Three high-amylose rice varieties, IR42, IR36, and IR62, with similar chemical composition including amylose content (26.7-27.0%), were cooked under the same conditions and tested for in vitro digestibility as well as blood glucose and insulin responses in healthy human volunteers. The starch-digestion rate and the glycemic and insulin responses were the highest in IR42, followed by IR36 and, then IR62. The differences were not due to unabsorbed carbohydrate but were related to their physicochemical properties, such as gelatinization temperature, minimum cooking time, amylograph consistency, and volume expansion upon cooking. When the three varieties were cooked for their minimum cooking time, they had the same degree of gelatinization and their starch-digestion rates and glycemic responses were similar. We conclude that amylose content alone is not a good predictor of starch-digestion rate or glycemic response. Rice varieties with similar high-amylose contents can differ in physicochemical (gelatinization) properties and this, in turn, can influence starch digestibility and blood glucose response.

No abstract

A new histochemical method for detecting glucosinolates in rapeseed (Brassica napus L. ’Midas’) methanolic extracts and rapeseed (Brassica campestris L. ’Candle’) hand-cut sections has been developed using N,2,6-trichloro-p-benzoquinoneimine (TCQ) as the staining reagent. The specificity of TCQ was established by the following experiments. (1) TCQ was used as a spray reagent for detecting thio sugars separated from (a) crude and (b) partially purified rapeseed extracts on silica gel coated chromatograms. By comparison, the reaction of TCQ was relatively more selective than that of alkaline silver nitrate as it detected fewer spots on the chromatogram. (2) Rapeseed extracts and glucosinolate (GS) standards were analyzed on the same plate by one- and two-dimensional chromatography. After spraying with TCQ two of the three spots originated from the extract had the same color (yellow) reaction and similar Rf values as those of 3-butenyl GS and 2-hydroxy-3-butenyl GS. (3) Gas chromatography was used to identify the TCQ-reactive compounds present in the rapeseed extract. 3-butenyl GS and 2-hydroxy-3-butenyl GS were present as major constituents while 4-pentenyl GS, 2-hydroxy-4-pentenyl GS and an hydroxyindolylmethyl GS formed the minor entity. The use of TCQ for detecting glucosinolates in situ was established by the following microscopic studies. Hand-cut sections were prepared, stained with TCQ and examined microscopically. Protein bodies found inside cells of the cotyledon were the only stained (yellow in color) structures. The number of yellow-colored protein bodies decreased if the sections were left untreated at room temperature for more than 10 min prior to staining. Treatment of the sections with distilled water, 70% methanol or myrosinase before staining diminished the stainability of the protein bodies.Key words: Rapeseed structure, glucosinolates, chromatographic analyses, N,2,6-trichloro-p-benzoquinoneimine