Investigation of drying conditions on bioactive compounds, lipid oxidation, and enzyme activity of Oregon hazelnuts (Corylus avellana L.)

Hazelnut kernels obtained from the commercial processes were analyzed for proximate composition, bioactive compounds, lipid oxidation, and enzyme (lipase, peroxidase, and polyphenol oxidase) activities and compared among three cultivars (Barcelona, Yamhill, and Jefferson) and two agricultural practices (with and without fertigation for Jefferson). The influence of drying temperature (38, 43, and 49 °C) and relative humidity (RH, 40 and 60%) on drying characteristics (drying rates of inshells and corresponding moisture content (MC) and water activity (aw) of kernels when inshells reached ∼10 g/100 g MC or equilibrium MC (MCeq)), bioactive compounds, lipid oxidation, and enzyme activity of the kernels were investigated. Oleic acid and α-tocopherol were the predominant fatty acids and vitamin in hazelnuts. Yamhill contained the highest phenolic (0.12 mg GAE/g), vitamin E (14.26 mg/100 g, α-tocopherol), and lowest unsaturated/saturated fatty acids ratio (8.7) among cultivars. Drying characteristics and chemical and enzymatic reactions of hazelnuts varied depending on drying condition and cultivar of nuts, in which drying at 43-49 °C and 40% RH improved drying efficiency and retained quality of dried hazelnuts. This study suggested the ideal drying conditions that could produce dried hazelnuts with optimal range of MC and aw for retaining bioactive compounds and minimizing lipid oxidation and enzyme activity.