The impact of steeping, germination and hydrothermal processing of wheat (Triticum aestivum L.) grains on phytate hydrolysis and the distribution, speciation and bio-accessibility of iron and zinc elements

Abstract

Chelation of iron and zinc in wheat as phytates lowers their bio-accessibility. Steeping and germination (15 °C, 120 h) lowered phytate content from 0.96% to only 0.81% of initial dry matter. A multifactorial experiment in which (steeped/germinated) wheat was subjected to different time (2-24 h), temperature (20-80 °C) and pH (2.0-8.0) conditions showed that hydrothermal processing of germinated (15 °C, 120 h) wheat at 50 °C and pH 3.8 for 24 h reduced phytate content by 95%. X-ray absorption near-edge structure imaging showed that it indeed abolished chelation of iron to phytate. It also proved that iron was oxidized during steeping, germination and hydrothermal processing. It was further shown that zinc and iron bio-accessibility were respectively 3 and 5% in wheat and 27 and 37% in hydrothermally processed wheat. Thus, hydrothermal processing of (germinated) wheat paves the way for increasing elemental bio-accessibility in whole grain-based products.

Impact of Cereal Seed Sprouting on Its Nutritional and Technological Properties: A Critical Review

“…Lemmens et al. () found that Zn was also detected in the pericarp tissues after sprouting, but it especially accumulates in the developing coleoptile and radicle, suggesting that Zn ions play a key role in their meristemic tissues (Ozturk et al., ).…”

“…While the outcomes of such studies are rather diverse, it can be concluded that a decrease in phytate content leads to a significant increase in mineral bioaccessibility. A 15% decrease in phytate content in wheat as a result of sprouting has been found to lead to an increase in Fe and Zn bioaccessibility from 4.6% to 14.1% and from 2.5% to 14.6%, respectively (Lemmens et al., ). A 30% decrease in phytate content in sorghum as a result of sprouting has been found to increase the Fe and Zn bioaccessibilities from 10% to 20% and from 8% to 15%, respectively (Afify et al., ).…”

“…These enzyme activity levels vary with the cereal and the conditions of sprouting. A 3-to 10-fold increase in phytase activity levels has been found in rice (Azeke, Egielewa, Eigbogbo, & Ihimire, 2011), rye (Bartnik & Szafranska, 1987), wheat (Azeke et al, 2011;Bartnik & Szafranska, 1987;Lemmens et al, 2018), barley (Bartnik & Szafranska, 1987), sorghum (Azeke et al, 2011), and oats (Bartnik & Szafranska, 1987) when sprouting for 4 to 5 days at 15 to 25°C. The phytase activity levels in sprouted rye are 2, 5, and even 12 times higher than those in sprouted wheat, barley, and oats, respectively, when sprouting for 3 days at 20°C (Bartnik & Szafranska, 1987).…”

“…The most mobile mineral ions during seed sprouting are those of K, Ca, and Zn, while Mn and Fe ions are less mobile (L. Lu et al, 2013). Lemmens et al (2018) found that Zn was also detected in the pericarp tissues after sprouting, but it especially accumulates in the developing coleoptile and radicle, suggesting that Zn ions play a key role in their meristemic tissues (Ozturk et al, 2006).…”

Zinc fortification as a tool for improving sprout hygienic and nutritional quality: a factorial design approach

“…Such results are expected and are in agreement with those of Pongrac et al In this study, the use of water with high zinc content increased wheat sprout zinc content (+232.9%). Moreover, the increase in zinc content might be related to the evolution of phytates after sprouting: In fact, a previous study of Lemmens et al showed an increase in phytase activity exceeding 3‐fold in wheat germinated for 48 h. Consequently, a decrease in phytate content is recorded and more zinc ions, previously chelated by phytates, are released. Luckily, the sprouting bioprocess also increases zinc bioaccessibility in wheat, as demonstrated previously …”