BASIC FOODS 1: Water

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Questions and Answers

What is the amount of energy required to raise the temperature of 1 gram of water by 1°C?

1 joule

1 calorie (correct)

1 kilocalorie

10 joules

How many calories are required to melt 1 gram of ice?

40 calories

80 calories (correct)

60 calories

100 calories

What is unique about the specific heat of water?

It is the same as that of oil

It is lower than that of oil

It is higher than that of any other substance (correct)

It is not unique at all

What happens to the kinetic energy of water molecules as the temperature drops?

It decreases Signup and view all the answers

What is the term for the process by which 80 calories of heat are lost per gram of water?

Heat of Solidification Signup and view all the answers

What happens to water when it is completely frozen?

It becomes less dense Signup and view all the answers

What happens to the cells of plants and animals when frozen foods are thawed?

They become ruptured Signup and view all the answers

What is the freezing point of pure water?

0°C (32°F) Signup and view all the answers

What is the characteristic of a coarse dispersion?

It will eventually settle out Signup and view all the answers

What is an example of a colloidal dispersion?

Sol in gravy or jellies Signup and view all the answers

What is the outcome of destabilization in emulsions?

Creaming or coalescence Signup and view all the answers

What is the effect of adding salt or sugar to a solution on its freezing point?

It lowers the freezing point. Signup and view all the answers

What is the term for the decrease in freezing point of a solution compared to the pure solvent?

Freezing point depression Signup and view all the answers

What is the purpose of mechanical agitation in suspensions?

To create a suspension Signup and view all the answers

Why does adding salt to ice in making ice cream lower the melting point of the ice?

It lowers the melting point. Signup and view all the answers

What is the result of sedimentation or flocculation in suspensions?

Separation of the particles Signup and view all the answers

What is the function of suspensions in food products?

To give food a particular shiny appearance and smooth mouthfeel Signup and view all the answers

What is the temperature at which a solid changes to a liquid?

Melting point Signup and view all the answers

How many calories of heat are required to raise the temperature of 1 gram of ice to its melting point?

80 calories Signup and view all the answers

What is the difference between a solution and a dispersion?

Solutions have dissolved particles, while dispersions have undissolved particles Signup and view all the answers

What is the term for the pressure produced by steam when water boils?

Vapor pressure Signup and view all the answers

What is the term for the stabilization of dispersions?

Dispersion stabilization Signup and view all the answers

At what temperature does water boil at sea level?

212°F (100°C) Signup and view all the answers

What is the amount of energy required to boil and vaporize 1 gram of water?

540 calories Signup and view all the answers

What is the main characteristic of Free Water in terms of its removal from food?

It is easily pressed and separated from the food Signup and view all the answers

What is the primary role of Free Water in foods?

To measure water activity Signup and view all the answers

What is the main difference between Free Water and Bound Water in terms of their availability?

Free Water is not available for microbiological activities Signup and view all the answers

Which of the following is an example of Free Water?

Fruits and vegetables Signup and view all the answers

What is the primary characteristic of Bound Water in terms of its temperature?

It remains unfrozen at temperatures below 0C or -20C Signup and view all the answers

What is the main difference between Free Water and Bound Water in terms of their removal from food?

Free Water is easily removed, whereas Bound Water is difficult to remove Signup and view all the answers

What is the primary role of Bound Water in foods?

To be incorporated into the chemical structure of other nutrients Signup and view all the answers

Which of the following is not a characteristic of Free Water?

Food becomes frozen at temperatures below 0C or -20C Signup and view all the answers

What is the primary function of dehydration in food preservation?

To reduce the water activity of food Signup and view all the answers

What happens to bacteria when they come into contact with heavily salted food?

They lose their water and die by dehydration Signup and view all the answers

What is the purpose of adding solutes like sugar, salt, and propylene glycol to food?

To limit bacterial growth Signup and view all the answers

What is the range of water activity values?

0 to 1 Signup and view all the answers

What is the process called when a solvent moves through a semi-permeable membrane to equalize the solute concentration on both sides?

Osmosis Signup and view all the answers

What type of food typically has a lower water activity?

Dried fruits and vegetables, dried milk, and beans Signup and view all the answers

What is the result of adding a solute to pure water?

The water activity decreases Signup and view all the answers

What is the purpose of osmosis in food preservation?

To draw water out of food and prevent bacterial growth Signup and view all the answers

Study Notes

Water Properties

Free water: lightly entrapped but easily pressed, easily separated from food, measures water activity, example: fruits and vegetables, baked bread, then toast (evaporates water)
Bound water: incorporated into the chemical structure of other nutrients, not easily removed and resistant to freezing or drying, not available to act as a medium for dissolving salts, practically unavailable for microbiological activities

Measuring Heat Energy (Calories)

Calories: measurement of heat energy, 1 calorie = the amount of energy required to raise 1 gram of water 1°C (measured between 14.5°C and 15.5°C at normal atmospheric pressure)
Melting: to melt 1 gram of ice requires 80 calories (heat is absorbed)
Freezing: this process will release 80 calories per gram (heat is released/lost)

Specific Heat

Water's high specific heat makes it unique among compounds on earth
Hydrogen bonding between water molecules means it takes more energy to heat water than any other substance
Example: same temperature, oil (burning hot) vs. water (lukewarm)
High water content enables animals to withstand hot and cold temperatures

Freezing Point

Temperature at which a liquid changes to a solid
When temperature drops to freezing (32°F/0°C at normal atmospheric temperature), ice can form
Heat of solidification occurs when at least 80 calories (0.08kcal) of heat are lost per gram of water
Water expands and becomes less dense when completely frozen (ice floats)
Frozen foods rupture the cells of plants and cells, diminishing texture quality

Melting Point

Temperature at which a solid changes to a liquid
Returning the same calories (80 calories) of heat to a gram of ice will cause it to reach its melting point and turn back into water
While the ice absorbs the 80 calories, there is no increase in temperature (latent heat)

Boiling Point

Boiling point: vapor pressure = atmospheric pressure
Water requires 540 calories (0.54 kcal) of energy per gram to boil and vaporize - heat is absorbed
Boiling point is reached when the pressure produced by steam equals the pressure of the atmosphere pushing down the earth
Reaches 212°F (100°C) at sea level

Dispersion Types

Colloidal dispersion: particles not settling out of suspension, example: gravy, jellies
Suspension: will eventually settle out, mechanical agitation is necessary, example: cornstarch mixed in water
Emulsion: liquid dispersed in another liquid, example: milk, butter, mayonnaise
Foam: gas dispersed in a liquid, example: whipped cream, meringue

Dispersion Destabilization

Solutions are stable, but unstable colloidal and coarse dispersions can separate out
Emulsions – can either cream or coalesce
Suspensions undergo either sedimentation or flocculation

Water Activity

Measure of the amount of available free water in foods, ranges from 0 to 1
Below 0.85, do not support bacterial growth
High in water activity supports bacterial growth, example: milk, meat, vegetables, and fruits
Dehydration preserves food by reducing water activity

Osmosis and Osmotic Pressure

Osmosis: movement of a solvent through a semi-permeable membrane to the side with the higher solute concentration, equalizing the solute concentration on both sides of the membrane
Osmotic pressure: the pressure or pull that develops when two solutions of different solute concentration are on either side of a permeable membrane
Salting used as preserving foods – it draws water out of food and to itself

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