Why are tropical fruits generally much sweeter than temperate?

[studiot]

I have noticed that fruits native to tropical or sub tropical regions ( eg figs, dates, melons, peaches, bananas ) are generally much sweeter than fruits from temperate regions (eg apples, pears, gooseberries, blackberries...)

Can anyone suggest good reasons for this?

1) is there any evolutionary advantage?

2) Is it simply the extra sunshine?

[StringJunky]

7 minutes ago, studiot said:

I have noticed that fruits native to tropical or sub tropical regions ( eg figs, dates, melons, peaches, bananas ) are generally much sweeter than fruits from temperate regions (eg apples, pears, gooseberries, blackberries...)

Can anyone suggest good reasons for this?

1) is there any evolutionary advantage?

2) Is it simply the extra sunshine?

Possibly 2 because they have more sunshine, for longer periods and warmth to make the sugars. If you notice, the largest temperate fruits are smaller too than the largest tropical ones. 

[Sensei]

What is "purpose" of fruits? They have to attract animals, which will eat them, digest and expel. Animals concentrate on eating fruits they like to eat, leaving other parts of plant undamaged. Additionally seeds are spread at much longer distance than they could reach simply failing at ground and remaining there, in close distance to original plant. Animals don't want to eat fruits they don't like, so branches of evolution of unpleasant to consume fruits are cancelled by them.

Edited September 5, 2018 by Sensei

[John Cuthber]

5 minutes ago, Sensei said:

What is "purpose" of fruits? They have to attract animals, which will eat them, digest and expel. Animals concentrate on eating fruits they like to eat, leaving other parts of plant undamaged. Additionally seeds are spread at much longer distance than they could reach simply failing at ground and remaining there, in close distance to original plant. Animals don't want to eat fruits they don't like, so branches of evolution of unpleasant to consume fruits are cancelled by them.

Is the purpose of fruit different in the Tropics, or is this  not actually an answer to the OP's question?

Generally, there are more  things growing in the Tropics, so there  is more competition to get eaten (that's an odd concept...) 
So, there's more sunlight available to make sugar and more incentive to do so too.

Some plants cheat.
https://en.wikipedia.org/wiki/Stevia

Edited September 5, 2018 by John Cuthber

[Ghideon]

 

1 hour ago, studiot said:

generally much sweeter

I dont want to be picky but by sweet do you mean the taste or the measured sugar contents? I intend to give this some thought and want to get started in the right direction.

13 minutes ago, Sensei said:

Animals don't want to eat fruits they don't like

Interesting point. Do animals in varying climate have different needs, giving raise to different evolutionary advantage in different climate zones? Sweeter food is an advantage in hot climate?

[Carrock]

There's the additional complication that most of these fruits are cultivars bred to be much less variable than wild fruits. I'd think lack of sunshine is the main reason tropical cultivars are selected to be sweeter than temperate cultivars.

 

From mainly childhood memory in Scotland:

Ripe wild strawberries are tiny and less sweet than cultivars but with a much better texture. They were quite rare in Scotland and I may have mostly eaten them from one large patch spread by runners. I preferred them to cultivars but that may have been because they were so hard to find.

Wild blackberries aka brambles are much more variable. Ripe blackberries range from very sweet and tasteless to very acidic. I prefer the somewhat acidic ones and I suppose some birds and animals do too; there may be nutrients lacking in the high sugar blackberries. When I've bought blackberries they've never been as sweet as the sweetest wild blackberries.

An interesting question is whether wild tropical fruits are typically sweeter than wild temperate fruits.

1 hour ago, Sensei said:

Animals don't want to eat fruits they don't like, so branches of evolution of unpleasant to consume fruits are cancelled by them.

Bit more complicated. Many fruits taste bad and/or may be poisonous to some animals so that only preferred creatures e.g. birds spread them more efficiently.

e.g. deadly nightshade tastes quite good to humans but you won't come back for a second helping.

[studiot]

1 hour ago, Ghideon said:

 

I dont want to be picky but by sweet do you mean the taste or the measured sugar contents? I intend to give this some thought and want to get started in the right direction.

Interesting point. Do animals in varying climate have different needs, giving raise to different evolutionary advantage in different climate zones? Sweeter food is an advantage in hot climate?

Well both I think, but I am perfectly willing to hear from those who know more.

As far as I know there are no naturally occurring 'supersweet' compounds, and I thought fructose was the main fruit sugar.

I also meant to mention that to my taste maize (sweet corn) is sweeter than oats, rye, wheat or barley.

 

 

[mistermack]

_{In the tropics you get more monkeys and apes that are specialist fruit eaters. Maybe our order of mammals have sweeter preferences than animals that evolved in more temperate zones.} 

_{I remember reading some time ago that apes had their purple patch about 20 to 40 million years ago, and have been in decline ever since, losing out to monkeys, because monkeys can tolerate more bitter fruit, at a less ripe stage. So they get there first, and clean up, and the apes find the fruit gone, by the time they would have been able to eat it. So a lot of the tropical fruits might have evolved to attract apes that are now extinct.}

[studiot]

3 minutes ago, mistermack said:

more bitter fruit, at a less ripe stage

Do they shop in Tesco?

[mistermack]

1 minute ago, studiot said:

Do they shop in Tesco?

I like fully ripe fruit. I can't eat Tesco bananas. I have to leave them out in a bowl till they get brown spots on the skin, or buy the special bargain ones that have supposedly "gone over".

What the hell are sloes about though? They're technically a wild plum, but have you ever bitten one? It takes half an hour to get the creases out of your face. I can't imagine what function they serve. I think the stones have arsenic in them as well. They can't have evolved just to go in gin.

[studiot]

The fruit of the blackthorn needs to be once frosted to be ripe (a bit like brussel sprouts).

[Ghideon]

35 minutes ago, studiot said:

Well both I think

From memory I subjectively find local strawberries sweeter than e.g. apples, and strawberries require a lot of sun. But sugar* content tables suggest that strawberries generally contain less sugar than apples. So in this case sun, sugar content and taste didn't correlate in the way I expected. I'll have to rethink this, my idea about correlation between measured sugar content and sunshine for a fruit or berry does not seem to work.  

*)There are several types in fruits according to https://en.wikipedia.org/wiki/Fructose 

 

[StringJunky]

10 minutes ago, Ghideon said:

From memory I subjectively find local strawberries sweeter than e.g. apples, and strawberries require a lot of sun. But sugar* content tables suggest that strawberries generally contain less sugar than apples. So in this case sun, sugar content and taste didn't correlate in the way I expected. I'll have to rethink this, my idea about correlation between measured sugar content and sunshine for a fruit or berry does not seem to work.  

*)There are several types in fruits according to https://en.wikipedia.org/wiki/Fructose 

 

I think acid vs sugar balance and even acid type (citric, malic etc) between the fruits will make your taste judgement for sugar content unreliable.

[studiot]

Interesting detail in the link Thanks +1

[Sensei]

32 minutes ago, Ghideon said:

From memory I subjectively find local strawberries sweeter than e.g. apples, and strawberries require a lot of sun. But sugar* content tables suggest that strawberries generally contain less sugar than apples.

(Modern) strawberries are created by human..

"The garden strawberry was first bred in Brittany, France, in the 1750s via a cross of Fragaria virginiana from eastern North America and Fragaria chiloensis, which was brought from Chile by Amédée-François Frézier in 1714.[2] "

https://en.wikipedia.org/wiki/Strawberry

 

3 hours ago, Sensei said:

Animals concentrate on eating fruits they like to eat, (...)

...and humans made their own, sweeter, bigger, less vulnerable for insects, etc. etc...

 

https://en.wikipedia.org/wiki/Breeding_of_strawberries

 

Edited September 5, 2018 by Sensei

[CharonY]

As already mentioned most fruits we consume are the product of extensive breeding. Also many fruits are originally from different climate zones, which makes assessments difficult. Surely taste is not a good indicator if carbohydrate contents, either.

So I am not sure whether OP can be easily validated.

[studiot]

18 hours ago, CharonY said:

As already mentioned most fruits we consume are the product of extensive breeding. Also many fruits are originally from different climate zones, which makes assessments difficult. Surely taste is not a good indicator if carbohydrate contents, either.

So I am not sure whether OP can be easily validated.

 

Thank you to those who have pointed out the distinction between sugar content and sweetness. I am more concerned with observed (therefore subjective) sweetness.

I would also like to observe there is considerable difference in sweetness within some categories eg cooking apples v eating apples.
This may be due to string junky's highly pertinent comment that fruit also contains fruit acid.

But maybe you are misunderstanding my observation.
I don't suggest that all tropical fruits are sweeter than all temeprate ones or that there is not a range of sweetness within either category.
In fact there is probably a fair measure of overlap and a plot would look something like this.

 

[StringJunky]

2 hours ago, studiot said:

 

Thank you to those who have pointed out the distinction between sugar content and sweetness. I am more concerned with observed (therefore subjective) sweetness.

I would also like to observe there is considerable difference in sweetness within some categories eg cooking apples v eating apples.
This may be due to string junky's highly pertinent comment that fruit also contains fruit acid.

But maybe you are misunderstanding my observation.
I don't suggest that all tropical fruits are sweeter than all temeprate ones or that there is not a range of sweetness within either category.
In fact there is probably a fair measure of overlap and a plot would look something like this.

 

I think the answer lies in the amount of volatiles and their perceived aromaticity. Tropical fruits are generally more aromatic. I found this interesting Quora post:

Quote

Moreover, the volatiles seemed to account for why panellists had reported some tomato varieties to taste sweeter than others that had far more sugar. The team tested a variety called Yellow Jelly Bean, for instance, and another called Matina. The Yellow Jelly Bean has 4.5g of glucose and fructose in 100 millilitres of fruit and rated about a 13 on a scale used for perceived sweetness. The Matina has just under 4g but rated a whopping 25. The major biochemical difference between the two was that the Matina had at least twice as much of each of the seven volatiles as the Yellow Jelly Bean did. When the team isolated those volatiles from a tomato and added them to sugar water, its perceived sweetness jumped.

They've also investigated blueberries and strawberries, among other fruits. Strawberries have much less sugar than blueberries but are consistently rated much sweeter. Bartoshuk and colleagues suggest that this is because strawberries have so many more volatiles – something like 30 – than blueberries, which have “maybe three”, Bartoshuk estimates. They found that adding strawberry volatiles to sugar water boosted perceived sweetness even more than the tomato volatiles did, and adding volatiles from both together doubled it.

Scroll down a bit: https://www.quora.com/Why-do-fruits-taste-sweet

 

 

[John Cuthber]

On 9/5/2018 at 7:48 PM, John Cuthber said:

Some plants cheat.
https://en.wikipedia.org/wiki/Stevia

 

On 9/5/2018 at 9:45 PM, studiot said:

As far as I know there are no naturally occurring 'supersweet' compounds

Isn't 100 times sweeter than sucrose good enough?
OK, how about 2000 times as sweet?

https://en.wikipedia.org/wiki/Thaumatin

or 

https://en.wikipedia.org/wiki/Monellin

[CharonY]

3 hours ago, studiot said:

 

Thank you to those who have pointed out the distinction between sugar content and sweetness. I am more concerned with observed (therefore subjective) sweetness.

I would also like to observe there is considerable difference in sweetness within some categories eg cooking apples v eating apples.
This may be due to string junky's highly pertinent comment that fruit also contains fruit acid.

But maybe you are misunderstanding my observation.
I don't suggest that all tropical fruits are sweeter than all temeprate ones or that there is not a range of sweetness within either category.
In fact there is probably a fair measure of overlap and a plot would look something like this.

 

If your question is based on an evolutionary point of view, it will be difficult as one would have to identify the original variant and compare their carbohydrate contents. But I am not convinced that you won't see a much higher overlap. Also a question with regard the climate is also what climate they originally tolerate and what modern cultivars do. 

Peaches, for example are grown in temperate zones. But then they also tend to have less sugar than apples. Mangos are also lower or comparable to apples. The question is also what you define as tropical, figs are typically not considered tropical, for example.

But even if we take current cultivars as example, you will find many tropical fruits at the bottom (i.e. low carbohydrate fruits), such as lemons and melons. 

Edited September 6, 2018 by CharonY

[studiot]

Thank you for the thoughts about the effect of 'aroma' on perceived taste, SJ. +1

I believe there is something about that in Atkins book 'Molecules' (highly recommended if you haven't seen it)

 

Thank you for the link John Cuthber.

I see the sweeter fruit you link to comes from the tropic.

Quote

Wikipedia

The thaumatins were first found as a mixture of proteins isolated from the katemfe fruit (Thaumatococcus daniellii Bennett) of west Africa.

 

1 hour ago, CharonY said:

If your question is based on an evolutionary point of view, it will be difficult as one would have to identify the original variant and compare their carbohydrate contents. But I am not convinced that you won't see a much higher overlap. Also a question with regard the climate is also what climate they originally tolerate and what modern cultivars do. 

Peaches, for example are grown in temperate zones. But then they also tend to have less sugar than apples. Mangos are also lower or comparable to apples. The question is also what you define as tropical, figs are typically not considered tropical, for example.

But even if we take current cultivars as example, you will find many tropical fruits at the bottom (i.e. low carbohydrate fruits), such as lemons and melons. 

 

I did lump tropical and subtropical together.

Yes I expect you can fiddle the overlap figures any way you like and probably proove that the cooking apples on my Bramley tree are sweeter than the Pearmains next to them.
But I know what 99.9% of the population would choose as an 'eating apple'.

Yes many melons are pretty insipid, but this year, Tesco has had some half decent water melons as sweet as any I have had in Turkey or the Middle East or South Africa.

I agree that you have found one class of sub tropical fruit - citrous - lemons, limes,  grapefuit etc that are less sweet.

But this is not a game of matching the best agains the worst.

As far as I know there is no temperate fruit that comes anywhere near the fig - just look at the figures in Sensei's link

[mistermack]

From an evolutionary point of view, you have to ignore all the cultivated varieties, and find out what benefit the plant gets from it's fruit. As the only one I can think of is seed dispersal, you need to know what animals are eating the fruit, and what kind of dispersal they get from it. 

An elephant is likely to have different tastes to a bird, and scatter seeds in a different way. So from the plant's point of view, it wants it's seeds to survive being eaten, and be attractive to some efficient transporter. It can get highly specific, like with hummingbirds and some flowers. A plant responds to a client animal, and the animal responds to the plant. Some animals rely on the fruit for energy, like the hummingbird and nectar. Others get more subtle benefits as well, like us humans, and our five a day requirement.

So the difference in fruit from region to region is likely to be related to the animals that are eating it. Or were eating it, in the case of extinct animals.

[CharonY]

16 hours ago, studiot said:

I agree that you have found one class of sub tropical fruit - citrous - lemons, limes,  grapefuit etc that are less sweet.

But this is not a game of matching the best agains the worst.

I was specifically addressing your graph. According to your hypothesis temperate would dominate in the lower range of sugar content. What I intended to show is that this is not the case. If we really plot all fruits (even if we ignore the issues with cultivation) the bars would clearly not separate. Of course, your graph does not weigh for number of species. We should also dispense with the notion of "tasting sweet" as it is not an objective measure of carbohydrate content. In addition, the issue is that if you live in temperate climates, the fruit you get in grocery stores are typically harvested in an unripened state.

But then, there is the issue of categorization. You basically distinguish between temperate and non-temperate (and it seems that you put Mediterrenean climate also into the "tropical" section).The challenge here is that the former category likely has fewer edible fruits than the latter. From this alone, I would expect that the warmer climate fruits would both, top the high, as well as the low end of the proposed chart (and also note that in OP there was a  highly limited selection to begin with).

That all being said, climate can affect sugar content in fruits, though not necessarily the way OP has outlined it. There are studies using the same cultivars in different soils and climate zones, for example that have shown that cultivation differences and different timing in blooming does affect texture, sugar and acid content of fruits, for example.

An example from in watermelon has shown that faster growth due to higher temperature resulted in higher water accumulation and hence, stronger dilution of sugar content, for example. I.e. if you limit or slow its growth, the sugar content will be higher. 

In other words, while the general structure of fruits will be dependent on adaptation to its environment (including fruit eaters and pollinators), it is also heavily influenced by current growth conditions. 

Edited September 7, 2018 by CharonY

[studiot]

16 minutes ago, CharonY said:

An example from in watermelon has shown that faster growth due to higher temperature resulted in higher water accumulation and hence, stronger dilution of sugar content, for example. 

This is an interesting comment can I amend it slightly from "higher water accumulation" to "higher rate of water accumulation".

This would be consistent with the idea that sometimes the plant can accumulate water faster than it can produce sugar.

 

Certainly planting in different soils is well known to have a major impact.

When I moved from the chalk in the Thames basin to the marl in Devon I was suprised at the change in the taste of blackberries.
This I have noticed continued consistently over many years.
It is also true that there are fruits from each category which will not grow in the other, for example cloudberries.

 

Yes I made no secret of my choice of inclusion in my categories, and tried to spell them out as well as I could.

I point I meant to make about the sketch graph was that each grouping will have its own centroid and it is the position of that centroid, rather than the extremities which would be statistically significant.

 

I would not accept that the range of fruits in temperate regions is less than in tropical, perhaps just so if the sub tropical is also included. But look at the map of how little (habitable) land there is between capricorn and cancer alone.

[CharonY]

1 hour ago, studiot said:

This is an interesting comment can I amend it slightly from "higher water accumulation" to "higher rate of water accumulation".

Not sure whether the distinction is relevant in this context as total water content also differs (though one leads to the other, of course, assuming constant retention). 

1 hour ago, studiot said:

I point I meant to make about the sketch graph was that each grouping will have its own centroid and it is the position of that centroid, rather than the extremities which would be statistically significant.

Well considering the broad range found, I doubt that measures of the means would yield significant differences. I have not seen data that would back either one up, though. What one could do instead is trying find a regression between climate zone and sugar content. But even limited to the list you provided that does not seem to hold true. The two fruits with the highest sugar content (date, fig) are from Mediterrenean climates (which are also often considered to be in the temperate/mesothermal zone, perhaps extending to the arid climate. Melons, as discussed are actually fairly low in content. Peaches are about the same as blackberries (i.e. low) but as mentioned they actually grow in colder climates. In fact, the only truly tropical/subtropical fruit is the banana.

 

1 hour ago, studiot said:

I would not accept that the range of fruits in temperate regions is less than in tropical, perhaps just so if the sub tropical is also included. But look at the map of how little (habitable) land there is between capricorn and cancer alone.

I think you may be using different definition than in the OP. Based on OP it seemed that you excluded everything that requires mild winters (such as the Mediterranean, looking at figs). But here you seem to limit it to entirely tropical areas (unless I misunderstand you). But again looking at fruits listed in OP, those listed as tropical seem to span a larger band than those listed as temperate. As mentioned if we use the more classic definitions of climate zone and move the Mediterranean into the temperate band, I would agree with you. But then the OP kind of falls apart as we only end up comparing bananas to all the other fruits.

Perhaps it would be beneficial if we agree on certain climate bands as base category and then look into the fruit that originate from each of them to compare carbohydrate content. The categories as outlined in OP seem to be a bit  inconsistent to me to test the hypothesis outlined in OP.

 

Edit: thinking in broader terms, I think it is fair to say that environmental factor, including nutrient availability, water, sunlight etc. can be considered the boundary conditions of how much carbohydrates can be diverted into fruits and then selective conditions (e.g. competition with other plants) shape the final outcome.

By shifting climate zones, the boundary conditions change. But the individual outcome would be defined from the precise multifactorial niche the plant finds itself over time. My guess is that it would be very difficult to try to break it down to simple factors.

Edited September 7, 2018 by CharonY