Determination of the soluble dietary fiber fraction in yacon (Smallanthus sonchifolius) root and flour by enzymatic-gravimetric method and high pressure liquid chromatography

Abstract

This study aimed at determining the total dietary fiber contents in yacon root pulp (YRP) and yacon flour(YF) by the AOAC enzymatic-gravimetric method, and fructans by high performance liquid chromatography(HPLC). The YF was put through the process of cleaning, sanitizing, bleaching, and YRP was dried at 55 °Cfor 48 hours. The chemical composition of the YF and YRP was determined, being the total fiber contentsthe sum of the determinations by enzymatic-gravimetric method and HPLC. High contents of total dietaryfiber were detected in the dry mater of both YRP and YF samples (33.14 and 50.76%, respectively), beingmostly fructooligosaccharides [FOS] (37.97 and 40.97%, respectively), and substantial inulin contents (26.10and 20.75%, respectively). The chromatogram also showed high contents of fructose, glucose and sucroseas the sole source of carbohydrates besides fructans, inulin and FOS. The enzymatic-gravimetric methodsare considered the most suitable for routine analysis of dietary fibers, but are ineffective for determiningoligosaccharides with polymerization degree less than 12, as yacon. Thus, a complementary method, suchas HPLC, needs to be carried out to quantify the exacting dietary fiber contents in this root.