Dynamic elastic properties of some fruits during growth and development

Abstract

The dynamic elastic properties of the flesh of apples, peaches and pears were evaluated to determine whether these properties were significantly altered during growth, development and maturation of the fruit. Mechanical resonance within specimens of flesh removed from the fruit was measured during various stages of development, and Young's modulus of elasticity, the shear modulus, Poisson's ratio and internal friction (damping) were calculated. Young's modulus for Late Elberta peaches decreased rapidly from 1925 × 10 5 dynes/cm 2 three weeks prior to the estimated date of picking maturity to 195 × 10 5 dynes/cm 2 two weeks after estimated maturity. Kieffer pears had a more gradual decline from 2884 × 10 5 to 1151 × 10 5 dynes/cm 2 over a three-month growth period. For apples, Young's modulus of elasticity generally declined during the period between 90 and 115 d after full bloom, then remained relatively unaffected and, finally, declined as the fruit ripened on the tree. Average values for apples at intermediate stages of maturation ranged from 780 × 10 5 dynes/cm 2 for Mcintosh to 1300 × 10 5 dynes/cm 2 for Rome Beauty. The results of dynamic measurements of Young's modulus were generally higher than those from quasi-static tests previously reported for apples. For apples and pears, internal friction (loss coefficient) decreased during the growing season. After maturation, internal friction of apples increased as the fruit ripened on the tree. The average loss coefficient for peaches increased from 0·090 to 0·143 as the fruit developed, matured and ripened. Poisson's ratio ranged from 0·020 for overmature Rome Beauty apples to 0·236 for Rome Beauty in the early stage of maturation, to 0·391 for Kieffer pears approaching maturity. Results indicate that the fruits studied have certain measurable dynamic mechanical properties, some of which change significantly with growth and development and hence may be of value as an index of maturity or readiness for harvest. Further exploitation of the techniques used in this study may result in a better understanding of the engineering properties of fruits and in more objective characterization of the textural attributes of such commodities.