Solid phase microextraction (SPME) was evaluated for use in the quantification of aroma volatile production by Granny Smith apples during cool storage. Particular attention was paid to quantifying alpha-farnesene (3,7,11-trimethyldodeca-1,3(E),6(E),10-tetraene) due to its involvement in superficial scald, a disorder of cool stored apples. Comparison between SPME and solid phase extraction (SPE) showed that the SPME fiber had greater adsorption of high molecular weight (MW) volatiles such as alpha-farnesene. When sampling by SPME, these higher MW volatiles did not equilibrate between apples, headspace, and fiber within sampling times as long as 90 min, while lower MW volatiles equilibrated within 5 min. This behavior was also shown by a simple model system consisting of five selected volatiles dissolved in an involatile, lipophilic liquid (squalane). The less volatile high MW aroma compounds evaporated slowly from the surface of the apples and were depleted from the headspace because of very rapid adsorption by the SPME fiber. The amount of alpha-farnesene adsorbed by the fiber increased with air movement through the system. In a static headspace system, the amount of alpha-farnesene adsorbed by the fiber decreased nonlinearly with increasing distance from the apples, due to adsorption onto the glass walls. While SPME is ideal for rapid, qualitative determination of apple headspace volatiles, the slower equilibration of higher MW volatiles limits its use for quantification in more complex systems.

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Preharvest bagging of pear fruit (Pyrus communis L. 'Doyenne du Comice') with micro-perforated polyethylene bags c. 30 days after full bloom did not affect fruit size and weight, density, maturity, and flesh content of N, P, K, Ca, and Mg. Bagged fruit had a greener and lighter skin colour than non-bagged fruit, whereas the development of blush on the sunny side was not different between treatments. Bagged fruit had less cuticle deposition, whereas the wax content of the cuticle was not different between treatments. Fruit skin permeance to water (P' H2O ) and fruit weight loss were not different between treatments. Permeance to CO 2 (P'co 2 ) and O 2 (P'co 2 ) were lower for bagged than for H02008; non-bagged fruit. Accordingly, internal partial pressure of O 2 (p i o2 ) was lower and internal partial pressure of CO 2 (p i co2 ) was higher for bagged than for non-bagged fruit. However, these differences in fruit internal atmosphere between treatments were not large enough to result in significant differences in rates of skin background colour change and respiration during shelf life after 8 weeks in cold storage. With prolonged cold storage the differences between treatments in fruit skin background colour were reduced (bagged fruit de-greened more than non-bagged fruit) while the differences in firmness were increased (bagged fruit had more substantial softening than non-bagged fruit). Fruit bagging did not affect the incidence of senescent scald, senescent breakdown, and diseases after 6 months in cold storage followed by 7 days of shelf life.

A mathematical model was developed to characterize the interaction of fruit O2 uptake, steady-state O2 partial pressures in modified-atmosphere (MA) packages ([O2]pkg), and film permeability to O2 (Po2) from previously published data for highbush blueberry (Vaccinium corymbosum L. `Bluecrop') fruit held between 0 and 25C. O2 uptake in nonlimiting O2 (Ro2max,T) and the [O2]pkg at which O2 uptake was half-maximal (K½T) were both exponentially related to temperature. The activation energy of 02 uptake was less at lower [O2]pkg and temperature. The predicted activation energy for permeation of O2 through the film (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{E}_{\mathrm{a}}^{\mathrm{P_{\mathrm{o}_{2}}}}\) \end{document} kJ·mol-1) required to maintain close-to-optimum [O2]pkg across the range of temperatures between 0 and 25C was ≈ 60 kJ·mol-1. Packages in which diffusion was mediated through polypropylene or polyethylene would have values \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{E}_{\mathrm{a}}^{\mathrm{P_{\mathrm{o}_{2}}}}\) \end{document} of ≈ 50 and 40 kJ·mol-1, respectively, and would have correspondingly greater tendencies for [O2]pkg to decrease to excessively low levels with an increase in temperature. Packages that depend on pores for permeation would have an \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{E}_{\mathrm{a}}^{\mathrm{P_{\mathrm{o}_{2}}}}\) \end{document} of <5 kJ·mol-1. Our procedure predicted that, if allowed to attain steady-state conditions, packages with pores and optimized to 2 kPa O2 at 0C would become anaerobic with as little as a 5C increase in temperature. The results are discussed in relation to the risk of temperature abuse during handling and marketing of MA packaged fruit and strategies to avoid induction of anaerobiosis.

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