The stage of seed development influences iron bioavailability in pea (Pisum sativum L.)

Abstract

Pea seeds are widely consumed in their immature form, known as garden peas and petit pois, mostly after preservation by freezing or canning. Mature dry peas are rich in iron in the form of ferritin, but little is known about the content, form or bioavailability of iron in immature stages of seed development. Using specific antibodies and in-gel iron staining, we show that ferritin loaded with iron accumulated gradually during seed development. Immunolocalization and high-resolution secondary ion mass spectrometry (NanoSIMS) revealed that iron-loaded ferritin was located at the surface of starch-containing plastids. Standard cooking procedures destabilized monomeric ferritin and the iron-loaded form. Iron uptake studies using Caco-2 cells showed that the iron in microwaved immature peas was more bioavailable than in boiled mature peas, despite similar levels of soluble iron in the digestates. By manipulating the levels of phytic acid in the digestates we demonstrate that phytic acid is the main inhibitor of iron uptake from mature peas in vitro. Taken together, our data show that immature peas and mature dry peas contain similar levels of ferritin-iron, which is destabilized during cooking. However, iron from immature peas is more bioavailable because of lower phytic acid levels compared to mature peas.

Improving pulse crops as a source of protein, starch and micronutrients

“…The relationship between phytate concentration and iron bioavailability was further supported by a study of Moore et al . (), which showed that lower phytate levels in immature peas correlated with better iron bioavailability compared to mature peas. Bowman–Birk inhibitors, protease inhibitors that reduce the digestibility of protein, are encoded by two genes ( TI1 and TI2 ) in pea.…”

“…Because phytate accumulates while seeds mature, immature peas, widely consumed as garden peas or petit pois, have a lower phytate concentration than mature peas but the same concentration of iron–ferritin (Moore et al . ). It has been shown that the iron: phytate ratio in peas is positively correlated with iron bioavailability and is higher in immature than mature pea seeds.…”

“…Plant ferritin is located in plastids, meaning that ferritin–iron is surrounded by several membranes, which can hinder the release of iron during digestion (Moore et al . ); however, ferritin–iron in purified form has good bioavailability (Lönnerdal et al . ; Perfecto et al .…”

“…In addition to being an excellent source of protein, starch and micronutrients, pulses may contain anti‐nutritional compounds that can interfere with the absorption of minerals (Moore et al . ) and digestion of protein (Clemente et al . ).…”

“…Previous research on pulse crops has focused on improving agronomic traits such as yield, with limited research on the nutritional improvement of these crops . In addition to being an excellent source of protein, starch and micronutrients, pulses may contain anti-nutritional compounds that can interfere with the absorption of minerals (Moore et al 2018) and digestion of protein (Clemente et al 2015). Genetic breeding could help to optimise beneficial nutrients while reducing the levels of anti-nutrients in pulse seeds.…”