Effects of Temperature and Loading Characteristics on Mechanical and Stress Relaxation Properties of Sea Buckthorn Berries. Part 2. Puncture Tests

Puncture force and energy were measured at different loading velocities and probe diameters for two cultivars of sea buckthorn berries of various sizes at several ambient temperatures. In addition to the puncture properties, the firmness-temperature coefficient, the compression coefficient (Kc), shear coefficient (Ks), and the apparent modulus of elasticity were determined. The tests showed that the Sinensis cultivar was generally firmer than the Indian Summer cultivar. With an increase in the berry temperature, the puncture force and energy decreased significantly. The sea buckthorn berry showed a negative firmness-temperature coefficient (FT) which ranged between –0.362 and -0.627% per degree. The puncture force and energy for the large berries of the Sinensis cultivar was significantly higher than that for the small berries. With an increase in loading velocity from 0.3 to 9 mm/s, the puncture force and energy increased significantly. Puncture force and energy also increased as probe diameter increased. As expected, puncture force and energy decreased as storage time increased to 14 d. The mean values obtained for Kc and Ks ranged from –1.079 to -1.575 N/mm and from 0.657 to 0.817N/mm, respectively. The apparent modulus of elasticity of the sea buckthorn berries ranged between 0.24 and 1.25 MPa.