Lab Cat

13 Mar 2011

Science on Sunday: Glycemic Index

Filed under: Health, Nutrition, Science — Tags: , , , — Cat @ 1:49 pm

One of the problems with science is how it is reported in magazines and newspapers.  Also how it is reported on the web can be a problem.  This problem came to light for me when I was reading the free magazine “Better Nutrition”.  In the February issue there was a short article on “The best weight management diet” which talked about a New England Journal of Medicine article which showed that high protein-low glycemic index diets were better for maintaining weight loss.  This sound realistic and was confirmed by reading the article, but what peeked my interest was the table of glycemic index values in the Better Nutrition article because apparently sourdough bread has a lower GI (54) than white bread (100).

This did not seem possible as sourdough bread is essentially made from the same ingredients as white bread with a different starter is added instead of yeast for proofing.  There is nothing in the process of making sourdough bread that should change the carbohydrates, which are from wheat flour.

So I looked up how glycemic index was measured.  What I found was that glycemic index (GI) ranks foods by how quickly they increase blood sugar (glucose) levels.  Foods that increase blood sugar rapidly after being consumed have a high GI.  For example, honey has a GI of 85 and sucrose, table sugar, has a GI of 70. Conversely foods which are slowly digested and absorbed have a low GI.    Examples of these foods are green vegetables (GI = 15) and dark chocolate with greater than 70 % cocoa solids (GI = 22).

GI is measured by feeding measured portions of the test food containing 10 – 50 grams of carbohydrate to 10 healthy people after an overnight fast.  Blood samples are taken at 15-30 minute intervals over the next two hours and used to construct a blood sugar response curve. The area under the curve (AUC) is calculated to reflect the total rise in blood glucose levels after eating the test food.  The results for a test food is divided by the results of the standard containing the same amount of carbohydrate, either glucose or white bread are used as standards, and multiplied by 100.  The result gives a relative ranking for each tested food.  There is some concern, firstly that the standards used are different and secondly two hours after a meal is too short.  Food is known to stay in the stomach for over 4 hours, so longer term blood glucose monitoring might be better.

The glycemic index was developed at the University of Sydney (Australia) originally to aid people with diabetes control their blood sugar levels.  Low GI diets are useful for people with diabetes as it allows them to regulate their blood sugar levels and this in turn helps with insulin levels and may reduce insulin resistance for people with Type II diabetes.

So the more I read, the less likely it seemed that sourdough bread could have a lower glycemic index than white bread, which by the way, in some measurements of GI is set as the reference with a GI of 100 and in others, where glucose is the reference, white bread has a GI of 70.  Yes, not even the measurements of GI are standardized.

Interestingly it seems that the reason the high protein/low glycemic index diets work is that protein fills you up and after eating a meal that is high in protein you are more satisfied.

References

http://heartscanblog.blogspot.com/2010/02/is-glycemic-index-irrelevant.html

http://www.glycemicindex.com/

http://en.wikipedia.org/wiki/Glycemic_index

http://thefoodfarce.com/49/

http://voices.washingtonpost.com/checkup/2010/11/in_theory_losing_weight_and.html

http://articles.latimes.com/2010/nov/26/news/la-heb-diet-20101126

http://www.extension.iastate.edu/publications/n3450.pdf

Thomas Meinert Larsen, et al, Diets with High or Low Protein Content and Glycemic Index for Weight-Loss Maintenance N Engl J Med 2010; 363:2102-2113 doi:10.1056/NEJMoa1007137

21 Jul 2009

Non-Enzymatic Browning Introduction 2

Food tastes best when browned.

Food tastes best when browned.

Food in always complex unless you are studying something quite simple such as a beverage with few ingredients (vitamin water, anyone?).  Even sucrose has a complex chemistry, more of which I will share in a future post.  So individual NEB reactions cannot be isolated in food.  Quite often intermediates and products from one reaction become intermediates in another reaction, especially in the Maillard reaction. Thus, most food chemistry textbooks use Non-Enzymatic Browning (NEB) as synonymous with the Maillard reaction. However, the other NEB reaction cause browning in food without the use of enzymes.

Both caramelization and lipid oxidation cause browning in certain foods, i.e. sugar-based and fried foods, respectively. Ascorbic acid degradation is significant in food with a low pH (high acidity) especially in citrus juices.  The reaction of flavanoids is important in highly colored foods as the colorful anthocyanins degrade and lose their color.  The reaction of flavanoids may also be important in soy protein, but less because of a color change and more due to a lose of isoflavones.

NEB Intro Part 1

23 Jun 2009

Non Enzymatic Browning

My major interest in food chemistry is how food changes during processing and storage.  I am especially interested in how color changes take place.  The reactions I am interested in are called Non Enzymatic Browning reactions to differentiate them from the browning that occurs when you cut an apple or banana, which involves an enzyme.

Non enzymatic browning (NEB, non enzymic browning) reactions are the most important reactions in food, and, no, I am not biased.   Just image the aroma of melting chocolate, freshly baked bread or  a roasting leg of lamb, the golden color of a croissant, the dark amber color of a well brewed beer; caramels, toast.  These are all caused NEB reactions.

There are five different NEB reactions and I intend over the next few months to write about each of them:

  1. Caramelization – browning of sugar, especially sucrose
  2. Lipid Oxidation – the oxidation of fats and oils; including rancidity
  3. Break down of flavonoids – highly c0lored compounds can also lose their color
  4. Degradation of ascorbic acid (Vitamin C) – AsA is unstable even without oxygen
  5. The Maillard Reaction –  reaction between carbonyl compounds and amino acids

Numbers (3) and (4) are not typically on a list of NEB reactions, but I did my thesis on ascorbic acid browning and it definitely goes brown without oxygen and without enzymes.  The degradation of flavonoids is one I have added and came to me in flash of inspiration when at a conference.  I am sharing it with you now, so this is new even though I had the idea three or four years ago.

More later…

12 Mar 2009

Knitting Delays Dementia

Filed under: Science — Tags: , , — Cat @ 3:07 pm

Mum heard on the BBC World Service that knitting can reduce depression in older women:

Apparently physical therapists and doctors have noticed that old ladies (and perhaps men – not mentioned) who are in pain and depressed, improved a lot when they took up knitting.  They used less medication, were more cheerful and their  memories improved.

Doctors think it may be the movements in knitting that help to calm patients.  They also suggest that knitting groups overcome feelings of isolation and making nice things makes the ladies feel  less useless.

They are starting a proper research programme in Bath to sort out the different factors.

I did a quick search and all I could find was this on BBC Health, which is more about dementia than depression:

Those who had during middle age been busy reading, playing games or engaging in craft hobbies like patchworking or knitting were found to have a 40% reduced risk of memory impairment.

So pick up those needles and stop your mind from deteriorating.

27 Jan 2009

Simple Sugars: Fructose, glucose and sucrose

Glucose, fructose, sucrose

Glucose, fructose, sucrose

Simple sugars are carbohydrates. Glucose and fructose are monosaccharides and sucrose is a disaccharide of the two combined with a bond.  Glucose and fructose have the same molecular formula (C6H12O6) but glucose has a six member ring and fructose has a five member ring structure.

Fructose is known as the fruit sugar as its make source in the diet is fruits and vegetables. Honey is also a good source.

Glucose is known as grape sugar, blood sugar or corn sugar as these are its riches sources. Listed in food ingredients as dextrose.

Sucrose is the sugar we know as sugar or table sugar. Typically extracted as cane or beet sugar. If sucrose is treated with acid or heat, it hydrolyzes to form glucose and fructose.  This mixture of sucrose, glucose and fructose is also called invert sugar.

Nutritionally, these sugars are the same as they all provide 4 Cal/g. This is true for starch and other digestible carbohydrates too. Of the three sugars, fructose is the sweetest and glucose the least sweet, so typically less fructose can be used than table sugar (sucrose) – if sucrose has a sweetness of one, fructose is 1.7 and glucose 0.74

Fructose is more soluble than other sugars and hard to crystallize because it is more hygroscopic and holds onto water stronger than the others. This means that fructose can be used to extend the shelf life of baked products more than other sugars.

Wikipedia has lots information on sugars, including information on the three I am interested in fructose, glucose and sucrose.

14 Jan 2009

Molecular Gastronomy is Part of Food Science

In a recent issue of Food Technology, the magazine for IFT members, Hervé This responds to the suggestion that molecular gastronomy is part culinary art and part science. He gives a very good summary of the differences between cookery/culinary, food science and food technology:

“Cooking is a technique (sometimes an art) and the objective is to make food.”

“On the other hand, molecular gastronomy is a science. It is performed in a laboratory.”

“Furthermore, science is not technology. Thus, applied science cannot exist. Application involves technology (from techne, doing, and logos, study). When examining mechanisms of phenomena, the goal is not to apply knowledge (application), but rather to produce it.”

He admits that he himself had problems during his thesis of separating out science from technology but he states very strongly that molecular gastronomy is science and molecular cooking is using the results from molecular gastronomy to create new food items or improve old ones. This’ Ph.D. thesis, on Physical Chemistry of Materials, was entitled Molecular and Physical Gastronomy or the equivalent in French.

The confusion between the science, art and technology of food is present in food science. That there does not appear to be a final definition of molecular gastronomy adds to this confusion, especially as chefs have taken over this term, rather than using This’ preferred Molecular Cooking. Khymos gives a good summary of the different definitions.

I do have problems with the fact that Molecular Gastronomy is so trendy and considered to be the saving of the world’s food supply.  [So I exaggerate? What's the problem?] Many articles about Molecular Gastronomy and the restaurants that practice molecular cookery appear to have never heard of food science.  So I appreciated the fact that This states that molecular gastronomy is part of food science but I struggle to place it within the traditional subject areas of food science.  It overlaps mostly with food chemistry.  At least This’ part of Molecular Gastronomy is heavily physical chemistry based.  The research undertaken is more directly relevant to cooking and culinary arts than much of food chemistry.  For example, my research on the Maillard reaction has few direct practical applications, unless you are willing to mix amino acids and sugars together in your kitchen.  I still would not recommend eating the results of my research.

Within the article he gives an excellent summary of what science is – the idea of testing a hypothesis to give new information which increases our knowledge of a system.   I might even use some of these ideas for teaching.

References

Hervé This Molecular Gastronomy vs. Molecular Cooking Food Technology December 2008 (PDF)

2 Dec 2008

Tasty Tuesday: Food Preservation Introduction – Reducing Moisture availability

Filed under: Food, Science — Tags: , , , — Cat @ 7:37 am

The biggest problem with food is that it is unstable. Even relatively stable food products change over time. There are two ways in which these changes occur.

  1. Internal changes to the chemical make up of food. A good example would be loss of vitamins
  2. Spoilage caused by microorganisms. Moldy bread is a good example.

Preserving food has been going on for centuries. Without it humans would have been unlikely to stop being nomadic. By preserving food it allowed them to have a food supply throughout the seasons and not move to where there was fresh food growing. Later on, preserving food allowed for travel long distances where there was no certainty that fresh food existed, including off the planet.

Preserving food is essential a way to extend the shelf life of that food. Shelf-life to food scientists has a particular meaning representing when the food quality has deteriorated either from a sensory perspective or from a chemical perspective. Obviously, sometimes these are the same thing.

There are two ways in which to consider food preservation, how does food go bad and how can we stop it. How food deteriorates depends a lot on the particular food item. For example high moisture foods are more likely to have bacterial damage than low moisture foods. Living foods under changes after harvest; this includes the fact that fruit and vegetables continue to respire even after being picked and the fact that muscle protein changes after the slaughter process. I could write about all of these changes but that would be several posts long, if not unending.

More interesting is what do we do to preserve food and what changes does that cause to the food item. The commonest way to preserve food is to reduce the available moisture content, which is also known as the water activity.  Drying can be done by drying, salting, and making jams or jellies.  In the latter process, the food is preserved with large amounts of sugar. This reduces the water availability because sugar is hygroscopic and holds on to that water for itself. The fruit, and it typically is fruit that is preserved in this way, is also cooked which destroys enzyme activity, unfortunately degrade thermal unstable vitamins and softens the cell walls. For fruits high in pectin, softening the cell walls releases the gum which, when the jam is cool, sets. This gives jams and jellies their firm structure. Pectin can be added to fruit low in pectin so that the preserve sets. Even though this is a way of preserving, fruit that would normally last a week or two can now be kept up for a year, changes to the fruit preserves will take place during storage. Light colored jams will darken. Unsurprisingly, reduced sugar preserves are not a long lasting as regular preserves.

Dried fruits are common and drying is also used a lot for meat preservation. Drying or dehydration is the removal of moisture, the dryer the better as far as shelf life is concerned. There are many ways to dry foods, from sun drying to freeze-drying and spray drying. The latter two being more likely commercial methods, whereas heat drying and sun drying could be carried out at home. The method of drying alters the food in different ways. For example, freeze drying results in the formation of food products that are very little changed from the original – just without any moisture. As the new Strawberry pieces in cereals show – adding moisture back results in almost original fruit piece. Well, sort of. Spray drying, which is commonly used for liquids such as milk or juices, results in a fine powder.

Salting, smoking, and curing are mostly used for meat and fish. The addition of salt or smoke causes dehydration of cells through osmosis – the water moves out of cells into the salty surroundings. This causes the cells to die or become temporarily inactivated. This includes bacterial cells as well as food cells. Thus, bacteria cannot grow. However, the food itself is very different from fresh. We have got used to this as bacon, lox, kippers and ham are all treated in this way.

As you can see removal of available water does not have to occur by dehydration, other techniques such as adding salt or sugar have the same effect.

References:

  1. Shephard, Sue Pickles, Potted and Canned
  2. Bennion, Marion and Scheule, Barabar, Introductory Foods

24 Nov 2008

Music Monday: The World in Six Songs, Daniel Levitin, A Book Review

Filed under: Science — Tags: , , , — Cat @ 8:23 am

Can the World be described by six songs? If so, what would the topics be and why? The question Daniel Levitin tries to answer in his new book “The World in Six Songs” actually appears to be can songs be divided into six categories? He obviously thinks so and his six themes are Friendship, Joy, Comfort, Knowledge, Religion and Love. The book is more than that, as he also describes how music effects us, emotional and mentally. He, like many musicians, myself included, is convinced that music does have a positive effect on us:

For example, we know that singing releases endorphins (again, a “feel good” hormone) but why is not known; and this lack of causal understanding makes many scientists uncomfortable about the connection between singing and endorphins.

However, he accepts that this means that he has a bias when it comes to research:

Scientists are in the business of wanting proof for everything, and I find myself caught somewhere in the metaphysical middle on this issue. As a musician, I’m reminded on a daily basis of the utterly ineffable, indescribable power of music.

But unfortunately current research showing this effect of music just has not been done, or done badly if it has been done at all:

On the research front, many of the studies on the effectiveness of music therapy are not performed to rigorous scientific standards, and so their claims remain unproven.

In fact, he goes on to compare some of the music therapy research with research done with potential psychic sense and not positively.

His thesis is a continuation of the thesis first presented to us in his first book, “Your Brain on Music” in which he totally disagrees with Steven Pinker who refers to music as “auditory cheesecake” meaning that our appreciation of music is an enjoyable side effect of language development. When I first read this quote from Pinker I decided that Pinker must be tone deaf and obviously has never MADE music himself. So it seems that I share the same bias as Levitin.  Levitin does suggest that since neurochemical states in the brain motivate us to act and emotion and motivations evolved together; the fact that music makes us feel good it motivates us to… fall in love, feel happy, get more energy and go to work, learn tasks, follow religion and so on.

But how does this fit with songs?  What is a song? Anything sung, apparently:

By definition, “a song” is a musical composition intended or adapted for singing. One thing the definition leaves unclear is who does the adapting. Does the adaptation have to be constructed by a professional composer or orchestrator, as when Jon Hendricks took Charlie Parker solos and added scat lyrics (nonsense syllables) to them, or when John Denver took Tchaikovsky’s Fifth Symphony and added lyrics to the melody? I don’t think so. If I sing the intro guitar riff to “(I Can’t Get No) Satisfaction” by The Rolling Stones (as my friends and I used to do frequently when we were eleven years old), I am the one who has done the adapting, and even if separated from the vocal parts of that song, this melodic line then stands alone and becomes a “song”: by virtue of my friends and I singing it. More to the point, you can sing “As Time Goes By” with the syllable “la” and never sing the words – you may have never have seen Casablanca and you may not even know that the composition has words – and it becomes a song by virtue of you singing it.

He concentrates mostly on popular music because he is mostly interested in what music makes us tick:

I’m particularly interested in that portion of musical compositions that people remember, carry around in their heads long after the sound has died out, sounds that people try to repeat later in time, to play for other; the sounds that comfort them, invigorate them, and draw them closer together.

The discussion in the book was hard to follow as I lacked the depth of music knowledge required. It should have come with a CD. I have since discovered that clips of the songs are on the book’s website. Unfortunately, the book I read is back at the library. Perhaps when it comes out it paperback and I have time to read it leisurely, over the summer rather than during the first month of a new semester at a new college teaching new classes, I might try again and work through some of his arguments.

I enjoyed “This is Your Brain on Music” which was about the neuroscience behind our responses to music. It was fascinating. I tried to review it but found the detail overwhelming. I still have part 2 of my review in my drafts folder!

Other References

http://cogweb.ucla.edu/Abstracts/Carroll_C98.html
http://www.boston.com/news/globe/ideas/articles/2006/09/03/survival_of_the_harmonious/
http://nanopolitan.wordpress.com/2006/09/24/is-steven-pinker-right-about-the-evolutionary-irrelevance-of-music/
http://ebbolles.typepad.com/babels_dawn/2006/09/did_music_prepa.html

14 Sep 2008

Sunday Science Snippet

Filed under: Science — Tags: , , , , — Cat @ 4:09 pm

In last week’s New Scientist I saw a link to this website that has videos for all the elements in the periodic table. The videos are about 3 – 4 mins long. Here is an example with the video for potassium.

It is a good website for any one interested in or learning chemistry.

31 Aug 2008

Sunday Science Snippet: Microcosm by Carl Zimmer

Filed under: Science — Tags: , , , — Cat @ 12:09 am

This book was great at bringing new biology, molecular biology and microbiology concepts together.  As a food scientist I know a little about each of these topics but not how the details fit together.  Now having read Microcosm I have a much better understanding of the details.  Life is very impressive and Carl makes it even more so while addressing many topical issues including evolution and biotechnology.  He manages to address these strongly but without bias so the reader is left to make up their own minds (or not) on the issues.

The section about biofilms was the most interesting as this was new science for me. A biofilm occurs when bacteria, such as E. coli, grow together in a huge mass.  This enables them to survive more demanding conditions that when freely floating single cellular organisms.

There are lots of reviews online. Probably the best place to start is Carl’s website for Microcosm, followed by various reviews (1, 2, 3, etc.) and Scienceblogs’ bookclub discussed Microcosm, which concentrated on the New Science of Life aspect of the book.

There is even a YouTube video:

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