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[前沿追踪] The durian

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发表于 2008-2-11 16:46 | 显示全部楼层 |阅读模式

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Mankind suckles at nature's spiky teat
The durianThe durian is a large, spiky fruit, native to the tropical rainforests of South-East Asia - where is is known as "the king of the fruits". It is known to those who hate it for its penetrating, powerful smell - and to those who love it for its wonderful taste. SeedsThe durian - for whatever reason - has very large seeds - too large to pass through the guts of many creatures - and this rules out many potential seed distribution vectors. The durian seed relies upon being discarded after its fruit is eaten (much like a mango pit) - and the raw seeds contain toxins that are effective at discouraging most of those who would try eating them. BarrierMany fruit "prefer" to be eaten by birds (or fruit bats) - since these represent some of the best long- distance transportation vectors. Some fruit actively discourage being eaten by creatures such as large mammals - using toxins. However some fruit also do not seem to mind being eaten by large mammals. Among these are a number of tropical fruit - bananas, rambutan, mangoes, papaya, pomegranates, organges and gua. However many of these fruit face a difficult problem - how to make themselves attractive to animals without also becoming the prey of all manner of insects (who do not represent a very attractive vector for their seeds). Some take to poisons - strong enough to deter insects, but easily dealt with by the liver of a large animal. Others he taken to using a protective barrier - thick enough to discourage insects - but removed easily enough removed by a sufficiently large creature. Bananas, oranges, rambutan, mangoes, pomegranates, jackfruit and breadfruit he adopted the "barrier" solution - with some success. However none of them he taken the approach of using a physical barrier to the same heights that the durian has. The durian doesn't just he a skin: its flesh and seeds are secured inside a well-defended fortress. Durian rind is not just impenetrable to insects - the innumerable sharp spikes also represent a defense against the beaks of birds, rodents - and all manner of small creatures. However the durian's rind is also self-opening - when the durian is ripe it cracks along internal fault lines, and starts to open all by itself. The practiced eye can sometimes make out these "lines of structural weakness" by the effect they he on the spines on the outer shell - though they can sometimes be difficult to identify. PhotoOnce opened, the flesh of the durian looks rather like custard. Here's a photograph of the inside of a durian:
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MammalsIt seems that the durian is choosy about who eats it. It appears that it is especially targetting large mammals. It is probably doing this since large mammals are the ones most likely to transport its large seeds significant distances - and who are most likely to be able to trerse natural barriers.  .TasteThe durian can afford to be choosy about who eats it - because it is in demand. Some of the phrases used to describe it: "the king of fruits", "the fruit of the gods", "ciar of fruit", "the most delicious food on earth" - give some hint about how it tastes. The experience is not easy to describe for those who hen't yet tried it. The texture is like a sort of slighly fibrous custard. The taste is unique. Custard, almonds, and perhaps a hint of garlic. Or perhaps banana, papaya, vanilla, and - rotting onions. To those who appreciate it, eating durian is often an incredible, beautiful experience. The variety provided by all the different durian strains adds to the overall effect.  .SmellA fallen, ripe durian announces its presence to the world by a pungent aroma that spreads for a considerable distance. The smell is so distracting to humans that there are signs up througout South-East Asia prohibiting people from taking the fruit into hotel rooms or onto public transport. The smell is quite effective at alerting animals in the vicinity to the presence of the durian. There are several distinct durian aromas. The fresh durian has one smell, a ripe durian that has just cracked opens smells rather differently, and after that the stench of decomposition starts to dominate the durian's aroma. Durian pulp has its own smell - though this is perhaps not so penetrating and intense. Both are rather thick, foetid, penetrating smells - that hint of moisture, decomposition, and - somehow - sex. Durians are attractive to a great many creatures. However not all of them can get at the flesh. It can take considerable strength and intelligence to open a durian. Being large is essential - and hing hands - or a large crushing implement is helpful. The rind often resists damage even after being dropped from a substantial height.  .SizeSome large durians are difficult to eat all at once - due to their large size, substantial fat content and filling nature. Many modern durians are even more inflated in size - by selective breeding. Large size was probably foured by the fruit - since the larger the fruit, the longer it is likely to trel before being discarded. Fortunately, each durian comes equipped with its own "peduncle" - a stalk that is useful for carrying it around with - assuming you he hands, of course.  .Orang-outangAmong the creatures capable of gaining entry to fruits such as jackfruit and durian are orang-outangs. These share the durian's environment in Indonesia - and are important seed distributors in the forests there. They are especially keen on eating durians. They rip them open with their fingers and teeth. Orang-outangs he an advantage over most durian consumers - in that they can climb into the trees and pick the fruit themselves - if they choose to. Today, human beings are the main vector for distributing the durian's seed. How long this has been the case is not known. It may be that between them the great apes he been the most important distributors of durian seeds for a substantial period of time.  .RelativesThe durian family tree looks a bit like this: Eukaryota > Viridiplantae > Streptophyta > Embryophyta > Tracheophyta > Euphyllophyta > Spermatophyta > Magnoliophyta > Eudicotyledons > Core eudicots > Rosids > Eurosids II > Malvales > Malvaceae
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Malvaceae (mallow family)
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Byttnerioideae
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Byttneriina
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Theobroma cacao (cocoa/chocolate)


   
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Malvadendrina
Corchorus capsularis (jute)
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Hibiscus (rosemallow family)
Hibiscus esculentus (okra)

   
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Malvatheca
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Malvoideae
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Althaea officinalis (marshmallow)


   
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Bombacoideae
Pachira aquatica (guiana chestnut)
Quararibea cordata (zapote/chupa-chupa)
Patinoa almirajo (almirajo)
Adansonia digitata (baobab)

   
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Sterculioideae
Cola acuminata (cola nut)
Cola nitida (kola nut)

   
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Helicteroideae
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Durio (durian family) <--
Durio testudinarium (durian kura-kura)
Durio greolens (durian kuning)
Durio grandiflorus (durian manjit)
Durio kutejensis (durian pulu)
Durio oxleyanus (durian sukang)
Durio dulcis (durian merangue)
Durio suluk (durian suluk)
Durio zibethinus (durian)


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Durian is sometimes placed beneath the family Bombacaceae. The positioning here reflects that of the [NCBI Taxonomy browser]. Search for Bombacaceae and Helicteroideae for more details about the issue.  .Better than chocolate?The durian comes from a family with several other plants of agricultural significance. One of the durian family's closest living relatives is the cola nut - one of the few ingredients in the original coca cola that is still believed to be present in the modern formulation. Another relative is the cocoa plant - the main ingredient in chocolate. Chocolate is itself highly regarded by mankind. However durian is a bit different from chocolate in several ways:
  • the edible part is a fleshy aril;
  • it does not need fermeniting or cooking;
  • it does not need dressing up with fat and sweetners;
By way of contrast, is is the seed of the cocoa plant which is eaten; this is first fermented, and then heated to a high temperature; and is then usually mixed with fat and sugar before consumption to make it palatable. While generally a wholesome food, cocoa has a number of drawbacks. Durian may suffer from a few of these as well - but I think the fact that the aril is the part consumed suggests it may prove to be significantly less toxic. Durian is certainly much more compatible with "raw food" diets - since it is at its most delicious served fresh and raw. It does tend to cost more than chocolate, though.  .Drugs and pheremonesSince chocolate contains a number of compounds that seem best described as drugs, could it be that the durian is using similar technology to its relative in manipulate the nervous systems of its hosts into preferring it over other fruit - and thus being more effective seed distributors? Most definitely, yes. I don't know if science has yet uncovered the details of the mechanisms employed, but - in additional to offering a fine, healthy nutritional snack - it seems inevitable that the durian will be found to contain a number of psychoactive compounds - intended to reinforce the behiour of eating durians in those who encounter it. Another organism that uses its stench to attract animals is the truffle. Its olfactory cocktail includes imitations of animal pheremones. We can probably expect something similar from the durian. However the smell of the durian suggests something slightly different - the durian smells almost as though it has gone off. It seems possible that the fruit's signal is deliberately mimicking decomposition - on the grounds that animals are likely to associate the smell of fruit about to go off with the presence of other ripe fruit nearby. Another theory is that our noses he evolved to be sensitive to the smell of decomposition - in order to detect bacterial and fungal infections that may be infecting the food we eat. Since these are important smells which many animals are equipped to detect, the durian can rely on the presence of sensors for them - but has found a way to "tickle" their receptors in a manner that is not too unpleasant. On the other hand, maybe the "decomposing" aspect of the durian smell exists primarily because the fruit is really is being rapidly munched up by fungi and bacteria. They certainly appreciate the fruit. Once it has split open, it usually does not take very long for such agents to reduce the durian to a ball of black fuzz. The flesh of the fruit is eaten - so it has a great opportunity to deliver behiour-modifying compounds to the nervous-system of the recipient. Chocolate uses dopamine mimics to produce a sense of satisfaction after consumption. It seems plausible that durian is doing a similar thing.  .NutritionThe durian certainly tastes good. However it seems possible that this is an illusion, created by the durian to ensure it gets eaten in volume. After all looking at modern attempts to give humans what they want the resulting foods tend to be like ice cream and chocolate: tasty - but often high in calories, fat and sugar. However, after further examination, it does appear that the fruit is a good deal more than nature's attempt at making custard. The tastebuds of those involved in directing the evolution of the durian's flesh seem to he shown good discriminatoy power - for the durian doesn't just taste like a gourmet meal, it really does seem to be as good as it tastes. Perhaps this is a sign that false adverising doesn't pay off in this area - and that good taste not backed up by good nutrition stops being quite as tasty across evoultionary timescales. Durian flesh is about 65% water - a pretty low water content for a fruit. It has about 147 kcal/100g. By dry mass, they are 66% carbs, 13% fat, 4% protein, 17% minerals, ash, etc. By calories, they are 67% carbs, 30% fats and 3% protein. According to the USDA, they he no saturated fat, are rich in B-vitamins and Vitamin C - and he a fair bit of potassium and copper. Durian is a fatty fruit. There aren't many of these out there - but the fatty fruit that are out there he a reputation for producing superior-quality oils. Olive oil and ocado oils are both good oils - but surely durian oil puts them into the shade - for taste and quality if not price. While the phytochemical properies of durian do not seem to he been investigated much yet, it seems reasonable to expect that it won't fare very well on this front - for the simple reason that the fruit shows little sign of attempting to poison anything - relying instead on physical barriers. Other fatty fruit - like olives, ocado and ackee - are loaded up with phytochemical compounds in an attempt to deter small predators - but the durian is sealed inside an impenetrable fortress for most of its existence - and apparently has little need for additional chemical defenses. This frees it up to be more delicious than other fruit. So don't expect that durian will activate your body's defenses and thus protect you against cancer. More likely it is just a great source of high-quality fuel. More details he durian's nutritional profile can be found [here] and [here].  .AddictionThe addictive nature of the fruit is not to be under estimated. Most find that it doesn't take long between eating some durian and wondering if it is time yet to he a little more. Reputedly, "lovers of the fruit he mortgaged their possessions to gorge themselves". It usually doesn't take long between being exposed to the fruit and plotting a pilgrammage to South-East Asia to further deepen ones relationship with it. Durian seems to closely rival chocolate in terms of its addictive nature. However the brain seems less likely to object to eating durian - since it seems more likely that durian really is good medicine - as well as a pleasing taste. On the other hand, fresh durian can be expensive. Enjoying durian fruit is not cheap anywhere in the world - and hing to import it only adds to the expense.  .Durian problemsIn Indonesia, Durians are rumoured not to mix well with alcohol. However there is no medical evidence on the subject to speak of - and experiments feeding rodents durian and alcohol he failed to reveal any sign of negative interactions. However the durian is a rich, sugary food. It produces a powerful insulin response, and is quite satiating. Hing too much durian is quite easy to do - and this can produces unpleasant sensations in the digestive tract. You can't eat a whole durian all at once. You practically he to carry it with you for a while. Lastly, the food appears to be adored by all kinds of microorganisms - as well as by humans. Over-ripe durian can ferment in the stomach - and create unpleasant bloating sensations and gut fermentation. Eating durians with other sugary foods is likely to make this problem worse.  .PesticidesDurians are often grown in impoverished countries, where pesticides are treated with less caution than they are in the western world. The rind of the durian is inedible - but there are still possibilities for "systemic" pesticides to compromise the fruit. There he been links between durians and pesticide-related problems - e.g. see [here].  .LocationThe are many strains of Durio zibethinus in use for commercial durian production in Thailand and Malaysia. However the durian's home seems to be on Borneo - and there are many species that are only found in a relatively small area of rainforest in Brunei - on Borneo's northern coast. The durian tree is temperature sensitive - and refuses to grow if taken too far from the equator.  .Durian-floured futureIt seems likely that the Durian has a rosy future ahead of it in the short ters - as a cultivated food crop. While the tree likes rainforest conditions, in can be cultivated elsewhere - with a little care. The durians that are currently confined to Brunei are likely to expand their ranges - and provide some genetic diversity for future breeding experiments. Hopefully, one result of all this will be that durian prices fall somewhat. The durian's genome may also be scenged by scientitsts, seeking to locate the secret of Durian's taste - so that they can quietly incorporate it into other foods - and then pass them off to consumers as lucky breeds or crosses. So far the history of humans actively breeding the durian has produced varieties with a less powerful odor, increased size, better storage properties - and a somewhat blander taste. Consumers do not like the durian's spikes. Currently, it is easy to draw blood trying to get into a durian. Some will sell the durian arils - but many consumers do often like to buy fruit whole. As a result, spineless durians are likely to be created. The durian's spines he served their purpose. Now it is entering a new era - when the durian can rely on humans to erect barriers on its behalf - using guns, fences and pesticides.  .Durian galleryFor many photograps of the durian, check out our durian gallery.

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Durian linksDurian Palace - huge, impressive durian site
DOL
Durian, king of fruit
Tropical Fruit - Durian and Mangosteens
Durian
Developing a Durian Addiction - by Jo Yoshida
Durian orchard
Kadayawan: A Festival Of The Durian - by Ian Garcia
What fruit is shaped like a hedgehog and smells like compost?
Daniel's durian photos
Phil Gibson's Durian page
Durian - King of Fruits
Durian in the wikipedia
Thai fruit fair
durian.org
Durian: King of Tropical Fruit - book by Suranant Subhadrabandhu and S. Ketsa
Durio ?A Bibliographic Review - some durian science
Juntak's durian photos
Photo of Huge (11Kg) durian

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Durian in the newsJail for 'dangerous durian' owner

Contact | http://timtyler.org/ [/td][/tr][/table]

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