PHY 123 - Food, Fire, and Physics EXAM 1

Which is an example of a chemical leavener used to cause dough to rise?

Baking Powder

A polymer made up of sugar molecules is a ...

Polysaccharides

If food A is a solid at room temperature and food B is a liquid at room temperature, that suggests ...

... the molecules in food A have a stronger intermolecular force of attraction.

How many different types of amino acids are there?

20

Along with a glycerol backbone, what are triglycerides composed of?

3 fatty acids

What percentage of water (water content) is raw meat?

75%

What is a reasonable temperature to temper chocolate?

90 F

What is the impact of fats on gluten formation? A) Fats weaken the structure of gluten and thus make the final product more tender or flaky. B) Fats strengthen the structure of gluten and thus make the final product more tender or flaky. C) Fats coat the starch molecules, making them hydrophobic.

A

What is a hydrogen bond?

An attraction between 2 molecules. For example, in a water molecule, the oxygen is slightly negatively charged and the hydrogen are slightly positively charged. Thus the oxygen from one water molecule is attracted to the hydrogen of another water molecules.

Egg whites are about 90% water. When making a hard-boiled egg, what happens to that water? A) The boiling water drives it off. The water leaves the egg white which causes the egg white to cook. B) The bonds inside the water molecules are broken and the oxygen and hydrogen atoms form new amino acids. C) A majority of water remains in the egg white, but the water is trapped in the coagulated protein network.

C

Describe conduction

Conduction transfers thermal energy is exchanged through collisions.

Why do egg whites go from liquid to a solid when cooked?

Egg has proteins, these proteins are globular. Once denatured, the globs are freed, which makes them available to bond with each other.

What is an advantage of using the sous vide cooking approach?

It can fine tune the denaturing of proteins in the food and gives a chef great control over the texture and uniformity of the cooked food.

Some amino acids are labeled as hydrophobic. If you made a protein out of only hydrophobic amino acids, what structure would it likely have when placed in water?

It would form a tight ball in the water

What happens to bread as it is kneaded?

Kneading forms bonds between glutenin and creates elastic sheets of proteins.

Which is the main protein denatured in a medium-rare steak?

Myosin

Food A has a water content of 40% and a water activity of 0.65. Food B has a water content of 45% and a water activity of 0.55. If put in contact, what direction will water molecules migrate?

On average, water molecules will move from Food A to Food B.

Why is it sometimes recommended to cook meat in two stages?

One stage is to brown the surface, the next stage is to raise the internal temperature of the meat to the desired texture.

Egg white begins to thicken at 145ºF/63ºC and becomes a tender solid when it reaches 150ºF/65ºC. The protein that causes this transition in texture is ...

Ovotransferrin

Green beans are sometimes cooked by steaming. When the steam condenses onto the green beans, it releases a large amount of energy. Why?

Phase transitions absorb or release energy (Latent heat)

Why does a potato become soft when cooked?

Potato has a lot of water in it, but it is around the starch molecules, all the water goes into the starch molecules, causing them to swell and become soft.

Potato starch has more amylose molecules than corn starch, but corn starch has more amylopectin than potato starch. Based on this information, which one do you think is a better thickener?

Potato starch (Amylose expands easier due to its single line structure)

If held at a constant temperature of 63°C over many hours, egg yolks will continue to thicken and increase in viscosity. Why?

Proteins in the egg yolk continue to denature. As proteins denature, the yolk becomes thicker.

Why can salted meats (ham, bacon, corned beef) be kept uncooked for many months as compared to unsalted meats (chicken thigh or steak)?

Salts reduce the water activity of the meat, preventing spoilage.

The Onsen egg is a Japanese culinary creation in which an egg (in its shell) is cooked in a hot spring (temperature about 63°C) for a couple of hours. What is true about the globular proteins in the egg when it is removed from the hot spring?

Some of the globular proteins have denatured and coagulated, but many have not.

TRUE OR FALSE: Amylose and Amyleopectin are carbohydrates

TRUE

TRUE OR FALSE: Covalent bonds are stronger than hydrogen bonds

TRUE

TRUE OR FALSE: Water molecules move due to water activity, not water content.

TRUE

Why does long grain white rice become hard when cooled?

The amylose molecules in the rice align when cooled. This results in the harden texture.

The amino acid cysteine contains sulfur. Why is this amino acid important for gluten formation?

The cysteine amino acid on one glutenin molecule can form a bond (disulfide bridge) with a cysteine amino acid on another glutenin molecule, these bonds contribute to the gluten network.

While being heated, a wet starch granule increases in size. Why?

The heating process is allowing water to penetrate the granule and swell.

Travel mugs that do an excellent job of minimize heat transfer often have a double-wall vacuum design. In particular, the cup has two walls (an inner surface and an outer surface) and between the walls is air at low pressure. What concept is important when considering why this is a successful design?

The low thermal conductivity of air.

Why does kneading dough change its elastic behavior?

The process of kneading creates networks and gluten by forming bonds between proteins.

What does it mean when a protein denatures?

The protein loses its natural structure bychemical or physical means.

After cooking meat, like a steak, it is recommended to let the meat rest at room temperature before carving. Why?

The protein network needs to relax and bind to the water in the meat.

Why can corn starch be used as a thickener?

The starch granules in the corn starch swell with water and impede the flow of water.

By pushing on a steak, an experienced chef can determine if it is rare, medium rare, medium, or well done. Why?

The steak gets stiffer when cooked. This occurs because the proteins in the steak denature and coagulate.

If eggs are 74% water, why aren't they watery?

The water isn't free.

Why do tough cuts of meat require a long time to cook?

Tough cuts of meat have a lot of collagen, and collagen requires both high temperature and long time to denature and hydrolyze.

Why does sugar dissolve in water?

Water is composed of polar molecules, and sugar is a polar molecule.

What are the 3 modes of heat transfer?

convection, conduction, radiation

TRUE OR FALSE: A chicken breast has more collagen than a chicken leg.

FALSE: A chicken leg has more collagen due to where it is located on the body, collagen is like a buffer between bones.

TRUE OR FALSE: By weight, flour contains more proteins than carbohydrates.

FALSE: Flour contains more carbs than protein (by weight)

The overall shape of a protein can range from a long, extended, mostly helical molecule with a few kinks or loops, to compact, elaborately folded molecules that are called globular proteins. What type of protein is found in egg whites?

Globular