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Modification of alpha-farnesene levels in cool-stored `Granny Smith' apples by ventilation

Adam J. Matich, Nigel H. Banks and Daryl D. Rowan

Postharvest Biology and Technology Vol: 14 Issue: 2 Page 159-170

1998

บทคัดย่อ

Modification of -farnesene levels in cool-stored `Granny Smith' apples by ventilation

`Granny Smith' apples (Malus domestica Borkh) were arranged sequentially in low density polyethylene (LDPE) plastic tubes and ventilated with humidified air at 1°C to characterise the effect of ventilation on the accumulation, oxidation and evaporative depletion of -farnesene from the apple cuticle. Evaporation of -farnesene into the air stream produced a vapour phase concentration gradient along the tubes, with a concomitant decrease in the rate of evaporation of -farnesene from the fruit with distance down the tube. The concentration of -farnesene in the apple wax rose 13-fold during the first 5 weeks of cool storage and decreased thereafter. In contrast, that in the air rose to a maximum value at between 10 and 15 weeks' storage time and then decreased. Concentrations of -farnesene oxidation products (conjugated trienes) in the wax increased steadily with storage time, but were not markedly affected by ventilation and were not well correlated with -farnesene concentrations. Mass transfer coefficients between 1 and 19 nmol s-1 m-2 Pa-1 were obtained for evaporative loss of -farnesene from the apple surface. These coefficients are 10¯200 times greater than those for the permeance of the fruit skin to metabolic gases which suggests that loss of -farnesene occurs by evaporative release from the cuticle wax, rather than diffusion through the skin. Mass balance calculations for the depletion of -farnesene from the apples indicated a high rate of accumulation of -farnesene during the first 5 weeks of storage followed by a short period of rapid depletion and then a longer period of gradual depletion. This suggested that the rate of loss of -farnesene from the surface of the fruit depends more on storage time than on its concentration in the wax. Comparison between concentrations of -farnesene in ventilated and non-ventilated fruit supported these conclusions and suggested that reduction of superficial scald by ventilation may not be explicable merely by enhanced evaporative depletion of -farnesene.