Hazelnut kernels (Corylus avellana L.) mechanical and acoustic properties determination: Comparison of test speed, compression or shear axis, roasting, and storage condition effect

The aim of this work was to compare different texture test conditions for the evaluation of instrumental mechanical and acoustic properties of raw and roasted hazelnut (Corylus avellana L.) kernels cv. Tonda Gentile Trilobata (TGT). A comparison of compression and shear tests, test speed (0.2, 1.0, 10.0 mm/s), and analyzed axis (x, y, z) combinations was performed. Joint mechanical and acoustic emission acquisitions were used for the first time on hazelnut kernels. The compression test method using 1.0 mm/s speed and analyzed on the x-axis showed the lowest variability of the results. These conditions were then used to evaluate raw kernels during 12 months of storage, conducted in-shell (at ambient temperature) and shelled (refrigerated, vacuum, frozen, with nitrogen modified atmosphere). The main differences among storage conditions were evidenced in rupture force, rupture slope and acoustic maximum peak parameters.