Retention of glucosinolates during fermentation of Brassica juncea: a case study on production of sayur asin

Abstract

Fermentation can reduce the concentration of health-promoting glucosinolates in Brassica vegetables. The endogenous enzyme myrosinase is hypothesised to mainly responsible for the degradation of glucosinolates during fermentation. In order to retain glucosinolates in the final fermented product, the role of myrosinase activity during the production of sayur asin was investigated. Sayur asin is a traditionally fermented product of Indian mustard (Brassica juncea) commonly consumed in Indonesia. It is prepared by a spontaneous fermentation of withered (sun-dried) B. juncea leaves. The leaves of B. juncea contain a substantial amount of the aliphatic glucosinolate sinigrin. Three withering methods were investigated to obtain B. juncea leaves with different myrosinase activities prior to fermentation. Results show that withering by oven at 35 °C for 2.5 h and by microwave at 180 W for 4.5 min reduced myrosinase activity by 84 and 74 %, respectively. Subsequently, sinigrin was not detectable in the leaves after 24 h of incubation in the fermentation medium. However, withering by microwave for 2 min at 900 W inactivated myrosinase completely and produced sayur asin with a sinigrin concentration of 11.4 µmol/10 g dry matter after 7 days of fermentation. This high power-short time pretreatment of B. juncea leaves contributes to the production of sayur asin containing significant levels of health-promoting glucosinolate. In this study, the effect of myrosinase activity during Brassica fermentation was quantified, and optimised production methods were investigated to retain glucosinolate in the final product.