Abstract
Tubers of yacon (Polymnia sonchifolia or P. edulis), a crop native to the Andean Highlands, contain a large amount of oligofructans. We investigated fluctuation of fructose, glucose, sucrose and oligofructan (GF_2-GF_9) contents during growth and storage by using an HPLC. The average degree of polymerization (DP) of these sugars in the tubers increased during growth. The DP reached to 4.3 at harvest, and decreased again during storage. Glucose, sucrose and GF_2 decreased, whereas the oligofructans larger than GF_4 increased during growth. At harvest, total oligofructan content reached to 67% of dry matter, and the ratio of GF_2-GF_5 accounted for about 70% in the total sugars. Inulin and starch contents in the tubers were only less than 0.23% and 0.04% of dry matter, respectively. The tubers were stored in 3 ways : a soil pit in field, at 5℃ and 25℃. After 2 weeks, total oligofructan content decreased 21% in the soil pit, 33% at 5℃ storage and 41% at 25℃ storage. Oligofructan contents decreased gradually and fructose, glucose and sucrose contents increased during each storage. To efficiently obtain oligofructans from yacon tubers, it will be necessary to prepare them from the tubers just after harvest. For eating yacon tubers, it will be suitable to store them for several weeks.
