THE OCCURRENCE AND DISTRIBUTION OF FREE ALKALOID SOLANIDINE IN NETTED GEM POTATOES

Abstract

Free alkaloid solanidine was detected in concentrations up to 200 p.p.m. or 33% of the total glycoalkaloid level in bitter Netted Gem potatoes. Dormant tubers of this variety are readily induced to a rapid glycoalkaloid synthesis by exposure to intense solar radiation and near-freezing temperatures, conditions frequently encountered during the potato harvest in northern areas. Under such conditions solanidine is rapidly produced in excess of amounts that could be bound as solanine, the formation of which would likely be limited by the availability of the glycosidic sugar components. The glycosidic binding of the initially synthesized solanidine proceeds at a very slow rate during the subsequent tuber rest period. Distribution studies revealed that the potato peels, representing about one seventh of the whole tuber weight, contained solanine and solanidine, respectively, at concentrations 2.5 and 6.2 times higher than the remaining tuber tissue, or approximately 30% of the total glycoalkaloid amount.The occurrence of the free alkaloid solanidine at certain times in potato tubers of the Netted Gem variety demands a serious reconsideration of any toxicity studies which have been based on the sole use of crystalline solanine, and which have disregarded the possible existence of the free alkaloid in tuber tissues.