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Isocratic HPLC techniques were developed for the quantitative analysis of sugars in raw and baked sweet potato roots. The major sugars in raw roots: sucrose, glucose, and fructose, were quantitated with a cation exchange resin column (Aminex HPX-87C) heated to 75°C using HPLC-grade Hz0 as the mobile phase and refractive index detection. The major sugars in baked roots (convection oven or microwaved) were maltose, sucrose, glucose, and fructose. They were quantitated with an aminopropyl bonded phase column (BioSil Amino 5s) at 21°C using a 70% CHaCN:30% Hz0 mobile phase and refractive index detection. Over 95% recoveries of all sugars added to sweet potato roots were obtained.

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The quantity and pattern of carbohydrate-related changes during storage root development differed among six sweetpotato cultivars [Ipomoea batatas (L.) Poir. `Beauregard', `Heart-o-Gold', `Jewel', `Rojo Blanco', `Travis', and `White Star']. Measurements were taken for individual sugars, total sugars, alcohol-insoluble solids (AIS, crude starch), and dry weight (DW) at 2-week intervals from 7 to 19 weeks after transplanting (WAT) in two separate years. Sucrose was the major sugar during all stages of development, representing at least 68% of total sugars across all cultivars and dates. Pairwise comparisons showed `Heart-o-Gold' had the highest sucrose content among the cultivars. Sucrose content increased by 56% for `Heart-o-Gold' over the 12 weeks of assay, ranking first among the cultivars at 17 and 19 WAT and possessing 27% more sucrose than the next highest ranking cultivar, `Jewel', at 19 WAT. Fructose content profiles varied among and within cultivars. `Beauregard' showed a consistent increase in fructose throughout development while `Whitestar' showed a consistent decrease. The other cultivars were inconsistent in their fructose content profiles. Glucose content profiles were similar to those for fructose changes during development. The relationship between monosaccharides was fructose = 0.7207 × glucose + 0.0241. Cultivars with the highest fructose and glucose content could be selected by breeders after 13 WAT. Early clonal selection for high sucrose and total sugars is less promising because substantive changes in clonal rank occurred for sucrose and total sugars after 15 WAT. Cultivars ranking the highest in total sugars had either more monosaccharides to compensate for a lower sucrose content or more sucrose to compensate for a lower monosaccharide content. The relationship between DW and AIS was similar (AIS = 0.00089 × DW), and DW and AIS increased with time for most cultivars. Cultivars with high DW and AIS can be selected early during storage root development.

Summary Sweetpotato [Ipomoea batatas (L.) Lam.] cv. ‘Beauregard’ roots were cooked using three different heat‐processing techniques (baked in a conventional oven, baked in a microwave oven, and boiled). Total phenolic content, individual phenolic acids, and antioxidant capacity were determined using Folin‐Denis assay, HPLC (high‐performance liquid chromatography), and DPPH (1,1‐diphenyl‐2‐picrylhydazyl) assay, respectively. The skin tissue (raw or processed) contained the highest concentration of total phenolics. All heat‐processing methods resulted in a significant loss in total phenolic content and antioxidant capacity of the skin tissue. However, compared with the other processing methods, conventional oven baking resulted in greater losses in antioxidant capacity of skin tissue. Total phenolic content ranged from a low of 1.58 mg chlorogenic acid equivalent g−1 dry tissue weight in boiled pith tissue to a high of 17.7 mg chlorogenic acid equivalent g−1 dry tissue weight in raw skin tissue. The antioxidant capacity was highest in raw skin tissue (22.9 mg Trolox equivalent g−1 dry tissue weight). Chlorogenic acid was the principal phenolic acid found in all sweetpotato tissues. Caffeic acid and three isomers of dicaffeoylquinic acid (diCQA) were also identified and quantified.

Phenolic acids are one of the several classes of naturally occurring antioxidant compounds found in sweetpotatoes. Simplified, robust, and rapid methodologies were optimized to quantify total and individual phenolic acids in sweetpotato roots. Total phenolic acid content was quantified spectrophotometrically using both Folin-Denis and Folin-Ciocalteu reagents. The Folin-Ciocalteu reagent gave an overestimation of total phenolic acids due to the absorbance of interfering compounds (that is, reducing sugars and ascorbic acid). Individual phenolic acids were quantified by high-performance liquid chromatography (HPLC) using the latest in column technology. Four reversed-phase C18 analytical columns with different properties (dimensions, particle size, particle shape, pore size, and carbon load) were compared. Three different mobile phases using isocratic conditions were also evaluated. A column (4.6 x 150 mm) packed with 5-microm spherical silica particles of pore size 110 A combined with 14% carbon load provided the best and fast separation of individual phenolic acids (that is, chlorogenic acid, caffeic acid, and 3 isomers of dicaffeoylquinic acid) with a total analysis time of less than 7 min. Among the 3 mobile phases tested, a mobile phase consisting of 1% (v/v) formic acid aqueous solution: acetonitrile: 2-propanol, pH 2.5 (70:22:8, v/v/v) gave adequate separation. Among the solvents tested, aqueous mixtures (80:20, solvent:water) of methanol and ethanol provided higher phenolic acid extraction efficiency than the aqueous mixture of acetone.

Crude protein and mineral content in six sweet potato cultivars and total carotenoids in four orange-flesh cultivars after different storage treatments were determined. On a fresh weight basis, crude protein between cultivars ranged from 1.362.13 g/lOOg, phosphorus from 38-64 mg/lOOg, potassium from 245-403 mg/lOOg, calcium from 20-41 mg/lOOg, magnesium from 13-22 mg/lOOg and total carotenoids from 5-l 1 S mg/lOOg. Carotenoids slightly increased after curing and short term storage at either 7", 15.6", or 26.6"C. Centennial contained the most protein, phosphorus, magnesium, and carotenoids of all cultivars. Travis contained the lowest amount of protein, phosphorus and potassium, but more carotenoids than Jewel or Jasper.

Sugar concentrations in baked roots of six different sweet potato (fpomoea batatas (L.) Lam.) cultivars were determined at harvest, after curing (32"C, 90% RH for 10 days), and during 46 wk of storage at 15.6"C. Maltose was the major sugar and sucrose the secondary sugar in all cultivars at harvest. Maltose decreased during curing and over long term storage. Sucrose, glucose, and fructose concentrations increased during curing and through at least 4 wk of storage in the orange-flesh cultivars. Sucrose concentration was always greater than either monosaccharide. Cultivars differed in sugar concentration and pattern of sugar change during storage.