Reduced Phytate Content by Sourdough

Whole-meal cereals are good sources of minerals such as K, P, Mg, Fe, and Zn; but without treatment, the bioavailability is poor for minerals stored as phytate, an insoluble complex with phytic acid (myoinositol hexa-phosphoric acid, IP6). The content of phytate is 6 mg/g rye grain (115), 3-4 mg/g in flour of soft wheat and 9 mg/g in hard wheat flour (116). Phytate accounts for more than 70% of the total phosphorus in cereals, and it can be degraded during the bread-making process due to the activity of endogenous phytase and thus liberate the bound minerals when the ester-bound phosphoric acids are hydrolyzed. The pH-optimum of rye phytase is found to be at pH 6.0 (115).

Sourdough fermentation has been shown to be more efficient than yeast fermentation in reducing the phytate content in whole bread (—62% and —38% respectively) (113). The prolonged fermentation with sourdough enhanced acidification and led to increased solubility of Mg and P. Five different strains of LAB isolated from sourdoughs have been tested for their ability to degrade phytic acid, but no difference was observed among the strains in the levels of phytic acid hydrolyses (117).

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