Direct evaluation of the total antioxidant capacity of raw and roasted pulses, nuts and seeds

Pulses, nuts and seeds represent an important part of human diet in many countries and epidemiological studies associated their consumption with many health benefits. These foods are often consumed after roasting that may destroy some bioactive compounds, but it can also form antioxidant compounds through the Maillard reaction. In this paper, a direct procedure for the extraction-independent measurement of the total antioxidant capacity named QUENCHER was applied to raw and roasted pulses, nuts and seeds. The results highlighted a high value of total antioxidant capacity (TAC) for some raw seed and pulses showing marked inter-varietal differences among beans examined. TAC value measured by QUENCHER was generally higher than that found using multiple extraction procedure. The effect of roasting on the TAC is the result of the thermal degradation of naturally occurring antioxidant compounds and the formation of new Maillard reaction products having antioxidant activity. In most of the foods studied, the final balance was negative with a substantial loss of antioxidant activity upon roasting. The main driver of the final TAC is the presence of reactants: in rich-starch materials, such as chickpea, cashew and borlotti beans, roasting is accompanied by a progressive increase in TAC, which is likely related with the formation of antioxidant Maillard reaction products.