Influence of boiling and autoclave processing on the phenolic content, antioxidant activity and functional properties of pistachio, cashew and chestnut flours

Nuts are a rich source of nutritional compounds with beneficial effect on health. The objective of this study was to evaluate the effect of heat and/or pressure processing on protein and phenolic compounds (anthocyanins, flavonols, tartaric esters and total phenols) content, antioxidant activity and functional properties of pistachio, cashew and chestnut flours. Phenolic compounds content was increased in pistachio, cashew and chestnut after heat combined with pressure processing. Antioxidant activity resulted almost not reduced by harshest autoclave condition (138 °C, 2.56 atm, 30 min) and even, was increased in chestnut. The antioxidant activity, determined by dimethyl-ρ-phenylenediamine (DMPD) as well as oxygen radical absorbance capacity (ORAC) assays, was positively correlated with phenolic compounds content. Boiling and autoclave treatments increased water holding capacity (WHC) and water absorption capacity (WAC) in the three analysed tree nuts, and oil holding capacity (OHC) raised in processed pistachio and cashew defatted flours. Emulsifying and foaming capacities of pistachio, cashew and chestnut were negatively affected by processing as well as chestnut gelation capacity. Therefore, pistachio, cashew and chestnut flours maintaining, or even increasing, their phenolic content and antioxidant activity can be obtained by combining heat and pressure processing