Effects of roasting conditions on hazelnut characteristics in a two-step process

A 3-factor Box–Behnken experimental design was applied to study the effects of operative conditions on hazelnut color and texture in a two-step roasting process, with the first step carried out under moist conditions. The analysis of effects and the response surface models showed that, in the chosen experimental conditions, the only significant factor was the treatment time of the second step, which affected both hazelnut texture and color. The ultrastructures of a selected design sample, roasted under moist or dry conditions in the first step, were compared to that of a conventional roasted sample. The accelerated storage of these three samples highlighted that the first step, carried out under the selected moist conditions, leads to a delay of peroxide formation. The increased preservation of cellular integrity observed by scanning electron microscopy and, possibly, the content of tocopherols both seemed to contribute to the extension of hazelnut shelf-life.