrolysis.Temperature,p H,metal ions and other compounds have been reported to affect enzyme activity.They can either improve the functionality of enzymes or inhibit enzyme activity.In this paper,the effect of cooking time and addition of exogenous myrosinase(MYR)from moringa seeds on the yield of ITC was studied.We also looked at how temperature,p H and metal ions affect myrosinase activity as it plays a major role in the conversion of glucosinolates to sulforaphane.The results showed that raw broccoli produced a significantly high ITC production,which decreased by almost 40%after being microwaved for 1 min.Introducing exogenous MYR by adding ground moringa seeds to cooked broccoli caused a notable increase of 38%.At p H 4.0-6.0,MYR showed an optimal activity,and the thermal stability of MYR from moringa was better than that from broccoli.The kinetic study showed that the K_mvalue of Moringa MYR was 0.454.After assessing the effect of five metal ions on the activity of myrosinase by measuring glucose and sulforaphane yield,we observed that Zn²⁺improved the functionality of the enzyme myrosinase hence it could be its cofactor.Ascorbic acid,a non-metal ion,significantly improved the yield of both glucose and ITCs.The other metal ions(K⁺,Fe²⁺,Fe³⁺and Na⁺)lowered the yield of both glucose and sulforaphane.The effect of EDTA on myrosinase activity was also assessed and we noticed that the yield of both sulforaphane and glucose was slightly lowered at high concentrations of EDTA,meaning that moringa may contain very low concentrations of metal ions.This study was novel in reporting that adding ground moringa seeds to cooked broccoli enhanced ITC formation.