Impact of traditional and microwave roasting on chemical composition of hazelnut cultivar 'Tonda di Giffoni'

Roasting is a widespread practice for the preservation of hazelnuts. Because traditional treatments conducted by electrical ovens are associated with high energy costs and production of undesired chemical compounds, roasting based on microwaves has been tested by scientists in recent years as an attractive alternative to traditional process. In this study the impact of traditional and microwave roasting on the chemical composition of the Italian hazelnut cultivar 'Tonda di Giffoni' was investigated. Kernels roasted using microwave and microwave - infrared combined treatments showed dry weight, colour and fracturability values similar to those obtained by traditional treatment. Microwaves preserved hazelnut phenol compounds showing a loss of 7.5% with respect to unroasted hazelnut, whereas loss of total phenols higher than 44% were observed in traditional roasted hazelnuts. Microwave roasting produced the lowest amount of free Nε-(carboxymethyl)lysine (CML): 865.4 μg/kg, whereas up to 2,314.6 μg/kg was detected in traditional roasted hazelnuts. Microwaves roasting produced the lowest heat damage. Preservation of antioxidants compounds and production of lower CML matched the advantage of saving time and energy costs: 4 min of treatment and energy density of 6 kJ/kg for microwave roasting, while 40 min and 95 kJ/kg for traditional one.