Steeping and germination of wheat (Triticum aestivum L.). I. Unlocking the impact of phytate and cell wall hydrolysis on bio-accessibility of iron and zinc elements

Abstract

In wheat aleurone cells iron and zinc ions occur as phytate structures. Phytate and arabinoxylan cell wall material resist digestion in the human gastro-intestinal tract resulting in very low mineral bio-accessibility. During wheat germination, enzymes make nutrients available for plant development and, when used in foods, for human uptake. We here provide understanding of the impact of the wheat matrix on mineral bio-accessibility. A multifactor experiment in which wheat was subjected to multiple combinations of steeping time (8–36 h), steeping temperature (15–40 °C), germination time (0–120 h) and germination temperature (15–30 °C) showed that steeping for 36 h at 15 °C and germination for 120 h at 26 °C decreased phytate content from 0.96% to 0.65% of initial dry matter (idm) and increased water extractable arabinoxylan content from 0.48% to 1.34% of idm due to phytase and endoxylanase action, respectively. While the iron and zinc bio-accessibility in the wheat grains was 5 and 3%, respectively, that in the germinated grains was 6 and 8% when the cellular matrix was preserved, and 22 and 21% when it was mechanically disrupted. This study thus revealed that controlled steeping and germination of wheat can substantially improve mineral bio-accessibility when the cell walls are broken down.