Cereal Chem. 76(5):629-637Structures and properties of starches isolated from different botanical sources were investigated. Apparent and absolute amylose contents of starches were determined by measuring the iodine affinity of defatted whole starch and of fractionated and purified amylopectin. Branch chainlength distributions of amylopectins were analyzed quantitatively using a high-performance anion-exchange chromatography system equipped with a postcolumn enzyme reactor and a pulsed amperometric detector. Thermal and pasting properties were measured using differential scanning calorimetry and a rapid viscoanalyzer, respectively. Absolute amylose contents of most of the starches studied were lower than their apparent amylose contents. This difference correlated with the number of very long branch chains of amylopectin. Studies of amylopectin structures showed that each starch had a distinct branch chain-length distribution profile. Average degrees of polymerization (dp) of amylopectin branch chain length ranged from 18.8 for waxy rice to 30.7 for high-amylose maize VII. Compared with X-ray A-type starches, B-type starches had longer chains. A shoulder of dp 18-21 (chain length of 6.3-7.4 nm) was found in many starches; the chain length of 6.3-7.4 nm was in the proximity of the length of the amylopectin crystalline region. Starches with short average amylopectin branch chain lengths (e.g., waxy rice and sweet rice starch), with large proportions of short branch chains (dp 11-16) relative to the shoulder of dp 18-21 (e.g., wheat and barley starch), and with high starch phosphate monoester content (e.g., potato starch) displayed low gelatinization temperatures. Amylose contents and amylopectin branch chain-length distributions predominantly affected the pasting properties of starch. MATERIALS AND METHODS MaterialsChinese taro, mung bean, waxy rice, sweet rice, green leaf canna, lotus root, water chestnut, and cattail millet starches were isolated in the laboratory as reported by Lim et al (1994). Waxy amaranth I was isolated by the alkaline method (Myers and Fox 1994). Waxy amaranth II and normal glacier barley starch were isolated by a combination of mild alkaline and protease treatments (Radosavljevic et al 1998). Green banana starch was provided by A. R. Bonilla, University of Costa Rica. Waxy maize, amyloseextender (ae) waxy and dull (du) waxy maize starches were gifts of Cerestar, USA (Hammond, IN); potato and wheat starches were purchased from Sigma Chemical Co. (St. Louis, MO);

Ongoing research to develop digestion-resistant starch for human health promotion integrates the disciplines of starch chemistry, agronomy, analytical chemistry, food science, nutrition, pathology, and microbiology. The objectives of this research include identifying components of starch structure that confer digestion resistance, developing novel plants and starches, and modifying foods to incorporate these starches. Furthermore, recent and ongoing studies address the impact of digestion-resistant starches on the prevention and control of chronic human diseases, including diabetes, colon cancer, and obesity. This review provides a transdisciplinary overview of this field, including a description of types of resistant starches; factors in plants that affect digestion resistance; methods for starch analysis; challenges in developing food products with resistant starches; mammalian intestinal and gut bacterial metabolism; potential effects on gut microbiota; and impacts and mechanisms for the prevention and control of colon cancer, diabetes, and obesity. Although this has been an active area of research and considerable progress has been made, many questions regarding how to best use digestion-resistant starches in human diets for disease prevention must be answered before the full potential of resistant starches can be realized.

Starch synthase IIIa (SSIIIa)-deficient rice (Oryza sativa) mutants were generated using retrotransposon insertion and chemical mutagenesis. The lowest migrating SS activity bands on glycogen-containing native polyacrylamide gel, which were identified to be those for SSIIIa, were completely absent in these mutants, indicating that they are SSIIIa null mutants. The amylopectin B 2 to B 4 chains with degree of polymerization (DP) $ 30 and the M r of amylopectin in the mutant were reduced to about 60% and 70% of the wild-type values, respectively, suggesting that SSIIIa plays an important part in the elongation of amylopectin B 2 to B 4 chains. Chains with DP 6 to 9 and DP 16 to 19 decreased while chains with DP 10 to 15 and DP 20 to 25 increased in the mutants amylopectin. These changes in the SSIIIa mutants are almost opposite images of those of SSI-deficient rice mutant and were caused by 1.3-to 1.7-fold increase of the amount of SSI in the mutants endosperm. Furthermore, the amylose content and the extralong chains (DP $ 500) of amylopectin were increased by 1.3-and 12-fold, respectively. These changes in the composition in the mutants starch were caused by 1.4-to 1.7-fold increase in amounts of granules-bound starch synthase (GBSSI). The starch granules of the mutants were smaller with round shape, and were less crystalline. Thus, deficiency in SSIIIa, the second major SS isozyme in developing rice endosperm affected the structure of amylopectin, amylase content, and physicochemical properties of starch granules in two ways: directly by the SSIIIa deficiency itself and indirectly by the enhancement of both SSI and GBSSI gene transcripts.

Scanning electron micrographs of the granules of 54 starches obtained from a wide variety of plant sources, consisting of roots and tubers, grains, maize, peas and beans, fruits and nuts, and small granule starches, are presented as a comparative study of their sizes and morphologies. All micrographs are presented at a magnification of 1500X with the addition of micrographs of 600X for the very large granules and micrographs of 10,000X for the very small granules.

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Twelve pumpkin cultivars (Cucurbita maxima D.), cultivated in Iowa, were studied for their seed oil content, fatty acid composition, and tocopherol content. Oil content ranged from 10.9 to 30.9%. Total unsaturated fatty acid content ranged from 73.1 to 80.5%. The predominant fatty acids present were linoleic, oleic, palmitic, and stearic. Significant differences were observed among the cultivars for stearic, oleic, linoleic, and gadoleic acid content of oil. Low linolenic acid levels were observed (<1%). The tocopherol content of the oils ranged from 27.1 to 75.1 μg/g of oil for α-tocopherol, from 74.9 to 492.8 μg/g for γ-tocopherol, and from 35.3 to 1109.7 μg/g for δ-tocopherol. The study showed potential for pumpkin seed oil from all 12 cultivars to have high oxidative stability that would be suitable for food and industrial applications, as well as high unsaturation and tocopherol content that could potentially improve the nutrition of human diets. Keywords: Pumpkin seed oil; pumpkin seed; oilseed; winter squash; Cucurbitaceae; fatty acid; tocopherol

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