APPLE BRUISING THRESHOLDS FOR AN INSTRUMENTED SPHERE

Commercial packing lines were tested by using an Instrumented Sphere ( IS). Typical impacts on packing lines were identified and simulated in the laboratory. Impact tests were conducted on freshly picked 'Gala', 'Splendour', 'Fuji', 'Braeburn', and 'Granny Smith' apples grown in H awkes Bay, New Zealand. Bruise areas produced by impact onto flat stee l, rubber, hard plastic tubing, and a solid hard plastic bar were foun d to be linearly correlated with the peak acceleration recorded by an IS dropped from the same height over the range from 6 mm up to 143 mm. The area of the larger of the two bruises produced by fruit-to-fruit impacts was also linearly related to peak acceleration recorded when t he IS was dropped onto another fruit from the same height. From the ex perimental data, the drop height required to produce a critical bruise with an average area of 100 mm2 (as measured with the skin removed) w as calculated for each variety and each surface. By calculating the co rresponding IS output at this drop height for each surface, a threshol d potential bruise boundary was produced on a velocity change against acceleration graph. The boundary curve included curved surfaces and ap ple-to-apple impacts, and as a result was different in shape to the bo undary described in other studies. These differences are discussed and accounted for by differences in the nature of the impact surfaces use d. It is suggested that this boundary calculation technique could prov ide a more reliable indicator of handling equipment performance than p revious methods, especially in handling systems where apple-to-apple i mpacts are of importance.