ABSTRACT

Whole cereal products, particularly breads, are valuable sources of dietary fibre, vitamins, minerals and phytochemical compounds. However, the bioavailability of minerals differs mainly due to the presence of phytate, which could decrease mineral bioavailability. Phytate is predominantly present in unprocessed food, but can be degraded during the germination of seeds or food processing. Hydrolysis of phytate to partially phosphorylated myo-inositol esters is a way to overcome the negative effect of phytate on mineral absorption. Many investigations have been carried out to reduce the amount of phytate in foods by different processes and/or the addition of exogenous phytases.
The main objective of this investigation was to improve the nutritional value of bakery goods through new strategies for developing high quality products, providing more dietary fibre and higher mineral bioavailability. The inclusion of wheat bran at different levels and particle size with a-amylase and phytase enzymes; the use of phytase-producing bifidobacterial strains as new bakery starters; and the utility of whole amaranth flour as a potential nutritious breadmaking ingredient were the strategies proposed in order to reach the main goal. The nutritional, technological and sensorial quality of final products was evaluated. The effect of formulation on the phytate/mineral molar ratio, the iron dialyzability and ferritin formation in Caco-2 cells as a measure of cell Fe availability were also assessed. Combining wheat bran with amylolytic enzymes and phytase decreased the negative effect of bran addition on the rheology of the product and improve the hydrolysis of phytates. The use of phytase-producing bifidobacteria (GRAS/QPS), either through direct and indirect process, produced breads with similar characteristics in terms of technological and sensory quality comparing to controls, but with significantly lower amount of phytates. For preserving the product quality and increase the nutritional value, the amount of amaranth flour in bread formulation reached at a compromise value. The strategies investigated allowed to improve the nutritional value of new bakery products by including gradually whole grain flours, increasing the mineral and natural fibre contents, and decreasing the residual phytate with better iron accessibility. Iron bioavailability still was negatively affected by low residual phytate content, so further refinement of these developments is encouraged for reaching negligible levels or complete dephytinization in order to improve iron uptake.