Bakers Journal

Features Nutrition Technical
Neutralizing the Carbs


November 29, 2007
By Kanak Udani

Topics

A look at the challenges of lowering the glycemic impact of carbohydrates with a new product made from a white kidney bean extract.

kidneyA concept that has been around for many years, the Glycemic Index (GI) has recently captured media attention as a diet trend.  Glycemic index diets promote foods with a low GI. The GI measures how quickly the body breaks down carbohydrates into sugar (glucose for energy). Carbohydrates that are processed quickly have a high GI and cause a quick rise in glucose and subsequently insulin levels. These include simple carbohydrates and refined starches.

Carbohydrates that are processed slowly, such as most unprocessed grains, have a low GI resulting in a slower rise in glucose and insulin levels. The GI diet has become increasingly popular because numerous studies have linked a high GI diet to obesity, type 2 diabetes and increased risk of heart disease.

Several methods have been tested to lower the glycemic index of baked goods. These methods include the addition of soluble fibre, psylium, blackgram fibre, barley or the substitution of simple starches with more resistant starches.

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One interesting approach in its early stages is the addition of a white kidney bean extract. In clinical studies, this extract has been shown to delay the digestion and absorption of carbohydrates, and reduce the GI of starchy foods. It works by temporarily inhibiting the action of the digestive enzyme called alpha-amylase that is responsible for breaking down starches into sugar. In clinical and animal studies, the bean extract has been shown to be safe with no adverse side effects or drug interactions. The belief is that by adding it into the baking process, it could inhibit or delay the breakdown of complex carbohydrates into their more absorbable substances. This delay in digestion may slow the stomach’s absorption of glucose, and therefore slow the rise of insulin to lower the glycemic impact of high-carbohydrate baked goods.

Incorporating this white bean extract into baked goods made with yeast-raised dough such as breads and pizzas, without affecting their quality has been challenging. When incorporated into an existing baked good, the resulting product must be comparable in appearance, texture and taste to the original product, and liked by consumers as much as the original product. The test product must also be formulated to take into consideration serving size and the appropriate amount of extract used. As well, it should have a comparable shelf life.

A key factor in the development of low GI baked goods is the effect of the extract on yeast during the preparation of the dough. It should not be added during dough fermentation as it has a negative impact on the rising process of yeast. Another important factor is the type of flours used, particularly the amylase enzyme content of those flours. For example, rye flour contains high levels of alpha-amylase, which makes it difficult to bake with this particular extract.

Using the requirements described above, a study to find ways to incorporate the white kidney bean extract in baked goods was recently done at the Centre for Human Nutrition at UCLA. Amoung the products developed were three varieties of breads, cheese pizza, coffee cake and muffins.

Several trials and variations were needed to develop successful prototypes of control and test products with the extract. Key factors that influenced the product performance were the order and method of adding ingredients, and the time and temperature to bake. Prototype samples of both control products and test products were then evaluated by an outside consumer research company. In a taste-test questionnaire with 35 male and female testers from the San Francisco area, the results were positive.

Wheat Bread: The control and test scored the same for overall appearance but the test was better liked for overall texture while the control was better liked for overall taste.

Multigrain bread: The control and test were liked similarly by consumers but the test was better liked for overall appearance, texture, taste and general opinion.

Rye bread: Consumers liked the control significantly more in appearance, but the test scored higher for overall taste.

Cheese pizza: The test was liked better for appearance, texture, taste and overall opinion.

Coffee cake: The test rated higher for appearance, texture and taste. The control and test were rated equally in overall opinion.
Blueberry muffins: The control rated higher for appearance and overall opinion. The test and control were rated equally for overall taste, and the test scored higher for texture.

Dr. Kanak Udani provides consulting services for Pharmachem Labs, manufacturers of StarchLite, a proprietary white kidney bean extract.
References:
1. B. H Meyer et al., “Inhibition of starch absorption by alpha-amylase inactivator given with foods”, Lancet 1(8330) p. 934 (1983).
2. P. Layer, et al., “Partially purified white bean amylase inhibitor reduces starch digestion in vitro and inactivates intraduodenal amylase in humans” Gastroenterol.:88(6), pp. 1895-1902 (1985)
3. C. B Hollenbeck et al., “Effects of a commercial starch blocker preparation on carbohydrate digestion and absorption: in vivo and in vitro studies” Am J Clin Nutr, 38(4), pp. 498-503 (1983)
4. M. Boivin et al., “Effect of a purified amylase inhibitor on carbohydrate metabolism after a mixed meal in healthy humans” Mayo Clin Proc; 62(4), PP. 249-255 (1987)
5. R. Maheshwari et al., Actue and Chronic Toxicity Studies of Phaseolamin 2250. Report to Sponsor. (2002)
6. E. J Pyler, Baking Science and Technology, I, II


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