Lab Cat

13 Mar 2008

E is for…

Filed under: abc along, Basic Concepts, Food — Tags: , , , — Cat @ 5:00 pm
Easter Eggs

I love Cadbury’s Creme Eggs and have done since my first child minder, who used to work at Cadbury, brought me a half dozen of damaged or second creme eggs – you know the ones rejected for retail. I am cheating by showing Easter Eggs as the rest of this post is about hen’s eggs. Jennifer of The Spirit Trail also chose eggs as her ‘E’ and here is her lovely picture of her hens’ eggs:

eggs

Hen’s Eggs are amazing. Full of nutrients, especially protein, vitamins A, B and D and iron. The protein in egg has the highest protein efficiency ratio and is often used as the example protein as a comparison for other food proteins as it contains all the amino acids in the right ratio. More nutritional facts about hen’s eggs can be found at the American Egg Board’s website.

Eggs are very versatile. They can be eaten directly as boiled eggs, fried eggs, omeletes, scrambled eggs and poached eggs. Additionally the proteins in eggs can also be used

  • to help food set (e.g. egg custards),
  • as a foam to add air and volume (e.g. sponge cakes),
  • to clarify,
  • to give color,
  • as an emulsifier (e.g. mayonnaise).

The two different major proteins, egg white or albumin and egg yolk, respond differently to heat as they coagulate at different temperatures. Albumin starts coagulating at ~63 oC and yolk at 70 oC. The difference between their coagulation temperatures allows us to have cooked eggs with runny yolks. Egg yolks undergoing protein coagulation is the basis behind egg custards, including creme brulee.

For coagulation to occur the native protein first unfolds, scientists call this denaturation. As heat increases the proteins rearrange and eventually they coagulate or gel. This occurs with egg albumin when it turns from clear to cloudy white. This picture shows what happens when proteins unfold and then coagulate:

Coagulation

The Exploratorium has more information on the science of eggs including how to make a naked egg.

References:

Barham: The Science of Gooking

McGee: On Food and Cooking 2nd Edition

McWilliams: Introductory Foods

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8 Feb 2008

Food Allergies

Filed under: Basic Concepts, Food, Health — Tags: — Cat @ 8:00 am

Professor Richard E. Goodman, from Nebraska-Lincoln visited the local Institute of Food Technologists’ (IFT) section and gave a very interesting talk about food allergies. He is an active member of FARRP (Food Allergy Resource and Research Group), which is a resource for the food industry to test for and research known and potential allergens.

In this post, I tried to summarize the bits I remember but as I did not take notes, I found this information on the web. Thus, if anything is wrong, it is my fault, not Dr Goodman’s.

Food allergy is an adverse clinical reaction to food due to any type of abnormal immune response to food protein.

There are two mechanisms by which a food allergy can trigger the immune system. The first is IgE-mediated:

ige1cell

IgE-mediated food allergies are mostly immediate reactions, occurring within in minutes to hours of ingestions. The IgE response is the cause of anaphylactic shock, which is the cause of death after eating peanuts and bee stings. In this case, the allergic response is so extreme that it causes the air passages to swell; blood pressure drops leading to the inability to breathe and eventually, if not treated, it is fatal.

The second mechanism, which is mentioned by Dr Goodman and on the Act Against Allergy website, is Non-IgE mediated and involves the interaction of T-cells with the allergen and the part of the body where it is located.

Non-IgE mediated food allergies are usually delayed, taking 24 -48 h for a reaction.

Key symptoms of food allergies include hives, hoarse voice and asthma. In a severe reaction, there may be low blood pressure and blocked airways. Other symptoms that may occur include abdominal pain, angioedema (swelling, especially of the eyelids, face, lips, and tongue), diarrhea, difficulty swallowing, light-headedness or fainting, nasal congestion, nausea, and oral allergy syndrome (OAS). Symptoms of OAS are:

  • Itchy lips, tongue, and throat
  • Swollen lips (sometimes)

This last interested me. I have already discussed the problems I have when drink alcoholic beverages, especially beer, but I also have OAS in response to fennel and ginger*.

Common food allergens seem to vary depending on where you live. In the US, since January 2006

…the Food and Drug Administration (FDA) is requiring food labels to clearly state if food products contain any ingredients that contain protein derived from the eight major allergenic foods. As a result of the Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA), manufacturers are required to identify in plain English the presence of ingredients that contain protein derived from milk**, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, or soybeans in the list of ingredients or to say “contains” followed by name of the source of the food allergen after or adjacent to the list of ingredients.

source

[highlights mine]

Peanuts, treenuts and shellfish are the most common foods to trigger anaphylactic shock.
In Europe, the EU directive since November 2005 states that:

The 13 main food allergens must be listed: gluten-containing cereals, shellfish, fish, egg, peanut, soy, milk, tree nuts, celery, mustard, sesame seed, lupine and mollusks. Products derived from these allergens must be named without exception if used as an ingredient. In addition, sulfite must be listed if more than 10mg/kg is used.

Source

Currently, the only way to prevent an allergic response to a food item is avoidance. Ephedrine can be used, via an EpiPen to stop an anaphylaxis response, but will not prevent the reaction occurring again.

More food allergy links:

MedicineNet

FamilyDoc: Just the Facts

emedicineexcerpt

 

There is also a consumer advocacy and support group: The Food Allergy and Anaphylaxis Network (FAAN).

Footnotes

*I have another response to ginger in that it irritates my urethra (the passage from the bladder out) and so when I eat or drink anything gingery (ginger beer anyone), I have to remember to drink lots of water to reduce this irritation. I used to get, I thought, a lot of cystitis or infections in my urethra. Finally, I noticed that “infections” were linked to the day after when I went out for a curry, which was fairly frequent as a graduate student. Sigh. I probably should be grateful that curryhouses are not so common here in the US.

**Fortunately all the websites I found differentiate between food intolerance and food allergy. A food intolerance is when you cannot digest something properly, such as lactose. This means that the ingredient remains intact until the colonic microflora get hold of it. Then the gut bugs have a party. Seriously. A serious party.

13 Oct 2007

Effect of Solutes on Water

It seems that the stars are aligned or something for me to continue my discussion on water and material science. Not only did Dario comment on my Water Activity post asking me to discuss the relationship between glass transitions and water activity, but in a recent Friday Sprog post on Janet’s blog, she discussed phases of matter and a commenter talked about materials that was both solid and liquid. These materials are known as amorphous materials – there seems to confusion as to whether they are solid or liquid because they can have the behavior of both phases. Amorphous materials do not have the regular, ordered pattern of crystalline solids and they typically have more structure than a liquid.

Many foods are amorphous. In fact, very few foods are true crystalline solids or true liquids. Those that are; salt, sucrose, oils; are generally pure compounds. In most foods, water is present with solutes; salts and sugars; and polymers; proteins, complex carbohydrates, and lipids. These interfere with the standard behavior of pure water.

To get you started Janet has a great post about the typical three phases of matter that you meet in high school chemistry class, namely solid, liquid and gas. In that post she represents a great phase diagram:

Phase diagram from AES

 

This is a great representation for materials such as water that have a crystalline solid, ice, and when pure easily convert into a liquid. The point of change between ice and water is the melting point if you increase the temperature or the freezing point if you decrease the temperature.

As you add solutes to water the temperature of freezing/melting changes. Freezing occurs at a lower temperature. This is one of the colligative properties and is the reason why, as long as you don’t live anywhere really cold like Minnesota, a dilute solution of salt can be used as an antifreeze, as it freezes at a lower temperature than pure water. Here is a phase diagram from Spark Notes showing both the pure solution and the solution with dissolved solutes:

From Spark Notes

This is true of whatever solute you use, so sugar would have a similar influence on the freezing temperature. Thus, food freezes at a lower temperature than pure water. If you have ever seen the Alton Brown episode on Thanksgiving the turkey guy talks about the different temperatures and definitions of fresh, hard chilled and frozen turkey. They are also given here. For instance:

Any turkey labeled “fresh” in a food store has never been cooled to a temperature lower than 26°F, which is the point that turkey meat begins to freeze.

And:

[…]in order to be considered “frozen” a turkey must be cooled to a temperature of 0°F or below.

Obviously, hard chilled turkeys are stored between 0 and 26F.

So where does that get us?

Pure water has three phases: ice, water and steam (or solid, liquid and gas for other materials) and the phase change temperatures are influenced by the presence of solutes and polymers present in the liquid. Additionally, as a food freezes, the water typically freezes out, leaving behind a more and more concentrated solute liquid phase. This can result in an change in pH, viscosity amongst other properties. In some instances, the solute-liquid phase might never solidify. If a food is rapidly cooled to below the freezing temperature, a glass may be formed. A glass is an amorphous solid that has a disordered structure while behaving like a highly viscous solid. In some frozen foods, water will freeze to from crystalline ice and the solute-liquid phase will form a glass.

In my next post, I will discuss in detail the effect of sucrose on water and water activity. This is interesting because it is why we can make different candy types.

18 Sep 2007

Basic Concepts: What are Solutions?

Filed under: Basic Concepts, Chemistry — Cat @ 10:24 pm

In my last Basic Concept post when discussing why reactions occur, I left it rather vague as to what happens when substances dissolve. I suggested that no reaction had taken place because the chemical structure of the solutes had not really changed. Today I want to go into a little more detail as to what happens when solutes and solvents mix and discuss the difference between solution and liquid. We typically think of solutions as being a liquid mixture. But are all liquids solutions and all solutions liquids?

This question is a bit like the rhetoric around the series of statements:

My cat is gray. Are all cats gray?

To be able to answer the question as to the relationship between liquids and solutions we need to define what we mean by liquid and solutions. Janet in a post on phase changes describes:

A liquid has more intermolecular attractions holding the molecules to each other than the gas phase, but fewer than the solid phase. As a result, while the resulting clump of molecules is still nowhere near as compressible as the gas phase of the same substance would be, liquids don’t have rigid shapes, and they take on the shape of the containers you pour them into. The intermediate number of intermolecular associations (between gas and solid) means that the molecules in the liquid are sticking together but have some “wiggle room”.

Chambers Dictionary of Science and Technology defines liquid as:

A state of matter between a solid and a gas, in which the shape of a given mass depends on the containing vessel, the volume being independent. Liquids are almost as incompressible as solids.

The dictionary defines a solution (chem) as a:

Homogeneous mixture of two or more components in a single phase. Often refers specifically to a solution in water.

From this it would imply that solutions are special cases of liquids in the same way gray cats are a special case of cat. I quibble with the dictionary definition of solution (and fortunately so does this site for intro chemistry at OKState) as solutions can be solids in solids, liquids n solids, gases in solids, solids in liquids, liquids in liquids, gases in liquids, and gases in gases.

So having established that solutions are:

  1. A mixture of two or more components
  2. Typically but not always liquid
  3. Homogeneous

When discussing how components become a solutions, it is for convenience sake that the major component of a solution is termed the solvent and the other component(s) is(are) termed the solute(s). This helps chemists discuss what is going on when components of a solution are mixed. These are defined by the dictionary as:

Solvent: The component of a solution which is present in excess, or whose physical state is the same as that of the solution.

Solute: A substance that is dissolved into another.

Solutions typically occur by the solute being dissolved into the solvent. In the case of an aqueous solution of sodium chloride (table salt, NaCl), water is the solvent (aqueous is just the chemistry fancy way of saying in water) and NaCl is the solute.

Interestingly, different solutes dissolve in different ways. As I have posted about before, sodium chloride (NaCl) becomes ions of Na(+) and Cl(-) when mixed with water. This allows the salt to stay in solution because the bipolar nature of water means that water molecules surround the ions:

aqueous salt solution

Note that the partially positive hydrogen atoms of water face the negatively charged Cl ions and the partially negative oxygen atoms face the positively charged Na ions.

Organic molecules such as glucose, sucrose (table sugar) and vitamin C (ascorbic acid) are soluble because they have hydroxyl (OH) side chains. These form hydrogen bonds with water molecules.

glucose in water

The way that water molecules are arranged around the solute is known as solvation. This is defined as the association or combination of molecules of solvent with solute ions or molecules.

Not all organic molecules are able to dissolve in water. The familiar example being oil and water when making a salad dressing. Some organic compounds are able to partially dissolve into water. This makes them sparingly soluble and they partition into the water phase or form micelles with hydrophilic (water loving) groups facing the water molecule and hydrophobic (water hating) groups facing the inside of the micelle. This is how solutions such as milk are formed as suspended in water solvent are proteins and lipids.

Milk structure

Solutions are endlessly fascinating for food scientists and I will discuss more about colloids and suspensions in another post.

7 Sep 2007

Basic Concepts: Why Do Reactions Occur?

Filed under: Basic Concepts, Chemistry, Science — Cat @ 7:46 pm

I do not know why this thought popped into my head, but it seems that it is a fundamental question in chemistry. Why do certain molecules react and others don’t?

For example, acetic acid (vinegar) and sodium bicarbonate (baking soda) in the classic kitchen lab volcano experiment fizz nicely whereas when you add sucrose (table sugar) to a solution of sodium chloride (table salt) all that happens is that sucrose dissolves into the solution. In the former reaction the acetic acid and sodium bicarbonate reaction to form sodium acetate, carbon dioxide and water. In the latter reaction the molecules do not change, sucrose is no longer a solid but is dissolved into the solution*(1).

According to this website, reactions occur for two reasons:

1) The products have a low energy than the reactants

2) Products are more random (less ordered) than the reactants

Dealing with the first reason. Reactions are either exothermic or endothermic. Thermic means heat and exo means “outside” and endo means “within”. So reactions can occur either by giving off heat (exothermic) or by absorbing heat (endothermic). Endothermic reactions cannot occur unless heat is applied to the system. For example, water will not evaporate without added heat. Exothermic reactions are more likely to occur spontaneously. An example of an exothermic reaction is used in MRE kits by the military. When certain chemicals, e.g. lithium chloride, sodium hydroxide*(2), dissolve into water, they give off heat. Thus, their dissolution is exothermic. This is then used in the MRE to heat the provided food.

Unfortunately, we now cannot have any further discussions about why reactions occurring without meeting some thermodynamics. In particular, enthalpy and entropy. Rob Knop at Galactic Interactions has a good post about entropy from a physics perspective.

Entropy explains the second reason why reactions occur. Entropy is considered to be the disorder or randomness of a system and is related to the second law of thermodynamics. That is the law that most of us remember as order –> disorder. Or in my case an explanation as to why my bedroom was messy (neat –> messy as messy was the more disordered state). The more random or disordered the higher the entropy, which is, by the way, represented by S.

Enthalpy is a little tricker to understand. It is related to the heat energy of the system and is represented by H or ΔH where Δ is used to represent “a change in”. In the first reason for why reactions occur, enthalpy can be considered as an explanation. If:

ΔH = Hproducts – Hreactants

Then exothermic reactions have a negative enthalpy as the energy of the products is lower than the reactants and endothermic reactions have a positive enthalpy.

Entropy and enthalpy are linked, thus if the enthalpy of the system is such that the reaction appears to endothermic, the reaction can only occur if the entropy is increased. They are related by the equation for Gibb’s Free Energy:

ΔG = ΔH -TΔS

For a reaction to occur, ΔG needs to be negative.

So why do reactions occur:

1) The enthalphy of the products is lower than the enthalpy of the reactants

2) The entropy is higher in the final system than in the initial

3) ΔG of a system is negative

So that’s the best I can do. If I’ve got anything wrong*(3) or you need further explanation, please let me know in the comments.

*Notes

(1) Dissolution will have to be a topic of another blog. Janet at Adventures of Science and Ethics has a great post about phase change which is part of what is happening. For the pedantic chemists reading this post, dissolution can be exothermic or endothermic. I am discussing noisy and obvious reactions in this post.

(2) MRE heaters, known as flameless ration heaters are unlikely to contain sodium hydroxide as that is caustic soda. According to this website they contain iron, magnesium and sodium.

(3) I blame all errors on my dyslexia, which means exo and endo, positive and negative, left and right can, and do, have opposing definitions. I meant the other left (exo, positive) etc.

Further links

Why do reactions occur?

20 Mar 2007

Why Use Buffers?

Filed under: Basic Concepts, Chemistry — Cat @ 12:00 pm

This is part of a series on basic chemistry. See my posts on pH, acids and bases, strong and weak acids & buffers for earlier information.

I am going to approach this post by showing how Woo-practitioners (Quacks) who like to talk about the body being too acid and needing become more alkaline are talking nonsense. In fact, it should be a warning sign, if a treatment or diet mentions “restore your alkaline body pH” or “the secrets of an alkaline body” [1] it is distinctly woo. This is a big area for quackery. For example, I did a Google search on “alkaline body” and got approximately 24,000 hits.

So I am going to discuss human physiology.

We all are buffered. It is very important that the pH of the various body liquids remains within a tight range. Different body fluids may be at different pHs, but they are tightly controlled at that pH by buffering [2].

So why is the alkalinity body theory considered woo?
When you eat anything, it is digested [no arguments, right?] passing through the mouth, the stomach, small intestine, large intestine (AKA bowel, colon). Bits, if not most, are absorbed along the way. Different fluids in the digestive system are at different pH.

For example, the mouth typically has a resting pH around 6.3; and the presence of bicarbonate ions in saliva maintains this pH. This is not a true buffered system as the introduction of food can alter the pH and the bicarbonate salts neutralized the acids present (ref).

As food passes into the stomach, gastric juice is released. Gastric juice contains hydrochloric acid with a pH 1-4. Even when the stomach is full, the pH of the stomach will fall that low. It doesn’t matter what you eat, gastric acid will be produced to reduce the pH. Stomach enzymes are ineffective if the pH is higher.

High levels of HCl (pH 3) convert pepsinogen to pepsin, which is active at acid pH and kills ingested bacteria. (ref)

When food leaves the stomach and enters the small intestine, bile and pancreatic juices are released. Both of these are alkaline, partly to neutralize gastric juices, but also to act as a detergent, allowing the lipids to become more dispersed and available to enzymatic activity. Small intestine enzymes require this increase in pH to be able to function.

So given that food goes through all these changes in pH during digestion, it is unlikely that food can alter the pH of the body. Additionally, blood pH is closely regulated with an internal buffering system based around bicarbonate ions as well as serum proteins. I’ve posted on this before using this reference.

Thus, diet has little, if no, effect on the body’s pH. If your body’s pH is out of whack, you probably should check for an underlying illness.

So having sorted out those Quacks, why might we want to use buffers? The body already has buffers especially in the blood. If we want to study body functions outside of the body [known as in vitro] we would need to have a model that mimics the body especially the pH. If we did experiments at a different pH, the enzymes present might not function. For example, salivary amylase, which initiates starch digestion in the mouth, has a pH limit of 5.6-6.9, below and above which it cannot function.

As both plants and animal have natural buffering systems that means that food does too. When I am studying the Maillard reaction, I typically use model systems. This is not ideal, but removes any extraneous factors such as other reactions interfering with the reaction I am want to understand. This model systems are buffered at a pH typically found in food. When the pH is changed, a different reaction mechanism may even take place.

So buffers are important tools in chemistry allowing us to carefully control the pH.

Knowing the pH of a food product is important for food safety, as different micro-organism can or cannot grow when the pH is low. Acid-foods are more resistant to spoilage than low-acid foods, and are regulated differently.

[1] I cannot bear to put any more links in. Reading the two I posted is giving me a headache. Quick, I had better restore my brain’s alkalinity!

[2] Frustratingly I cannot find a list of body fluids showing their pH. If any body knows for one, please let me know if the comments.

9 Mar 2007

Buffers

Filed under: Basic Concepts, Chemistry — Cat @ 12:07 pm

In my last basic concepts post, I discussed strong and weak acids. This is also true of bases (alkalines). When dissolved in water, weak bases and acids do not fully dissociate, causing an equilibrium to exist between the acid (HA) and acid ion (A) (also known as the conjugate base):

HA + H2O ⇌ H3O+ + A

ref (1)

(more…)

27 Feb 2007

Strong and Weak Acids

Filed under: Basic Concepts, Chemistry — Cat @ 4:09 pm

In earlier posts, I discussed the concept of pH and acids & bases. If you remember, H+ ion concentration is often measured as pH as pH = -log [H+]. When dissolved in water, all acids undergo a dissociation reaction: (more…)

12 Feb 2007

Acids and Bases

Filed under: Basic Concepts, Chemistry — Cat @ 5:00 pm

Continuing my discussion of pH, with acids and bases. Some important background information:

  • Bases are also known as alkalis. So a basic solution is also an alkaline solution.
  • A proton is the equivalent of a hydrogen ion (H+).
  • In food, both the acidity and the sugar content are important. Our taste responses comes from a balance of the two. Some foods have a low pH/high acidity but do not taste sour due to their high sweetener content. A good example of this is cola, which has pH ~3.50 but does not taste sour because of the high sweetener (or non-calorific sweetener if you drink diet) content.

    An acid solution occurs when the pH is less that 7 and an alkaline solution is when the pH is above 7. You may have heard of something called litmus paper. This is a quick and dirty method to determine pH. Typically litmus paper turns red in acid and blue in alkali. Additionally, acids typically taste sour and bases taste bitter. If it helps, compare the taste of lemon juice with that of sodium bicarbonate. Lemon juice is an acid solution; it actually contains several acids; with pH 2.2. A solution containing just sodium bicarbonate (5% solution) should have a pH 8.6.

    There are several different definitions of acids and bases that are still useful and practical. Arrhenius defined an acid as a proton donor and a base as a compound that donates hydroxyl ions (OH).

    The reactions would look like this:

    Acid (AH) —->; A + H+

    Base (BOH) —->; OH + B+

    This was alter by Brønsted-Lowry theory of acids and bases, which kept the same definition for acids, but the definition for bases changed to:

    Bases are proton acceptors

    Finally, as far as I am concerned there is the Lewis Theory which is based on electrons rather than protons. A Lewis acid is an electon pair acceptor and a Lewis base is an electron pair donor.

    Any previously defined acid and base will count as a Lewis acid or base, but there are some compounds that are only Lewis acids or bases.

    During food processing it is important to maintain the pH and/acidity. Partly because bacteria cannot grow in a high acid environment. If the pH changed during processing, this would change the way the final product would have to be stored. One way pH is maintained in food and in our bodies, is through buffers. The success of buffers is dependent on the fact that certain acids are weak acids and do not fully dissociate to protons and relevant ions. This will be the topic of my next post on basic concepts.

    References

    Acids and Bases Tutorial

    Introductory Chemistry: Acids and Bases

    Background on acid-base reaction theories

    Lewis Acid and Bases

    6 Feb 2007

    The Hodge Scheme

    Filed under: Basic Concepts, Food, Research, Science — Tags: , , , , — Cat @ 5:00 pm

    Hodge Mechanism

    This is such a cool reaction mechanism. It was designed by John E Hodge in a what is now a citation classic. It sums up the Maillard Reaction, which is as complicated as the reaction scheme above suggests. This is such a classical scheme that it is known as the “Hodge Scheme”. I find that pretty impressive; it would be great if there was ever a “Lab Cat” reaction scheme.

    Hodge was an African American who gained an MA from the University of Kansas in 1940 and worked for the USDA for more than 40 years. Sadly, there was no Wikipedia page for this amazing man, so I started one. If any one knows anymore information about him, please, please add to the Wikipedia page.

    Reference:
    Hodge, J. E. (1953). “Chemistry of browning reactions in models systems.” Journal of Agricultural and Food Chemistry 1(15): 928-943.

    Citation Classic (pdf)

    John E Hodge Bio

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