Do Fruit or Veg lose Nutritional Value when Cooked?

So I've heard a lot of different people saying that when you cook fruit and vegetables by boiling, steaming, frying or baking them you somehow decrease the amount of vitamins and nutrients within the fruit or vegetable. I thought that I'd research this further to see if there were any; optimum cooking methods, specific fruits or vegetables which should be eaten raw or vitamins which are very affected by heat.

There are many different molecules within fruit and vegetables that have positive effects on the body and they all respond in different ways to the cooking processes. I will be discussing examples that I found interesting within 3 groups; water soluble vitamins, fat soluble vitamins and beneficial enzymes. And then lycopene as an exception. If you want to know more about vitamins that I have not discussed in detail below please look in my bibliography for interesting articles about all kinds of nutrients and what effect cooking has on them.

First of all why do we cook fruit and vegetables? We cook fruit and vegetables to soften the cellulose fibres which makes the fruit and veg much easier to eat and to digest . We also cook fruit and veg to improve their taste.


Raw broccoli does not sound very appealing to me. However, according to recent research raw may be the best way to eat broccoli. This conclusion is based upon the fact that broccoli contains the enzyme myrosinase which, in the presence of water, chops off the glucose group of a glucosinolate (a natural component of almost all plants in the order brassicaceae (e.g. watercress, horseradish, broccoli)) The remaining molecule converts to either an isothiocynate, a nitrile or a thicyanate molecule. Isothiocynate is the standard product which is a good thing for humans because isothicynate can bind to mutated p53 proteins to increase cell death of cancer cells (p53 proteins regulate the cell cycle and therefore function as a tumour suppressant). It has also been shown to induce phase II detoxification enzymes which are involved in xenobiotic metabolism of carcinogens. Detoxification is a specific pathway which processes chemicals that are no longer needed by the body. Xenobiotic metabolism is a type of detoxification in which toxins are neutralised, solubilised and then transported to secretory glands. A carcinogen is any substance that is an agent in directly causing cancer therefore the neutralisation of these substances and expulsion from the body can only be a good thing. Inside the plant myrosinase and glucosinolates are stored in separate places and only come into contact when the plant is subjected to physical injury. Now this is the catch because this means isothicynates can only be produced when your teeth start to break down the broccoli or horseradish or watercress etc. s is why we want to preserve these enzymes. Enzymes denature at high temperatures as the hydrogen bonds break destroying the tertiary structure of the enzymes which also alters the shape of the active site, rendering the enzyme useless. This means that the effects are very different as chewing raw broccoli will convert glucosinates into isothiocynates which has beneficial affects whereas when you chew cooked broccoli the enzyme has been denatured therefore no reaction takes place myrosinase comes into contact a glucosinate :( So vegetables containing myrosinase and glucosinates are better consumed raw...


Such as:

• Broccoli
• Cabbage
• Brussels sprouts
• Cauliflower
• Kale
• Bok choy
• Rutabaga
• Collard greens
• Radishes
  

Lets move on to water soluble vitamins, such as vitamin B and C. As their name suggests, these vitamins dissolve in water and therefore when fruit or veg are boiled or steamed these vitamins are leached out. Water soluble vitamins tend to be less stable in air, water and heat which means fruit and veg containing these should not be stored too long, boiled too long or boiled in excessive water as these will all decrease the retention of vitamins.


An extremely unstable water soluble is vitamin C (which is also known as ascorbic acid). It is unstable because it is a strong reducing agent and hence rapidly oxidised to form dehydroascorbic acid. During this oxidation process the ascorbic acid loses 2 hydrogen atoms and 2 electrons. Dehydroascorbic acid is more readily transformed by a non-enzymatic reaction to a compound with no antiscorbutic activity. This non-enzyme reaction is irreversible. Therefore to preserve vitamin C our goal is to stop ascorbic acid being oxidised. The oxidisation has a few catalysts including copper, ascorbic acid oxidase and catalase. The last 2 both being enzymes. These enzymes catalyse a reaction we want don't want to happen, hence to slow this reaction as much as we can our aim is to destroy these enzymes. We can do this by heating them to a high temperatures (as I explained earlier in this post). Heating up the enzyme will break the hydrogen bonds thereby changing the shape of the active site which means the substrate (ascorbic acid) no longer fits. This means that the enzymes can no longer catalyse the oxidation, the oxidisation can still happen but it is much slower. However, as Vitamin C is water soluble it shouldn't be boiled excessively as the vitamin can leach out of the fruit or vegetable in question. A study suggests that fruit and veg that contains vitamin c should be boiled at 100 degrees for a minute and then eaten for a maximum amount of this important vitamin.


Fruit and Veg Containing Vitamin C:

• Papaya
• Bell Peppers]
• Broccoli
• Brussels Spouts
• Strawberries
• Pineapple
• Oranges
• Kiwifruit
• Cantaloupe
• Cauliflower
  

On the other end of the spectrum are fat soluble vitamins A,D,E and K which are more stable and resistant to air, water and heat.

An example of a fat soluble vitamin is beta carotene (it's converted to Vitamin A in the body). Beta carotene is embedded in a matrix with protein. If the matrix is not destroyed the body will only absorb a small percentage of the beta carotene. Chopping up the fruit and veg helps to break down this matrix and heating also breaks it up by denaturing the protein by breaking the hydrogen bonds of the tertiary structure which releases even more beta carotene. Unfortunately while the fruit and vegetables are cooked some of the beta carotene is leached out during the cooking process. Around 10-15% of beta carotene is lost by stir-frying or boiling whereas only 5% is lost when the fruit and vegetables is baked or roasted.

Lycopene ( a red pigment in fruit and veg) is an exception; it increases with cooking. Rui Hai Lui, the professor of food science at Cornell University, found that the level of cis-lycopene (a type of lycopene) rose 35% when cooking tomatoes for 30 minutes at 88 ⁰C.

A raw tomato has what is called an all trans configuration which means that the lycopene molecules are in a linear form whereas the lycopene that circulates in the human bloodstream is a cis-isomer of lycopene which has a bent form. This suggests that the cis-lycopene is absorbed more readily by the body. By heating up trans-lycopene with a bit of oil the shape of the trans-lycopene can be changed; the molecule is restructured so that it becomes bent under these conditions. The transport of cis-lycopene into the bloodstream and tissues is easier; so there will be higher levels of the antioxidant in body cells and the blood.
Fruit and Veg Containing Lycopene

• Tomatoes
• Watermelon
• Pink guava
• Red bell pepper
• Papaya

Honey Roast Peaches

Serves 4

Ingredients :
4 tbsp Butter
3 tbsp Honey
2 Peaches
4 Dollops Yoghurt/Cream/Mascarpone/Ice cream

Method :
1. Preheat the oven to 180 ⁰C.
2. Wash your peaches and then prepare them by cutting them in half and removing the stones.
3. Place them in your baking dish with the fruit flesh facing upwards.
4. Place a knob of butter on each half peach.
5. Then drizzle the peaches liberally honey
6. Put the peaches in the oven for 15-20 minutes then remove the dish from the oven and spoon the honey syrup over the peaches and place the dish back in the oven for a further 7. 10 minutes. Keep an eye on them though!!
8. Serve them with a dollop of something creamy, I used yoghurt, and drizzle some of the syrup over the top. Yum :)

Bibliography

[1] S. Subramanian, "Fact or fiction: Raw veggies are healthier than cooked ones," Scientific American, 2016. [Online]. Available: http://www.scientificamerican.com/article/raw-veggies-are-healthier/. Accessed: Jul. 25, 2016.

[2] A. L. Garcia et al., "Long-term strict raw food diet is associated with favourable plasma β-carotene and low plasma lycopene concentrations in Germans," BJN, vol. 99, no. 06, 2007. [Online]. Available: http://journals.cambridge.org/download.php?file=%2FBJN%2FBJN99_06%2FS0007114507868486a.pdf&code=d2b3d1dceeeb2eac9a01ec5fab104dcd. Accessed: Jul. 25, 2016.

[3] V. Dewanto, X. Wu, K. K. Adom, and R. H. Liu, "Thermal processing enhances the nutritional value of tomatoes by increasing total Antioxidant activity," Journal of Agricultural and Food Chemistry, vol. 50, no. 10, pp. 3010–3014, May 2002.

[4] S. T. Talcott, L. R. Howard, and C. H. Brenes, "Antioxidant changes and sensory properties of carrot Puree processed with and without Periderm tissue," Journal of Agricultural and Food Chemistry, vol. 48, no. 4, pp. 1315–1321, Apr. 2000.

[5] Demand Media and S. Busch, "Cooked vs. Raw for Beta-Carotene,". [Online]. Available: http://healthyeating.sfgate.com/cooked-vs-raw-betacarotene-9187.html. Accessed: Jul. 25, 2016.

[6] "Glucosinolate," in Wikipedia, Wikimedia Foundation, 2016. [Online]. Available: https://en.wikipedia.org/wiki/Glucosinolate. Accessed: Jul. 25, 2016.

[7] BBC, "Oxidation of food," in BBC, 2016. [Online]. Available: http://www.bbc.co.uk/education/guides/zyq22hv/revision/6. Accessed: Jul. 26, 2016.

[8] "Ascorbate in cell culture -- importance and uses of ascorbate in serum-free eucaryotic," Sigma-Aldrich. [Online]. Available: http://www.sigmaaldrich.com/life-science/cell-culture/learning-center/media-expert/ascorbate.html. Accessed: Jul. 26, 2016.

[9] Z. I. Kertesz, R. B. Dearborn, and G. L. Mack, "VITAMIN C IN VEGETABLES IV. ASCORBIC ACID OXIDASE*," 2003. [Online]. Available: http://www.jbc.org/content/116/2/717.full.pdf. Accessed: Jul. 26, 2016.

[10] S. Lehman, "What are Glucosinolates and why are they good for me?," in Verywell, Verywell, 2016. [Online]. Available: https://www.verywell.com/what-are-glucosinolates-and-why-are-they-good-for-me-2505908. Accessed: Jul. 27, 2016.

[11] "Vitamin," in Wikipedia, Wikimedia Foundation, 2016. [Online]. Available: https://en.wikipedia.org/wiki/Vitamin. Accessed: Jul. 27, 2016.

[12] . [Online]. Available: http://www.dummies.com/health/nutrition/healthy-eating/eating-clean-dummies-2nd-edition/. Accessed: Jul. 27, 2016.

[13] "Primary information of p53 gene,". [Online]. Available: http://www.bioinformatics.org/p53/introduction.html. Accessed: Jul. 27, 2016.

[14] T. G. M. Foundation, "Vitamin C," 2001. [Online]. Available: http://www.whfoods.com/genpage.php?tname=nutrient&dbid=109. Accessed: Jul. 27, 2016.

[15] Demand Media and J. Sheehan, "Does cooking food reduce the vitamin content?,". [Online]. Available: http://healthyeating.sfgate.com/cooking-food-reduce-vitamin-content-5164.html. Accessed: Jul. 28, 2016.

[16] K. Torrens, "Raw vs cooked," BBC Good Food. [Online]. Available: http://www.bbcgoodfood.com/howto/guide/raw-vs-cooked. Accessed: Jul. 28, 2016.

[17] G. Haase and W. L. Dunkley, "Ascorbic acid and copper in linoleate oxidation. 11. Ascorbic acid and copper as oxidation catalysts," 2002. [Online]. Available: http://www.jlr.org/content/10/5/561.full.pdf. Accessed: Jul. 28, 2016.

[18] T. W. Team, "The best way to eat your vitamins," WellnessFX, 2014. [Online]. Available: http://blog.wellnessfx.com/2014/09/02/best-way-eat-vitamins/. Accessed: Jul. 28, 2016.

[19] "Turning up the heat on tomatoes boosts absorption of Lycopene,". [Online]. Available: http://researchnews.osu.edu/archive/lycoproc.htm. Accessed: Jul. 28, 2016.

[20] "Metabolic detoxification - enzymes, toxins, liver - life extension health concern," LifeExtension.com, 2016. [Online]. Available: http://www.lifeextension.com/protocols/metabolic-health/metabolic-detoxification/Page-01. Accessed: Jul. 28, 2016.
[21] "Carcinogen," in Wikipedia, Wikimedia Foundation, 2016. [Online]. Available: https://en.wikipedia.org/wiki/Carcinogen. Accessed: Jul. 28, 2016.

The Oven and its Temperamental Temperature

So this week I have devised an experiment. We have a fan oven which means that the heat should be evenly distributed throughout the oven however, I've had my doubts about whether that really is the case. For example my mum has noticed that when we make pizzas and bake them in the oven the ones on the top shelf of the oven cook faster than the ones on a lower shelf. So I decided to investigate this using shortbread. I decided to use shortbread because it's quite simple to make but also it is also fairly universal; all the recipes use similar ingredients with similar methods. Therefore my conclusion is relevant for all shortbread baking. 

I used a BBC GoodFood recipe (find the recipe here) that seemed simple enough for me to recreate. Unfortunately I did not have rice flour so instead I used ciabatta flour, reassuring myself with the fact that it could not be a factor in deciding which batch tasted the best as they would all have the weird flour. I made a batch, divided the dough into equal portions and I baked each individually at a different shelf in the oven for the same length of time and at the same temperature. I decided to then feed my family one shortbread from each of the oven shelves (A, B and C) in a blind food test. I set up a questionnaire which asked the subject to note down which shortbread they thought tasted the best.

My hypothesis is that the top shelf shortbread will taste the best.

There were unfortunately many limitations with my experiment. Even though I used a ruler to measure the length and width of each shortbread, the thickness of each shortbread 'bite' was different as I didn't actively measure it. This was a mistake as the thickness makes a huge difference in the baking time which then affects the crumbliness and chewiness of the shortbread. This could definitely affect the popularity of the shortbreads.

Also I didn't have 3 trays that were exactly the same! 2 were the same but the third tray that I used was deeper and was a metallic silver colour which could have affected the baking of the shortbreads. Metallic silver colours are worse radiators whereas the black trays are good emitters of heat. This meant that the shortbreads were surrounded by completely different environments temperature wise without including the different shelves.  

The biscuits were not distributed evenly across the trays they were skewed over to a side and I think that the shortbreads on the far right and left baked faster than the middle shortbreads. This hypothesis requires further testing.

Sadly I could not put all the shortbread trays in at the same as I don't have 3 arms and I also couldn't remove all three trays at the same time so some trays were in the oven a fraction longer than others and unfortunately I didn't write down which these were or even coordinate the loading and removal of the trays to equalize the total times the trays spent in the oven.

My experiment was also on quite a small scale only 5 subjects took part and filled out the questionnaire after the tasting the shortbreads which means that the results I gathered weren't the most reliable.

However, even though we have established that it wasn't a fair test the results show that the top shelf in the oven produced the best tasting shortbread though the middle shelf was not far behind. This makes sense as shortbread should have a short and crumbly texture and the top of the oven is often the hottest. This is because when the air in the oven heats up the particles gain kinetic energy and therefore move faster and further apart which makes hot air less dense than less hot air so the hotter air rises. So it makes sense for the top shelf shortbread to be the crumbliest and yummiest shortbread.
Because the votes weren't very evenly spread across A,B and C this experiment suggests that there is a difference in temperature in ovens, even in very good fan ovens.

On to the results...

The graph below shows that the majority of people voted that the Top Shelf shortbread tasted the best followed extremely closely by the Middle Shelf shortbread. The interesting thing is that no one voted for the Bottom Shelf shortbread and this suggests that there was a difference in temperatures at the different levels in the oven as otherwise the votes would have been more or less evenly distributed across A, B and C.

Therefore, in conclusion the best oven shelf for baking shortbread is the top or middle one. However, keep an eye on them because they'll burn quicker at the top too! To achieve a more reliable conclusion this experiment should be repeated with more subjects and a greater effort to control more variables for example the thickness of each shortbread.

...Welcome

Hello,

I'm Carlotta and I love food. No, I don't think you understand I love food. I love eating it, making it, thinking about it... Even my favourite TV shows are mostly all cooking shows (if you were wondering my favs are the Masterchefs, GBBO (of course), Food Detectives and The Chefs Protégé just to name a few)

Number 2 in my list of favourite things is learning how things work. Being able to explain why something happens is extremely satisfying. I can't understand why you wouldn't want to know exactly why some fruits are sweeter than others or why biological washing detergents only work at relatively low temperatures or why music can affect your taste buds.

Recently, I watched  Chef Vs Science: The Ultimate Kitchen Challenge on BBC 4 in which a scientist Mark Miodownik went head to head with a Michelin star chef Marcus Wareing. It was a competition in which both had to cook a set dish each using their own methods and I absolutely adored it.

The kitchen was approached in completely different ways which as well as being very thought provoking made me want to try some of these methods out myself. I mean of course without the fancy equipment and machines because I am neither a chef nor a fully fledged scientist at this point.

It took me a while before I realised just how intertwined science and food was and Chef Vs Science played a big part in  helping to catalyse this thought process. When I had that eureka moment (took me long enough) I wanted to explore every aspect of this area; the irreversible Maillard reaction, how different vitamins and food stuffs interact with the body, why people are allergic to certain foods and how all of this scientific knowledge could improve my cooking techniques (I definitely need improving). I wanted to know the how's and why's behind the crowd pleasers, splitters and even upsetters.

With my As exams coming to close I finally have a bit of free time again and rather than wasting this valuable time, resting and relaxing, I decided to actually seek answers to the many questions I have about the complicated biochemistry of food. I wanted to log my research into explanations behind common reactions and the results of my experiments so that if I ever forget any of my findings I have a place where I can easily access all the answers. Hence this blog.


Carlotta

P.s I've spoken to a few friends and they did not completely understand the title or why I thought it made any sense however I decided to go against the mass consensus because I loved it and I had already created that domain. So for any of you who are confused about what this blog is (and let's be honest that'll be all of you) it's a food blog where I will share recipes that I have found or created which will be  accompanied with a scientific explanation or a scientific experiment that will hopefully expand your knowledge and further your interest in different areas of chemistry and biology.

How does yeast work?

 YEAST in dough

Yeast is a microorganism it's proper name is Saccharomyces Cerevisiae which literally means “sugar-eating fungus”. The eukaryotic (the cells have a nucleus or nuclei) yeast fungus respires to release energy. It is known as a "sugar-eating fungus" because when yeast respires aerobically glucose (a form of sugar) is used up and converted to energy. The energy allows the yeast cells to grow, repair and function.

The aerobic respiration equation is Glucose + Oxygen --> Carbon dioxide + Water + Energy.

However, in flour the sugar is starch (a polysaccharide) and the sugar in the white granulated stuff you put in your tea exists as sucrose (a disaccharide).
Yeast can break down sucrose into glucose and fructose by producing an enzyme called invertase which catalyses the hydrolysis of the disaccharide. To break down the starch in flour malted barley can be added to the flour for enzymatic balance. This means the flour has more active enzymes and this is usually in the form of more alpha amylase enzymes. These enzymes which can also be found in saliva break down the complex sugars and starch into simple sugars for example maltose. The yeast can produce the enzyme maltase which is able to break down maltose into two glucose molecules.

All of this glucose is then digested by the yeast and used in respiration and fermentation. Fermentation can also be known as anaerobic respiration and the fermentation equation is Glucose --> Ethanol + Carbon dioxide. Fermentation happens when the yeast is in an oxygen-less environment and is an equation catalysed by the enzyme zymase. As you can see alcohol is produced however this evaporates during the baking process as ethanol has a very low boiling point.

Both of these reactions of yeast produce carbon dioxide these bubbles of gas get trapped in the sticky dough and when the dough is baked in the oven the bubbles of carbon dioxide expand causing the dough to rise.

Snail Cinnamon Rolls:

I found this recipe on Rosanna Pansino's YouTube Channel, she made a YouTube video in which she made extremely cute snail rolls explaining the steps of the process. I have tried to note down and summarise this to make it slightly easier if you would like to recreate her amazing idea. I suggest you watch her video here !

Ingredients :

For the Rolls

(4) Cups Flour:
(1/2) Cup of Sugar:
(1) Packet of Yeast:
(1) Tsp Salt:
(1) Cup Warm Milk
(1/3) Cup of Butter (76g)
(2) Eggs

For the Filling
(1) Cup Light Brown Sugar:
(2-1/2) Tbsp Cinnamon:
(2) Tbsp Flour:
(1/3) Cup Butter (76g)


Method :

1. Warm the milk slightly in a pan and then dissolve the yeast in the warmed up milk and mix together.
2. Add the sugar and 1 cup of flour and mix again.
3. Cover the mixing bowl with cling film and leave to rise for 30 minutes.
4. When half an hour has passed add the salt, the 2 eggs, the butter and the remaining flour then mix together.
5. Flour your work surface and knead the dough for 5 minutes.
6. Use a bit of olive oil to grease a bowl and put your lump of dough into the bowl, cover with cling film and leave the dough to rise for 1 hour.
7. While the dough is proving make your filling – mix the sugar, cinnamon and flour together in a bowl.
8. When the dough has finished proving punch it down in the bowl and then roll it out to be around 21 inches by 16 inches (this is what Rosanna Pansino suggests).
9. Butter the top of the dough and then sprinkle the cinnamon filling so it is covering the whole surface of the rolled out dough.
10. Choose a long side and start rolling the dough back up into a swiss-roll like structure.
11. When the dough is all rolled cut the cinnamon rolls around 2 inches thick. I suggest you refer to Rosanna's video to fold them into a snail like shape.
12. Then bake at 180 degrees Celsius for 25 minutes until they are golden brown.