Preconditioning: delayed cooling after harvest reduces storage disorders in white-fleshed nectarine and peach

Agriculture Victoria research suggests that growers and exporters may be able to implement preconditioning to reduce the risk of storage disorders among fruit destined for domestic or export markets where fruit is likely to be stored at low temperature for two weeks or more.

Key findings to emerge from nectarine and peach preconditioning trials:

  • Preconditioning to 12 or 18°C for 48 hours directly after harvest significantly reduced flesh browning among Majestic Pearl nectarine and Polar Queen peach during cool storage of up to 6 weeks compared to fruit that was immediately cooled down to 2°C directly after harvest;
  • Flesh firmness of preconditioned fruit was slightly lower during cool storage than among immediately cooled fruit but these differences are unlikely to reduce marketability of fruit after cool storage;
  • Preconditioned Majestic Pearl had higher flesh juiciness after a shelf life period at 18°C, suggesting that immediately cooled fruit may have had higher mealiness.

Talk from Summerfruit Webinar series 2020: Managing fruit quality for export

Stonefruit delayed cooling - John Lopresti, from Agriculture Victoria
Webinar 2nd September 2020 (48min 54sec). John Lopresti, from Agriculture Victoria, presents at the Summerfruit Industry webinar series 2020, talking on a key topic for industry:  Stonefruit delayed cooling.

Webinar presentation - PDF opens in new window (Note: this document does not meet WCAG 2.0 accessibility guidelines.)

Webinar - Video Transcript

Hi everyone. My name is John Lopresti, Ag Victoria. And today I'll be talking about some work we've done looking at. delayed cooling or also known as preconditioning to attempt to reduce storage disorders during cool storage in stone fruit. Some of you may have heard of delayed cooling or preconditioned, air conditioning.  Over the years there has been research done in this area, but we did things slightly differently to attempt to make it viable or a possibility to actually implement commercially. So we'll talk about that in a little while. So today we'll cover, 'why preconditioning, why make it work in reducing storage disorders?  It's also known as delayed cooling, or stepwise cooling, it's all the same thing. It's basically a treatment directly after harvest where you are not fast cooling the fruits. You're putting it at slow cooling step before cooling down to zero to two degrees. So I'm going to use those terms interchangeably today.
I'm going to look at how we ran out trials. What approach we took, then results from Majestic Pearl nectarine and Polar Queen peach from the trials we ran last season, and then how can we potentially implement this preconditioning treatment, commercially, which may be of interest to some of the growers out there.
So storage disorders are a problem and over the life of the current Serviced Supply Chains project, we've done a lot of trials and we've found a lot of issues to longterm cool storage. So many current varieties are susceptible. Standard practices in Australia, is gernerally to cool, immediately off to harvest, which may actually increase the risk of storage disorders.
The other issue is that sea freight into importing countries can take well over three weeks. And many of the cultivars we grow, potentially can't, don't have that kind of storage potentially. And also this cooling and warming after harvest. So we who the fruit quickly then warms up again for packing. Then we call it down again. And then if the goes to the freight forwarder for air freight fumigation, it gets warmed up again. So it's traveling through this kill zone of between three and eight degrees, multiple times, which isn't good for the fruit. So preconditioning may, in some ways, also help solve that problem.
And this figure I've got on the right here. This was, Glen Hale, did an outturn assessment in China at last season. This is Flavoured Pearl, a very good variety with good storage potential. And once he received the fruit 32 days, after 32 days of sea, well not sea frieght, total from harvest to the end of sea freight. You ripen the fruit over 8 days, so day 33 - 34 and onwards. And as you can see, there was no change in firmness and no change in maturity. So basically this fruit had been damaged to the point where it didn't ripen at all. Now that's scary to think that can occur, fruit that's been sea freighted, in a variety that's that's supposed to be quite a good performer, storage wise. There was no flesh browning, but it just didn't ripen, so it could be an indicator of a storage disorder there.
So why preconditioning, this is a bit technical. There's been a lot of work done on it, but that, but basically I like to think of it this way. Imagine, you're in a sauna, you're in a sauna at 35- 40 degrees, and then you step out into minus two degree environment. You're going to get a bit of a shock, but the human body is quite complex and our physiology can adapt. Well, in a way stonefruit can't. So, when you have a stone fruit, they immediately, they begin to ripen we could say, all proteins and enzymes and the fruit that are activated, which are related to producing ethylene, breaking down the cell walls, so fruit softens, and energy and metabolism. The issue is that, if you're immediately cool, these proteins and enzymes aren't activated. Where as preconditioning during preconditioning, a warm phase after harvest, these proteins are partially activated . You put the fruit in cold storage, then there's these enzymes and proteins remain there, ripening's delayed.  But immediate cooling, then cool storage, there's low temperature stress. And then when you try to ripen the fruit out of cold storage, normal ripening occurs in the precondition fruit, but in the fast cooled fruit, the fruits unable to ripen properly because these proteins and enzymes that are required were never activated. I'm simplifying it, but that's basically the theory behind it.
So looking at this, previous, there's been quite a bit of work done overseas on preconditioning, but the issue is that with their approaches, obviously they didn't look at our varities because a lot of the research is quite old. When they have harvested the fruit for the trials, they based it on fruit firmness, not actual fruit maturity, and this is an issue because you can have quite a wide range of maturity at harvest, when you pick the fruit, the firmness can be pretty much the same as measured. So firmness isn't generally a very good indicator of differences in physiological maturity. They generally use a single preconditioning temperature, usually 20 degrees. They only have a few storage periods and rippening periods during the trial. And if you want to measure mealiness via fruit, how juicy the fruit is, that usually you do what you measure using expressible juice, which basically sampling a small part of each fruit to measure how juicy the fruit eats, which may not be representative of the whole fruit.
So in our trials, what we did a little bit differently was we obtained fruit that was very uniform in harvest maturity based on fruit ripeness, rather than firmness, using a DA meter. We had two preconditioning temperatures, 12 and 18 degrees because we wanted to see that this preconditioning work at 12 is because that's a temperature that is more likely to be commercially implemented than 18.  We ran the trial similar to what a grower could potentially implement commercially. Multiple cool storage and ripening periods, and we measured the juiciness of fruit on the whole fruit, not a small section, which I think is very important. And the two trials were majestic, the cultivators we looked at were Majestic Pearl, white flesh nectarine and Polar Queen from Shepparton, a  white peach that is highly susceptible to storage disorders.
And this is how we ran the trial. So from the left, we monitored a maturity for several weeks before commercial harvest. Then went in, harvested the fruit, on one day. Then we segragated the fruit into maturity classes and selected the middle class, which is a commercial, we call commercial onset maturity class. And that made up about 75% of the fruit we actually harvested.  So it was quite representative of that harvest. Then we assigned the fruit randomly to 3 preconditioning temperatures, 48 hours, two degrees, 12 degrees, 18 degrees. The two degrees we can call immediate cooling. or standard commercial grower practice, so that your standard cooling, fast cooling down to two degrees.
After the 48 hours, we fruit into trays, assigned them to cool rooms of two degrees, and we had four cool rooms for replica Corcool rooms, and then weekly removals for quality assessment. At each weekly removal, we ripen the fruits for 3 days and five days at 18 degrees. And a few more notes here, because it's important to understand and methodology because we tried to implement it in a way, as I said that the growers could potentially implement it.  Fruit was harvested at 25 degrees and into preconditioning treatments are about 22 degrees. All fruit it was cooled to preconditioning temperature within seven hours of going into those temperatures. So pretty fast, dropping temperature.  48, the treatment was 48 hours, which included both the cooling from harvest tiemperture and the preconditioning. And as I said, fruit stored for up to six weeks at two degrees with weekly removals, and then ripening.
Okay. So that's the background. Oh, there's one more, actually one more background, which is quality assessments. We did the standard quality assessment, fruit maturity, colour, flesh firmness, soluble solids, titrated acidity. Flesh browning incidence, and severity. And from majestic Pearl, we measured the free juice using a technique I came up with using an olive press, and a way of chopping up the fruit that was very consistent and used the whole fruit. And I was the only one that did the assessment for the juice so that we only had one single assessor. So you minimize the errors if you use more than one assessor. So basic quality assessments.
OK.  Now let's talk about Majestic Pearl. So the idea, on the left here, the idea was that fruit that went into each storage, which removal, period, and each treatment was the same maturity. You want us to take that factor out of impacting on potential storages disorders. Say, I don't look at the graph on the left. The fruit at harvest was assigned to all these different storage periods and treatments, and it's basically all the same maturity so we actually managed to ensure that we had caught the same maturity across all the fruit, across the whole trial, which is really important and this is true physiological maturity. The graph on the right is how the physiological maturity based on DA ,on the DA value or DA meter, how that changed during storage and ripening. And as you can see among the 3 treatments, pre-conditioning treatments, two, 12, and 18, there was very little difference in ripeness over the life of the experiment, which is good to see. So we can basically say the fruit the fruit ripened similarly among the three preconditioning treatments. So, just to demonstrate that physiologically the fruit was pretty much the same across the trial as the fruit  during storage and then ripen and among the three treatments. Now, a question that growers might ask you is, you're holding the fruit at 18 degrees at 12 or 18 degrees for two days, isn't that going to impact on fruit firmness during storage? Yes, it will, and this is the result we had from Majestic Pearl. So this is fruit directly out of cool storage at two degrees after zero, seven, 14, 21, 28, 35 days. This is flesh firmness and the three pre-conditioning treatents. And as you can see, yes, the fruit that was immediately cooled to 2 degrees, remained a little bit firmer than preconditioned fruit T 12, and I8 degrees, but this difference wasn't, up to about 28 days of cool storage. wasn't particularly large. All fruit was about five kilos. Yes, fruit is a little bit softer, but commercially, I don't think it will have a major impact. After 35 days, you're getting a bit more softening as expected in the precondition fruit. But if we look at end of sea-freight being 28 days then there's not that much difference in fruit softening over that period. And then if you ripen the fruit  for 3 days after each storage period, it's basically very little difference in firmness. If you call one and a half kilos, a firmness, the eating firmness at the dotted red line, well all three treatments are basically eating firmness, apart from ripen day zero, 7 day storage and onwards, after 3 days of ripening, pretty much get down to eating quality after 3 days. So again, very little difference between treatments. So all this is good. It means that you can precondition it at that high temperature, 12 or 18 and fruit softening isn't a major issue.
Some may argue otherwise, but I don't think it is. The issue of course is chilling injury or flesh browning. And this is Majestic Pearl six weeks at two degrees. which is on the left and then, Oh, sorry, six weeks of two degrees, and then ripening at 18 degrees for three days, which is on the left and then ripen for five days, which is on the right.  And they're the different preconditioning treatments. Up the top ,two degrees, and 12 dgrees and 18. And I've actually marked with black dotted lines or circles, we would call chilling injuring and flesh browning. And as you can say, the two degree fruit in both cases, has high severity and higher incidnece of chilling injury.  If you go down to the 18 it appears to be less and I'll show you the data and it actually is. I averaged across the whole, the fruits it's actually significantly different. So that's visually what we tended to see. Six weeks is a long time at two degrees, but the way that sea freight is operating at the moment, it's not out of the rounds of possibility that the importer will have fruit that has been stored five weeks since harvest, five to six weeks. That's not outside the realms of possibility when you got an sea freight taking four weeks.
The data to back up our plan that preconditioning works. This is, so we saw no flesh browning up to three weeks of storage, but this data is, here is, 4, 5, 6 weeks of storage. And at each storage time, you've got ripen for zero days directly out of storage, then three days and five days. So four weeks after five days of ripening, we see a little bit of flesh browning in the two degree immediately cold treatment. And as we move along to five and six weeks as fruit ripens, you see a big difference in expression of flesh browning incidents. So that after say six weeks and 3 days of ripening, you've got 35% incidence in the fast cooled fruit, and then significantly lower flesh browning in the 12 degree, 10 degree preconditioning fruit.
So there's a big, an, a physically significant difference there, a clear advantage to preconditioning. and if we look at how severe the browning was, this last season the browning severity was quite low compared to other seasons that we've tested Majestic Pearl, where we found much higher severity, but even with low severity, there is a difference in flesh browning severity with preconditioning, reducing it significantly again, statistically significantly. As you can see, especially after five and six weeks and afterwards. So it's pretty clear 18 degrees with older work on other varieties, that preconditioning has an impact on reducing the potential risk of storage disorders.
And, now this is a little bit more complicated, but even measuring the amount of free juice expressed from fruits, there was a treatment effect. So preconditioned fruit generally, were juicier at each storage period and  after each ripening period,. And I've just circle, circled, that red circle sort of highlights the fact that you're getting at two weeks and three weeks, you're getting juiciness of 35, 36% from the precondition fruit at 18 and significantly lower juiciness at fruit that would be preconditioned at two degrees. And these first 3 weeks there was no sign of flesh browning.  Are we actually seeing flesh dryness or mealiness much earlier than flesh Browning in this fruit free weeks? Because the fruit that was fast called two degrees, the juiciness is very low that you're looking at 12% and 24%, which is very low after three weeks and after, ripeninig. So the juiciness, this measurement could be showing us that the fruit are drying out, the texture is changing, becoming meally, but there still is no sign of it in terms of flesh browning. But if we actually go to four, five, and six weeks of storage, where there was flesh browning, we see a similar story where the preconditioned fruit is jucier at five weeks and six weeks, the patterns the same.
At six weeks, juiciness is reduced in all the treatments because the fruits basically gone beyond its storage potential, but at week four and five, it's clear that precondition fruit are juicier. and we need to remember that you might ask yourself while the precondition fruit is probably softer and riper,  no it's not. The ripeness of fruit among each treatment, is exactly the same as I showed before. So this is fruit, that's of similar ripness yet the preconditioned fruit is jucier, so important finding, I think.
Okay. So Majestic Pearl preliminary findings. Pre-conditioning seems to reduce storage disorder, incidents, and severity beyond three weeks. Preconditioned fruit appears to be juicier, or we can say less mealy at a similar ripeness during storage and ripening. We did find that there was similar fruit, maturity, ripeness among all the treatment, treatments, at each removal, which is a good sign. It means that preconditioning at higher temperatures isn't speeding up the actual physiological ripeness of the fruit, which we don't want. Preconditioned fruit softens, marginally faster during extended storage, but it's unlikely this marginally faster softening doesn't, won't necessarily have an impact on commercial export storage potential. And we did find a lower disorder incidence and severity than previous years, and that could be down to a number of factors, which I probably won't discuss here, but, we harvested this fruit from Cobram, which is a cooler climate versus warmer climate fruit that we've used in other seasons. Harvest maturity can be an issue, which we couldn't look at. We did look at, but I'm not gonna discuss here. So there are other factors.
I'm going to go through Polar Queen. We didn't do fruit juiciness with Polar Queen because I ran out of time, but the data's pretty much, similar and the results are similar. So again Polar Queen maturity at harvest was the same across all fruit that we assigned to different, preconditioning temperatures and storage periods. And then on the right hand side, you see how the fruit ripened over the storage period. That shouldn't be one to see six days, that should be seven 14, 21, 28 and 35 days. My apologies, forgot to change that. But as you can say, pretty much the same ripeness at each removal as we saw for Majestic Pearl.
In terms of fruit firmness ,after storage, with no ripening during that 5 week storage period, it gave no difference in fruit firmness among the conditioning treatments. So preconditioning basically had very little impact on fruit softening relative to fast cooling or medium cooling. Again, a good sign, and a surprising sign in a sense, but that's the result.
This is, now if you look at this and it looks a bit strange that's because it is. So on the left is the fruit firmness after ripening for three days at 18 degrees. So after no storage or seven days storage, the fruit ripened down to, down to one Kilogram, which you'd expect after three days at 18. But as the storage period increased, fruit firmess after ripening actually increased. It happened at five days of ripening as well. Now that's a little bit weird. It should remain well bellow two kilos after three days of ripeing. So what's obviously happening is this fruit's been damaged, and it's storage potential, this is a white peach, ()  is very short. And this strange behavoiur in firmness is demonstrating that. In saying that, preconditioned fruit had a firmness, which means that ripening a little bit more properly than fast cooled fruit, but still the cultivar, the variety has limited storage potential, so not even pre-conditioning can improve its quality because it just can't store for that longer period.  This is what this is telling us.
And if we look at what happened with Polar Queen. This is chilling injury after five weeks at two degrees on the left and then five weeks at two degrees and ripened for three days. And as you can see, it's not what we want to see, very high levels of flesh browning and mealiness, particularly after ripening regardless of the preconditioning treatment. But in saying that, even this picture, you can see, you see the two degree preconditioning treatment, the fruit among that treatment, the severity of the browning appears to be higher than the 18 degree fruit and even 12 degree fruit. And we can show that in some tables. Again, it looks complicated the figure, but not really say you start from a storage period of zero weeks, one week, two weeks, three weeks, four weeks and five weeks. I want you to focus on the first three weeks. So the left side of the figure. This is flesh browning incidence, and yes, flesh browning incidence was high, even within the first 3 weeks of storage. But as you can see the preconditioning treatment, particularly the 18 degree one, did reduce the incidents of flesh browning. If we focus in on the two week storage period, three and five days of ripening, you've got  50% incidents in the two degree preconditioning treatment, 45 in the 12 and only five in the 18 degrees.
And then if we've got five days of ripening, there's no, flesh browning incidents in the precondition fruit at 18 degrees compared to very high levels in the other preconditioning treatments. So again, they show that preconditioning works except, beyond two to three weeks, this cultivar just hasn't got the storage potentials, so you get very highly levels, very high incidents of flesh browning. If you look at severity, yeah. You get a post random wall as well as much. Most of the, other than the majestic Pearl, again, within the first two to three weeks, preconditioning reduced, The level, the degree of the severity of fish Brown relative to these standard calling at two degrees beyond in week four and five, it did reduce it, but it's still very high considering that a severe severity score above two, two and a half is.
Basically means the fruit is unmarketable in terms of consumer eating, you wouldn't be able to market that fruit. So it just demonstrates that the variety does have a major impact on storage potential, obviously. And how and where the preconditions beneficial or not. But in both varieties, we do see a benefit, one form or another.
Okay. So finishing off the results before we go to commercial implementation. Hopefully you'll see, you agree, or you may have questions, but  you agree that the data suggests that preconditioning dose work. So preconditioning 12 and 18 degrees reduces storage disorders, compared to immediate cooling at two degrees, which is our current standard practice.  And this is among fruit of similar harvest maturity. So we removed any effect of differences in harvest maturity. So which made it easy to demonstrate that there is an effect, it's there and we showed it.  Eighteen degrees, a preconditioning treatment at 18 degrees was marginally more effective than 12 degrees, but both preconditioning treatments, were more effective and significantly more effective than, just standard cooling down to two degrees after harvest.  Variety, as we know, still the limiting factor for cool storage potentials. So can apply these treatments. You can do all sorts of things, but if the variety isn't up to extended storage periosd, there's very little you can do. So other factors may impact on this, the size of the preconditioning effect, how well preconditioning works, and that could be orchard climate prior to harvest and during fruit growth, whether you harvest unripe fruit, where it can be a tendency for export that we have a little bit unripe. That could impact on how preconditioning affects storage disorder risk. So there are other factors we need to look at.
Alright. There's only, I think three slides left and we're going to talk about commercial implementation. The issue with what we do in Australia is that it's a little bit different anecdotally, from what occurs overseas, our own competitors. Because of the large throughput and volumes, my understanding is that they don't cool their fruit directly after harvest, immediately cool to two degrees because they're moving the fruit so quickly that they actually harvest and pack and then cool. So in a way they're unintentionally preconditioning fruit, whereas we, harvesting, fruit that's 25 to 35 degrees Celsius, or let's say 20 to 30 degrees, maybe 35 is a bit extreme, bringing it in and then fast cooling down to one degree Celsius. And as we've shown the data shows, it's probably not the best practice. So what I've drawn up here is a bit of a process for how a grower can potentially implement delayed cooling or preconditioning. So If we go, start at the top, we harvest the fruit at the right maturity, commercial maturity, not earlier. We pull the fruit to 12-20 degrees. Let's say 12 degrees as a realistic temperature for commercial use. We cool it in fruit bins down to 12 and then leave it at that temperature for 48 hours. So the combined cooling and treatment time is 48 hours maximum. Then we can do two things. We can immediately pack the fruit, or we can, as in some cases, growers will delay the packing, leave the fruit ion the bins and put it back in the cool room.
So then we go for the process. Once you've, once it's preconditioning treatments completed, then the pack. If you immediately pack, you grade, pack, and pelletize, then place the fruit on pallets, the packed fruit at two degrees and cool down to, you want to one to  two degrees, which is normal practice, and then you store the fruit until it gets transported for domestic market or export.
On the other hand, if you want to delay packing, and keep the fruit in your bins, which happens, I can imagine quite a bit if you've got high volumes coming in and you haven't got the market for the fruit yet, then you'd cool the fruit down to one, two degrees in the bins, again standard practice. Then store the fruit in the bins, and then you want to minimize the period, the storage period in those bins at zero to two degrees, and then you'd grade and pack in the similar manner.
So the process is simple. All you're doing is adding a preconditioning treatment before the packing or the cooling part of the process. The other thing I've added, which is a green arrow is after immediately packing the fruit, you might actually, if you're confident and want to take a risk,  you may not cool the fruit at all, you might actually transport it to the freight forwarder for air  freight, at 8 to ten degree. Fumigate the fruit at 18 and then the freight forwarder pulls it down to two. And what that process is doing, is you're actually avoiding cooling the fruit and warming the fruit up again through that kill zone. Now I'm not suggesting that we try to implement this straight away because you have to have a lot of confidence in your transporter and in the whole process.  But when you think about cooling fruit down to zero to two degrees for air freight and then that fruit warming up at the freight forwarder for 18 for fumigation, and the issue with fruit condensation, moisture on the fruit surface, and the issues that can cause during fumigation, that potentially in the future could be a path you can take if you can do things very quickly within 60 hours. Get the fruits of the freight forwarder. I'm talking about very integrated post harvest processes, packing, grading, packing, and transport. So to summarise,I suggest, implementation would involve harvest fruits of the final cooling operation whether on packed fruit, cooling the pack fruit or cooling down to 2 degrees in bins has to be conducted within 48 to 60 hours of harvest. And initially maybe safer to use a preconditioned temperature above 10 degrees, but don't go to 18, because I mean commercial implementation of 18 degrees, takes a little bit of a skill and understanding your logistics. So 10 degrees or 12 degrees is probably safer.
Ideally implement this for all chains, export or domestic. Otherwise it gets messy trying to separate fruits for domestic market and for export markets. So it's much simpler to just go through the preconditioning treatment for all fruit that comes in to your shed.  First in first out handling is a must. You preconditioned fruit, and that fruit has to go out first, relative to other fruit that's coming. And avoid the temptation  to pick early or slightly unripe fruit to minimize a risk, if you're worried about preconditioning, because then, the likelihood is that you're not getting any advantage of preconditioning because the fruit you  picked was too unripe and there's going to be other issues during cool storage and ripening for that unripe fruit.
So that's, final slide here. So just to continue on commercial implementation .A lot to take in, but I said this all will be available on the HIN website, and I'm happy for anyone to ask questions after this last slide.
So a few other issues to look over in terms of commercial implementation.  As I said precondition all the fruits then cool to one to two degrees, whether you pack immediately or you leave the fruit in bulk bins for lighter packing. Really, if you try to implement this, the first time you actually need to monitor fruit temperature from harvest and during preconditioning because you need to understand how uniform temperatures are among bins, even within a fruit bin during the preconditioning and cooling. How quickly spread cooling to that  precondition temperature, and how does harvest temperature effect preconditioning treatment? Youn know, how long is it sitting at very high temperatures before it drops down to that 12 degrees? So it's, there's a bit of work in understanding temperature management from harvest and through that cooling process. Preconditioning and air freight. Is it necessary? Strictly, no, because you can get fruit airfreighted into your importing country, say within four days, and then, you assume that the importer will sell that through, market that fruits on with weeks. it's not extended storage, so it shouldn't really need pre- conditioning. But then again, you don't know what they're going to do with your fruit. They might store it for two or three weeks until they've got the right marketing.  So again, it might be worth doing, as I said, preconditioningq all your fruit regardless of the market.
And as I showed you, if a riskier approach is not to cool your fruit down to two degrees at all and get straight to the freight forwarder to avoid this issue of fruit condensation during warming and fumigation. I am not suggesting that you implement this next season, although I've talked to a few growers and they're thinking about trying it. If you are maybe implemented on a very small scale, do some testing in your own coolrooms. Precondition them, store a sample of fruit in your cool rooms for three or four weeks, and then have a look.  Because each grower needs to adjust their own harvest and cooling, current harvest and cool room logistics to their new logistics that include precondition. And one of the major issues that growers will have is a second cooll room to actually, that can be dedicated to precondition. Many growers only have one whole room for the cooling. And so it's going to be quite difficult to implement this preconditioning step.
I think that is all.
Mark. Yeah. So a lot of information there, but, as I said, I'm happy to take questions or, anyone can look once you put that on the HIN website, people can have a look at it themselves.
Thanks, John. It's actually a few questions that have come through all. So I'll start the first one with Noel. So can you track early indications of either browning or juiciness with DA meter measurements?
You would track it. You have to have an understanding of how fruit ripens, so DA or even a firmness measurement can indicate, as I showed for Polar Queen, can indicate that ripening isn't going, is abnormal where instead of firmness or the DA value, reducing down to an expected level, one & a half Kilogram firmness, or a DA value of 0.2, that you expect to occur after ripening, if the fruit's not getting to that point, you've gotta be suspicious that it's been damaged, even if there's no flesh browning, is that normal ripening occurring?  And, you might be able to, if you actually squeezed the fruit, you might be able to detects a lack of juice, but if you don't want to go through that process, I think abnormal, changing firmness or increasing firmness during storage and ripening and no dropping in the DA meter value is a good sign, or potential sign that something abnormal is happening. I think that's, that's how you'ed go about monitoring potential storage disorders without the flesh browning component.
Yeah. Okay.  Another attendee put through a question that I think you've answered. I consider the benefits of preconditioning fruit, but how can some growers do it if they only have one cool room?
Yes. And I had, and I had, yeah, we only do the science here. We don't trie... When it comes to actual infrastructure and logistics, if you believe it's really important for your operation, you may have to install  another ooll room, it may not need to be as, as large as your current cool room, but at the end of the day, if you want to implement this, the other option is to bring the fruit in and leave it in the shed. But then, the shed temperature might be 25 degrees or 30 degrees. So you're know, the preconditioning is occurring at a very high temperature, so we don't want that. So I don't see any way around it, than installing a cool room dedicated to preconditioning, where fruit comes in from harvest, the room's set at 12degrees. You leave your fruit in there for two days, and then you run your packing operations, or you move the fruit to your mind cool room at two degrees, one to 2 degrees, so it really does require that second cool room, I hate to say.
Yeah. Yeah. Another question John, the DA meter reading was about 0.6, for Polar Queen,  compared to Majestic Pearl of 1.1. Does the DA meter reading have an impact on storage performance?
Christine  next week will talk all about harvest maturity and using the DA meter. And yes, it does. The DA reading is giving you an idea of physiological maturity. So at harvest different cultivars have a different DA value at which we consider them to be a commercial maturity or onset maturity, where they're just at the point of producing ethylene and that's, for each cultivators that's the point we say you should be picking  the fruit. But that point is measured by the DA meter. That value will vary among cultivars. So for example, we just did Pearl, that value's around ,at harvest, about 1.1 - 1.2 DA units.  Whereas for Polar Queen, it's probably about 0.8. So it does vary amoung cultivars.  Yes. The  DA meter reading will give you an idea of the storage performance, because a lot of DA meter reading usually aquaits to riper fruits. So a shorter storage duration, it would be expected as the fruit is riper at harvest. Yeah and Christine will cover all of that next week.
. Do you think we should precondition fruit for the domestic market or air freight or is it just for sea feight?
Okay. So for domestic market, if you're a grower and a going to store your fruit, extended period of time, that's over two weeks, and I don't know if growers do that, they might store fruit and wait for the right opportunity, market opportunity or may not, but if you going to store it for more than 2 weeks, precondition.  And for air freight, as I said, it's probably not necessary, but you don't know what's happening to your fruit once the importer receives it and they may store the fruit for two or three weeks, you don't know. And certainly for sea freight, this is where it's, that it could see a lot of benefit when we know that sea freight is taking well over 21 days, just the sea freight component. So anything you can do to minimize the risk of storage disorders over that long period of time while it's worth while we're doing.
But in saying that the reason I didn't, I only, I suggested that you do it for all fruit is just purely logistical because. You as a grower, how do you separate at harvest? Are you going to separate fruit food, your different markets? It's really hard to do it's just easier to just precondition everything and then you can make marketing decisions.
certainly if you know that a certain batch of fruit that she passes has going for it, You're not that. specifically then you might not want to precondition, but I don't see how in the heat of the, I bet very busy. How does steam period, you're going to be able to sit sacred, bad fruit at the harvest stage.
most growers would have stole the fruit and then you might pre preconditioned at all. And then you got rod, I've got a market export market here or domestic market and send it off there. So it just for simplifying the logistics. that I think that's probably why it's just, if you're going to implement just precondition, have a single process for your missional fruit that you harvest.
Okay, great. Okay. Last question we've got here is from Andrew McNish. Could growers install a refrigerated container during the season to provide another cold room at the ideal temperature?
Good idea. Andrew. They could, I think it needs, the issue is that it's about the volume of fruit coming in. So you could have refrigerated containers set at 10 to 12 degrees. It's just a matter of how many do you need and fit in those bins. I think it was basically, we're talking about preconditioning in bins, so it's about the volume of fruit and capacity to actually precondition that fruit coming in. That's the issue. So yeah. I mean something where you could bring in a portable cool room of a sufficient size or something like that. They are options. Yes, rather than spending the money on, expensive infrastructure and another cool room. yeah, but that's again for the grower to determine if they're going to implement this.
Okay. Michael asks is the length of preconditioning required a different for each variety? Okay. As far as, based on what past literature and past research, and that, I can't see I'm any the work being done on the length of preconditioning time. 48 hours. They've tried 24. They've tried 48 and 48 seems to work better. But, we just don't have enough information on whether there's a varietal aspect to that. Whether you may only need 24 hours for some varieties and some varieties you might go to 36 hours, we don't know, and that's part of work that we'd like to do into the future for some of our other cultivars, to look at those aspect of it. Also looking at fruit maturity and how preconditioning affects, how preconditioning, the effects of preconditioning charge with commercial maturing versus slightly unripened fruit, which is likely to be harvested in some cases. yeah. No we don't have that information as yet.

Effect of preconditioning on storage disorders and fruit firmness

Preconditioning at 12 and 18°C for 48 hours of commercially mature Majestic Pearl nectarine reduced incidence of flesh browning after cool storage for 4, 5 and 6 weeks, followed by a shelf life period of 3 and 5 days (Fig. 1). No flesh browning symptoms were observed directly out of cool storage during the six week storage period. Preconditioning at 18°C rather than at 12°C appeared to be more effective in reducing flesh browning symptoms, but both preconditioning temperatures more than halved the incidence of flesh browning after cool storage for 5 and 6 weeks followed by a shelf life period, compared to fruit that was cooled immediately.

Figure 1. Incidence of flesh browning during cool storage and ripening of commercially ripe Majestic Pearl nectarine fruit that was immediately cooled (2°C) and preconditioned (12 and 18°C).

In light of these positive results, a grower or exporter may ask whether preconditioning also increases the rate of fruit softening during cool storage or sea freight. We found that flesh firmness of preconditioned fruit was slightly lower than among immediately cooled fruit during extended cool storage, but differences were minimal and inconsistent (Fig. 2), and unlikely to significantly impact on marketability of fruit after cool storage or export. For example, after 28 days of cool storage at 2°C (i.e., a likely storage duration encountered between harvest and the end of sea freight export), both immediately cooled and preconditioned fruit had an average flesh firmness of between 5 and 6 kgf.

Figure 2. Change in flesh firmness during cool storage of commercially ripe Majestic Pearl nectarine fruit that was immediately cooled (2°C) and preconditioned (12 and 18°C).

Polar Queen peach was highly susceptible to storage disorders during cool storage at 2°C. Flesh browning symptoms appeared among immediately cooled fruit after two weeks of cool storage and a shelf life period. All fruit showed flesh browning symptoms after cool storage for 3, 4 and 5 weeks. After cool storage for 3 weeks and subsequent shelf life for 3 and 5 days, preconditioning at 18°C reduced incidence of flesh browning by 35% compared to fruit that was immediately cooled (Fig. 3).

Flesh browning development Figure 3. Flesh browning development among immediately cooled (2°C) and preconditioned (12 and 18°C) Polar Queen peach fruit stored for 5 weeks at 2°C. Red circles indicate fruit with chilling disorders.

Preconditioning and commercial implementation

Commercial preconditioning of stone fruit as described in Figure 4 may reduce the risk of storage disorders where cool storage duration from harvest to retail is at least two weeks for domestic markets and air freight export chains, and at least three weeks for sea freight export chains. Incorporating step-wise cooling into current cooling, packing and storage operations requires an additional cool room set at a preconditioning temperature of 12°C. If immediate grading and packing is conducted after preconditioning, then fruit will need to be cooled down to 0 to 2°C on the pallet prior to further storage and/or transport. If fruit are stored in bulk bins after preconditioning, then it should also be cooled and stored at 0 to 2°C, although it is recommended that grading and packing of this fruit is completed as soon as possible.

It may also be possible to avoid cooling fruit down to 0 to 2°C after grading and packing if it is destined for air freight export, and if efficient and rapid transport is available at 8 to 10°C to directly ship packed fruit to the freight forwarder. The advantage of this process, apart from avoiding the cooling of fruit through the ‘kill zone’ prior to transport, is that the time required to warm the fruit to 18°C for fumigation prior to air freight is significantly reduced, as is the risk of condensation on fruit, which may occur under current practice where the freight forwarder receives fruit at below 3°C.

In general, when handling stone fruit it is important to reduce the number of times that fruit is cooled, or warms up, through the ‘kill zone’ of 3 to 8°C, a temperature range that is associated with increased risk of storage disorders during cool storage. Regardless of the step-wise cooling protocols adopted by individual growers and exporters, temperature monitoring from harvest onwards is recommended to fine tune preconditioning and storage operations. Furthermore, a ‘first-in, first-out’ approach is necessary to ensure that preconditioning among any batch of harvested fruit does not exceed 48 hours, as excessively-long cooling at 12°C could increase the risk of excessive fruit softening further along the supply chain.

Future trials need to be undertaken among other susceptible cultivars to verify these preliminary results, and to also understand the impact and interaction of harvest maturity, orchard climate during fruit growth, and preconditioning, on flesh disorder incidence and severity during extended cool storage followed by a ripening period.

Preconditioning process Figure 4. Possible step-wise cooling and handling logistics after harvest for nectarine and peach cultivars destined for export or domestic markets.

Project acknowledgement

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