Organic acids lower GI of bread.

Organic acids, like those formed during sourdough fermentation, can be used to give bread products a low glycemic index (GI). The GI is a ranking of carbohydrates based on their immediate effect on blood glucose levels. Carbohydrates that breakdown quickly during digestion have the highest GIs. Carbohydrates that break down slowly, releasing glucose gradually into the blood stream, have low glycemic indexes.

Low GI diets can help people lose weight. Low GI diets can improve the body's sensitivity to insulin. Low GI can improve diabetes control. But a major problem is that our most important starch rich foods, such as potato and bread, have high GIs. So we should identify factors that lower the rate of starch digestion or prolong the uptake of glucose to the blood.

Organic acids form during the sourdough fermentation of bread. Depending on the type of bacteria used for the fermentation, different amounts of organic acids are formed. Lactic acid lowers starch digestion in the small intestine. Propionic and acetic acids lower the rate of gastric emptying. Bread modified toward a lower GI with lactic acid is able to improve both postprandial glycemia and glucose tolerance at a subsequent meal in healthy people.

Swedish scientists found that lactic acid only lowered the GI of bread if it was present during starch gelatinization. Gluten was required for the lactic acid effect to occur, suggesting that important interactions are formed between the starch and gluten. Moreover, enriching the product with gluten could further lower the GI. Lactic-acid-containing wheat bread showed a beneficial semi-long-term effect on glucose tolerance in obese rats and is a potential functional food. The researchers also found that the effect of lactic acid in bread products made of wheat or barley-wheat at an 80-to-20 ratio could be enhanced by adding pure wheat gluten to the dough.

Bread that was modified toward a lower GI by adding lactic acid during the baking process improved glucose tolerance after a 14-day intervention in obese, hyperinsulinaemic Zucker rats. The rats that were fed lactic-acid-baked wheat bread improved their glucose tolerance after two weeks. No improvement in the glucose occurred during the same period in rats that had wheat bread without lactic acid and wheat bread with added lactic acid.

Further information. Elin Ostman, Department of Applied Nutrition and Food Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden; phone: [phone]; fax: [phone]; email: [e-mail].