Food Deterioration and its Causes

Main Idea

What is food deterioration, and how can food science minimize its effects?

Food deterioration includes:

changes in organoleptic quality (how something is perceived by a sensory organ)

nutritional value food safety aesthetic appeal color

texture flavor

To some degree, all foods undergo deterioration after harvest. The role of food science is to minimize negative changes as much as possible.

CATEGORIES OF DETERIORATION

occurs when a food is consumed that contains a chemical toxic to humans. Staphylococcus aureus and Clostridium botulinum produce toxins. Molds in foods produce mycotoxins like aflatoxin that are not destroyed by heat.

Insect damage can be minor, but this wounds the tissue for additional damage by microorganisms.

Controls for insects include pesticides, inert atmosphere and cold storage.

Insects:

The three general categories of food deterioration are: Physical Chemical Biological Factors that cause food deterioration include:

light, cold, heat, oxygen, moisture, dryness, other types of radiation, enzymes, microorganisms, time, industrial contaminants and macroorganisms (insects, mice, and so on).

Table 1. Useful ShelfLife at 70 F

Food Days Meat 1 to2 Fish 1 to 2 Poultry 1 to 2 Dried, smoked meat 360+ Fruits 1 to 7

Table 1. Useful ShelfLife at 70 F

Food DaysLeafy vegetables 1 to 2Root Crops 7 to 20Dried seeds 360 +

SHELF LIFE AND DATING OF FOODS

There is a time limit for the usefulness of all foods. This time limit depends on the type of food, the storage conditions and other factors. If food is held at about 70 F (21 C) its useful life varies as shown in Table 1.

SHELF LIFE AND DATING OF FOODS

Shelf life is the time required for a food product to reach an unacceptable quality. This length of time depends on the food item (Table 1), the processing method, packaging and storage conditions. Food manufacturers put code dates on their products. "Pack date" is the date of manufacture. The date of display is called the "display date," and the "sell by date" is the last day to sell. Some foods have a "best used by date," or the last date of maximum quality. The "expiration date" indicates when the food is no longer acceptable.

WHAT CAUSES FOOD DETERIORATION?

Specific causes of food deterioration are listed below. Deterioration can be caused by one or more of the following:

Microorganisms such as bacteria, yeast and molds; Activity of food enzymes; Infestations by insects, parasites and rodents; Inappropriate temperatures during processing and storage; Gain or loss of moisture; Reaction with oxygen; Light; Physical stress or abuse; and Time.

Bacteria, yeast, mold

Thousands of species of microorganisms exist, and a few hundred are associated with foods. Not all are bad; in fact, some are desirable in food preservation. Microorganisms are found in the soil, water and air; on animal skins, plant surfaces and digestive tracts; but they are usually not present in healthy tissue.

Bacteria are single-celled organisms occurring in three shapes: round (cocci), rod (bacilli) and spiral (spirilla and vibrios). Some produce spores which are resistant to heat, chemicals and other adverse conditions.

Bacteria, yeast, mold:

Yeasts are the largest of the microorganisms but are still single cells, and some produce spores.

Molds are larger than bacteria. They are often filamentous and they all produce spores.

In foods, these microorganisms attack basically all the food components -- including sugars, starches, cellulose, fats and proteins. Depending on the food and the microorganism, the action on food could be to produce acids, making the food sour, or to produce alcohol. Some microorganisms produce gas, making the food foamy, while others produce unwanted pigments or toxins.

Bacteria, yeast, mold:

Environmental conditions that affect microbial growth include temperature and oxygen. Microbes that prefer cold temperatures are said to be pyschrophilic. Mesophilic microorganisms prefer normal temperatures, while thermophilic microorganisms prefer hot temperatures. Bacteria or molds that require atmospheric oxygen are said to be aerobic, while those yeasts and bacteria that do not require atmospheric oxygen are called anaerobic. Facultative microorganisms are adaptive, and can survive in either aerobic or anaerobic conditions. Obligative microorganisms are capable of survival in only one or the other situation.

Foodborne disease:

Humans may be infected by eating a food containing a microorganism. Infections can be caused by Clostridium perfringen, Salmonella sp., Escherichia coli (E. coli 0157) and several others. Food intoxication

Food enzymes:

All foods from living tissues have enzymes. Most of these enzymes will survive harvest or slaughter. At the time of harvest or slaughter, enzymes that control digestion and respiration proceed uncontrolled and cause tissue damage. Some of the post-harvest enzymatic reactions are actually desirable, as in the ripening of tomatoes and the aging or tenderizing of beef. Enzyme action can be controlled by heat, chemicals and radiation.

Heat and cold:

Normal harvest temperatures range from 50 to 100 F. The higher the temperature, the faster biochemical reactions occur. In fact, the rate of chemical reactions doubles with each 10 degree rise in temperature. On the other hand, sub-freezing temperatures damage tissues. Cold temperatures may also cause discoloration, change the texture, break an emulsion and denature protein. Chilling can injure the tissue of fruits as well.

Oxygen:

Chemical oxidation reactions can destroy vitamins (especially A and C), alter food colors, cause off-flavors and promote the growth of molds.

PRINCIPLES OF FOOD PRESERVATION

Food preservation involves the use of heat, cold, drying (water activity or Aw), acid (pH), sugar and salt, smoke, atmosphere, chemicals, radiation and mechanical methods.

Heat:

Most bacteria are killed at 180 to 200 F, but spores are not. To ensure sterility, you must have wet heat at 250 F for 15 minutes. High acid foods require the same temperature of heat for less time.

Cold:

Most microbial growth slows at temperatures under 50 F. Some bacteria, called psychrophiles, actually thrive at relatively low temperatures and will continue slow growth. Foods frozen at less than 14 F usually do not have any free water, so these foods also benefit from low water activity to help protect against microbial growth. Freezing may kill some but not all of the microorganisms.

Drying:

Drying reduces the water activity (Aw) in a food. Since microorganisms contain about 80 percent moisture, drying or dehydrating the food also dehydrates the microorganism. Changing the amount of water in a food also alters the rate of enzyme activity and other chemical reactions.

Acid:

As the food becomes more acid (lower pH) the heat required for sterilization is reduced. For example, the pH of corn is about 6.5. At 226 F, 15 minutes are required to destroy C. botulinum spores. The pH of pears is about 3.8 and only 5 minutes are necessary to destroy C. botulinum at 226 F. Acid may occur naturally in foods, be produced by fermentation or be added artificially.

Sugar, salt and smoke:

Sugar, salt and smoke are chemical means of controlling food deterioration. The addition of sugar or salt to a food item increases the affinity of the food for water. This removes the water from the microorganism through osmosis.

Smoke contains formaldehyde and other preservatives. The heat involved with adding the smoke helps reduce the microbial populations and it dries the food somewhat.

Atmosphere:

Changing the storage atmosphere reduces food deterioration. The growth of aerobes is slowed by removing the oxygen, while providing oxygen limits the growth of anaerobes. Adding carbon dioxide or nitrogen also slows deterioration.

Chemicals:

Chemical additives such as sodium benzoate, sorbic acid, sodium or calcium propionate and sulphur dioxide retard the growth of microorganisms, modify enzyme activity, inhibit chemical reactions or modify the structure of foods

Radiation:

Radiation includes X-rays, microwave, ultraviolet light and gamma rays. Radiation can destroy microorganisms and inactivate enzymes.

Food Sanitation

Definition: protection from contamination

Must include all functions operations Food products

Ongoing / Dynamic (ever changing) “Sanitation is a Way of Life”

Temperature Control

Food Temperatures:

Danger zone (40ºF to 140ºF)ThermometersMonitor temperaturesThawing

Hygiene and Personnel Practices

People are the # 1 consideration Rules:

Setting Following Breaking

Hygiene and Personnel Practices

Sanitation program is an attitude Willingness Effort Ongoing training

Hygiene and Personnel Practices

Personnel Training: Appropriate sanitation principles Food handling practices Manufacturing controls Personal hygiene practices

Sanitation Principles/Food Handling

Training Should instill understanding of processing

steps Technology for each product Where problems exist Desire to satisfy consumers Guard consumer’s interests

Manufacturing Controls/Essential Operations Personnel

Must be trained in critical elements Importance of these operations Monitoring these operations Action to be taken

Certification Programs Ex. Heat processing equipment Develop specific training programs

Hygienic Practices

Communicable diseases/ Injuries Hand Washing Personal Cleanliness/ Conduct

Communicable Diseases

Restricted access for People known to carry or suffer from transmitted

diseases through food Restricted from any food-handling areas

Persons afflicted with Infected wounds Skin infections Sores Open cuts

Completely covered Secure waterproof

Hand Washing

Facilities Hot water hand washing station Convenient to food handling area

Personnel Wash hands with soap Warm running, potable water Must be washed

After handling contaminated materials Using toilet facilities

Disinfectant hand dips

Personal Cleanliness/Conduct

Must be maintained in food handling operations PPE

Sanitary clothing Hair covering Footwear Properly maintained PPE Gloves Remove all jewelry Tobacco, gum, and food are not permitted

EXERCISES

1. Read the labels on food in your home, in a grocery store or on items you buy during the day. Make a list of the date codes on five different foods. List the "sell by date," the "best used by date," and the "expiration date" for as many of the foods as you can. Discuss these in class.

EXERCISES:

2. Leave a food such as meat, bread, fruit and so on at room temperature and describe the changes in food quality. Discuss these with the class and try to categorize the changes and their causes.

EXERCISES:

3. Why is the occurrence of E. coli 0157 in food such a worry?

EXERCISES:

4. What is the chemical makeup of enzymes and how many enzymes exist?