Why Does Food Spoil?
What are the three main causes of food spoilage and deterioration discussed in class?
Microorganisms, enzymes, and other chemical reactions.
What are the three types of microorganisms discussed in class that can cause food spoilage?
Bacteria, yeasts, and molds.
What is one thing microorganisms need to grow in food?
Available water, nutrients, suitable temperature, or suitable acidity. Oxygen requirements vary.
What happens to the color of a freshly cut apple when it begins to brown?
Its exposed flesh changes from a light color to brown.
What food preservation method uses cold temperatures to slow the growth of microorganisms?
Refrigeration
Name two changes you might notice when food begins to spoil.
Changes in smell, color, taste, or texture; slime, gas, or visible mold.
Are molds and yeasts types of bacteria or fungi?
Fungi
Why is moist food often a good environment for microorganisms?
Because microorganisms need available water for their cells to function, and moist food often provides water and nutrients.
What gas in the air is involved in the browning of a cut apple?
Oxygen
How does drying help preserve food?
It removes available water that microorganisms need to grow.
What is oxidation?
A chemical reaction involving oxygen that can cause changes in food, such as browning or rancidity.
How do bacteria usually reproduce?
By dividing into two cells.
Name four of the six factors discussed in class that influence microbial growth.
Any four: moisture, temperature, time, nutrients, oxygen, and acidity (pH).
What is the name of the enzyme involved in apple browning?
Polyphenol oxidase.
How does pickling help prevent food spoilage?
It creates an acidic environment that inhibits the growth of many microorganisms
Why can food begin to change even when no bacteria or mold are present?
Because naturally occurring enzymes and other chemical reactions can change food without microorganisms.
What are hyphae?
Microscopic, branching, thread-like structures that make up the growing network of mold.
How do microorganisms use the nutrients found in food?
They use enzymes to help break down food molecules, such as proteins, sugars, and fats, so they can obtain nutrients for energy and growth.
Why can lemon juice help prevent or slow the browning of an apple?
Its acidity slows the enzyme involved in browning, and its vitamin C can interfere with the browning reaction.
Why does freezing not necessarily kill all microorganisms in food?
Freezing slows or stops the growth of many microorganisms while food remains frozen, but it does not reliably kill all of them. Some can survive and grow again when conditions become favorable.
Explain why a food that looks and smells perfectly normal might still be unsafe to eat.
Some harmful microorganisms do not cause noticeable changes in a food's appearance, smell, or texture. Therefore, food can contain harmful microorganisms without showing signs of spoilage.
Explain one difference between the way yeast grows and the way mold grows and reproduces.
Yeast is usually single-celled and often reproduces by budding, while mold grows as branching threads called hyphae and produces spores.
Two pieces of food contain similar nutrients, but one is very dry and the other is moist. Which is generally more favorable for microbial growth, and why?
The moist food, because microorganisms need available water to carry out the chemical reactions necessary for growth and reproduction.
Why does a cut apple begin to brown within minutes, while visible mold may take days to appear?
Browning is a chemical reaction involving enzymes already present in the apple and oxygen. Mold is a living fungus that needs time for its spores to germinate, grow, and form visible structures.
A student wants to preserve food without using refrigeration. Name two preservation methods they could choose and explain how each changes the conditions microorganisms need to grow.
Any two appropriate examples:
Drying removes available water.
Salting or sugaring reduces available water.
Pickling increases acidity.
Appropriate heating destroys many microorganisms.
Fermentation encourages selected microorganisms to produce substances, such as acids, that inhibit others.