Exposing preclimacteric ‘Cripps Pink’ apples to 3 days at 20°C resulted in increased weight loss, but no other significant quality effects over control fruit. The response of preclimacteric apples to a break in the cool chain is cultivar dependent. DeLong et al. (2004) found that a 7 day delay to cooling of ‘Honeycrisp’ apples had no effect on fruit firmness, soluble solids and titratable acidity after storage for 4 or 6 months in refrigerated air. Johnston (2001) reported that delays in cooling ‘Royal Gala’ and ‘Cox’s Orange Pippin’ apples for 2 to 4 days before storage resulted in fruit being softer (when compared to those not delayed) upon storage. Brookfield (1996) reported significant losses of firmness and hue angle at the end of 12 weeks cool storage in ‘Royal Gala’ and ‘Pacific Rose’ cultivars; a loss in firmness only for ‘Braeburn’ apples and no significant effect for ‘Fuji’ apples, as a result of a delayed time to cool before storage.
At 20°C, the loss of the quality of postclimacteric ‘Cripps Pink’ apples as measured by stiffness (Figure 4.9), hue angle (Figure 4.11), titratable acidity (Figure 4.12) and weight loss (Figure 4.13) was more rapid than at the cool storage temperature of 0°C as most clearly illustrated by the steepening curves during the simulated 2 week shelf life period. This more rapid rate of loss of hue angle, stiffness and weight loss at 20°C generally resulted in significant differences between exposed and control apples on return to cool storage.
The observed reduction in product quality on return to cool storage after a short time exposure to warmer temperatures agrees with research for other apple cultivars and fruit. In Alwan and Watkins’ (1999) study of intermittent warming of ‘Cortland’, ‘Delicious’ and ‘Law Rome’ cultivars, firmness losses were generally larger for fruit exposed to 20°C for 1 day every 1 or 2 weeks in comparison to fruit stored constantly at
0.5°C. Similarly, Johnston (2001) reported that an intermittent warming treatment (2 days at 10°C or 2 days at 20°C after 10 days at cool storage temperatures) for the ‘Royal Gala’ and ‘Cox’s Orange Pippin’ apple cultivars resulted in a lower firmness of the warmed fruit on return to cool storage, in comparison to fruit not warmed. Similar to the results for apples, greater reductions in hue angle and firmness were reported in tomatoes exposed to intermittent warming treatments (Artes et al., 1998).
Brookfield et al. (1998) found that apple cultivar had a significant effect on response to exposure to 4°C or 10°C during coolstorage at lower temperatures. ‘Royal Gala’ apples were observed to be affected significantly with temperature abuse treatments being less firm, more yellow, and more greasy at the completion of the simulated coolchain, whereas ‘Braeburn’ apples only showed minor effects on loss of firmness and development of yellow, and ‘Pacific Rose’ apples showed no effect at all.
In this research differences in quality were established as a result of a previous exposure to 20°C when fruit were returned to cool storage, however these differences were not necessarily translated to significant differences in quality after a period of subsequent shelf life temperatures (Figure 4.10). Similar outcomes (i.e. a significantly softer product while in storage as a result of intermittent warming which is not maintained in a subsequent shelf-life period), have been demonstrated with intermittently warmed tomatoes (Artés et al, 1998) and peaches (Zhou et al., 2001).
In this work, rates of change of stiffness of ‘Cripps Pink’ apples at 0°C were found to be dependent on previous time temperature history. A single temperature exposure was observed to not influence the rate of stiffness change (Figure 4.9). However, for fruit exposed to two or three exposures to 20°C, rates of stiffness change in subsequent cool storage were significantly less than control fruit (Table 4.4). In addition, exposures to 20°C later in storage were observed to cause a larger effect of change in stiffness while at 20°C (Figure 4.9b). While initially, these results look unusual, confidence in the accuracy of the result is provided by the continued and constant loss of stiffness observed in the control treatments. These results are in contrast to those of Johnston (2001) who found that the softening rate of ‘Royal Gala’ and ‘Cox’s Orange Pippin’ at any temperature between 0-20°C was not influenced by exposure to another temperature, when firmness was assessed with a penetrometer. Recent research presents scepticism about the acoustic firmness technique, especially with respect to the influence of water loss (Roth et al., 2005) and the interpretation of the results with respect to consumer preferences (Johnson and Dover, 2005). Although these results may be true for stiffness (acoustic firmness) there is no means of ascertaining whether this trend would be
observed for penetrometer firmness, nor how these results would transfer to consumer acceptability.
With the exception of weight loss, it would seem that a break in temperature control of up to 3 days has little effect on the quality of ‘Cripps Pink’ apples presented to the consumers. While short times at higher temperatures can cause statistically significant quality changes at the time of higher temperature, exposure does not accelerate quality losses on return to cool storage and the differences caused are reduced during the shelf life period.