Mechanical properties of the skin and the flesh of apples

Usual puncture tests were applied to study texture properties (deformation, failure load, firmness, and toughness) of apple skin and apple flesh. The difference between overall puncture load displacement (whole fruit) and that measured without skin provided a satisfactorily precise result related to mechanical behavior of the skin itself. This procedure is applied to evaluate changes in skin and flesh properties of Golden Delicious apples, both during cold storage (2 degreesC, 96% relative humidity) and ripening at constant room temperature (20 +/- 1 degreesC). Highest decreases occur in deformation (10%), firmness (50%), and toughness (69%) of the apple flesh early during the cool storage. Concurrently, the highest increases are related to the contribution of the skin to the overall firmness (43%) and to the overall toughness (15%). During forced ripening, the skin plays a great part in the relative changes in all the measured overall properties. Storage conditions (relative humidity and temperature) affect highly the percent contribution of the skin to the overall firmness. Additional experiments are carried out after a 210;days cool storage on four apple varieties (Fuji, Golden Delicious, Granny Smith, Pink Lady) to compare their mechanical behaviors. Differences in overall and skin toughness were found between varieties. Percent contribution of the skin to firmness value is alike for all apple varieties tested after a 210 days storage at 2 degreesC. The contribution of the skin in the overall firmness is not a variety feature.