Harvest / Post harvest
Harvest / Post harvest
John Lopresti, former researcher from Agriculture Victoria, introduces predicting fruit quality for stonefruit export, part of the Serviced Supply Chain project
As a component of the Serviced supply Chains project, we've developed flesh firmness and shelf life calculators for Australian stonefruit for growers and exporters, that are able to predict changes in quality and reminding shelf life along cold chains, either in domestic markets or during sea or air freight.
And these calculators are based on three factors. Harvest maturity as measured by harvest flesh firmness, the temperature, as well as the duration along each stage of the cold chain. And by inputting these numbers, we can look at different export and cold chain scenarios to get an understanding, to obtain an understanding of the changes in fruit quality, along the chain, depending on temperature management, as well as stage duration or stage period, as well as be able to estimate the remaining shelf life or fruit at various stages along the cold chain.
This will allow grower exporters to test some of their own export and cold chain scenarios and see what impact their temperature management and their handling of fruit, of stone fruit has on flesh firmness, fruit quality, and shelf life as it moves along cold chains.
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A flesh firmness and shelf life calculator has been developed for stone fruit. The calculator is based on fruit quality data collected from a range of storage and simulated air and sea freight experiments over four years for ‘Majestic Pearl’ nectarine. This first version of the fruit quality calculator provides a prediction of flesh firmness and remaining shelf life (RSL) at various stages along the cool chain from harvest flesh firmness, storage and handling duration, and fruit temperature. For example, a grower, exporter, importer or retailer can use the calculator to determine RSL by assigning a preferred minimum target flesh firmness depending on their marketing requirements and minimum quality standards. The calculator can also be used to estimate RSL and flesh firmness for domestic cold chains, particularly where fruit is designated for cool storage prior to distribution and marketing.
Australian stone fruit growers and exporters will be able to access a non commercial version of the shelf life calculator for testing potential secarios (this calculator has been developed for Australian stonefruit producers and exporters only).
Users will be able to input their own fruit temperatures and stage durations for cold chain scenarios of interest, or applicable to their circumstances or markets, and obtain estimates of changes in flesh firmness or RSL, as a result of differing cold chain conditions.
It is envisaged that an online dashboard will be developed to predict RSL along cold chains for up to six stone fruit cultivars, incorporating the capacity to select one of two harvest maturities (i.e., pre-commercial and commercial maturity) per cultivar, as well as flesh firmness at harvest. In the future, it is hoped to develop dashboards that can utilise cold chain temperature data collected in ‘real-time’, allowing growers and exporters to track flesh firmness and RSL of monitored fruit, for example, whilst it is in cold storage, being exported, or being handled in the importing country by the importer or retailer.
In the following sections the features of the stone fruit quality calculator, and its potential to allow comparison of different cold chain scenarios, is demonstrated for both flesh firmness and RSL based on a simplified export cold chain as described in Figure 1. Although at present the calculator is based on data for ‘Majestic Pearl’ white-fleshed nectarine, the predictions generated by the calculator may be generalised to other white-fleshed nectarines for the purposes of comparing the effects of different cold chain scenarios.
Figure 1. Simplified export cool chain used within flesh firmness and shelf life prediction calculators.
The flesh firmness calculator can be used to estimate changes in fruit firmness along export cold chains incorporating five storage and handling stages (Fig. 2a & 2b). Users are required to input three parameters: average harvest flesh firmness in the blue cell of the calculator, stage duration in days (i.e., green font), and average stage temperature in °C (i.e., blue font). Once this information is typed into the relevant cells based on the cold chain scenario of interest, estimated flesh firmness will be calculated after each cold chain stage. Flesh firmness estimates assume that no storage disorders, such as chilling injury, develop in fruit along the cold chain, as it is known that storage disorders negatively impact on fruit flesh texture, slow fruit ripening, and thus will affect estimates of flesh firmness.
In the first example below, flesh firmness is estimated for ‘best’ case (A) and ‘worst’ case (B) sea freight export scenarios assuming a harvest flesh firmness of 8 kgf which is typical for white-fleshed nectarines of commercial maturity. In the ‘best’ case temperature management scenario (A), where stage durations are minimised (but still realistic), after 26 days of handling from harvest at 2 to 3 °C the estimated flesh firmness after sea freight is 6.5 kgf. In this scenario the importer only stores the fruit for two days and dispatches it for distribution to the retailer at 5.3 kgf firmness, with the consumer able to purchase fruit at the retailer with a fruit firmness of 3 to 5 kgf, assuming an average fruit temperature of 5 °C during distribution and retailing.
Figure 2a. Estimated flesh firmness for a ‘best’ case scenario (A) sea freight export chain.
Figure 2b. Estimated flesh firmness for a ‘worst’ case scenario (B) sea freight export chain.
On the other hand, in the ‘worst’ case scenario B, the sea freight stage duration has increased to 27 days, and importer storage to 7 days, with slight increases in importer and retailing average temperatures, resulting in an estimated flesh firmness of 3.9 kgf after sea freight, and fruit dispatched from the importer at a firmness of 1.4 kgf, which would allow little time for retailing, as fruit with a flesh firmness of 1 kgf or below are generally considered fully ripe. Among both scenarios there is little change in estimated flesh firmness during a ‘Harvest to freight forwarder’ duration of 5 or 7 days at 3 °C, with flesh firmness changes at low temperature only apparent after the relatively long sea freight stage.
Note that the uncertainty in the estimated flesh firmness will vary with handling stage, with the estimates for very firm (i.e., > 6 kgf) or very ripe fruit (i.e., < 2 kgf), likely to be more accurate than firmness estimates during importer storage and retailing, with approximate uncertainties of ± 0.5 kgf and ± 1 kgf, respectively.
In the second example below (Fig. 3a & 3b), flesh firmness is estimated for ‘best’ case (A) and ‘worst’ case (B) air freight export scenarios also assuming a harvest flesh firmness of 8 kgf at commercial maturity. In the ‘best’ case temperature management scenario (A), air freight temperature averages 8 °C for one day with no estimated change in average flesh firmness after air freight and minimal change in firmness during importer storage at 4 °C for 7 days. Even after a distribution and retailing leg of five days at 5 °C, average flesh firmness remains above 3 kgf, providing ample time for retailing and consumer purchase.
In the ‘worst’ case air freight scenario (B), both ‘Harvest to freight forwarder’ and ‘Importer storage’ stages are longer, with an air freight temperature of 14 °C. Interestingly even at this relatively high temperature, little change in estimated flesh firmness is observed after sea freight, but its consequences are clear after importer storage, combined with a slightly longer storage duration at 5 °C, resulting in a flesh firmness of less than 3 kgf prior to dispatch by the importer. Thus it appears that the negative impact of a short duration spike to a relatively high temperature during air freight is likely only to be observed after cool storage of more than one week.
Figure 3a. Estimated flesh firmness for a ‘best’ case scenario (A) air freight export chain.
Figure 3b. Estimated flesh firmness for a ‘worst’ case (B) scenario air freight export chain.
An alternative to estimating flesh firmness directly is to utilise the calculator to predict RSL along the cold chain. In the examples provided below, an importer or retailer can use previous stage temperature and duration data, (from ‘real-time’ temperature monitoring, if available) to estimate RSL, based on a selected minimum average fruit firmness at which point fruit must be dispatched (by the importer) or sold (by the retailer). Again, users are required to input three parameters: minimum flesh firmness before dispatch or sale is necessary (in the orange cell of the calculator), stage duration in days (i.e., green font), and average stage temperature in °C including importer storage temperature (or retailer stage temperature) (i.e., blue font) (Fig. 4). With this information in the relevant cells, RSL until fruit reaches the minimum allowable flesh firmness is estimated.
In the first example below, RSL is estimated as 4.9 days at an importer storage temperature of 2 °C for a ‘best’ case (A) sea freight export scenario including 23 days of sea freight, assuming the white-fleshed nectarine was harvested at commercial maturity and a minimum allowable flesh firmness prior to dispatch of 4 kgf (Fig. 4a & 4b). In a ‘worst’ case scenario (B) with the same minimum allowable firmness of 4 kgf and cool chain stage duration and temperature as scenario (A) but where the importer storage temperature is now 6 °C, estimated RSL has now reduced to less than two days, clearly demonstrating the effect on shelf life of sub-optimal storage temperatures.
Uncertainty in the estimated RSL will generally vary according to the number of cold chain stages prior to RSL calculation, with higher accuracy usually in estimates after sea or air freight and increasing uncertainty in RSL estimates after importer storage or retailing. Uncertainty in RSL estimates based on current fruit quality models is likely to be ± 1 to 3 days, with the larger uncertainty likely among later cold chain stages.
Figure 4a. Estimated remaining shelf life during importer storage at 2 °C (A) after sea freight.
Figure 4b. Estimated remaining shelf life during importer storage at 6 °C (B) after sea freight.
An example of how the RSL calculator has been designed to provide useful information when recommended storage durations are exceeded and firmness thresholds reached is provided in Figures 5a and 5b. In cold chain scenario A, fruit have been stored at low temperature for 31 days between harvest and the end of sea freight, and although the importer has approximately one day to dispatch fruit based on a minimum firmness of 4 kgf, a warning has appeared in the RSL column indicating that the recommended ‘storage’ duration for this cultivar has already been reached, increasing the risk of storage disorders developing along the remaining cold chain. With this warning an importer may decide to dispatch the fruit immediately to minimise the potential for storage disorders. Note that the maximum recommended storage duration will generally be different for each cultivar.
If the storage duration from harvest through to the end of sea freight is below this maximum threshold then a ‘continue’ message will be displayed in the RSL column (cold chain scenario B). In this case the importer storage temperature is 4 °C, and at this temperature fruit will have virtually no shelf life prior to reaching a minimum firmness of 4 kgf, and thus the calculator will display a warning in the RSL column. In this situation, an importer may be able to reduce their storage temperature and potentially increase RSL by 1 or 2 days if they cannot reduce the minimum firmness threshold below 4 kg due to customer quality requirements or standards.
Figure 5a. Information provided by RSL calculator warning that total recommended sea freight storage duration (A) has been exceeded resulting in an increased risk of storage disorders during importer storage and retailing.
Figure 5b. Information provided by RSL calculator warning that minimum flesh firmness (B) has been exceeded resulting in an increased risk of storage disorders during importer storage and retailing.
In another example using the calculator to determine RSL during retailing (Fig. 6a & 6b), RSL is estimated at approximately 7 days (i.e., cold chain scenario A) after air freight at 10 °C and importer storage of one week at 4 °C, where an average temperature of 4 °C is assumed during distribution and retailing. In this case, RSL is based on a minimum threshold flesh firmness of 2 kgf and represents the threshold at which point fruit would be considered unmarketable to consumers. An increase in average retailer temperature from 4 to 10 °C as in cold chain scenario B (i.e., poor temperature management within this stage), demonstrates that RSL will fall from 7 days to approximately 3 days, giving the retailer little time to market the fruit.
Figure 6a. Estimated remaining shelf life during retailer handling at 4 °C (A) after air freight and importer storage.
Figure 6b. Estimated remaining shelf life during retailer handling at 10 °C (B) after air freight and importer storage.
The effect of changing the minimum flesh firmness threshold at which point the importer needs to dispatch fruit is demonstrated in the sea freight cold chain example provided in Figures 7a & 7b. In both scenarios A and B, stage temperatures and durations are the same, but minimum threshold firmness is set at 5 kgf in (A), and 4 kgf in (B), resulting in a corresponding increase in RSL for the importer from approximately 1 day (A) to 5 days (B). This example demonstrates how lower threshold firmness provides greater flexibility in terms of the marketing window. Of course whether the threshold firmness can be altered will depend on the marketing channel and on quality standards agreed to by the importer and retailer.
Figure 7a. Estimated remaining shelf life during importer storage after sea freight with minimum flesh firmness allowable prior to dispatch set at 5 kg (A).
Figure 7b. Estimated remaining shelf life during importer storage after sea freight with minimum flesh firmness allowable prior to dispatch set at 4 kg (B).
The calculator was developed by the Decision Aid Team as part of the Serviced Supply Chain project. 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.