13 - ‘Making bread with sourdough improves mineral bioavailability from reconstituted whole wheat flour in rats’. Nutrition and Cancer. 19(6):524-30.

Wistar rats were fed one of the following experimental diets for 21 d: control, reconstituted whole wheat flour (white flour plus bran), yeast bread, and sourdough bread. The apparent mineral absorption and intestinal fermentation were measured in each animal.

Phytate contents in yeast and sourdough bread were lower than in reconstituted whole wheat flour (?52% and ?71%, respectively). Total cecal pool of short-chain fatty acids, in particular the butyrate pool, was significantly increased by the ingestion of unrefined products. Calcium homeostasis was not modified by these nutritional conditions, whereas magnesium absorption was significantly greater in rats fed the control and sourdough diets than in those consuming whole wheat flour and yeast bread. Magnesium kidney excretion was slightly stimulated by sourdough bread. Compared with the control diet, iron balance was significantly reduced by reconstituted whole wheat flour diet. Yeast bread making counteracted the deleterious effects of whole wheat on iron absorption, whereas sourdough bread making enhanced iron absorption. Further, liver and plasma iron and transferrin saturation levels were lower in rats adapted to the flour diet than in other groups. Zinc absorption was strongly depressed in the presence of unprocessed reconstituted whole wheat flour in the diet, but yeast fermentation afforded a zinc assimilation comparable to the control diet, whereas the sourdough bread led to maximal zinc absorption. Copper absorption increased significantly when rats were fed the sourdough bread, whereas unprocessed whole flour depressed copper absorption (?41% versus control diet).

This study highlights the importance of the slow fermentation process on increasing the bioavailability of essential minerals and thereby extracting the maximum nutritional benefits from whole wheat bread using the sourdough process. Although this study was conducted on rats and not humans, it still presents valuable insights on the mechanism by which long slow fermentation improves the availability and absorption of minerals thereby making sourdough bread nutritionally superior compared to other fast fermented breads.