John Lopresti, researcher from Agriculture Victoria, introduces Effect of Airfreight temperatures on Stonefruit for export, part of the Serviced Supply Chain project

Video transcript: Effect of Airfreight temperatures on Stonefruit

As part of the Serviced Supply Chains project, we were interested in really determining the impact of temperature management on stone fruit quality, and particularly during air freight, and a subsequent cold storage period, because we tend to make assumptions about how high temperatures impact stone, fruit quality assuming that high temperatures must reduce fruit quality and increase the rate of fruit softening during subsequent storage and handling. So we wanted to test this hypothesis and on two cultivars Flavoured Pearl nectarine, and Polar Queen white peach, and we looked at three different air fright temperatures of eight degrees, which is considered a normal air freight temperature, 12 degrees and 16 degrees over a 24 hour period. After these cultivars were handled at these three temperatures to simulate air freight, we put them into storage for up to four weeks to see what impact that the higher airfreight temperatures had on subsequent fruit quality after storage and the results were really interesting.

For example, with Flavoured Pearl nectarine, we saw no significant impact on the rate of fruit softening during storage. So 24 hours at 16 degrees and 24 hours at eight degrees which simulated different air freight temperatures, had very little impact on Flavoured Pearl nectarine quality, which was a real surprise.

On the other hand, Polar Queen peach, which we know has a short storage life, was impacted by higher air freight temperatures. So an air freight temperature of 16 degrees caused Polar Queen peach to soften much more rapidly than an airfreight temperature of 8 degrees during a subsequent cool storage period. So again, demonstrating that temperature management is critical, but it's actually more critical for some cultivars than others, and robust cultivars, such as Flavoured Pearl nectarine can handle, can better handle spikes in temperature share along the cold chain.

This study indicates that temperature spikes during air freight export may increase the rate of fruit softening and ripening as measured by IAD (i.e., rate of quality loss) during subsequent cool storage and ripening, but also suggests that the impact of higher temperatures is influenced by cultivar.

‘Flavour Pearl’ white-fleshed nectarine: results suggest that the impact of temperature spikes during air freight on subsequent flesh softening and ripening rate is minimal for this robust nectarine cultivar.

‘Polar Queen’ peach: air freight (AFT) treatment at 16 °C significantly and consistently increased the rate of flesh softening compared to treatment at 8 °C during a 4 week storage period and subsequent ripening. Fruit treated at 12 °C also had higher rates of fruit softening, but differences in fruit firnmness between the 8 and 12 °C AFT treatments were not significant at any cool storage or ripening assessment.

Main objectives

  1. Determine the effect of air freight treatements (AFT), storage duration and ripening period on changes in flesh firmness and index of absorbance difference (IAD) as an indicator of fruit maturity.
  2. Determine the effect of AFT, storage duration and a ripening period on the incidence and severity of flesh browing (FB) as an indicator of chilling injury.
  3. Understand the influence of cultivar and AFT on changes in flesh firmness (FF) and development of FB symptoms.

On this page:

Background

Good temperature management along stone fruit cool chains is considered the primary factor in minimising quality loss such as flesh softening, shrivel and fungal rot development (Kader, 2002). Optimum storage temperature for stone fruit cultivars is 0 to 2 °C, with storage temperatures of 4 to 8 °C to be avoided due to the their potential for initiating abnormal changes in fruit flesh known as chilling injury (Lurie and Crisosto, 2005). These disorders are usually characterised by delayed or arrested ripening, dry and rubbery flesh, flesh browning (FB) symptoms, and loss of flesh juiciness, known as mealiness. Fruit storage above 8 °C is considered sub-optimal due to acceleration of fruit respiration and metabolic activity with initiation of fruit ripening that is obviously not desired along supply chains prior to consumer purchase at retail. Among the various stages along fruit cool chains, air freight (AF), including loading and unloading of pallets, is considered a high risk stage with the potential for fruit to be exposed to sub-optimal ambient temperatures. Australian stone fruit growers and exporters in particular have indicated that there is a lack of understanding of the real impact on fruit quality, directly afterwards, and during subsequent cool storage, of these relatively short but high temperature spikes along the cool chain (Personal comm., Montague Fresh P/L). Also of specific interest to exporters and importers is the effect of AF temperature spikes on flesh softening during subsequent cool storage below 3 °C prior to distribution and marketing.

Experiments were conducted in 2018-19, and 2019-20, on ‘Polar Queen’ peach, and ‘Flavour Pearl’ nectarine, respectively, to determine the effect of three AF temperatures (AFT) on stone fruit quality after subsequent cool storage and ripening that was intended to simulate importer storage and a marketing period. ‘Polar Queen’ is a white-fleshed peach cultivar with a relatively short storage life, and is highly susceptible to storage disorders such as flesh browning (FB), whilst white-fleshed ‘Flavour Pearl’ is a relatively robust nectarine cultivar that has low susceptibility to storage disorders.

Experimental methods

‘Polar Queen’ and ‘Flavour Pearl’ were commercially harvested from orchards in Shepparton and Swan Hill, respectively, packed for AF export, delivered to the freight forwarder within five days of harvest, with AF temperature treatments applied to fruit within seven days of harvest. After commercial harvest, packing and delivery to the freight forwarder, each cultivar was transported to Agriculture Victoria Research facilities at AgriBio Centre and stored overnight at 0 °C and 90 % RH. IAD measurements were made using a DA meter on all ‘Flavour Pearl’ fruit prior to AFT treatment to ensure that fruit assigned to each AFT treatment were of similar physiological maturity, whilst ‘Polar Queen’ fruit were randomly sampled and assigned to AFT treatments without measurement of IAD prior to treatment.

Approximately 700 fruit were randomly sampled from supplied cartons with equal numbers assigned to one of three AFT treatments consisting of a simulated commercial AF duration of 24 h at either 8, 12 or 16 °C. As AF duration to export markets is usually between 8 and 13 h, the 24 h of simulated AF in the experiment included a period for land transport, loading and unloading of consignments, and potential delays before and after AF (i.e., simulation of a worst-case scenario). After simulated AF, all fruit were stored for up to four weeks at 2 °C, and fruit quality was assessed at weekly intervals directly out of storage, and after ripening for three days at 18 °C.

The AF simulation experiment for each cultivar was designed as a RCB split-split-plot with treatment factors of AFT, cool storage duration and ripening period. There were five replicates of each treatment with the experimental unit consisting of five fruit. The main plot consisted of AFTs of 8, 12 or 16 °C for 24 h. Storage duration treatments (1, 2, 3 or 4 weeks of storage at 2 °C post-air freight after each AFT) were a split of the main plot and ripening period treatments (0 or 3 days at 18 °C after each storage duration) were a further split of the storage duration sub-plot.  At each removal, fruit were assessed for FF, IAD, and FB incidence and severity. Methods used for fruit quality assessments are described in the ‘Stone fruit quality assessment methods’ summary report.

Results and Discussion

Fruit maturity (IAD) before AF simulation

Little difference in mean IAD was observed between experimental units of ‘Flavour Pearl’ fruit assigned to each AFT treatment, cool storage duration and ripening period (Fig. 1); mean IAD and standard error (SE) for all AFT treatments was 0.50 ± 0.02 SE. For ‘Polar Queen’ peach, mean IAD’s and SE’s for the AFT treatments of 8, 12 or 16 °C were 1.15 ± 0.03, 1.22 ± 0.05, and 1.22 ± 0.04, respectively (results not shown). For both cultivars, these results show that fruit were of similar maturity prior to AF simulation.

Graph: Mean index of absorbance difference (IAD) in ‘Flavour Pearl’ nectarine assigned to each air freight temperature, cool storage duration and ripening period treatment

Figure 1. Mean index of absorbance difference (IAD) in ‘Flavour Pearl’ nectarine assigned to each air freight temperature, cool storage duration and ripening period treatment, after delivery of packed fruit from the freight forwarder; “Ripe” indicates a ripening period at 18 °C for 3 days after cool storage at 2°C; error bars show ± standard error of the mean from the five replicates per treatment; different letters within a storage duration or cool chain stage indicate significant differences among air freight temperature treatments at P < 0.001.

Effect of AF temperature and storage duration on FF

For ‘Flavour Pearl’ nectarine, no significant difference in FF was found between AFT treatments prior to, or directly after, AFT treatment, and no significant difference was found in FF between treatments after storage at 2 °C for 1 or 4 weeks (Fig. 2) (noting that no fruit quality assessment was conducted after cool storage for three weeks prior to ripening). Unexpectedly after two weeks of storage, fruit treated at an AFT of 12 and 16 °C were significantly firmer than those treated at 8 °C, but this result appears to be an anomaly considering that this difference due to AF temperature was not observed in other storage durations. All AFT treatments resulted in a significant decrease in FF after four weeks of cool storage compared to all other cool chain stages, with all fruit having a FF of approximately 42 N indicating that fruit had partially ripened after four weeks storage duration at 2 °C. No significant difference was observed between fruit treated at the three AF temperatures after air freight simulation or storage for 1, 2 or 3 weeks and ripening at 18 °C for 3 days (Fig. 3), with FF under 10 N indicating that fruit were at eating ripe stage regardless of AFT treatment.

Graph: Effect of air freight temperature treatment and storage duration at 2 °C on flesh firmness for ‘Flavour Pearl’ nectarine

Figure 2. Effect of air freight temperature treatment and storage duration at 2 °C on flesh firmness for ‘Flavour Pearl’ nectarine; error bars show ± standard error of the mean from the five replicates per treatment; different letters within a storage duration or cool chain stage indicate significant differences among air freight temperature treatments at P < 0.001; no fruit removal after 3 weeks of storage.

Graph: Effect of air freight temperature treatment, storage duration at 2 °C, and ripening at 18 °C for 3 days

Figure 3. Effect of air freight temperature treatment, storage duration at 2 °C, and ripening at 18 °C for 3 days, on flesh firmness for ‘Flavour Pearl’ nectarine; error bars show ± standard error of the mean from the five replicates per treatment; different letters within a storage duration or cool chain stage indicate significant differences among AF temperature treatments at P < 0.001.

For ‘Polar Queen’ peach, no significant difference in FF was found between AF temperatures prior to or directly after AFT. In contrast, after storage at 2 °C for 1, 2, 3, or 4 weeks, FF was significantly and consistently lower in fruit that underwent the 16 °C AFT treatment compared to fruit treated at 8 °C (Fig. 4).

During cool storage at 2 °C, no significant difference in FF was found between fruit treated with an AF temperature of 8 or 12 °C. Although FF means were adjusted to account for the significant effect of flesh browning (FB) on FF, means adjustment for FB incidence may not fully account for the impact of AF temperatures and storage durations on FF. Similar results were found after ripening of fruit at 18 °C for 3 days after storage at 2 °C with FF significantly and consistently lower in fruit that underwent the 16 °C AFT treatment compared to fruit treated at 8 °C (Fig. 5). Among AFT treatments, a FF of less than 20 N after storage at 2 °C for 1, 2 or 3 weeks and ripening was only observed in fruit exposed to the 16 °C air freight temperature, indicating that for this cultivar a lower AF temperature reduced the rate of fruit ripening, although greater FB incidence and severity in fruit treated at 8 and 12 °C may have also impacted on ripening behaviour.

Graph:Effect of air freight temperature treatment and storage duration at 2 °C on flesh firmness for ‘Polar Queen’ peach

Figure 4. Effect of air freight temperature treatment and storage duration at 2 °C on flesh firmness for ‘Polar Queen’ peach; error bars show ± standard error of the mean from the five replicates per treatment; different letters within a storage duration or cool chain stage indicate significant differences in air freight temperature treatments at P < 0.001; means adjusted for flesh browning incidence (P = 0.003).

Graph:Effect of air freight temperature treatment, storage duration at 2 °C, and ripening at 18 °C for 3 days, on flesh firmness among ‘Polar Queen’ peach

Figure 5. Effect of air freight temperature treatment, storage duration at 2 °C, and ripening at 18 °C for 3 days, on flesh firmness among ‘Polar Queen’ peach; error bars show ± standard error of the mean from the five replicates per treatment; different letters within a storage duration or cool chain stage indicate significant differences between air freight temperature treatments at P < 0.001;means adjusted for flesh browning incidence (P = 0.003).

Fruit maturity (IAD) during storage and ripening

Prior to and after AFT treatment, no significant differences in mean IAD were observed between treatments for ‘Flavour Pearl’ nectarine, with similar results obtained during storage at 2 °C for 1, 2 or 4 weeks (Fig. 6). Interestingly, the overall changes in IAD that indicate relatively normal fruit ripening behaviour during storage, were not closely correlated to FF, particularly after storage for 1 or 2 weeks, with little change in FF after these storage durations.

Graph: Effect of air freight temperature treatment, and storage duration at 2 °C or cool chain stage, on index of absorbance difference (IAD) for ‘Flavour Pearl’ nectarine

Figure 6. Effect of air freight temperature treatment, and storage duration at 2 °C or cool chain stage, on index of absorbance difference (IAD) for ‘Flavour Pearl’ nectarine; error bars show ± standard error of the mean from the five replicates per treatment; different letters within a storage duration or cool chain stage indicate significant differences among AF temperature treatments at P < 0.001; no fruit removal after 3 weeks of storage.

The effect of AFT on mean IAD was much more apparent for ‘Polar Queen’ peach with significant differences between all treatments post-AF, and after storage at 2 °C for one week (Fig. 7). The largest difference in IAD was greater than 0.3 between the 8 and 16 ° AFT treatments observed after this later storage period. Significant differences in IAD between AFT treatments generally corresponded with differences found in FF during the cool storage period with the proviso that although fruit appeared to ripen normally based on IAD, FF results showed that were still well above a FF of 20 N even after storage for 3 or 4 weeks, particularly those fruit that underwent AFT treatment at 8 or 12 °C.

Graph: . Effect of air freight temperature treatment and, storage duration at 2 °C or cool chain stage, on index of absorbance difference (IAD) for ‘Polar Queen’ peach

Figure 7. Effect of air freight temperature treatment and, storage duration at 2 °C or cool chain stage, on index of absorbance difference (IAD) for ‘Polar Queen’ peach; error bars show ± standard error of the mean from the five replicates per treatment; different letters within a storage duration or cool chain stage indicate significant differences among AF temperature treatments at P < 0.001.

Effect of AF temperature and storage duration on FB

No FB symptoms were observed for ‘Flavour Pearl’ nectarine after cool storage or ripening whilst in ‘Polar Queen’ peach high FB incidence and severity were observed in all AFT treatments directly out of storage at 2°C after 3 and 4 weeks (Fig. 8). After storage for 2 weeks, significant differences in FB incidence and severity were found between all AFT treatments with a 71 % absolute reduction in FB incidence in fruit treated at 16 °C compared to those treated at 8 °C. Similarly, AFT treatment at 16 °C reduced FB severity 86 % in relative terms, with high severity observed for ‘Polar Queen’ treated at 8 °C, rendering this fruit unmarketable. A similar pattern was observed after storage for 3 weeks but with significant differences in FB incidence and severity only found between the 8 and 16 °C AFT treatments, and with all fruit being unmarketable after this cool storage period (i.e., FB severity score > 2.5). No FB symptoms were observed in this cultivar directly out of storage after one week.

Graph: Effect of air freight temperature treatment and storage duration at 2 °C on flesh browning incidence (left) and severity (right) among ‘Polar Queen’ peach

Figure 8. Effect of air freight temperature treatment and storage duration at 2 °C on flesh browning incidence (left) and severity (right) among ‘Polar Queen’ peach; error bars show ± standard error of the mean from the five replicates per treatment; different letters within a storage duration indicate significant differences among air freight temperature treatments at P < 0.001.

After storage at 2 °C for one week and ripening at 18 °C for 3 days, significant differences in FB incidence and severity were found between all AFT treatments with a 64 % absolute reduction in FB incidence in fruit treated at 16 °C compared to those treated at 8 °C (Fig. 9). Similarly, after storage for 2 weeks and ripening, a significant difference in FB incidence was found between the 8 and 16 °C AFT treatments, but FB incidence was greater than 40 % in all treatments, with the ripening period inducing a greater increase in FB incidence in fruit treated at 12 and 16 °C than in fruit treated at 8 °C.

FB severity was significantly different between all AFT treatments after storage at 2 °C for one week and ripening, with fruit treated at 8 °C being unmarketable. FB severity after cool storage for 2 weeks and a ripening period was significantly higher in fruit treated at 8 °C than in fruit treated at 16 °C, but with a greater relative increase in severity in fruit treated at 16 °C than in fruit from other AFT treatments compared to ripening after one week of storage. Although significant differences in FB severity were found between AFT treatments directly after storage for 3 weeks, no such differences were observed after the ripening period with severity scores above 3 regardless of AFT treatment. High FB incidence and severity was observed in all treatments after cool storage for 3 weeks and a ripening period with all fruit being unmarketable after ripening. No ripening assessment was conducted among fruit stored at 2 °C for 4 weeks.

Graph:Effect of air freight temperature treatment, storage duration at 2 °C and ripening at 18 °C for 3 days on flesh browning incidence (left) and severity (right) for ‘Polar Queen’ peach

Figure 9. Effect of air freight temperature treatment, storage duration at 2 °C and ripening at 18 °C for 3 days on flesh browning incidence (left) and severity (right) for ‘Polar Queen’ peach; error bars show ± standard error of the mean from the five replicates per treatment; different letters within a storage duration indicate significant differences among air freight temperature treatments at P < 0.001.

Conclusions

For ‘Flavour Pearl’ white-fleshed nectarine, little difference in FF or IAD was observed after AFT treatment of 8, 12 and 16 °C for 24 h and cool storage at 2 °C for up to 4 weeks or a subsequent ripening period at 18 °C for 3 days. These results suggest that the impact of temperature spikes during air freight on subsequent flesh softening and ripening rate is minimal for this robust nectarine cultivar.

For ‘Polar Queen’ peach, AFT treatment at 16 °C significantly and consistently increased the rate of flesh softening compared to treatment at 8 °C during a 4 week storage period and subsequent ripening. Fruit treated at 12 °C also had higher rates of fruit softening, but differences in FF between the 8 and 12 °C AFT treatments were not significant at any cool storage or ripening assessment.

This study indicates that temperature spikes during air freight export may increase the rate of fruit softening and ripening as measured by IAD (i.e., rate of quality loss) during subsequent cool storage and ripening, but also suggests that the impact of higher temperatures is influenced by cultivar.

No FB symptoms were observed among ‘Flavour Pearl’ nectarine after cool storage or subsequent ripening. In contrast, among ‘Polar Queen’, all fruit were unmarketable beyond two weeks of cool storage regardless of AFT treatment. However, higher AFTs of 12 and 16 °C reduced both the incidence and severity of FB after cool storage for one and two weeks, and also after one week of cool storage followed by ripening. The positive effect of a short storage period at higher temperatures relatively soon after harvest as found in this study is unsurprising given that these effects have also been observed during a storage temperature fluctuation experiment in ‘September Bright’ nectarine, and subsequently confirmed in preconditioning experiments conducted on ‘Majestic Pearl’ nectarine and ‘Polar Queen’ peach.

Literature cited

Kader A.A. (2002). Postharvest Biology and Technology: An Overview (Chapter 4). In Postharvest technology of horticultural crops, Publication 3311, University of California Agriculture and Natural Resources, 39-48.

Lurie S. and C.H. Crisosto (2005). Chilling injury in peach and nectarine. Postharv. Biol. And Technol., 37:195-208. doi:10.1016/j.postharvbio.2005.04.012

Acknowledgement

The Serviced Supply Chains project is funded by the Hort Frontiers Asian markets Fund, part of the Hort Frontiers Asian strategic partnership initiative developed by Hort Innovation, with co-investment from Agriculture Victoria, the Department of Agriculture and Fisheries Queensland (DAFQ), Montague Fresh (summerfruit), Manbulloo (mangoes), Glen Grove (citrus), the Australian Government plus in-kind support from University of Queensland and the Chinese Academy of Sciences.