Changes in neutral and malonyl ginsenosides in American ginseng (Panax quinquefolium) during drying, storage and ethanolic extraction

摘要

Changes in the neutral and malonyl ginsenosides of American ginseng roots (Panax quinquefolium) were examined during drying, storage and extraction. Freshly harvested roots dried at 40, 55 or 70℃ in a hot air drier showed a marked decrease in the time taken to dry as the air temperature increased but the colour of roots dried at 70℃ was darker than the desired cream colour. Increasing the drying temperature decreased the concentration of total ginsenosides but with an increase in the neutral ginsenosides and a decrease in malonyl ginsenosides. Dried root powder, stored at 5, 20 and 30℃ in air of low humidity, showed a decrease in the concentration of total ginsenosides at all temperatures with the rate of loss increasing at higher temperatures. The concentration of malonyl ginsenosides showed the same trend but the concentration of neutral ginsenosides did not significantly change during storage at any temperature. Extraction of ginsenosides, from dried root powder with aqueous ethanol, varied with the ethanol content. Maximum extraction of neutral ginsenosides was obtained with 70% ethanol while, for malonyl ginsenosides, it was 40% ethanol and 60% ethanol for total ginsenosides. The ratio of neutral to malonyl ginsenosides in the extract increased as the proportion of ethanol in the solvent increased. The findings show that the relative proportions of neutral and malonyl ginsenosides vary considerably during postharvest handling and reinforce the need to measure both types to obtain the true level of total ginsenosides.