Influence of roasting on the water sorption isotherms of nuts

This work studies the influence of the roasting process on sorption isotherms of almond, hazelnut and peanut over the normal range of storage temperatures (5, 25 and 45 degrees C) The results obtained showed that water sorption properties of unroasted nuts are affected by fat content. The monolayer moisture content and water affinity (sorption heat, Q(s)) increased when the nut fat content decreased. After roasting, a more homogeneous water affinity was observed for the different products, although fat content still affected the monolayer capacity. Also, roasting reduced monolayer moisture content and Q(s) values in each sample and made the moisturizing process less spontaneous (decreasing the thermodynamic driving force). These results are consistent with an increase of the hydrophobicity of the cellular components of nuts due to the enhancement of lipid interactions. The water binding properties of active points in the roasted products were reduced and, hence, some water sorption active points disappeared.