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Abstract
The testing of a simple, non-invasive method for internal atmosphere determination of potato tubers (Solanum tuberosum L.), which also can be used to determine individual lenticel resistance to gas diffusion, is described. The method involved sampling from a 0.34-ml chamber fixed over a lenticel following equilibration of its contents with the tuber's internal atmosphere. Equilibration time and the lenticel's resistance to gas diffusion were estimated from oxygen or carbon dioxide contents taken at two or more time intervals using first-order rate equations. In mature ‘King Edward’ tubers harvested in 1984 and kept at 5°C and 80% RH for 4 weeks, the mean 99.9% equilibration time of CO2 content was 4.4 ± 0.75 hr. In a second experiment on mature ‘King Edward’ tubers harvested in 1985 and stored for up to 12 weeks at 4° and 80% RH, the mean 99.9% equilibration time for O2 content was 6.0 ± 1.17 hr. Repeated rapid sampling from single chambers on tubers increased sample CO2 contents but had no measurable effect on O2 contents. Sealing areas of periderm around sampling chambers demonstrated that potato tuber flesh has a significant resistance to gas diffusion, which can give rise to measurable O2 gradients within undamaged tissue.
Positions of every individual kiwifruit were mapped on each of five eight-year-old vines on a T-bar training system before harvest. The proportion of excessively soft kiwifruit (< 1.0 kgf penetrometer reading at 20C) after 130 days coolstorage at 0C on individual vines ranged from 7 to 45%. Fruit at the distal ends of fruiting canes were significantly heavier and firmer (mean wgt 108.5 gms, mean firmness 1.22 kgf) than fruit closest to the main leader (105.6 gms, 1.18 kgf). Conversely, for multiple clusters, fruit on spurs adjacent to the fruiting cane were heavier than those at the terminal end (109.9 and 103.8 gms), respectively, though firmness of these fruit did not differ significantly. The firmest fruit had less nitrogen, less potassium, less phosphorus and more calcium than the soft fruit. Potential means by which this information could be used to improve fruit storage quality will be discussed.
Steady-state oxygen diffusion in flesh of apples (Malus domestics Borkh. cvs. Braeburn and Cox's Orange Pippin), Asian pears (Pyrus serotina Rehder. cvs. Hosui and Kosui), and nectarines [Prunus persica (L.) Batsch. cvs. Red Gold and Sunglo] was studied using a nondestructive method at 20C. Fruit flesh was found to exert a significant resistance to O2 diffusion resulting in measurable O2 gradients between tissues immediately beneath the skin and those at the fruit center for all these fruits. The magnitude of these O2 gradients varied between crops and cultivars and depended on the respiration rate and on effective O2 diffusivity in fruit flesh (De). Values of Dc varied with the cultivar and were broadly consistent with intercellular space volume. The range of De values obtained suggested that 02 diffusion in fruit flesh takes place in a combination of series and parallel modes in the intercellular space and fluid/solid matrix of the flesh. The results imply that O2 diffusivity in flesh tissues must be taken into consideration in the determination of critical external O2 level in controlled/modified atmosphere (CA/MA) storage.
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 (Po
2) from previously published data for highbush blueberry (Vaccinium corymbosum L. `Bluecrop') fruit held between 0 and 25C. O2 uptake in nonlimiting O2 (Ro
2
max,T) and the [O2]pkg at which O2 uptake was half-maximal (K½
T) 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 (
Research quantified contributions to total variation in water vapor permeance from sources such as cultivar and harvest date in `Braeburn', `Pacific Rose', `Granny Smith', and `Cripps Pink' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. In a study on `Braeburn' fruit from eight orchards in Central Otago, New Zealand, >50% of the total variation in permeance was associated with harvest date. This variation was the result of a large increase in water vapor permeance from 16.6 to 30.2 (se = 0.88, df = 192) nmol·s-1·m-2·Pa-1 over the 8 week experimental harvest period. Fruit to fruit differences accounted for 22% of total variation in permeance. Interaction between harvest date and orchard effects explained 7% of the total variation, indicating that fruit from the different orchards responded in differing ways to advancing harvest date. Tree effects accounted for only 1% of the total variation. Weight loss from respiration [at 20 °C and ≈60% relative humidity (RH)] comprised 3.04±0.11% of total weight loss, averaged across all harvest dates. In a second study of fruit of four apple cultivars, almost 30% of the total variation in water vapor permeance was associated with cultivar differences. Mean water vapor permeance for `Braeburn', `Pacific Rose', `Granny Smith', and `Cripps Pink' fruit was 44, 35, 17, and 20 (se = 4.3, df = 300) nmol·s-1·m-2·Pa-1 respectively. Over 20% of the total variation was associated with harvest date and arose from a large increase in water vapor permeance from 21 nmol·s-1·m-2·Pa-1 at first harvest to 46 nmol·s-1·m-2·Pa-1 (se = 5.3, df = 200) at final harvest, 10 weeks later, on average across all four cultivars. There was large fruit to fruit variation in water vapor permeance accounting for 25% of the total variation in permeance values. Tree effects only accounted for 4% of the total variation. Water vapor permeance in `Pacific Rose'` and `Braeburn' increased substantially with later harvest but values remained relatively constant for `Granny Smith' and `Cripps Pink'. A simple mathematical model was developed to predict weight loss from `Braeburn' fruit. Based on these findings, it appears worthwhile to increase the stringency of measures to control weight loss in `Braeburn' and `Pacific Rose'` apples, particularly those harvested late in the season.