oa South African Journal of Clinical Nutrition - The effect of extrusion processing on the glycaemic index of dry bean products

Volume 18, Issue 3
  • ISSN : 1607-0658
  • E-ISSN: 2221-1268



Both wheat pasta and dry beans have low glycaemic indices (GIs). However, it has been shown that several factors, including method of processing, may influence the GI of a food. Extrusion of dry beans is a relatively new dry cooking process and provides a convenient alternative to the ingestion of dry beans.

To determine the GI of pasta and muffins made from extruded dry-bean flour.
Ten healthy male and 10 healthy female students participated in this study. The subjects resided in the Metabolic Unit of North-West University during the period of testing. Subjects randomly consumed test meals of glucose (reference), bean muffins, whole-wheat muffins and pasta (men only) on different days. The Englyst method was used to determine the 50 g glycaemic carbohydrate portion. Fasting capillary blood samples were taken, the test foods were administered, and further capillary samples were taken at 15, 30, 45, 60, 90 and 120 minutes after the subjects had started to ingest the test meals. The area under the glycaemic response curve for each test and subject was calculated where the GI is based on the area under the blood glucose response curve above the baseline value only.
The GI of the muffin baked with extruded dry-bean flour (mean 53, 95% confidence interval (CI) 42 - 64) was not significantly different from that of the whole-wheat muffin (mean 55, 95% CI 42 - 69). The mean GI of the extruded dry-bean pasta was 83 (95% CI 58 - 108). Both the extruded dry-bean muffins and the whole-wheat muffins fell in the top border of the low-GI category, while the GI of the extruded dry-bean pasta fell within the high-GI category.
Several factors may have contributed to the high GI of the dry-bean pasta. The composition of the pasta and the extrusion process (which seems to alter particle size, antinutrient activity and resistant starch content), are most likely to have influenced the GI of the extruded dry-bean products.

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