Changes of linamarase, alpha-hydroxynitrile lyase and peroxidase isozymes during postharvest deterioration of cassava tubers
1998
Thakorn Sornwatana | Montri Chulavatnatol (Mahidol Univ., Bangkok (Thailand). Faculty of Science. Dept. of Biochemistry)
Linamarase and alpha-hydroxynitrile lyase are enzymes involved in cyanogenesis which is responsible for cyanide toxicity associated with the consumption of cassava (Manihot esculenta Crantz). Linamarase hydrolyzes linamarin into acetone cyanohydrin and glucose and alpha-hydroxynitrile lyase catalyses the dissociation of acetone cyanohydrin into acetone and toxic hydrogen cyanide. Previous studies have shown that peroxidase increases during post-harvest in cassava tubers deterioration. After a prolonged storage at room temperature for 7 days, activity of peroxidase increases 2 times in the cortex and 5 times in the parenchyma. However, linamarase and alpha-hydroxynitrile lyase activities decrease in both the cortex and the parenchyma. In this paper, the cassava peroxidase was extracted from cassava roots using 0.1 M imidazole pH 6 containing 10 percent glycerol. Using non-denaturation gel electrophoresis, cassava peroxidase was separated into 3 groups; positively charged, negatively charged and neutral groups. During postharvest, roots after storage for 7 days showed increases in the positively charged peroxidase of both the cortex and the parenchyma. In contrast, the negatively charged and neutral peroxidases of both the cortex and the parenchyma decreased. The changes may reflect the role of isoperoxidases in the deterioration of cassava roots during post-harvest.
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