Sourdough bread: Starch digestibility and postprandial glycemic response

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Abstract

To evaluate the influence of sourdough fermentation on starch digestibility in bread, four experimental breads were obtained, prepared from two different wheat flours (whole or white) by two different leavening techniques (sourdough and with Saccharomyces cerevisiae). Products were analyzed for their starch, fiber and resistant starch (RS) content and then submitted to in vitro hydrolysis with porcine alpha-amylase. On the same breads, postprandial blood glucose was evaluated in healthy human subjects. Both sourdough fermented breads gave glycaemic responses significantly lower (p < 0.001) than the corresponding products leavened with S. cerevisiae. On the contrary, the presence of fiber did not influence the glycaemic potential of breads. RS levels were higher in the sourdough products, whereas no differences were observed either in the rate of starch hydrolysis or in the degree of polymerization of the starch residues after the in vitro hydrolysis. We may conclude that sourdough fermentation is a technique able to reduce the glycaemic response to bread and that the mechanism does not seem related to the rate of starch hydrolysis.

Section snippets

In vitro study

The bread products were tested in vitro to determine the rate of starch hydrolysis following incubation with pepsin and pancreatic α-amylase (Granfeldt et al., 1992). About 2 g of each sample were dissolved in triplicate in 20 ml of NaCl 0.9% and at 37 °C for 5 h into 500 ml containers filled with 500 ml of 20 mM Na, K-phosphate buffer (pH 6.9) placed in a stirred water bath. Dialysis tubing (13 cm strips) of three different molecular weight cut-offs (3000/6000–8000/12,000–14,000 DA, Spectra Pore no.

In vivo study

Eight healthy volunteers (four women and four men), age 24 ± 1 years, BMI 22.0 ± 0.5 kg/m2 (mean ± standard deviation) participated in the study. The bread test meal were provided in amounts corresponding to 50 g of available carbohydrates and served with 500 ml of water (Wolever et al., 1991). The subjects consumed the test products as a breakfast in random order after an overnight fast. Finger prick capillary blood samples were taken before the meal and at 15, 30, 45, 60, 90 and 120 min after the meal.

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