A Trip Which Sparked Curiosity (Part 3)

A Burst Of Colour

imageThe Christmas festivities are well under way, and we all know how colourful this season can be. Red, green, yellow, you name it, chances are there is a decoration in your house of that colour. Thinking about the sheer variety of colour I am surrounded by at the moment led me to dedicate my next post to a smaller, and often forgotten realm – the world of the invertebrates.

Christmas to insects isn’t the same, for many insects can only see the higher part of the visible light spectrum and part of the ultraviolet light spectrum. An exhibit in the Natural History museum showed what some flowers could look like through an insect’s eyes, and I was curious about what difference in anatomy caused this interspecies variation in vision.

It’s all about the receptors

Many insects that can detect ultraviolet light have eyes which contain ultraviolet light receptors which aren’t present in human eyes. Human eyes contain three types of photoreceptors, we are trichromatic; red, blue, and green [1]. When light enters the eye, its wavelength determines whether it is absorbed by these receptors, and the combination of signals produced by the photoreceptors due to the light absorbed is what determines which colour the brain perceives (as a quick side note; discussing colour perception is very theoretical, as, the sensors stimulated and colour of light absorbed can be scientifically proven, however, how the brain of the organism interprets those signals is impossible to state with 100% accuracy. Predictions can be made, but perception of colour is in the eye of the ‘bee-holder’ only after all [2].).

imageInsects are trichromatic also, however they do not possess the receptor which absorbs red light. Instead, insects possess the ultraviolet light receptor, leading to many invertebrates being unable to sense red light but instead being able to sense light towards and in the ultraviolet spectrum. Each of the insect’s prismatic lens containing units (or ommatidia [3]) contains eight light detecting cells; four respond to yellow-green light, two respond to blue light, and the other two respond to ultraviolet light [2]. This fact has forced flowers to develop petals which are attractive to insects not only in the visible light spectrum, but also in the ultraviolet light spectrum.

One hundred and eighty

imageWhen looking at many petals in the visible light spectrum, they may seem drab and a bit boring to you and me, however, when placed under an ultraviolet lamp, or photographed with an ultraviolet camera, these petals reveal a hidden world. Patterns, like dart boards, suddenly appear and offer a small glimpse into the world of the invertebrate. Vibrant colours illuminating the pollen rich areas of the flower act as a target for the insects flying overhead [4]. They have adapted so their petals are not only attractive to the human eye in the visible spectrum, but they exploit the ultraviolet sensing ability of the insects to become highly practical in their marketing strategy. No beating around the bush, if the insect wants nectar, it knows exactly where to find it. With a precise flutter of the wings, the insect hits the bullseye, receiving a sugary reward.

Conclusion

The photoreceptors present in the eye is what makes all the difference when perception of colour is involved. Without the relevant receptor, an entire spectrum of colours is inaccessible and a world is hidden to us. Think about how different Christmas could be with just a simple receptor missing.

 

[1] HORSE ARMOR. (2016) Insect vision. [Online] Available from: http://www.horsearmor.net/pages/Insect-Vision.html [Accessed: 23rd December 2016]

[2] RIDDLE, S. (2016) How Bees See And Why It Matters. [Online] Available from: http://www.beeculture.com/bees-see-matters/ [Accessed: 23rd December 2016]

[3] [Online] Available from: http://cronodon.com/BioTech/Insect_Vision.html [Accessed: 23rd December 2016]

[4] STARR, B. (2013) Hidden Patterns: How A Bee Sees The World Of Flowers. [Online] Available from: https://www.visualnews.com/2013/04/08/hidden-patterns-how-a-bee-sees-the-world-of-flowers/ [Accessed: 23rd December 2016]

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A Trip Which Sparked Curiosity (Part 2)


The Infamous Horned Bill – Combining Physics And Biology In One Beak

Continuing on my travelimages around the Natural History Museum, I came across an odd shaped beak, cut in half. The main beak was structured how one would expect it to be structured – a curved shape with a spiderweb of bone fibre strands inside – however, the addition of, what I now know to be called, a casque confused me. This hollow mound atop the beak ignited the curiosity inside me, leading me to write my second post in this series about the gorgeous Rhinoceros Hornbills, and more importantly, the more practical functions of their striking beaks.

The Casque

The normal part of the beak is predominantly used how every other beak is used, nothing much unusual to report here, so rather than take you all through the “boring” part of the beak, I decided to only discuss the more extraordinary casque.

Acoustics

The main theory about the function of this weird structure is that it is used almost like a resonance chamber[1], to amplify the sound of the Rhinoceros Hornbill’s call.

The casque is a perfect shape to allow a certain number of whole sound waves to fit into it. This length is different for each species as their calls are different pitches, and the sound waves produced, therefore, have different wavelengths. When the bird then calls, some of the sound waves produced enter the casque. As more sound waves enter, the crests of these waves line up and produce a resultant wave with the combined amplitude of the initial waves. This has a resonating effect and the sound is therefore amplified.

Reinforcement

The casque is said to have reinforcement properties as well. Not only does it add structural integrity to the beak, but also adds weight to make the beak a more effective hammer[2], which is useful when cracking open the tough exoskeletons of insects, and when the female and offspring break out of the enclosed nest (see ‘brief side note’ below).

Another use for this splendid casque is in aerial jousting [3] – a competition males engage in for territory and mates – which is pretty much exactly what it sounds like. Two males fly at each other at great heights and clash casques, so the reinforcement comes in handy; protecting the birds from major injury.

Sexual Attraction

The casque not only has purely practical purposes. A large element is attracting a mate. It is the casque in Rhinoceros Hornbills which exhibits sexual dimorphism – the size of casque differs between male and female[3]. This differs between species; in some species the males have bigger casques, but in others the roles are reversed, and some species are even monomorphic (only one size of casque is present). However, the interspecies differences are driven by sexual selection pressures, as some species’ casques may have evolved to allow them to excel in other areas.

The casque’s colours are also important in sexual attraction. When the Hornbills are born, their beaks and casques are white, like our fingernails. However, as they grow older, they rub their beaks against an oil gland just underneath their tail feathers, imagesecreting an orange oil onto the beak. The cumulative applications of this oil are what create the tremendous bursts of colour on the beaks. This allows individuals to recognise each other and sometimes is helpful in visual signalling as well [2].

Although not always the case, sexual dichromatism can occur as well. As I discussed in my previous post about the King of Saxony bird of paradise, sexual dichromatism is something which occurs in most birds. Some species of Hornbills exhibit this dichromatism through the colours and patterns created on their casques [2]. These factors all combine to create the perfect display in order to look as attractive to the female as possible.

Brief side note

As I mentioned previously, the females and their offspring have to break out of the enclosed nest which the Hornbill parents create. I thought I ought to discuss this further, not least because I find it a particularly fascinating element of the Hornbill’s behaviour.

Once the female and male have mated and the female is ready to lay her eggs, the pair find a hollow tree cavity, build a nest, and proceed to seal the female inside. They do this by creating a imagepaste made from fruit, faeces, and mud, squashing this through their beaks against the side of the cavity entrance. The pair completely seal the cavity except from a slit which is left for the male to pass regurgitated fruit through to keep the female alive while she sits on her eggs, and the offspring alive once they have hatched until they are ready to leave the nest. The female will also use this slit to expel faeces and uneaten food, in order to keep the nest clean [4].

Three months after the eggs have been laid, the female breaks out of the nest. Working with her life partner, she reseals the cavity so the offspring can be kept safe for another three months; until they are able to break out of the nest by themselves. Both parents take care of the offspring until this point [4].

Conclusion

Many of us may have grown up seeing these beautiful birds in zoos and on the TV, so the Rhinoceros Hornbill’s beak may be something that we are used to seeing, however, I hope that this post has given a bit more of an insight into the adaptations which make this bird’s beak perhaps one of the most interesting. I have been surprised at the level of sophistication that the seemingly useless mound that is the casque has demonstrated as a structure, delving briefly into the world of physics and then returning to the familiar realms of biology to fully discover the functions of the beak’s most peculiar feature.

 

[1]WORLD LAND TRUST. (2016) Rhinoceros Hornbill. [Online] Available from: http://www.worldlandtrust.org/education/species/rhinoceros-hornbill [Accessed: 18th November 2016]

[2]JACKSON, T. (2013) What is the function, if any, of a hornbill’s casque? [Online] Available from: http://africageographic.com/blog/what-is-the-function-if-any-of-a-hornbills-casque/ [Accessed: 19th November 2016]

[3]NAISH, D. (2014) The Splendid and Remarkable Anatomy of Hornbills [Online] Available from: https://blogs.scientificamerican.com/tetrapod-zoology/the-splendid-and-remarkable-anatomy-of-hornbills/ [Accessed: 24th November 2016]

[4]NATIONAL AVIARY (2016) Rhinoceros Hornbill [Online] Available: https://www.aviary.org/animals/rhinoceros-hornbill [Accessed: 27th November 2016]

The Marine Iguana – what makes it so unique?

marine-iguana_robin-slater2

Similarly to thousands of others across the UK on a Sunday night, I was encapsulated by David Attenborough’s new TV programme, Planet Earth II. It was an hour which spiked my curiosity about one reptile in particular, the Marine Iguana, endemic to the Galapagos Islands. It caused me to take a look at what makes these so special, and so different from land iguanas.

These animals are not the prettiest, scaled and ancient in their appearance, however they do have some amazing ecological adaptations, making them truly unique. Surprisingly, despite their scary appearance they are herbivores, feeding as the only sea going lizard in the world [2]. Living on land but feeding in the oceans, Marine Iguanas feed on seaweed and algae, diving up to 30m and holding their breath for around 45 minutes [4]. As this is a habit unique to Marine Iguanas, it provides them with an abundant food source, allowing them to thrive on the Galapagos Islands [2]. Interestingly, it tends to be the male iguanas who feed under the surface, with female and young iguanas feeding on the algae from rocks on shore [3] – something I find somewhat chivalrous.

The temperature of the waters around the Galapagos islands mean that Marine Iguanas can never spend too long in the ocean, returning back to the warm of land as they are ectothermic, meaning they cannot regulate their body temperature, unlike mammals and birds [3]. This makes them much more reliant on the temperatures of their environment, warming in the sun and cooling in the shade – when it is cold, they move slowly until they have warmed up enough to feed, and when it is hot they actually physically cover each other for shade. At night, when the temperatures of the Galapagos Islands drop considerably, they gather in vast numbers to conserve body heat [3]. The temperature endurance of an iguana is truly remarkable, when feeding then can lose up to 10˚C of their body temperature [3] – a change which, in humans, can be fatal. For these exceptional animals, they merely bask in the sun to warm up.

So what is it that makes Marine Iguanas so exclusive and adapted to their environment? It’s their long and muscular tail, which moves in a sinuous motion to act a propeller, pushing them through the ocean similarly to crocodiles [3] and razor sharp teeth to scrape algae off rocks. They also have tremendously sharp claws to help them cling to rocks on shore and underwater, withstanding heavy currents – another adaptation to help them feed. However the adaptations don’t stop there, due to the salty nature of the seas, they even have salt glands connected to their nostrils which clean their blood of extra salt accidentally ingested whilst feeding underwater [1].

Almost every shoreline of the Galapagos Islands is scattered with Marine Iguanas, but these mysterious creatures differ from island to island. Marine Iguanas show their exceptional colours as they mature, with coal black young maturing into red, black, green and grey iguanas [2]. The most colourful of these is the Española Marine Iguana, who have earned the nickname ‘ Christmas Iguanas’ due to their festive colours. Breeding season, which varies again from island to island also has an impact on the colourings of these reptiles, predominantly the males. During this time, the males develop red patches, on ‘Hood Island’ the male will turn completely red, in order to attract a mate and appear the most superior [3].

These entirely unique creatures, found in such a small part of our world have some amazing feeding adaptations and as the only sea going lizard in the world, every effort should be made to preserve their species and environment. I think their behaviour is truly remarkable.

  1. http://animals.nationalgeographic.com/animals/reptiles/marine-iguana/
  2. http://www.galapagos.org/about_galapagos/about-galapagos/biodiversity/reptiles/#marine
  3. https://animalcorner.co.uk/animals/galapagos-marine-iguana/
  4. https://www.redmangrove.com/11-curious-facts-about-galapagos-marine-iguanas/

A BDG Manifesto

Today’s session started out in a similar procedure to all the previous BDG (Biology Discussion Group) sessions. The chair established the groundwork of the discussion/debate. Exchanges then took place in a civil and calmly manner for a major part of the session before all hell broke loose after a (not-so-accidental) controversial remark was made. And I for one have to say, it was GLORIOUS. Harry Delph was the first one to retaliate but a quick succession of heated exchanges between the religious and the heathens kept the spirit of the debate very much alive. Hannah Rushton, a fierce advocate of the environment and its complex ecosystems, made a very convincing case for the seemingly meaningless lives of starfish against grand design. Tarn, a believer whose faith is a force to be reckoned with, retorted with fiery fervour so intense she forgot she needed to breathe in those 30 seconds of righteous fury. The back-and-forth argumentation was a stark contrast to the initial 20 minutes of peaceful storytelling.

Today’s BDG sesh confirmed an inkling I have had about these weekly BDG congregations, namely, people actually look forward to BDG sessions in the days leading up to it. It’s not just a dour dialogue about highbrow academic topics. It is intense and passionate and loud and strong opinions are aroused during the course of these discussions. BDG is one of the few clubs where the role of peacekeeper is very much in demand. As far as I am concerned, it is not just a platform to discuss high-minded scientific ideas with impartial judgement; for many of us, it is catharsis. Sheer release of emotion. You can see it in how readily BDG members jump at the opportunity to voice their opinions. People have researched the topic and they’ve done their homework on the issue. They’re ready to show the results of their reading. Those lengthy monologues in our head culminate in a BDG session where it comes out in all its brilliant fury. There’s an element of spontaneity and also an informality in these gatherings that prevents these discussions from becoming too stilted. Not to mention the free food and the social aspect of these freewheeling dialogues.
I believe we’ve stumbled upon a magic formula here. BDG is that rare combination of being intellectually stimulating, socially accepting and most importantly, fun.
BDG is an appointed occasion for people to go on a verbal outburst without fearing the social consequences of offending someone. It is a designated time and place for people to explore and espouse radically different viewpoints that they normally would not.
Never in BDG has anyone walked away with bitter feelings. I think it’s important we acknowledge this in order to engage in these discussions more fully (e.g. I literally told Max to die in BDG today and we’re still friends – I think). What happens in BDG, stays in BDG.

What I’d like to propose is this, to outline the purpose of these Biology Discussion Sessions. By expressly articulating the purpose of BDG, I hope to clarify what these discussions are for, so that we can get the most out of these sessions. A BDG Manifesto that states clearly the objective of BDG itself. BDG is there for us to engage intellectually with scientific issues. The second, less obvious but equally important purpose of BDG is to serve as an outlet for all of the academic reading we do over the course of the week. If there is anything to show for our nerdiness; then it’s in these BDG sessions. Finally, (and this is the most important) the ultimate purpose of BDG is TO HAVE FUN. Because life is inherently meaningless, so we might as well have fun while we’re still here.
Peace out *mike drops*

The Giant Panda

image104I am an undoubted and avid Giant Panda lover, whether it be how much I secretly want to be able to eat and sleep all day or my desire to preserve such a species so close to extinction, I’m not entirely sure. Therefore, I deemed it only fitting that my first blog post should be about these creatures.
Somewhat surprisingly, the Giant Panda is incredibly well adapted to its environment, namely as a consequence of what I could only imagine to be a slightly monotonous diet of bamboo. One of the most evident of these adaptations is the ‘sixth toe’, actually an extension of the wrist bone of a Giant Panda. This gives the panda extra strength, which enables it to pull up shoots, pull off leaves and grasp bamboo. [1] This is crucial for a Giant Panda as 99% of their diet consists of bamboo shoots and leaves, [2] and thus being able to extract this plant easily is fundamental to their survival.

Pandas belong to the family of bears, the Urisdae family, and have a particularly well adapted jaw and head to again enable huge bamboo consumption, as it is a tough and firm plant. The jaw muscles of a Giant Panda need to be incredibly strong to chew such a plant (think of it as a human chewing toffee all day) and thus the cranial cavity of the giant panda has evolved to accommodate these larger jaw muscles [2], ensuring the survival of the Giant Panda as it allows for the vast consumption of bamboo, their main source of food.

Along a similar theme, the molars of a Giant Panda has evolved to be very large and frictionless, differing the Giant Panda again from the Urisdae family as it is a species which only uses its molars, whereas most other bears uses their canines to hunt and kill their food.

As eating is evidently what the Giant Panda is best adapted to do, the digestive system of a Giant Panda is also adapted to their favourite food, bamboo. The oesophagus of a Giant Panda has a tough lining to prevent tears, and the stomach is very strong and muscular as bamboo is a relatively hard food to digest, due to amount of cellulose it contains. For the same reason, unlike the rest of the Urisdae family the Giant Panda has a short intestine and a larger colon, as very little water is consumed by a panda each day and a very small amount of waste compared to the amount of food consumed.

Part of a Giant Panda’s undoubted charm is their slightly stocky appearance compared to most bears. Their legs have become more muscular and strengthened overtime, due to climbing trees for their average 20-40 pounds of bamboo a day [2]. As a result of this huge consumption of bamboo, Giant Pandas do not appear fragile, and actually weigh around 250 to 220 pounds [2] with their legs having to carry all this weight over long distances and up trees, for between 10-16 hours a day [2]. This is required to maintain the nutrition levels which are needed for the survival of pandas.

Consequently, while I can’t say my initial love of pandas came from their evolutionary features and not their ‘cute’ yet formidable appearance, it has certainly widened my interest and made them an even more fascinating creature – and yes, one I truly admire for their wholehearted commitment to bamboo.

1.    https://bioweb.uwlax.edu/bio203/s2007/barger_rach/adaptations.htm

2.     http://astridsecologyproject.weebly.com/pandas-physical-and-behavioral-adaptations.html

A Trip Which Sparked Curiosity (Part 1)

The King of Saxony’s Crown

 Very recently I visited the Natural History Museum in London for the first time in six years. I was immediately transported back to the last time I was there, completely filled with awe and wonder.

Investigating many of the exhibits sparked my curiosity and so I thought I would share with you, in a series of posts, what I found interesting and the further information I have discovered as a result of my curiosity.

The King of Saxony Bird of Paradise

I am going to start with one of the most peculiar of my discoveries; Pteridophora alberti, or more commonly known as the King of Saxony Bird of Paradise. What caught my eye about this tiny bird was the huge pair of head wires attached above its eyes which are, in most cases, double the length of the bird itself.[1]head-wires

These head wires consist of a shaft with fused barbs down one side, which have been greatly modified for their purpose; to attract a mate. As many of you may already know, in the animal kingdom, success is measured by the number of genes an individual passes down to the next generation, via the offspring, and the male King of Saxony Bird of Paradise has a very unusual way of increasing his chances of success.

The Dance of Love

A mating dance is not uncommonly associated with particular species of birds, however the mating dance of the King of Saxony Bird of Paradise is second only to that of the Magnificent Riflebird (which, let’s face it, isn’t a surprise based on its name). While many birds, like the Magnificent Riflebird and the Superb Bird of Paradise (again, another case of an appropriately named bird) show off their genetic prowess by puffing up their feathers and startling the poor female with bright flashes of colour[2], the King of Saxony Bird of Paradise takes a different approach.

A lonely male sits on a branch high in the canopy and waits for a female to pass by. 2ndWhen one catches his eye, he flies down to his chosen courtship branch and prepares for the performance.[1] He gets excited. His first display is a bit of a warm up, he bops up and down on his branch rhythmically, trying to attract the much sought after attention of the female, competing with other males in proximity. Increasing in emotion, the male King of Saxony then begins his call. Starting with a low buzz, his mating call not only rises in volume but also in pitch, eventually building to an incredibly ear-piercing screech, which, combined with several clicking sounds, will hopefully win over the female.

However, the female has not yet been wooed, and the spectacle is only just beginning. As the now fully enthused male King of Saxony reaches the climax of his dance, he puffs up his feathers and his head wires begin to rise. The sound of buzzing heightens, the magnificent head wires are now extended above the top of his head. Screeching begins, the feathers on his head puff up, and he brings his head wires perpendicular to the sides of his head. With a screech that gives the rainforests of Papua New Guinea its characteristic sound, the male King of Saxony waves his head wires in a well rehearsed manner, as to make the female fall instantly in love with him.

The Evolutionary Success

This routine has been practised and perfected and, subsequently, passed down through the generations, but it has not always been like this.

In the forests of Papua New Guinea, the climate is warm, food is abundant (at least for the King of Saxony Bird of Paradise) and predation is at a relatively low level. Therefore, the evolution of the King of Saxony has not been guided by the need to thermoregulate, or hunt, or even blend into surroundings [3], but by its ability to attract a mate. The female King of Saxony Bird of Paradise finds the male’s outrageous head wires and ear-piercing screeches hugely attractive (whatever floats your boat I guess), so that is what has steered evolution to produce this incredibly interesting looking bird. For a male King of Saxony Bird of Paradise, the longer your head wires and louder your call, the more likely you are to succeed in passing your genes to the next generation, and the lack of parental help the males give the females, means the males can continue to give their genes to several females in a year, further increasing their success.

Furthermore, it is also as a result of sexual selection that the female counterparts of3rd brightly coloured male birds are always so dull in comparison (sexual dichromatism). Females are picky when choosing a mate; they want the best genetic package for their offspring, so when it comes down to it, what the females look like doesn’t matter to male birds, as long as they get to pass down their genes. Females want the brightest, best looking and sounding male to hopefully pass strength, resilience and attractiveness down to their offspring, so the chances of survival are much greater. It has also been scientifically proven that, in birds, there is a positive correlation between brighter colours and better health.[4] Females also need to be able to camouflage themselves when sitting on their eggs, which could be another explanation for sexual dichromatism.

Conclusion

In conclusion, what I first thought was just a small bird with a big hair issue, is actually an incredibly interesting example of sexual selection, and just goes to show how far evolution will go to ensure the highest chance of success in the animal kingdom.

[1] BIRDS OF PARADISE PROJECT. (2016) King Of Saxony Giant Head Wires. [Online] Available from: http://www.birdsofparadiseproject.org/content.php?page=77 [Accessed: 24th October 2016]

[2] ARKIVE. (2012) Superb bird-of-paradise. [Online] Availabe from: http://www.arkive.org/superb-bird-of-paradise/lophorina-superba/image-G129246.html [Accessed: 24th October 2016]

[3] LARSON, S. (2016) The King of Saxony Bird-of-Paradise’s Courtship Freakout. [Online] Available from: https://www.junglesinparis.com/stories/the-king-of-saxony-bird-of-paradise-s-courtship-freakout [Accessed: 26th October 2016]

[4] SCIENTIFIC AMERICAN. (2016) Why are male birds more colorful than female birds? [Online] Available from: https://www.scientificamerican.com/article/why-are-male-birds-more-c/ [Accessed: 26th October 2016]

The Misconception of Unset Jelly

As an experimental cook, the conventional fruit which are set in jelly on top of a cake are not good enough. So, fuelled by the desire to find the most original combination of fruit that could adorn a cake creation whilst smothered in jelly, I managed to find a few unusual possibilities, until I met my nemesis: fruit, which no matter how long the jelly sat in the fridge, prevented it from setting.

This post looks at why, and the slight misconception which surrounds the idea that some fruit prevent jelly from setting.

An Introduction to Gelatine

What is gelatine?

Gelatine is a mild tasting protein that is derived from collagen in animal tissue, which in turn is a hard, insoluble, fibrous protein [1]. Collagen is the connective tissue protein that provides strength to muscles and tendons and resiliency to an animal’s skin and bones, meaning that in humans it makes up one third of the total protein content [1]. Furthermore, since it is a structural protein, collagen is found in many parts of an animal’s body as it helps to maintain the structure and shape.

Where does gelatine come from?

Most gelatine is manufactured from pig skin because around 30% of its weight is collagen [2]. Firstly, the pig skin is soaked in dilute hydrochloric acid for roughly 24 hours. This step leads to the unravelling of the crosslinking protein bonds in collagen, resulting in the free protein chains then being extracted. These are filtered, purified and dried into sheets or granules (powder) that contain around 90% gelatine, 8% water and the remaining 2% is salts and glucose [2].

How does gelatine work?

Gelatine has claimed the prize of being different to all other proteins typically used in a kitchen setting, partially because it is the only protein that has the power to thicken liquids. This is why gelatine thickened sauces are ‘crystal clear and syrupy’ rather than opaque and creamy like sauces which use starch or flour as the thickening agent [2]. Gelatine’s unique properties arise from that fact its response to heat is not one that is usually demonstrated by proteins. Normally, food proteins respond to heat by unravelling (meaning they lose their tertiary and potentially secondary structures), and then bonding to one another to coagulate into a firm, solid mass. This is demonstrated by an egg frying since the albumin (liquid protein of the white) firms up into a solid mass of egg white as it is heated. However, gelatine proteins do not readily form bonds with one another, meaning that although heat initially causes them to unravel and disperse like any other protein, the gelatine proteins never form new bonds. This results in the liquid that they are dispersed in remaining as a fluid. Furthermore, because gelatine proteins are also long and stringy, they tend to become interwoven and this leads to the hot liquid in which they are suspended to thicken, although not completely solidify when warm. As the gelatine gradually cools down, the protein strands line up next to each other and twist into long ‘ropes’ and turn the liquid into a firm gel [2].

Plot Twist from an Innocent Addition

Learning from my past experiences, the following fruit should not be added if you wish for your jelly to achieve its intended state:

  • Pineapple
  • Kiwi
  • Figs
  • Papaya
  • Pawpaw
  • Mango
  • Guava
  • Ginger root

There are, as always, some exceptions to this rule, however I will come onto this later.

An unexpected culprit

You may have noticed that some of the aforementioned fruit are quite acidic, such as kiwi, and for me, initially, this was why the jelly did not set. However, it was as I did more research that I realised this was not the case.

As far as I am aware, when we study enzymes at school, whether at GCSE or A Level, enzymes seem to take on the role of the keys to existence, the Gods of all things bright and biological, or words to that effect. Or an effect slightly less exaggerated.

And yes, I do not dare disagree with the importance of their function as biological catalysts, whether it be in the baby food industry, slimming food industry or even saving the world by being a part of biological washing powders which require a lower temperature.

However, enzymes are the reason behind your cake masterpiece having a ‘soggy top’ as a result of the jelly not setting, which would lead to a piercing ice-blue stare from Paul Hollywood himself, an ‘It’s a little informal’ comment from the Queen of baking, Mary Berry, and may even provoke Shakespeare’s ‘God has given you one face, and you make yourself another’ exclamation.

Why are enzymes the downfall of jelly?

The listed fruit contain enzymes, in particular, proteases. Pineapple, kiwi, papaya, pawpaw and mango all contain actinidin, papaya and pawpaw also contain papain, pineapple also has bromelain, figs contain ficain and ginger contains zingibain.

The reason that jelly sets is because the collagen proteins in the gelatine form a tangled mesh as a result of being interwoven, meaning that water molecules are trapped, as well as other components of the liquid, and this provides the gelatine its semisolid state when it cools [3].

gelatine-structure

Fig 1. The long gelatine molecules as seen in set jelly [4].

The proteases in the fruit act on gelatine protein, and this can be thought of as the proteases acting as scissors and ‘cutting up’ the long strands of gelatine protein into smaller pieces, so that they can no longer interweave and create a network to trap water and other liquid molecules, meaning the jelly does not set [4]. This is shown in figure 2 and figure 3.

enzymes-acting-on-gelatine

Fig 2. Scissors representing enzymes (proteases) acting on gelatine [4].

shorter-gelatine-molecules

Fig 3. Shorter gelatine molecules after protease action [4].

In addition, it is important to note that pineapple and kiwi contain far more proteases than the other listed fruit. The reason for this difference is unknown, however it may be linked to the idea of repelling pests. As a basic concept, animals and bacteria are made up of proteins meaning that essentially the high levels of proteases in the fruit will digest any of the pests trying to feed on the fruit [4].

Moreover, I should address the exception that I mentioned earlier in the post. The fruit has to be fresh in order for it to ‘rain unset jelly on your cake parade’. For example, canned pineapple will not ruin your showstopper. This is because during the canning process, the pineapple is heated to kill bacteria so that the pineapple can be in the can for a long period of time and not decay [4]. This process also denatures the enzymes which means that they no longer act on the gelatine protein and prevent the jelly form setting. The high heat causes the bonds in the protein of the enzyme to vibrate meaning the bonds break (hydrogen bonds break first). Since hydrogen bonds are an essential part of the tertiary structure of the protein (which create a fibrous chain or globular chain) and the secondary (which is responsible for the protein either being an alpha helix or beta pleated sheet), the two structures of the enzyme are lost. This results in the active site of the enzyme no longer being complementary to the substrate (the gelatine protein molecule), so that no enzyme-substrate complexes form, meaning the gelatine is not catabolised. As a result, the jelly sets in its normal fashion.

Overall, for me the misconception lies in the fact that the fruit which should not be added fresh are rather acidic, especially kiwi. This always seemed to mean that it is the acidic conditions that the prevent the jelly from setting rather than the presence of certain enzymes.

References

[1]   http://www.medicalnewstoday.com/articles/262881.php

[2] http://www.finecooking.com/item/63379/the-science-of-gelatin

[3] https://www.scientificamerican.com/article/bring-science-home-fruit-gelatin/

[4] http://www.thenakedscientists.com/HTML/experiments/exp/science-of-fruit-jellies/

Other websites used

http://chemistry.about.com/od/foodcookingchemistry/a/foods-that-ruin-jell-o.htm

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