Glucosinolate content and myrosinase activity evolution in three maca (Lepidium meyenii Walp.) ecotypes during preharvest, harvest and postharvest drying

Glucosinolate profiles, glucosinolate contents and myrosinase activity were evaluated in yellow, red and black hypocotyls of maca during pre-harvest, at harvest and during post-harvest drying. At harvest, six glucosinolates (GLs) were identified: 5-methylsulfinylpentyl, 4-hydroxybenzyl, benzyl, 3-methoxybenzyl, 4-hydroxy-3-indolylmethyl and 4-methoxy-3-indolylmethyl, of which benzyl glucosinolate was the most abundant in the three ecotypes, representing 80% of the total GLs. A significant increase in GLs was observed for the three ecotypes during the 90 days before harvest and during the 15–30 days of post-harvest drying. This was followed by an important decrease of GLs during the 30–45 day period, which was attributed to cell breakdown, due to fluctuations in temperatures during the drying process, and was correlated with a high myrosinase action. During the last period of post-harvest drying, GLs were much lower and correlated to lower myrosinase activity and lower maca hypocotyl humidity. A combination of artisanal and other processing techniques should be utilised, in order to best preserve maca glucosinolates.

Research highlights
► Glucosinolate (GL) profiles, contents and myrosinase activity are presented.
► Six different GLs that increased during 90 days before harvest were identified.
► During post-harvest drying, a significant increase in GLs was observed.
► Total GLs losses of 20–52% were observed during post-harvest drying.
► Traditional post-harvest drying should be revised to obtain higher GL content.