Factors that affect microbial growth:

Internal factors

a.pH of the food

Most microorganisms grow well at a pH of around 7 (6.6 – 7.5), while only few of them grow at pH below 4. Bacteria are more sensitive to ph requirements in comparison to yeast and moulds, which manage to grow across a pH range of 0 – 11.

b.Moisture content

It is common knowledge that drying of food enhances its shelf life.  Most spoilage and pathogenic bacteria in meat require a water activity in equal to more than 0.9, and the most tolerant bacteria is Staphylococcus aureus which continues to grow at 0.86. Most spoilage yeasts require a aw of 0.88, while spoilage moulds manage to grow at a aw of 0.80. If foods are dried to a final aw of 0.60 or lesser, the product becomes shelf stable.

c. Oxidation reduction potential

Aerobes require oxidized conditions for growth while anaerobes require reduced condition for growth. Microaerophiles, require slightly reduced conditions whereas facultative anaerobes grow in both reduced and oxidized conditions.

d. Nutrient content

Microbes require a source of energy, a source of nitrogen,vitamins and related growth factors and minerals in adequate amounts for their normal growth:

Antimicrobial constituents in food accord protection for foods against microbial growth. Certain biological structures such fascia in carcasses accords protection against microbial invasion to a certain degree.

External factors

a.Temperature of storage

The organisms classified as psychrophiles have an optimum temperature range of -2 to 7C. mesophiles have 10-40 C and thermophiles have 43 to 66 C. Meat preservation considers these things to ensure the proper storage of meat.

b.Gases in the environment

It is common knowledge that oxygen is required for aerobes and anaerobes do well in the absence of oxygen.

c.Relative humidity

Relative humidity has a role to play in both surface spoilage as well as deep seated spoilage.