RL 140609 Lecture 11: Proteins Part II [continued...]

Remembered 2 weeks ago when we entered the topic proteins, we were talking about wheat gluten (plant proteins). This week, we wrapped up the lecture with animal proteins, milk and egg proteins. Then I just realised that Dr. Chong left us a couple of questions unanswered, so I'm making use of this post to answer the questions as a form of revision. =)

RL 140609 Lecture 10: Clearing my debt....

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1. What are the wheat flour alternatives? Which are gluten-free, which are non gluten-free?

How well do you know your flour?

As I mentioned before,  gluten is a big big concern for celiac disease patients. So while they can't exposed to a tiny bit of gluten, they still want to enjoy wheat flour products such as cakes, breads, noodles, and pastries. In these cases, wheat flour have to be substituted by other kinds of flour. These substitutes can be totally free of glutenin and/or gliadin, which makes it totally gluten free, while others have a different ratio compared to wheat. All these could affect texture of a food, lesser in cakes and pastries, but more in breads and noodles. Functions and effects aside, what are the examples of gluten-free flour and non gluten-free flour?

Generally, grains are the items to watch out for gluten, while other parts of a plant such as tubers (potatoes), roots (tapioca) and legumes (soybeans, mung beans, etc) are gluten-free.

Most grains, including corn, buckwheat, and rice are totally 'gluten-free', which leaves a minority of grains to be non gluten-free (eg. wheat, barley and rye). Hence, celiac disease patients should totally avoid those grains. Oat is a special case where oats itself is gluten-free, but cross-pollination between wheat and oats are so common that some oats became capable of producing glutenin and gliadin, making it non gluten-free. Same goes to soybeans. For a more extensive explanation and examples, you could refer here. 

2. Whipping cream vs light cream vs half-and-half vs heavy cream?

Difference is in the fat content!

Half-and-half is the lightest of all, containing 12% fat, followed by light cream, 20%, then whipping cream 35%, and lastly heavy cream 38%. The higher the fat content, the creamier is it, and the more stable is also the foam formed. Hence, baking recipes (requires foaming) often call for heavy cream, while lighter cream is sufficient for cooking/beverage recipes (which does not requires foaming). 

More reading: here and here. 

3. Why does mustard has emulsifying properties?

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Mustard seeds has equal amount of fats, carbohydrates and proteins, and contains mucilage, a kind of plant glycoprotein. Mucilage is a polar molecule and is also able to interact with both water and fats, giving it the ability to form suspension. More details here.

4. Factors affecting coagulation of egg proteins...

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Promoting factors:

1. Salt: Salt forms ions in water and interact with ionic functional groups. This increases the ionic interaction between the polypeptide chain (salt bridge/attraction force) bringing them closer together, hence increasing the tendency of forming disulphide bonds.
2. Number of eggs: Increased number of eggs increased the concentration of egg protein, hence increased interactions, and thus easier to form dispulphide bridge. 
3. Vinegar/lemon juice: decrease pH, bringing the proteins towards the isoelectric point, causing the proteins to coagulate.

Obstructing factors:

Sugar: Sugar can react with the polar side chains of proteins by forming hydrogen bonds, making the side chains unavailable to react with another protein. As a result, the association of protein molecules is delayed.

5. Duck egg vs chicken egg...

It's said that duck eggs are more flavourful than chicken egg.. what say you?

Duck egg and chicken egg, what makes them different? Basically, the genetic composition would be different, since it's from two different species. Other than that, the chemical composition of the two are similar. The yolk contains majority fats, with duck having more than chicken, while the whites are just water and albumin. But there're still people who prefers duck egg more than chicken egg, cause they said it's richer and 'saltier'. Well, the saltiness might be because of the higher sodium content in duck egg, but I think it's basically just a myth since duck eggs are always preserved with salt. However, I can't deny that duck egg is much flavourful since it contains more fat, which could give the richer and creamier sensation. So, I guess it shouldn't be a big problem to substitute chicken egg with duck egg in a recipe. It might have a shorter texture and tastes richer and more moist. Bear in mind duck eggs are bigger than chicken eggs, it might not be advisable to substitute one-to-one. =)

That's about all for this week's reflective learning...

So long till the next post!
Dong