How to Control Biological Hazards and Food Quality?

Factors Affecting the Growth of Biological Hazards

The major factors affecting the Growth of Biological Hazards include;

· Intrinsic Factors

· PH

· Moisture

· Nutrients

· Antimicrobial Constituents

· Biological Structures

· Extrinsic Factors

1. Temperature

2. Humidity

3. gases

Intrinsic Factors

Intrinsic factor are the inherent parts of food. This is natures way of preserving plant and animal tissue from microorganisms. By determining the extent to which they exist in a given food, we can predict the types of microorganisms that are likely to grow and hence the significance of the hazards for a particular food or food group. The following is an explanation of the intrinsic factors we most commonly use in order to reduce the growth of microorganisms.

PH

In the unprocessed state, most foods such as meat, fish and vegetables are slightly acidic, fruits are moderately acidic, and a few foods such as egg whites are alkaline. Acidity has been a commonly used means of preserving food for thousands of years either naturally, through fermentation, or by the addition of weak acids (pickling).

Most microorganism grow best in the pH range of 6.6 to 7.5. Few microorganism grow at a pH of less than 4.0 Bacteria tend to prefer narrower ranges of pH than molds and yeasts, the pathogenic bacteria being the most fastidious. In general, molds and yeasts grow at a much lower pH than bacteria.

Moisture Content

Another one of man’s oldest methods of preserving food is to dry it. The water requirements of microorganisms is defined in terms of water activity (a_w). Water activity is a measure of the water present in a form that is available to microorganisms. The water activity of a substance can range from 0 to 1. Water has a water activity of s1.0, silicon has a water activity of 0.

The a_w in a food or solution may be reduced by removing water or adding solutes. When we dehydrate food we remove water. When we salt or add sugar to food we are adding solutes which lower the water activity and preserve the food.

The a_w of most fresh foods, is greater than 0.99. in general, bacteria require higher water activity levels for growth than molds. Most spoilage bacteria do not grow below a_w 0.91. Spoilage molds can grow as low as a_w 0.08. These figures apply for most, but not all microorganisms, in the case of food poisoning bacteria, Staphylococcus aureus can grow at a water activity level as low as 0.86. Halphiles (literally”salt loving”) are bacteria that can grow at a_w 0.75. xerophiles (“dry loving”) molds can grow at a_w 0.65. Microorganisms are able to survive at a wider range of water activity levels than those required for their growth.

Nutrients

Microorganisms may utilize suggers, alcohols, and amino acids as sources of energy. Fewer types of microorganisms utilize carbohydrates and fats. Most microorganism require B vitamins in the food in order to grow. Moulds and some bacteria are able to synthesize most or all of the B vitamins the require and hence may be found on food low in B vitamins such as fruit.

Antimicrobial Constituents

Some foods naturally contain substance that inhibit the growth of microorganisms. Cows milk, eggs, tea, fruits and vegetables all contain antimicrobial constituents.

For example, just two of the antimicrobial constituents in eggs are:

· Lysozme-an enzyme which destroys gram positive bacteria; and

· Certain proteins-which stop microorganisms from being able to use riboflavin and vitamin B6 as a nutrient.

Biological Structures

The natural covering of some foods provides good protection against the entry of microorganisms. Examples are the testa of seeds, the skin on fruit, the shell of nuts, the hide of animals, and the shell, cuticle and membranes of eggs. Once broken, of course, the risk of the food being spoilt is increased.

Extrinsic Factors

Temperature

Throughout the ages, humans have learned by trial and error ro exploit temperature in order to preserve food. Today, temperature is one of the most commonly used and critical factors in the production of food ;that is safe to eat.

Although microbial growth can occur between 34⁰C to over 90⁰C, most microorganisms grow within a smaller range. It is customary to place microorganisms into three groups based upon their temperature requirements for growth.

Classification Temperature Range for Growth Optimum Temperature Range Examples

Psychrophils Below 20⁰C S12⁰Cto 15⁰C

Physchrotrophs Below 35⁰C 25⁰Cto 30⁰C Pseudomonas ,Listeria ,Yersinia

Mesophiles 5⁰C to 476⁰C 30Cto 45⁰C Salmonella Staphylococcus

thermophiles Above 40⁰C 55⁰Cto 75⁰C Clostrtidium Bacillus

Just as moulds are able to grow over wide ranges of pH, water activity, and nutrient content, they are also able to grow over wider ranges of temperature than bacteria. Yeasts grow over the psychrophilic and mesophilic temperature ranges but generally not in the thermophilic range.

General quality characteristics, not just the safety, of the food must also be taken into account in selecting a storage temperature. For example, bananas keep better if stored at 13⁰C to 17⁰C than at 5⁰C. A large number of vegetables are favored by temperatures of approximately 10⁰C including potatoes, celery and cabbage.

The success of storage temperature depends to a great extend on the relative humidity of the storage environment.

Relative Humidity

The relative humidity is important in terms of the water activity of the food and the growth of microorganisms at the surfaces. If the water activity of a food is 0.60 and it is stored in a humid environment it will pick up moisture from the air and increase its water activity to a point where microbial growth can occur.

Foods such as chicken and meat tend to suffer from surface spoilage if improperly wrapped in the refrigerator do to the generally high humidity. In selecting the right relative humidity consideration must be given to both the growth of surface microorganism and the desirable quality of the food in its other aspects. Food stored under low condition of relative humidity may not be spoil by surface microbes but will become dry.

Gases

Carbon Dioxide

The storage of fo0od in atmospheres containing up to 10% carbon dioxide is referred to as “controlled atmosphere” storage. This method is commonly used for fruits and vegetables. Carbon dioxide has been shown to retard the fungal rotting of fruits.

Ozone

Ozone has a preservative effect on certain foods when added to the storage environment. It is effective against a wide range of spoilage microorganisms. Both CO₂ and O₃ are effective in inhibniting the spoilage of beef.

Sulfur Dioxide

Sulfur dioxide (S0₂) is applied to food and beverages as a liquefied gas, or more commonly, in the form of sulfite, bisulfite, or metabisulfite salts.

Aerobes Require oxygen in order to grow. Hence they grow on the exterior of foods. Bacillus subtilis Psuedomonads

Facultative Anaerobes Use oxygen in its presence but in its absence can still grow. Hence they can grow on the surface and interior of foods. Lactobacilli

Anaerobes Grow in reduced oxygen environment. Hence they prefer to grow in the interior of foods. Clostridium