Astringency, Diospyros, and promotion of microbial health in the colon

(writing in progress)

Astringency (https://en.wikipedia.org/wiki/Astringent) is a basic biological phenomenon, of which many naturalists may not be fully aware.

Astringency is what makes

• hides into leather (https://en.wikipedia.org/wiki/Leather_production_processes),
• the mouth feel dry when eating raw acorns (https://www.webmd.com/diet/are-acorns-safe-to-eat#:~:text=Acorns%20can%20be%20used%20in,with%20salt%20for%20a%20snack.), and
• tea into a healthy beverage.

Plants contain certain substances that bind on to proteins, polymerising them into an indigestible, plastic-like substance. This is a defence against plant-eating animals, because it denies the value of the protein to the consumer.

All food-digesting enzymes are proteins, and furthermore the mucus in saliva may also be similar enough to a protein to be bound by the tannins.

Certainly when one eats tannin-rich foods the lubricating effect of saliva (which is partly owing to mucus) is lost.

I see at least three adverse effects on the tannin-eater which might benefit the plant producing the tannin:

• the plant-eater profits less from the protein in the food,
• the plant-eater wastes precious enzymes because salivary and even gastric enzymes may be complexed with the tannins, and
• it is harder to chew and swallow food with minimal lubrication.

In our aboriginal state, humans had diets rich in astringent foods. One of the benefits of this may have been to promote healthy communities of bacteria in our colon.

Because astringency causes proteins to be resistant to digestion in our stomach and small intestine, it delivers the polymers to the large intestine, where it is available to certain bacteria. These, as part of our normal, healthy microbial community, promote absorption of nutrients, make vitamins, and boost immunity.

Modern, technically-developed cultures tend to have lost both astringent foods and an awareness of astringency, and this may have been at some cost to our health.

A noteworthy genus, w.r.t. astringency, is Diospyros.

Diospyros has two major associations, namely ebony and persimmons.

The fruiting strategy of Diospyros particularly involves astringency. One of the reasons why one does not get this clearly in anything one reads is that our culture tends to be ignorant about the whole concept of astringency.

And while this ignorance tends to limit our understanding of the natural world, it also – I suggest – has contributed towards making us less healthy in terms of diet and intestinal health.

From the point of view of the human consumer, one has to be educated to appreciate what Diospyros fruits are like: one has to realise that the fruit only becomes palatable when ‘post-ripe’ and one has to arrange to be able to consume the fruits at that stage, preferably by collecting and storing them.

The adjective ‘chalky’ which appears in Wikipedia is an inept attempt to describe the astringency normal in the full-size, ripe but not yet ‘post-ripe’ fruits of many spp. of Diospyros.

It is impossible for Wikipedia or any other source to describe these fruits sensibly without explaining the process of ‘post-ripening’, in which the astringency typical of unripe fruits generally is carried over to the ripe fruits in Diospyros.

The North American D. virginianus and the east Asian D. kaki as typical examples of the domestication of Diospyros, with which few will disagree because the persimmons sold in western shops are these extremely large fruits, representing extreme selective breeding of ebonies for increased size of fruit.
 
The best congener to which to refer is Diospyros lotus, which is what the ancient Greeks were referring to in ‘the lotus eaters’ as a consummate fruit. Indeed, the very name Diospyros means, in ancient Greek, ‘fruit of the Gods’.
 
The wild ancestor of Diospyros lotus occurs in the Caucasus region, so this fruit is indigenous to southeastern Europe and southwestern Asia, in deciduous forest.
 
The thing about D. lotus is that, although the plant was certainly domesticated long ago, there has been no selective breeding for either a) increased size of fruit or b) loss of the characteristic post-ripening process on which the dispersal strategy of the genus is based.
 
Western culture finds – or did until recently – the whole concept of persimmons to be somewhat strange, and it’s easy to assume that this is because persimmons are a kind of Oriental (or native American) fruit that happens to be geographically remote from Europe.

However, this is not true, because D. lotus is very much part of our European history in the same sense as our philosophy and our democracy and our legal system and indeed our language.

The thing is that D. lotus, although very much belonging to our cultural heritage as Europeans, and despite being so highly regarded by our ancestors that it was called ‘fruit of the Gods’, has been almost wholly forgotten by us.
 
To understand why D. lotus, although so highly regarded by ancient Europeans, is virtually unknown even to otherwise well-informed people, I come back to the central peculiarity of Diospyros as a fleshy fruit: its strategy of ‘post-ripening’.
 
In normal fleshy fruits, there is the unripe, growing stage (‘green’) and the ripe, full-size stage, the latter usually having some attractive colour to signal its availability to the fruit-eater and seed-disperser.

The main complication with this, in many taxa of fleshy fruits, is a ‘pre-ripe display’ in which the full-size fruit first turns yellow when unripe, before finally turning red or purple when ripe.

To summarise this normal process, fleshy fruits grow and then ripen and the colours are reliable indicators of these stages.

If any animal tries to eat the unripe fruit (in which the seeds are not yet ready to be dispersed), it will be put off by bad tastes including astringency (which is caused mainly by tannins).
 
The point about Diospyros is that it delays the full ripening of the fruit in an extreme way. Even when the fruit is full-size and brightly coloured, the astringency is retained.

For the astringency to be lost and the fruit to become palatable, the fruit-eater must wait for a stage of ‘post-ripening’ in which the fruit-pulp goes jammy and seems partly decomposed (although I don’t think there is any microbial involvement in this ‘autolysis’).
 
It is this ‘post-ripening’ that the Western consumer is ignorant of, and which makes the ‘fruit of the Gods’ of ancient Greece so obscure and unattractive to modern fruit-eating people.

Because the ancient Greeks and other European people were educated to realise how the fruits of Diospyros work, they could appreciate these fruits for their deliciousness when ‘post-ripe’ – well worth waiting for.

The ‘post-ripening’ of Diospyros has been bred out, selectively, in certain varieties of D. kaki, such as the ‘sharon fruit’ grown in Israel for the international market, but all this does is to reduce Diospyros to some generic or average fruit, which is ultimately pointless because all it does is to put this genus into a position of competing, in the market, with many other perfectly palatable but less obscure fruits.

Who needs persimmons when we have so many other fruits to choose from?

But if one understands the ‘post-ripening’ process of the original, wild spp. of Diospyros then one can appreciate the subtle flavours and textures of wild and domesticated persimmons.

In the case of D. kaki in particular, until recently this ‘post-ripening’ process was fully retained in even the most artificially-selected varieties with extremely large size and bright hues, because the Japanese and Chinese consumer had no wish to convert persimmons into some generic fruit – they appreciated the special qualities of ‘post-ripening’ Diospyros much as the ancient Greeks (and presumably Romans) did.

The following paper is fascinating and worth reading completely: http://vdi.sagepub.com/content/9/3/311.full.pdf.

Astringency is simple enough: tannins and other secondary compounds in plant matter are designed to bind to protein, which means that the protein content of the food is denied to any plant-eater that lacks a gut capable of fermenting the tannins before the gastrointestinal site of protein-digestion.

The combination of tannin and protein makes a kind of ‘plastic’ which passes through the human gut largely undigested, and the same is true for most animals lacking foregut-fermentation. In this way, the plant denies the plant-eater the profit of its meal in terms of protein, limiting damage to the plant by plant-eaters.
 
It is well-known that this strategy is applied by plants particularly to their unripe fruits (although it is also much used for shoots and leaves and even some seeds; sometime try to taste an avocado seed).
 
Few biologists have a clear concept of what astringency is, and even fewer will be capable of using the term ‘astringent’ in description of the mouth-feel or taste of food.

Our culture has been so successful in breeding out any astringency from domesticated plants that most people go for days, weeks or months without eating anything astringent, and when they do taste astringency they are incapable of describing it. Instead of calling what it is, i.e. astringent, they misdescribe this taste/mouthfeel as ‘bitter’, ‘acrid’, or even ‘tart’.

Astringency is quite different from bitterness (which usually comes from alkaloids, not tannins). In the case of Diospyros you’ve seen the term ‘chalky’ which is actually fairly indicative but is, again, illiterate and shows a real ignorance about what is one of the few categories of taste in the human sensory system and a widespread taste in the plant world.

Astringency has nothing to do with sourness, but so inept are most (>99%) of people in describing astringency that they even confuse it with sourness.
 
Astringency is classes as a ‘taste’ but it’s as much a mouthfeel as a taste because what happens is that the tannins bind to the proteins (enzymes etc.) in ones SALIVA.

The result is a ‘dry’, non-lubricated feeling in the mouth, to which the Afrikaans term ‘droog-my-keel’ refers (not one but various plants are thus named in Afrikaans, if memory serves).
 
I’ve previously explained how this concept of astringency is crucial to an understanding of the biological nature of Diospyros fruits and the relationship of this genus to its fruit- and seed-eaters and the dispersers and sowers of its seed.
 
But another point I’d like to make is how this ignorance about a major aspect of diet may have been to the detriment of human health.
 
Primitive gatherers would have been eating astringent foods all the time. Watsonia corms, for example, are astringent. Astringency is more the rule than the exception in the plant component in the diet of any hunter-gathering population.

I would not be surprised if the language of many paleolithic peoples had a dozen words for various types of astringency. Now we have only one, and most of us by far have no idea what it means.
 
If one were trying to take the shortest possible cut back to a healthy colon, with a diversity of microbes, would one be wise to seek out astringent foods first?

I suspect that the lack of astringency in modern diets has come at a considerable cost to our microbial community. Because astringency reflects the binding of protein by tannins, it follows that much of the protein in astringent foods finds its way, undigested, to the colon.

Although some of this may indeed pass out in the faeces, still thus complexed, I suspect that at least some is available to microbes and that various lineages of microbes depend on this source of amino acids.
 
One of the best ways to get astringency back into one’s diet would be to eat edible weeds.
 
https://aylestone8.wordpress.com/tag/droog-my-keel/
 
Astringent foods bind some of its own protein content, and carry it through to the colon where it provides some amino acids for the benefit of gut bacteria.
 
Question: does the stomach break down and digest animal protein so efficiently that there is absolutely none left when it reaches the small / large colon? Suggesting that plants are a richer source of protein for gut bacteria than meat, eggs etc is surprising.
 
It is not so much the protein-richness that matters, as the trophic niche for a certain range of bacteria that are normal in our colon, and on which we thus depend for immunity etc.

I refer to the normal healthy diversity of colonic bacteria (https://www.theguardian.com/lifeandstyle/2022/may/15/go-with-your-gut-tim-spector-power-of-microbiome).

I suggest that, just as it pays to eat resistant starch in aid of certain bacteria that like this substrate, so it pays to eat tannins because they too provide favourable conditions for part of our bacterial spectrum.
 
The modern western adult is plagued by weak digestion and low stomach acid. This would cause more undigested protein in their colons, not a deficiency. This would override your suggestion that we suffer from a lack of colon amino acids.
 
As I see it, there’s no shortage of protein in the colon of your average Macdonald’s eater, but that particular formula favours few good bacteria and some bad bacteria. So it is more that the amino acids have to be

• in the right form for the beneficial bacteria, and
• that having some component of tannin-complexed protein in the diet ‘adds a niche’ to the spectrum of niches for bacteria in the colon.

The best way to put all of this is that the normal healthy range of colonic bacteria in the human species includes various bacteria adapted for tannin-bound residues, and when these are lost from the diet the colonic microbial community is impoverished and undermined functionally.

Information on Diospyros lotus, a fleshy fruit highly valued in ancient Asia Minor and eastern Mediterranean, and still grown in Turkey, Black Sea and Pakistan
 
Although D. lotus can be grown as an orchard tree, ostensibly similar to a plum, it is far longer-lived than most orchard trees – which makes sense because it is, after all, an ebony, with relatively hard wood.
 
Diospyros lotus is typical of trees in the forest of Asia Minor in being winter-deciduous with autumn colours. Diospyros mespiliformis in Kruger Park retains autumn colours and leaf-fall with modified timing.
 
The fruits of D. lotus are about the same size as those of D. mespiliformis; although there are dozens or perhaps hundreds of cultivated varieties of D. lotus, it seems that increasing the size of the fruit relative to the wild ancestor has not been on the agenda of selective breeders for some reason.
 
Fruit colour in D. lotus is variable, sometimes orange and sometimes dark brownish.
 
The fruits of D. lotus remain astringent when ripe, until ‘post-ripe’. At this stage the fruit-pulp becomes jammy and the skin becomes almost translucent. The term ‘ripening’ takes on new meaning when it comes to Diospyros and I think the same is true for jackalberry.
 
The literature can be confusing because the fruits can be eaten when ripe as a medicinal food (for the various healthy qualities of astringency and despite the repulsive mouth-feel of astringency) and when ‘post-ripe’ as a most delicious fruit.
 
An interesting effect of the astringency is that in some cases bezoars can form in the human stomach from the plastic-like complex of tannins and proteins. This would presumably only happen if the person eats the ripe (as opposed to ‘post-ripe’) fruits.
 
There are no non-human primates in the natural habitat of wild, ancestral D. lotus in the Caucasus area, but if there were I think it’s safe to assume that they would eat the seeds along with the fruit, and because of this they would be relatively indifferent to the state of ripeness of the fruit.

I have not heard of humans eating the seeds; as far as I know the human consumer invariably spits out the seeds, which are too big to swallow and too hard to chew. I don’t know if the seeds are defended with toxins.
 
http://theindianvegan.blogspot.com.au/2012/10/all-about-date-plums.html
 
https://upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Diospyros_lotus_02.jpg/200px-Diospyros_lotus_02.jpg

http://nargil.ir/plant/images/pic/561/20160127124940Diyospyrus%20lotus.jpg
 
Certainly Diospyros but I’m not sure the following is D. lotus:
http://huntingny.com/forums/uploads/monthly_03_2014/post-899-0-11968100-1395272159.jpg

http://tcpermaculture.blogspot.com.au/2011/08/permaculture-plants-persimmons.html

http://2.bp.blogspot.com/_0dDGyrdbFDg/TQcvN0QJY9I/AAAAAAAAAvM/CX_qm9zlQq4/s1600/Amlook+ripe.jpg

http://farm7.static.flickr.com/6117/6355367157_66e73a249b.jpg

http://tcpermaculture.blogspot.com.au/2011/08/permaculture-plants-persimmons.html

http://herbs-treatandtaste.blogspot.com.au/2010/12/what-is-amlook-fruit-date-plum-or.html
 
D. dichrophylla is known as the poison peach, with Elsa Pooley stating “Fruit reputed to be poisonous” in her book on Trees of Natal. I recall reading somewhere else that the fruit are edible, so I have always been a bit confused with this shrub (going back 15+ years); I have never tried to eat the fruit because of the ‘poison peach’ name.
 
I suspect that this confusion of ‘poisonousness’ can be explained in the same way that so much else about Diospyros fruits can be explained: i.e. that the fruits are so astringent when ‘ripe’ that they taste poisonous and can even be effectively poisonous (please bear in mind the effects in the horse).

However, if one has the simple knowledge that they need to be ‘post-ripe’ before becoming palatable, then one will see the fruit for what I think it is, i.e. just another fairly typical persimmon. I dare say the ripe fruits of D. mespiliformis would taste horrible to the uninitiated, as well.
 
Does it surprise me that some Diospyros fruits would be poisonous for humans?
 
As far as I know, so species of Diospyros has toxic fruits in the usual sense. But on the other hand, most or all species of Diospyros have fruits that are so astringent, when ripe, that they are easily misunderstood.
 
Even domestic horse can suffer stomach problems from overeating unripe diospyros fruits:
  
Here’s some support for my interpretation of the extreme astringency of the ripe fruits of Diospyros as a plant defence against the wrong fruit-eaters, that is to say those fruit-eaters unlikely to disperse and sow the seeds in a way favourable to the plant.
 
In Diospyros, astringency is not just a chemical effect in which the plant denies some of the value of the food to the consumer.

The astringency is, instead, taken to such extremes that it can become a physical risk to the fruit-eater!

That a herbivore with as robust a digestive system (and teeth) as the domestic horse can suffer thus should leave us in no doubt that D. mespiliformis in Kruger National Park does likely have an effective defence against excessive consumption of its fruits by the chacma baboon, which probably cheats the mutualism by destroying the seeds along with the fruit-pulp.

No doubt many berries of D. mespiliformis are eaten and their seeds destroyed by the baboon, but the astringency seems quite capable of limiting this damage and thus ensuring that at least some of the berries remain to reach the ‘post-ripe’, completely non-astringent stage at which they are attractive to the real dispersers of the plant, namely the African civet and two species of jackals.

DIOSPYROS MESPILIFORMIS

I suspect that D. mespiliformis in Kruger National Park shows this ‘post-ripening’ as much as domesticated D. lotus does, with fruits of similar size (about 2 cm diameter).

The main difference is that D. lotus is a deciduous species from the Caucasus region, whereas D. mespiliformis is a virtually evergreen species from subsaharan Africa. I say ‘virtually’ because, on a visit to Kruger National Park in 2016, I noted that D. mespiliformis does in fact turn yellow in its ‘fall colours’ in the spring, i.e. it sheds all its leaves and then immediately grows new leaves without being bare in the way northern deciduous congeners stand bare through the winter.

Apart from the predictable differences in phenology, one could say that D. mespiliformis is so similar to D. lotus of the Caucasus – including in the relatively small size of the fruits compared with D. kaki and D. virginiana – that D. mespiliformis is a wild version of what the ancient Greeks referred to as ‘the fruit of the Gods’.

It should be no surprise that Africans in the Lowveld spare this tree when they clear the woodland for farming; the real surprise is that the virtues of D. lotus have been lost to us in our modern culture./Exactly how do harvesting, storing, and ripening work in D. mespiliformis?

Coming back to the ‘natural’, i.e. non-human dispersers of D. mespiliformis, this is how I think it works:

The fruits grow (green) and reach full size, whereupon they turn dull yellow but remain attached in the crown. They do not fall off naturally but tend to get knocked to the ground because there is so much disturbance of the crown in a land of primates and hornbills etc. Once on the ground, they tend to get eaten (when still astringent) by herbivorous animals such as antelopes.

But a precious few fruits survive to the ‘post-ripe’ stage to be eaten by the animals that really do serve the plant with seed-dispersal, i.e. jackals and the African civet. Such carnivores would not eat any astringent fruit, accepting only the fully ‘post-ripe’ fruit with its jammy consistency.

While the fruits are still attached to the crown, they are eaten by both primates (vervet monkey and baboon) and the green pigeon Treron, which (I hypothesise) tend to eat the fruits for the seed more than the fruit-pulp.

I.e. primates and Treron tend, I think, to grind up, digest and destroy the seeds.

Perhaps some of the hornbill spp. of Kruger National Park do swallow any ‘post-ripe’ fruits to be found still attached to the crown, and perhaps they do disperse the seeds intact – I don’t know and I suspect that until scientists have the right conceptual framework we’ll never know because at the moment scientists lack the appropriate search-images for data-collection.

In the process of all this destruction of fruits by birds and primates, some fruits get knocked to the ground in the ripe but still astringent stage, and are then picked off (and similarly destroyed) by the bushbuck (Tragelaphus sylvaticus), the impala (Aepyceros melampus), the bushpig (Potamochoerus larvatus), and even the common warthog (Phacochoerus africanus).

More loss of the seeds to grinding and digestion, these various animals again eating the fruits for the seeds and despite the fruit-pulp as it were.

But a precious few fruits survive all these seed-predators to express what the plant-animal mutualism is ultimately all about in the genus Diospyros – i.e. a certain guild of fruit-eaters (which includes large fruit pigeons in Australasia where there is such a limited fauna of mammals) which accept only the ‘post-ripe’ fruits, digest the jammy, now no longer astringent fruit-pulp, and defecate or regurgitate the seeds intact in acts of dispersal and sowing.

Is the link between ‘jackalberry’ and the divinely inspired lotus of Greek mythology could be an original and refreshing angle on D. mespiliformis?

Sexual reproduction in plants does tend to be so extremely wasteful that I’m tempted to invoke a basic trade-off between quality and quantity: the plant is adapted to spend enormous amounts of resources for a service that is qualitative rather than quantitative, a bit along the lines of ‘throwing money at the problem’.

If the African civet and jackal are the intended recipients, then the advantages of using them need to be considerable. Perhaps it is a civet midden that the tree is after? D. mespiliformis grows on termite mounds which suggests that it thrives in a nutrient rich environment. Perhaps it likes to germinate in a midden, and the termites in time come to the tree?

Perhaps the tree doesn’t mind losing 99.9% of its fruit/seeds to seed-destroyers as long as 0.1% end up in a civet midden which is heaven for a D. mespiliformis seeding for various physiological reasons related to its adaptation to nutrient-rich patches of soil in the landscape?

A civet midden is probably a tough place for a new termite queen to set up a nest, but once a tree has ‘taken over’ the midden then it might be the ideal place to start a fungus culture because it is a nutrient hotspot and the fungus will grow well (all micro-nutrients available in a decent quantity).

Another fact to consider is that at least some spp. of Diospyros are known to have taproots. I would be curious as to whether this is true as well for D. mespiliformis. Given that the tree has a taproot, it’s possible that this somehow helps a new colony of Macrotermes to establish at the base of the sapling? 

(writing in progress)

Publicado el 10 de agosto de 2022 por milewski