Breaks in CA in Combination with Breaks in Temperature Control at

5.3.2.1.Respiration Rate and Ethylene Production

Gas conditions used during the simulated shipping period were observed to substantially influence the respiration rate of the fruit (Figure 5.4a). Fruit shipped in air treatments were observed to consistently respire at approximately 20.0 nmol(CO2).kg-1s-1, 38%

higher than those in CA (14.5 nmol(CO2).kg-1s-1), with the treatment in air at 3°C (3AS)

respiring at the highest rate of 25.0 nmol(CO2).kg-1s-1. As observed for fruit stored in air

(Figure 4.4a) the rates of respiration at coolstorage temperatures were not influenced by any previous exposure to 3 days at 20°C (compare treatments TAS and 0AS, Figure 5.4). Notably, the respiration rate of fruit stored at 3°C in CA did

Figure 5.4, Effect of breaks in temperature control at time of load-out and choice of shipping atmosphere on ‘Cripps Pink’ (a) respiration rate; (b) ethylene

production; (c) firmness and (d) background hue angle. All fruit were stored at 0°C in CA (2% O2 and 1% CO2) for 122 days. After this treatments are different in

atmosphere and temperature (e), with CNT = 81 days at 0°C in CA; and TAS = 81 days at 0°C in RA; with all other treatments exposed to 3 days at 20°C in RA followed by for 3GS = 78 days at 3°C in CA; 3AS = 78 days at 3°C in RA; 0GS = 78 days at 0°C in CA;

0AS = 78 days at 0°C in RA. Bars shown for hue angle and firmness represent LSD (P<0.05). All treatments are not significantly different at times where no LSD bar is presented. Note the unplanned temperature variation that occurred at day 178 for 3 days

in all treatments of the experiment (e).

b. a.

d. c.

not differ significantly from that of both treatments at 0°C in CA, whereas the respiration rate of fruit in the treatment at 3°C in air (3AS) was consistently higher than the treatments at 0°C in air (TAS and 0AS).

Gas conditions during the simulated shipping period and exposure to breaks in temperature control both influenced ethylene production (Figure 5.4b). As observed for respiration rate, treatments that returned to air storage (TAS, 3AS, and 0AS) were observed to produce ethylene at a consistently higher rate than those returned to CA (CNT, 3GS, and 0GS). Exposure to 20°C for 3 days resulted in increased rates of ethylene production on return to coolstorage temperatures, irrespective of the gas conditions applied. The rates of ethylene production of fruit exposed to 3 days at 20°C were approximately twice that of fruit held at 0°C, whether in air (compare treatments TAS and 0AS) or in CA (treatments CNT and 0GS). This result is similar to that observed for fruit stored in air prior to exposure to periods at 20°C (Figure 4.4b).

An increase in temperature from 0°C to 3°C resulted in slightly greater respiration rates and ethylene production rates in air (compare 3AS to 0AS), while no clear differences were observed for fruit in CA (compare 3GS to 0GS, Figure 5.4a-b). This result supports previous findings for the respiration rate of ‘Golden Delicious’ apples (Andrich et al., 1998) and ethylene production in tomatoes (Sanders and de Wild, 2003) and ‘Conference’ pears (de Wild et al., 2003) in which storage temperature was observed to have little effect on the metabolic rates while the fruit were stored in low oxygen atmospheres. CA appears to mitigate physiological differences that might be expected as a result of small differences in temperature.

5.3.2.2.Firmness

Significant firmness differences between treatments were not evident until 160 days (Figure 5.4c) which is equivalent to approximately 40 days of simulated shipping time. Both treatments stored in air (at 0°C or 3°C) and previously exposed to 3 days at 20°C (treatments 0AS and 3AS) were observed to decrease in firmness at approximately 0.02 kgf.day-1 (prior to the unplanned temperature abuse), while all other treatments were not significantly different during the 80 days of simulated shipping (at 200 days, Figure 5.4c) and all softened at approximately 0.01 kgf.day-1. Similarly, Brookfield et al. (1998) found that significant differences in apples exposed to breaks in temperature control and those not exposed only became evident after further storage and/or temperature abuse and Johnston et al. (2006) found that on transfer from CA to air atmospheres, ‘Cox’s Orange Pippin’ apples have a 10 day delay period prior to softening at a more rapid rate.

Drake (1993) showed that a period of 30 days in RA following 30 days in CA could result in a significantly different apple firmness for one of ‘Cripps Pink’ parent cultivars, ‘Golden Delicious’.

Ethylene production had no influence on rates of firmness change in CA shipped fruit. Treatment 0GS produced ethylene at twice the rate of non-temperature exposed CA shipped fruit (treatment CNT, Figure 5.4b) and yet both treatments softened at the same rate. This result contradicts the findings for ‘Cox’s Orange Pippin’ apples, in which ethylene production in CA conditions are found to significantly influence rates of softening (Stow et al., 2000) and suggests that the response of apples to ethylene in CA is cultivar specific.

5.3.2.3.Colour

Differences in background colour between treatments exposed to 3 days at 20°C and those remaining in refrigeration were evident at the beginning of the simulated shipping period, with those treatments exposed to 3 days at 20°C having a substantially lower hue angle (being more yellow) than the other treatments (Figure 5.4d). In the subsequent 80 days of simulated shipping, the rates of hue angle change were also affected by gas storage conditions, with those treatments stored in CA changing in hue angle by 0.6 degrees on average, while those stored in air at 0°C lost 3.7 degrees of background hue over the same simulated shipping period.

5.4. FURTHER DISCUSSIONS AND CONCLUSIONS