Cereal Chem. 73 (5):588-592  |  VIEW ARTICLE

Nutrition

Effects of Heat Treatment of Barley Starches on In Vitro Digestibility and Glucose Responses in Rats (1).

Q. Xue (2), R. K. Newman (3), and C. W. Newman (4). (1) Contribution J-3080, Montana Agricultural Experiment Station. Partial funding for this research was supplied by the Montana Wheat and Barley Committee, Great Falls. (2) Metabolism and Nutrient Interactions Laboratory, Beltsville Human Nutrition Research Center, USDA-ARS, Beltsville, MD 20705. (3) Department of Plant, Soil, and Environmental Sciences, Montana State University, Bozeman, MT 59717-0312. Corresponding author. Fax: 406/994-3933. (4) Montana Agricultural Experiment Station, Montana State University, Bozeman, MT 59717-0312. Accepted June 27, 1996. Copyright 1996 by the American Association of Cereal Chemists, Inc. 

Starches were purified from barley flours milled from Waxbar, Glacier, high-amylose Glacier (HAG) and hull-less high-amylose Glacier (HHAG) cultivars. Wheat starch, maize amylopectin, maize amylose, and normal maize starch were used for comparative controls. Starches were either boiled or moisture-autoclaved (3 or 12 times) with subsequent cooling overnight, after which enzyme-resistant starch (ERS) was measured. In vitro digestibility and hydrolysis rates over time were determined. Postprandial glucose responses in rats were investigated with starches from Waxbar, Glacier, HAG, and wheat. Production of ERS varied from 0.6% in waxy starches to 18.6% in the high-amylose barleys, compared to 44.2% in maize amylose starch. Boiling of starches produced only marginal effects on digestibility and hydrolysis rates, and no effects on blood glucose levels in rats. Autoclaving, however, produced significant differences in digestibility and blood glucose responses between starch types. Digestibility of waxy starches was not changed in vitro (P > 0.05), but blood glucose in rats was increased (P < 0.05) after ingestion of autoclaved Waxbar barley starch. In contrast, digestibilities of HAG and HHAG starches were reduced by 14 and 20% (P < 0.001) after 3 and 12 autoclaving-cooling cycles. Autoclaved HAG starch significantly lowered glucose peaks in rats compared to Waxbar and Glacier starches at 30 min (P < 0.01). The in vivo results corresponded to the in vitro study, which demonstrated that digestibilities of different cereal starches followed the pattern: waxy > normal > high-amylose starches after heat-moisture autoclaving, possibly due to the formation of ERS from the amylose component.