Modified HPLC Detemination of Sugars in Sweet Potato

The tropical-type of sweet potato is the type commonly grown and consumed throughout the Antilles of the Caribbean Basin. Tropical-type describes varieties that exhibit either white, cream or light yellow-fleshed roots and are intermediate in sweetness. There is interest for the establishment of a quantitative basis for the selection of genotypes by sweetness. However, information on sugar concentrations for the tropical-type sweet potato is limited. Our research group has experienced difficulties in the quantification of glucose and fructose when using a previously developed HPLC technique. This technique was modified for the quantification of glucose, fructose, sucrose, and maltose in tropical-type varieties. Raw, boiled and microwaved roots were dried, then ground. Extractions were done with 80% ethanol. Glucose and fructose determinations were made with a cation exchange resin column (SugarPak I, Waters Corp.) and a mobile phase of CaEDTA and water. Sucrose and maltose were determined by using an amine-bonded silica column (Supelcosil LC-NH2, Sulpelco Corp.). For the latter determinations, the mobile phase was a solution of acetonitrile and water. Determinations were completed with a refractive index detector coupled to the HPLC system. Percentage of recovery of sugars depended on the variety. In raw samples, concentration of sucrose was higher than that of glucose and fructose, whereas maltose was not detected. After boiling or microwaving, maltose concentration increased dramatically and ranged from 11 to 18%.