Protein enrichment of wheat bread using defatted hazelnut and walnut meal as by-products

Bread is a staple food and consumers are looking for a product that not only tastes good, but also has a benefit, for instance – protein enriched bread. Bread, made using wheat flour (WF), mostly contains carbohydrates and some protein. A part of WF can be replaced by other flours with high protein content resulting in protein enriched bread. To increase protein content, researchers add pulse flour, nuts, protein isolates. Nuts are rich in unsaturated fatty acids, high-quality proteins, carbohydrates, and other bioactive molecules (e.g., phenolic compounds, vitamins). With the increasing market need of nut lipids, large amounts of defatted nut meal as by-product is produced. However, defatted nut meal is usually used as forage or fertilizer resulting in a waste of high-quality protein. It is essential to improve the utilization and the economic value of the defatted nut meal to encourage the development of nut industry. There is not much information about using defatted nut meal to increase protein levels in bread. Therefore, the main objective of this study was to evaluate the influence of addition of defatted hazelnut meal flour (HMF) and walnut meal flour (WMF) on WF technological properties and bread quality. Comparative study was carried out using defatted lupine flour (LF). The amounts of additives for bread fortification (17% WMF, 22% HMF, and 25% LF) were chosen so that the bread could be labelled as a "high protein” product according to the Regulation (EC) No 1924/2006 on nutrition and health claims made on foods. The results showed that the addition of tested products increased water holding capacity (WHC) and water binding capacity (WBC) of WF but had no significant effect on oil holding capacity (OHC). HMF and WMF had the highest WHC, HMF – also the highest WBC. Regarding gel hydration properties, HMF and WMF had higher water solubility index (WSI) but lower water absorption index (WAI) than WF. All additives increased the hardness of WF dough and bread (mostly LF and HMF), while 3% gluten addition significantly reduced the hardness of both dough and bread. In terms of sensory evaluation, bread with addition of WMF was the preferred bread by the consumers, while the bread with the addition of LF was the least liked.