Chem of Food & Cooking Exam 2

How is acidity related to pH?

The lower the pH, the more acidic a solution is. The higher the pH, the more basic (alkaline) it is. A pH of 7 is neutral.

If a solution has a pH of 3, is it acidic or basic? What about pH 10?

• pH 3 = acidic.

• pH 10 = basic.

What kinds of compounds can change the pH of a solution in water?

Acids and bases can change pH. Acids increase the concentration of hydrogen ions (H⁺), while bases decrease the concentration of H⁺ or increase hydroxide ions (OH⁻).

What are the categories of side chains in amino acids? How does each type contribute to the hydrophobic or hydrophilic character of a protein?

The three main categories are:

• Nonpolar: Hydrophobic; avoids water.

• Polar: Hydrophilic; interacts with water.

• Charged: Hydrophilic; interacts strongly with water because of electrical charges.

5. Describe the structure of proteins in terms of the distribution of hydrophobic and hydrophilic parts.

In many water-soluble proteins, hydrophobic side chains fold toward the inside, away from water, while hydrophilic side chains face outward, where they can interact with water. In membrane proteins, the distribution can be different because they interact with the nonpolar interior of cell membranes.

What happens when a protein is denatured? What conditions can denature proteins?

Denaturation occurs when a protein loses its normal three-dimensional shape, causing it to lose or change its function. Heat, extreme pH, alcohol, and certain chemicals can denature proteins.

How can denaturation change a protein solution into a gel-like material?

When proteins denature, they can unfold and stick together, forming a network that traps water. This changes the liquid into a thicker, gel-like material. Cooking an egg is an example of protein denaturation and aggregation.

What is a fatty acid?

A fatty acid is a molecule with a long hydrocarbon chain and a carboxyl group (–COOH) at one end. It is a building block of many fats and oils.

What components make up monoglycerides, diglycerides, and triglycerides?

• Monoglyceride: One glycerol molecule attached to one fatty acid.

• Diglyceride: One glycerol molecule attached to two fatty acids.

• Triglyceride: One glycerol molecule attached to three fatty acids.

Why are triglycerides considered nonpolar?

Triglycerides contain long, nonpolar hydrocarbon chains, and their polar glycerol groups are largely masked by ester bonds. Overall, triglycerides are predominantly nonpolar.

Why are triglycerides not soluble in water?

Water is polar, while triglycerides are mostly nonpolar. Because polar and nonpolar substances generally do not mix well, triglycerides do not dissolve in water.

What are hydrophobic molecules? What happens when they are placed in water?

Hydrophobic molecules do not interact favorably with water. They tend to cluster together or separate into a different layer rather than dissolve.

What are hydrophilic molecules? What happens when they are placed in water?

Hydrophilic molecules interact favorably with water. They often dissolve or disperse in water because they contain polar or charged regions.

What happens when a molecule has both hydrophobic and hydrophilic portions and is placed in water?

The hydrophilic portion interacts with water, while the hydrophobic portion avoids it. These molecules may arrange themselves into structures such as micelles or membranes.

What is the difference between saturated and unsaturated fats? What is a saturated fat saturated with?

• Saturated fat: Its fatty acid chains contain no carbon-carbon double bonds. They are saturated with hydrogen.

• Unsaturated fat: Its fatty acid chains contain one or more carbon-carbon double bonds.

What is a double bond in an unsaturated fat? What is doubled?

A double bond occurs when two carbon atoms share two pairs of electrons instead of one pair. The bond between the two carbon atoms is doubled.

What is the difference between cis and trans double bonds?

• Cis: The hydrogen atoms attached to the double-bonded carbons are on the same side, usually creating a bend in the chain.

• Trans: The hydrogen atoms are on opposite sides, making the chain straighter.

Why are fats with unsaturated fatty acids liquid at room temperature, while saturated fats are solid?

Cis double bonds create bends that prevent fatty acid chains from packing tightly together. This lowers their melting points, so many unsaturated fats are liquid at room temperature. Saturated fatty acids pack more tightly, giving them higher melting points.

What are major dietary sources of unsaturated fatty acids?

Plant oils, nuts, seeds, avocados, and fatty fish are major sources.

What are polyunsaturated fats?

Polyunsaturated fats contain fatty acids with two or more carbon-carbon double bonds.

How can hydrogenation change liquid oil into solid fat?

Hydrogenation adds hydrogen to carbon-carbon double bonds in unsaturated fatty acids. This reduces unsaturation and can increase the melting point, making the oil more solid.

What is a trans fat?

A trans fat contains at least one trans carbon-carbon double bond in a fatty acid. Trans fats can form during partial hydrogenation of oils, although small amounts also occur naturally in some animal products.

What is an omega-3 fatty acid? Is it more likely to be monounsaturated or polyunsaturated?

An omega-3 fatty acid has its first carbon-carbon double bond three carbon atoms from the methyl (omega) end of the chain. Omega-3 fatty acids found in nutrition are generally polyunsaturated.

Why do nuts high in polyunsaturated fats go rancid quickly? How can they be kept fresh longer?

Polyunsaturated fats contain multiple double bonds that are susceptible to oxidation, which causes rancid odors and flavors. Nuts can stay fresh longer when stored in airtight containers in a cool, dark place or in the refrigerator or freezer.

What are the components of milk?

Milk contains water, fats, proteins, lactose (milk sugar), minerals, and vitamins

What is the physical state of milk?

Milk is an emulsion and a colloidal mixture. It contains fat droplets and protein particles dispersed in water.

What components make up each state of milk?

• Liquid solution: Water with dissolved lactose, minerals, and some vitamins and proteins.

• Emulsion: Fat droplets dispersed in water.

• Colloid: Tiny casein protein particles, organized into structures called micelles, dispersed in water.

What is homogenization of milk? What is its purpose?

Homogenization breaks milk fat into smaller droplets and distributes them evenly throughout the milk. This prevents cream from separating and rising to the top.

What is the purpose of pasteurization? How is it accomplished?

Pasteurization uses controlled heating followed by cooling to kill harmful microorganisms and reduce spoilage organisms. It makes milk safer to drink and extends its shelf life.

How is ultrapasteurization different from standard pasteurization?

Ultrapasteurization heats milk to a higher temperature for a shorter time than standard pasteurization. It kills more microorganisms and extends shelf life. When packaged aseptically, ultra-high-temperature (UHT) milk can be stored unopened at room temperature.

What is lactose? What is lactose intolerance?

Lactose is the natural sugar found in milk. Lactose intolerance occurs when the small intestine does not produce enough lactase, the enzyme needed to digest lactose. Undigested lactose can cause gas, bloating, cramps, and diarrhea.

What happens when milk turns sour?

Bacteria convert lactose into lactic acid. The increased acidity causes the pH to decrease and can cause milk proteins, especially casein, to clump together. This creates a sour smell and taste and may cause curdling.

Whipping Cream, state whether it is a chemical or physical change and identify the components that change.

• Type: Primarily a physical change.

• What changes: Air is incorporated into the cream, and fat globules partially clump together to stabilize the foam.

Making butter, state whether it is a chemical or physical change and identify the components that change.

• Type: Primarily a physical change.

• What changes: Churning causes milk fat globules to join together into a solid mass of butter, separating much of the liquid buttermilk. The fat structure changes, but the fat molecules generally remain the same.

Making ice cream, state whether it is a chemical or physical change and identify the components that change.

• Type: Primarily a physical change.

• What changes: The mixture freezes, air is incorporated, and fat droplets help stabilize the structure. Water becomes ice crystals, while sugars, proteins, and other ingredients remain in the mixture.