Microbes

Objectives Describe how different microbes cause food spoilage.

Describe methods used in controlling food contamination.

Explain the methods used in preventing the growth of microbes in food.

Explain methods for decreasing food contamination

Microbes and Spoiled Food

Food Microbiology Food microbiology is the study of certain microbes and how they affect food.

MicroorganismsCan Alter the flavor, color, or odor of food.

Fruits and vegetables are still living before you eat them

Ripening May occur after harvest, as well as well as browning and softening

The natural fate of plant material after it dies is degradation by microbial action.

Molds

MoldsAre a Fungus

organisms that receive their nutrients from decaying organisms and can live almost anywhere where air and moisture are present.

Molds produce spores which can be carried through the air.

Spores can grow on substances with favorable characteristics for temperature, moisture, and nutrients

Benefits and Detractors of

Molds Used to add flavor and color to cheese

making soy sauces, citric acid, lactic acid, and many enzymes.

Penicillin and other antibiotics are produced with the help of molds.

Can also produce mycotoxins which are poisons and are a by-product of mold growth.

Mold Growth Temperatures Mesophiles grow at

room temperature (50° F–110° F).

Psychrophiles grow at refrigerated temperatures (less than 50° F).

Thermophiles grow at high temperatures (110° F–140° F).

Molds require oxygen in order to survive

Yeasts

members of the fungi family.Does not contain chlorophyll. Live mainly on sugars and starches or in high salt or sugar environmentsUsed to aid the fermentation process.

making bread, beer, and yogurt

BacteriaMost adaptable of all microbes

Bacteria associated with food spoilage are heterotrophic

Can get nutrients from almost anything

BacteriaSome bacteria under favorable conditions can reproduce every 20 minutes.

One cell can reproduce 17 million in only 8 hours.

Bacteria can also be classified as psychrophilic, mosphilic or thermophilic. Bacteria

die at a temp of 180°F. dormant spores can live indefinitely at this temperature.

Viruses

Among the smallest forms of life.

Must be viewed with an electron microscope.

All viruses are parasites.

lives off the genetic material of another organism.

Controlling Contamination

Contamination the process of a food item becoming unfit for consumption due to contact with an unclean organism.

Preventing contamination involves controlling four conditions

Relate to both the ingredients t and the environment where processed.

Controlling Air Movement

Molds, yeasts, and bacteria travel through the air.

If the movement of air is controlled, the chances for contamination are minimized.

This is one reason why large food processing machines are covered with lids.

Segregation

When foods are processed, each step is separated so that the contaminant does not travel from one step to the other.

Segregation is routine in food processing plants.

Most people are not as careful at home. The same cutting board may be used to cut different foods without being washed.

Temp Control Most food contaminants are mesophiles

grow at room temperature.

Food is rarely kept at room temperature for extended lengths of time.

Meat should be kept refrigerated before it is cooked.

After it is cooked, it should not be left at room temperature for long.

Foods should be kept below 40°F or above 140°F to prevent bacterial growth.

Moisture Control

Most microbes thrive in high-moisture environments.

High moisture environments are common at room temperature.

This is why food spoils less quickly when heated or cooled.

Controlling Microbe Growth Secondary to preventing contamination.

Effective prevention of contaminants makes the prevention of microbe growth easier.

Microbe growth prevention is carried out using one of two methods.

Controlling Microbe Growth

Death

can be attained using heat or by cooling.

halts the physiological deterioration and microbial action that occurs in fresh fruits and vegetables.

Heat is the most effective and least expensive method of killing the microbes.

Refrigeration destroys most of the microbes.

DeathFreezing

Extensive cell damage is created, which allows deteriorative enzymes to act rapidly upon thawing.

Blanching (treating with water at 140 to 150° F) inactivates these enzymes and preserves the quality of the product when thawed.

Rapid cooling after blanching prevents the loss of carbohydrates, vitamins, and minerals during the blanching process.

Fruit that is frozen may also be treated with ascorbic acid to retard oxidative processes.

Inhibition Preventing the growth of the microbes.

Involves altering the environment of the microbes so that they cannot thrive.

The environment may be altered by reducing moisture, adding chemicals or changing the pH level of the food.

Inhibition Food additives

Substances added to foods during processing to retain or improve desirable qualities or characteristics.

Examples

Sulfur dioxide

Potassium sorbate

Sodium propionate

Sodium benzoate

Processing Methods

Can be used to control microbial growth.

Foods can be

Frozen

destroying enzymes and microorganisms

Dried

to decrease moisture levels

Processing methods

Canned

Heated to high temperatures under pressure

inactivates enzymes but also kills spoilage bacteria.

High acid foods (fruits) require less heating during canning, since high acidity tends to reduce spores of anaerobic bacteria.

Tips for ConsumersControlling food pathogens

should be a high priority for anyone that handles food.

Tips to decrease or control food pathogens include:

Wash your hands and any surface that food comes in contact with regularly.

Cold foods should be kept at temperatures less than 40°F

Hot foods should be kept above 140°F

Cooked and raw food should always be kept separate. Keep utensils and dishes separate as well.

Tips for ConsumersMeats should never be

thawed on the counter. Use the refrigerator or microwave to thaw them.

Cooking should not be interrupted.

Vegetables and fruits should be washed before consumption.

Discard anything that looks suspicious

As a general rule, foods should not be left out for more than 2 hours.

Do not use foods that have passed their expiration date.

Summary Think of your kitchen at home, list 4 things in your kitchen that can cause possible microbial growth.

What is the Use for Food Additives?

What are the 4 major factors that you must control to prevent microbial growth?

Create a Venn Diagram comparing and contrasting yeasts, viruses and bacteria