Bread enriched with quinoa leaves – The influence of protein–phenolics interactions on the nutritional and antioxidant quality

This paper investigates the functional and potential biological properties of bread fortified with quinoa leaves (QL) in the light of protein–phenolic interactions. The addition of QL changed the textural properties of bread crumb. With the replacement of wheat flour by QL (1–5%), a linear increase in crumb hardness, cohesiveness and gumminess was observed. Fortification positively affected antioxidant properties and phenolic contents; however, in some cases experimental values were significantly lower than those predicted. The QL addition affected nutrient content and digestibility. The starch digestibility of the bread investigated in this study was inversely proportional to the percentage content of QL (the changes in protein digestibility were not so pronounced). Increasing peak areas of extracts obtained after digestion of fortified bread and the significant reduction of free amino groups confirm the presence of interactions between phenolics and proteins. The quality of fortified bread is strongly affected by phenolic compounds and food matrix interactions.