Fermentation of quinoa, canihua and amaranth to degrade phytate and improve mineral bioavailability

Sammanfattning: Plant-based diets are the main source of nutrients for vegetarians worldwide and for low-income inhabitants of developing countries, such as in rural areas of Bolivia. These diets may contain high levels of mineral inhibitors such as phytate that impairs mineral absorption in the human gut. Low intake of minerals in combination with mineral inhibitors is a critical factor leading to mineral deficiencies. In addition, there is an increasing interest in nutrient-rich pseudocereal grains such as quinoa, canihua and amaranth, as a source of high value proteins and gluten-free foods. Thereby, new processing methods that can improve the nutritional value as well as the sensory properties of these pseudocereal grains are being sought. The main aim of the present research was to evaluate the effect of fermentation on improving the bioavailability of iron, zinc and calcium in quinoa, canihua and amaranth. All three pseudocereal grains and flours were fermented spontaneously or with Lactobacillus plantarum 299v® to degrade the phytate content. Estimated bioavailability of iron, zinc and calcium was determined using phytate:mineral molar ratios. Iron, zinc and calcium accessibility of non-fermented and fermented pseudocereal flours was determined by in vitro assay. Bioavailability of iron and zinc of non-fermented and fermented quinoa and canihua flours was assessed using a rat model. In addition, acceptability of dry toasted and fermented quinoa was evaluated using a hedonic sensory evaluation. The results showed that among seventeen foods commonly consumed in rural areas of Bolivia, pseudocereals contained a comparable high level of minerals and phytate. Fermentation was more effective to degrade phytate in quinoa, canihua and amaranth flours (47%–93%) than in grains (12%–51%). The results suggested that phytate degradation was mainly due to endogenous phytase activity in different pseudocereals rather than the phytase produced by the fermentation culture. The estimated mineral bioavailability (phytate:mineral) of fermented quinoa, canihua and amaranth flours were increased between 1.5- and 4.2-fold and the mineral accessibility was increased between 1.7- and 4.6-fold as a consequence of the phytate degradation, which was between 1.8- and 4.2-fold. Regarding mineral bioavailability, iron concentration was higher in the livers (43%–52%) of animals fed fermented quinoa and canihua diets compared to the corresponding non-fermented diets. Moreover, iron and zinc content in the liver and femur of animals fed a diet with 60% fermented quinoa were higher to those of animals fed a diet with the same content of non-fermented quinoa. The iron retention in the liver was mainly influenced by iron and lactic acid content in the diet while zinc retention in the femur was mainly affected by phytate content in the diet. The fermentation process of quinoa created a challenging flavour profile. Dry toasting was found being effective in improving the sensory attributes of the fermented quinoa flour. Among the different samples tested, porridge prepared with raw quinoa flour fermented for 4 h followed by dry toasting had higher overall acceptability combined with a significant phytate reduction. In conclusion, fermentation proved to be an effective procedure for degrading phytate in quinoa, canihua and amaranth. Mineral accessibility (in vitro) was higher in fermented flours than in non-fermented, the in vivo bioavailability of iron and zinc was higher in diets containing fermented quinoa and canihua than in the corresponding non-fermented diets. In addition, dry toasting process improved the sensory attributes and acceptability of fermented quinoa flour.