Improving hazelnut shelf-life through an innovative roasting process

Hazelnut roasting is conventionally carried out in a single-stage toaster, in order to develop the typical roasting flavor, color and texture. Due to their high lipid content (about 60%) with 7-15% linoleic acid, roasted hazelnuts are prone to lipid oxidation, with negative effect on their shelf-life and of hazelnut-containing products. A two-step process with a preheating step under moist conditions, followed by high temperature dry roasting is suggested in the literature, in order to improve product oxidative stability. The aim of this work was to implement the two-step roasting process and to evaluate the modification kinetics of hazelnut characteristics under accelerated storage conditions. Besides, the ultrastructure of raw and toasted hazelnuts was studied, in order to better understand the effect of the innovative roasting process. In order to study the influence of operative conditions in the two-step process, a Box-Behnken experimental design was applied. Results showed that among considered factors (first step treatment time, second step treatment time and temperature), the treatment time of the second step was the only one significant (p