The Enzymatic Properties and Processing Stability of Myrosinase from Maca(Lepidium meyenii Walp.)
After extraction,dialysis and gel filtration chromatography,the myrosinase in fresh maca tubers was purified.The enzymatic properties,kinetic parameters of myrosinase were studied.Moreover,the effect of drying on the myrosinase activity and benzyl isothiocyanate(BITC)content of maca was investigated.The molecular weight of purified myrosinase was 190.9 ku determined by gel permeation chromatography(GPC).The results of enzymatic properties showed that the optimum temperature of myrosinase was 40 ℃,and the optimum pH value was 7.0.The metal ions Fe3+,Cu2+,Al3+,Mg2+,Zn2+,Ba2+had significant inhibitory effects on the myrosinase.The kinetic parameters Vmax=0.2383(μmol/L)/min,and Km=0.1425 mmol/L were determined by the method of Lineweaver-Burk.The myrosinase activity and BITC content of fresh maca were 0.7256 U/g and 3.3190 mg/g,respectively.The fresh maca samples were sliced and dried at the temper-ature of 50,60,70 ℃,and 80℃,respectively.As the drying temperature increased,the myrosinase activity in the maca sample significantly decreased,and the BITC content showed a decreasing trend.This study has improved the the-oretical study of the myrosinase from maca.It is proposed that drying maca at temperatures above 60 ℃ can effectively inhibit the myrosinase activity.These results may provide guidance for the processing and utilization of maca.
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