I'm Christine Frisina. I've worked in the Post-harvest group for several decades actually now, and I'm going to talk about some of the work that we've been doing on fruit maturity and harvest readiness. Part of the reason behind this is looking at results of poor outturn from exports, as well as, domestic removals from storage in particular things like flesh browning, flesh discoloration, mealiness, rubbery fruit and shrivel. We're looking at some of the reasons about why this has happened and how we measure harvest maturity, the impacts of cultivar on maturity, and I'm going to look at firmness and sweetness results from a few cultivars and looking at fruit development effect on those firmness and sweetness results, and also look at a couple of storage trial results from a couple of cultivars.
The fruit, that poor outturn is obvious, but, it's internal. Flesh Browning, you can see here on the left in particular, is quite severe in the Flavoured Pearl Nectarine. That was after three weeks of storage, a simulated storage or simulated shipping, plus two days return to ambient temperature. And that's where this flesh browning shows up. Majestic Pearl nectarine, one week, only one week of storage and it showed up this quite severe browning, which is not a good thing. This Polar Princess peach is actually a white peach. It looks like a yellow peach in this photo. That's how discoloured and off coloured the flesh has become after only two weeks of cold storage, plus two days of return to ambient temperature. Always these kinds of disorders show up after this return to ambient temperature. It comes out of cold quite okay, but it's the return to ambient temperature that shows up the problems. There's also mealiness, it dry, woolly and juiceless texture. You can just see the flesh here starting to break down. This is again, only a short time in storage at two weeks plus the two days - Yellow flesh nectarine. So it's supposed to be that yellow, but it's quite not an unpleasant colour overall. And rubberiness is where the cortex of the fruit, which is this kind of section here, compacts the cells. The cells all compact and it makes the firmness quite dense. And we can measure that without penetrometer equipment, which is linked to software on a computer. On the left, here is a normal firmness measurement where the pressure is measured and it goes up in a nice linear response and a nice almost opposite downslide after it's penetrated the fruit. In a rubbery piece of fruit, we noticed that the angle of the incline is much sharper and then there's a massive drop once the fruit has penetrated that section, where the cells are all, compacted close together, contracted close together. It's almost like a rubbery leathery kind of a result, and it can be seen here. Some of the problem is that the, the problems that the outturn has, is that they're mostly internal, as well as textural. It can lead to poor or dull skin colour, often no aroma and or poor flavour and sometimes off odours depending on the cultivars.
If we look at the effect of maturity on outturn, and some of this work has been done for decades, globally, we know that that immature fruit in particular are more likely to express some of those factors that I just discussed, the flesh Browning, the rubbery flesh, dryness, where the flesh isn't Brown, but, there's no juice in it. Discolour flesh, dehydration, including those rubbery and shrivelled factors and sometimes mealiness, which tends to be cultivar dependent in the immature fruit. If you pick the fruit over mature and store it for extended periods of times, you do get mealiness, flesh browning, and obviously shrivel. But that's not usually a maturity that is harvested for long-term storage.
So how do we look at harvest maturities? These are normally factors based on physical attributes, like colour, size, firmness, and sweetness. What we discovered through some of this long-term work that I've been doing, partly through the PhD that I was working with, with RMIT, but also, through other work, is that, the factors measure harvest readiness, not actually maturity.
So the fruit is harvest ready, but it's not actually ready to harvest. So this leads us to looking at physiological maturity, which we've been doing for a few years now, trying to look at it in different ways, where the fruit needs to be harvested, where it can progress through what we call ontogeny, which is, which is progress right through its full development and reach its organoleptic potential. That is that it get to taste and ripen properly and taste and smell like the variety that you expect. In that way, we need to use the physiologic maturity to measure the development stage of the fruit. So we know at the time of harvest, what we’re actually harvesting. But to do that, we need factors that can help us understand stage, easy factors to help us understand the stage at what the fruit is doing.
I looked at CO2 production, but discovered that it wasn't sensitive enough. The changes aren't big enough. There’s more variability in the changes in CO2 production. It's not as easily to discern the stages as it is with ethylene production. So that's a better of measure.
Just a quick look at fruit development, overall. This is a schematic that's been around for a while, but I pulled it out of a paper by Costin Romena who the Italian researchers have been looking at - this sort of work, fruit development, fruit maturity for a while as well. The growth, this is the basic sigmoidal growth pattern of a climacteric piece of fruit. The solid lines here represent climacteric changes as the fruit go through these different phases along the bottom of the chart. When we want to pick the fruit, we want to pick it before it hits this, this ripening phase here. We don't want it to be in that phase, but we need it to be well past it's, you know, mid stage of growth, because we need it to be a certain size and progressed enough. We've worked out is that to do that, we need to look at ethylene production in this phase, this section of the ethylene production chart here. Anything before this is still not producing ethylene, and it inhibits metabolic processes. There's things that haven't turned on, if you like, that haven't got to a stage where the fruit can progress through all of this full development and mature and ripen properly. So if we pick the fruit with this upkick of production, initial onset of ethylene, it will do those things that we talked about, that where it will progress through that ontogeny, it will develop and it will go through the full ripening phase properly. If we don't pick it at this stage, if we pick it a bit backward, the fruit in this section won't ripen properly. It won't be able to, because those factors haven't already been switched on, if you like, the metabolic processes and the pathways that are kicked in when the fruit go through ripening or it's proceeding phases, the fruit doesn't catch up so to speak. It does have some factors that will automatically switch on after the fruit has been harvested, which is what they call an abscission factor. So there's like a chemical response after a few days from harvest where the fruit realizes that it's not receiving anything from the tree and it will automatically start trying to get the seed ready for dispersal. So it will go through some of those processes, but they haven't reached the right stage previous to harvest for it to work properly. And I'm going talk about that a little bit further as well.
In doing this, we've worked out with ethylene production and correlating it to the index of absorbance difference meter or the DA meter, as most as you've come to learn it as, and this is a section from the horticulture industry network website that Mark was alluding to in the introduction. There's about 20 odd cultivars there at the moment. I've got three more to add soon, from work we did last summer. The stages of maturity that we really want to look at is this onset stage here. And some of the cultivars I'm going to talk about today in particular, are Snowflame 23, which is a white fleshed peach, August Flame peach, this one down here, and September bright nectarine. I'll also talk about a couple of extra white flesh nectarine and a peach that we've been working on as well.
So if we look at the Snowflame 23 white fleshed peach, an earlier season variety, this is firmness versus DA. So firmness on the left, DA across the bottom. The very right hand side of the chart is immature green, internal flesh scores, and the zero, the left hand side of the chart on the bottom is fully ripe fruit. We factor in the DA responses for this variety, the onset of ethylene hits in at about 0.9 and the climacteric flush hits in at about 0.3. So these are your no ethylene, onset and climacteric phases here. If you're looking at firmness as a maturity factor, this is where you would be harvesting your fruit, approximately five to six kilos. We've also got all these fruit in the no ethylene phase as well. That would be mistaken based on firmness alone, as ready fruit.
In the August flame yellow flesh peach, onset is about 1.3. Climacteric about 0.7. It's quite a firm peach. So, you know the bracket for harvesting is in about this range. You've got a few in the no ethylene, a few in the climacteric. It's actually not a bad response ethylene versus DA, but it's not great.
If we look at September bright, the climacteric flush starts at 0.5, the onset at 1.2. Again, you've got the onset firmness range in here, but you've also got a lot of fruit that if you're harvesting at a specific firmness would be in this range and it's these fruit here in this section, you know, just after the onset of DA, that would be roughly the same size and colour as the ready fruit. That is really the concern. But you've also got a few fruit over here in the climacteric that may be, you know, depending on the timing, maybe still included.
Diamond Pearl, white flesh nectarine. We did for the first time. I did for the first time this year. The firmness range is quite sharp. It drops quite quickly and after doing some work with it, we believe this may be a melting flesh variety. The onset is very low at 0.7 and it's a very short timeframe, a very short DA section to 0.3. The fruit is a very soft fruit with the firmness range quite low. If you're looking at onset as your, as your marker, you're looking at two to three kilograms of fruit firmness, and there's quite a few fruit, not in this one, but you can imagine that there would be more in this, in these gaps here, but there's still, you know, fruit in that range.
Sweetness as a factor of harvest maturity is not a good option. Sorry, this is Pola Princess. This was a cultivar that when I talked to one of the growers, they said they harvested it five times to try and get ripe fruit. When we looked at it, we discovered that it doesn't soften. There's no firmness changes at all from unripe fruit, right through to ripe fruit. There was very little ethylene production, like we're talking tiny, tiny, tiny amounts. If we didn't have a GC (Gas Chromatograph), well, there's no way we would have picked up any of it. And what we discovered is, this is what's called a suppressed ethylene producing variety. It does not, it needs a bit more work. It doesn't behave exactly the same as other climacteric fruit. There are a few. We don't normally have to deal with them, but this is one. And as I said, you can see the fruit doesn't soften.
Sweetness, is not a great option for looking at as a harvest readiness factor because the fruit is sweet all the way from, well under ripe, you know. 12% brix here for the white, early season white peach, is the bottom limit for this variety. So you’re getting fruit that ready as sweetness quite early on in the fruit development, and this goes for all the varieties we looked at. So fruit are ready to go quite early as far as sweetness goes. This was September Bright, Diamond Peal’s the same and Polar princess, which we showed there was suppressed ethylene for, is no different.
So if we look at firmness it seems to be the closest relating one, but we still have to be really careful because for each of the varieties, there's a crossover between the low range of the no ethylene and the high range of the onset. And we don't really want to go down to the low range of the onset fruit, if we can make it to that far. But you know, it depends on the variety.
Looking at long term storage in some of those cultivars - This is the Polar Princess. We determined maturities based on changing the, DA quite broadly. There were little differences between the overall firmness to start with, you know, a kilogram is really not that much in the real sense. Out of storage each week - so this graph shows each of these blocks here is a week of cold storage. And then these numbers here represent time at ambient temperature after they've been removed from two degrees. So out of two degrees at each of these time points, there is very little change in the overall firmness of the fruit on removal from cold storage. The fruit hold’s firmness quite well directly out of cold storage. Once it's for me from cold storage, there are differences. The fruit either drop dramatically or they hold a bit and then drop. So in all cases, the firmness of the no ethylene fruit held or appeared to go up, but, you know, that's the variation in fruit, in some cases it's only half a kilogram. So, I wouldn't say that's anything, but it takes a couple of days for that fruit to, to soften. With the other two maturities that we looked at, the fruit softened quite nicely. Once it's removed from storage. The onsite and climacteric fruit follow very similar trends. The no ethylene fruit does eventually soften, once it's had cold storage treatment, it does. But when it's harvested directly, there was no softening. This fruit was six days at eight degrees and it still was nearly seven kilos of firmness pressure. I don't know about anybody else, but that would break my teeth, or you'd need a knife. You'd want to cook those fruit, you know, like it's just not pleasant, eating texture unless you really liked hard fruit. You may as well be eating an apple. The one thing that we did note with these fruit is that after a couple of weeks of cold storage, so we're hitting the third week of cold storage, the firmness pressures after two and three days of ambient temperature started to increase. So where we would expect them to go down in a almost linear response, or they would always be decreasing, after three weeks of storage, the firmness started to increase in some of these fruit in the subsequent shelf life, compared to the previous weeks. This is what we can see as rubbery response in these fruit. So these fruit are turning rubbery and they're becoming juiceless as well. So they're losing juice from their cells and the cells are compacting, and it was much more noticeable in the no ethylene fruit. In the Diamond Pearl, which was the one that we considered to be a melting flesh fruit, the fruit, the profiles are all quite similar once the fruit has gone through its shelf life, it's simulated, ambient routine, returned to ambient temperature. You can see there's differences between all of the maturities in these green, yellow, and red marks where the green is no ethylene, the yellow is onset and the red is climacteric. The difference from putting them into storage to removal from storage at any given time point, and they soften quite quickly once they're removed from cold storage. This is strictly after harvest. So even directly after harvest in this case, the no ethylene fruit where we're softening rapidly. Again, with this fruit, by the time the three and four week periods of storage were completed, we were getting returned, increase firmness. So rubbery effect in these fruit. This was starting to happen in the other maturities as well. The effect on the climacteric fruit is more a leathery response as opposed to a rubbery response. It's a bit subjective but.
The next few slides I'm going to talk about are going to be all on the same variety. This is August flame, yellow flesh late season nectarine. Harvest is about mid February in Tatura. So we have our no ethylene onset, and our climacteric fruits. So immature, you know, premature and then ripe fruit. The same concept that they're held at, either no, one, two, three or four weeks of two degrees storage and then subjected to up to nine days of ambient return temperature. That was in the, this week, six days after one, two, three, and four weeks. The response is very similar to the previous cultivars. There's differences between the maturities straight after harvest, but once you return them, once you pull them out of cold storage and return them to warming, they softened quite quickly. The same effect we were getting in the previous varieties, in that, you know, by the time four weeks comes along, the no ethylene fruit are showing signs of rubberiness or dehydration.
This is IAD so this is the DA response to those exact same fruit from the previous slide. You can say that the trends are almost identical to the, to the firmness, which implies that there's a good relationship with that. Apart from the climacteric fruit, there's a difference there, but it appears that the fruit are ripening. So that it's not just a softening effect, it's a ripening effect. Now this is something that we have to be really careful of. The DA meter reads chlorophyll A in the flesh. So that will reduce as the fruit age, regardless of the maturity factor in the fruit. And I will show you that this is not necessarily ripening. And I'm going to look at these, this point here where the fruit all look like they're at the same maturity stage after three weeks storage, they've all caught up to each other. It looks like that, that these are the same, the same maturity factor, you could say that they were the same quality of fruit. But, what we've seen is this is images of aroma production by the fruit from that very point in time. So this is after three weeks of storage at two degrees, plus three days of shelf life for those exact same fruit. The chromatagrams that were provided by those, were captured by those fruit, by the emissions that those fruit put out, show that the no ethylene fruit, which is the top line here, the peaks of production of compounds that it's producing is far less intense, far less size than the other two maturities that we looked at. Some of these peaks are very important in terms of aroma profile in peaches and nectarines. And if they're not there, you can't pick them up. And so, so returning them to ambient temperature and expecting them to, um, watching them soften does not prove, it does not show that they are ripening properly. They are softening, but they aren't necessarily ripening. The disorder data that goes with that same trial also shows that the no ethylene fruit all had issues from the get go. So this is without, this line here is without any storage at all. It went straight into simulated marketing or, or ambient temperature and it showed that these fruit here had internal browning (this is internal browning, because I checked that just before) quite early. There was also rubbery fruit associated with these as well. So after, so that was initially after storage that, accelerated, and then at two weeks storage, we started getting increases in that onset section of fruit where we, we think that is the best option to harvest. So this was a bit of concern and it got markedly worse as the timeframe of storage increased. You can see for all of them that, apart from the climacteric fruit, which would have had senescent rots happening, as time progressed, uh, there was no problem at zero until this point. Zero here being that directly out of cold storage. Except by the time we got to four weeks, we were getting it here. A little bit about three weeks for the onset, but the, the thing is, is that we need to move this, um, the responses that are happening here to the right, we need to be able to push the fruit that bit more so that we can get three or four weeks of storage out of the fruit. Now it may be that this cultivar isn't suited to long term storage, but we do need to look at options that, that predispose the fruit to being stored for longer.
One of the things that this points out, and it's comments that have come from researchers that I've worked with over the years, that you can't make bad fruit good by using good processes, you can only keep good fruit adequate. If put good fruit into a good process then you'll get good fruit out. If you put bad fruit into a good process, you'll still get bad fruit out. So you need to be more, we need to be more vigilant in the type of fruit that goes into some of our systems, and the expectation that we have of what the outturn might be for whatever that system is.
So what we know so far is that the fruit with the same size, colour, sugar or firmness might not necessarily be at the same physiological development stage as each other. They, you know, you pick them on the same day, they'll be different. And that the fruit that isn't physiologically ready at harvest are more likely to result in the disorders that we saw after even short term, but definitely long term storage. And they include the mealiness, the browning, the rubberiness and the shrivelled aspects. The fruit that is immature will soften all fruit will soften, but the immature fruit will not ripen. There will be no organoleptic response that's suitable, and the volatile work that I did shows that you can't necessarily restart the metabolic processes after cold storage adequately, that the fruit that hadn't initiated that response before it went into storage, cannot restart it properly afterwards. And I think that's an important thing that we need to remember. And that goes into this ontogeny that I was talking about earlier, where the fruit needs to be harvested at a stage where it's capable of reaching its full organoleptic potential. That is the taste, smell, and texture that we associate with those varieties. So, we need to make sure the fruit is not just harvest ready, but it's ready to harvest!
Where to from here. We need to keep in mind that we measure physiological maturity and at the moment that's through ethylene production and correlating that with, with whatever instrumentation we can at the moment. That's the DA meter, which we can use in the field. I know that there's work being done overseas on DA meter loggers for in storage. There's also work on potential inline systems for packing lines, but I haven't heard any updated information on that recently. There's an app that Dario had been working on before he left, with Ruben's technology to make it easier for the download of data from the SD card. I've used it, and tested it for them to, you know, to look at usability and it works really well. I was quite impressed with it. And that should be ready within a couple of months, hopefully well, before the season starts, but, you know, I guess the season's not that far away really. We're also looking at a fluorescence meter with the Rubens technology group. We started looking at it last year. It's been in the process for a couple years, but we started looking at it last year. Preliminary testing shows that it's quite promising. Um, we're looking , it's being put into a program that I'm working on with the group up at Tatura, looking at sensor technology options for stone fruit. And that's one of the senses that we're looking at. It can, it can grab a larger spectra of data than the DA meter. So there's options to look at other associations, not just the de-greening of the fruit. So, it's hopeful that we might be able to pick out things like potential for storage disorders in some fruit that's, you know, that's in the wishful thinking basket, but you know, it's something that we will be looking at. There's a few other senses involved in that. I can’t think of them off the top of my head. There's also the option that John was talking about last week, where we link the proper maturity, physiological maturity factors in with the delayed cooling, which would shift, hopefully shift that onset of disorders and timing to that right a bit more where the, where the fruit will survive that bit longer in cold storage. Then there's work being done in Spain, looking at the NIR on a grading system where, which I know is still in, it's still in prototype. That's what I'm trying to say. My apologies. They're looking at, so they've got a prototype instrument. They haven't put it in a commercial situation yet, but that's their end goal. I'm trying to keep on top of that, but I haven't heard anything new on that yet.
But one of the things that I think we need to consider as an industry is that we use appropriate cultivars for what we're trying to do with the fruit that we breed. Cultivars that are actually suitable for storage, not just that they're super sweet or that they're sub acid or that they've got a big amount of blush on them or whatever the factors are at the moment, but that they actually get through a whole storage process, And that's become more and more important as the timelines to get from orchard to market, especially export market have lengthened in the last, you know, 10 years or so.
And I think that's all I have for now. Thank you.
Fantastic. Thanks Christine. It's a, it's interesting to see the work that you've been doing and that ‘harvest really, not ready to harvest’ comment and what this is really bringing forward in terms of improving the opportunity fruit quality. I've got quite a few questions coming through, actually.
So, Trevor Ranford started, [the question] it was quite early on in the piece, that's probably already been answered, but, what is causing, what is the cause of the browning? Is it cold or another physiological disorder?
We don't know for certain. It, you know, it could be something that a particular variety is already subject to. It could be, you know, they talk about heat shock in vegetables. It could be cold shock, which is some of that delayed cooling aspect that John was talking about, where the fruit are shocked, so the cells die off a little bit. We don't know for certain. Okay.
Okay. How many growers would a use a DA meter to determined fruit, maturity?
I honestly don't know at the moment. I know there's a few that have taken up the option, but I don't, I can't say I can't, I don't know the answer to that. I don't get information on who uses it and who doesn't.
So Summerfruit Australia limited is working with Daniel, which is Ruben's technology on a DA session with the new spreadsheet. So that must be to do with the spreadsheet that's going up on the www.hin.com.au.
Christine, what is a fluorescence meter, and what does it measure?
Okay. So the fluorescence meter, literally measures changes in fluorescence in the cells of whatever it's looking at. It can, it works like a spectrometer where it measures spectra at different wavelengths of light, in different light sources in this case, this one is uses different light sources. And the way those wavelengths behave can tell us different things.
What does it measure?
Well, it depends on what you're looking at. So each set of wavelengths can measure different aspects. So for example, the DA meter measures, between 580 and 670 nanometers I think, so all the wavelengths in that block were, no 670 and 720, my apologies. So all the wavelengths in that block measure chlorophyll A, and that's what it's looking for. So each group of wavelengths, and you're looking for peaks a bit like those chromatograms I showed where there's peaks at different structure times or time or frames, I guess, allude to information inside that, wherever your source is. So inside the fruit or in this case.
I know that I was talking with a Rubens technology recently, so that device, fluorescence meters, a device that connects up to an app on your phone, they're looking possibly to have it developed by October. We're hoping for this season to have that available to producers. So as soon as that happens I'll get something into a newsletter about that.
It's a lot more sensitive in terms of what it can pick up, and it can pick up things like, what we're looking or hoping for is that it will pick up the switch to tell the ethylene to produce. So it'll be a step before, in some cases of what's going on.
Just another comment. Summerfruit Australia Ltd is working with a CRC Food Agility project, that has commenced looking at the maturity topics. And this involves RMIT, …
That’s the project I mentioned I was working on.
Right with Rubens technologies and others. Good.
Michael asks, is it possible to find the DNA markers that determine good storage cultivars?
I don't know. Anything's possible, I would say as far as that goes. I know that it would take a long time, but you know, with that aspect, anything's possible, you have to, you have to find the work. Most of the work will be done in trying to find the factors that, that lead to the markers that he's talking about. And whether that's transferable across all cultivars, which you would hope, but, you know, if they're sensitive more sensitive than others, hopefully a DNA marker would pick that up. Definitely worth looking into.
A comment from Michael is that DNA markers could be critical for breeding.
Yeah, I agree. I agree completely. Like anything, anything that can help reduce some of those problems that we get with the, the variation in maturity and the storage disorders, I think would be fantastic.
Harvest / Post harvest
Photo: DA-Meter Measuring harvest maturity.
