Water Activity and Food Preservation

The video explains the difference between moisture content and water activity in food science. Moisture content refers to the amount of water in a food sample, while water activity measures the availability of free water for microbial growth and biochemical reactions. The video uses bread and cheese as examples to illustrate how these concepts affect shelf life. It also discusses methods to manipulate water activity, such as drying, adding solutes, and freezing, to extend the shelf life of food products.

What is the primary focus of the video?

• The nutritional value of water

• The difference between moisture content and water activity

• The process of fermentation

• The history of food preservation

How is moisture content defined?

• The vapor pressure of food over pure water

• The temperature at which water boils

• The amount of water in a food sample, expressed as dry or wet basis

• The amount of free water available for microorganisms

What does water activity measure?

• The total water content in food

• The density of water

• The amount of free water available for microorganisms

• The boiling point of water

Why does bread have a shorter shelf life than cheese despite having similar moisture content?

• Bread has a higher water activity, allowing more microbial growth

• Cheese is stored in colder environments

• Bread is more porous than cheese

• Cheese contains preservatives

What is the water activity level of bread compared to cheese?

• Bread: 0.3, Cheese: 0.9

• Bread: 0.7, Cheese: 0.7

• Bread: 0.95, Cheese: 0.5

• Bread: 0.5, Cheese: 0.95

Which food products have high water activity and spoil quickly if not refrigerated?

• Fresh meat and fish

• Dried fruits

• Frozen meals

• Canned vegetables

What type of microorganisms require lower water activity to proliferate?

• Molds

• Halophiles

• Yeasts

• Bacteria

Which method involves removing water to lower water activity?

• Freezing

• Drying

• Adding solutes

• Fermentation

How do humectants affect water activity?

• They increase the water activity

• They bind water, reducing free water availability

• They evaporate water

• They change the color of food

What happens to water activity when food is frozen?

• It fluctuates

• It remains the same

• It increases

• It decreases as water turns to ice