Factors Influencing Growth of Microbes in Food

In this factors influencing growth of microbes in food post we have briefly explained about intrinsic factors influencing growth of microorganisms in food and extrinsic factors influencing growth of microorganisms in food. Read on to learn more about factors influencing growth of microbes in food!

Growth of Microorganisms in Food

Intrinsic factors

Intrinsic factors influencing growth of microorganisms in food include pH, moisture content, oxidation and reduction potential, nutrient status, antimicrobial constituents and biological structures.

pH

Every microorganisms has a minimal or maximal, and an optimal pH influences growth of microorganisms in food. Microbial cells are significantly affected by the pH of food because they apparently have no mechanism for adjusting their internal pH.

In general, yeasts and molds are more acid tolerant than bacteria. Foods with low pH values (below 4.5) are usually not readily spoiled by bacteria and are more susceptible to spoilage by yeast and molds. Most of the microorganisms grow best at pH value around 7.0.

Moisture

The preservation of food by drying is a direct consequence of removal of moisture, without which microorganisms do not grow. The water requirement of microorganism is defined in terms of the water activity (aw) in the environment.

Water activity is defined as the ratio of the water vapour pressure of food substrate to the vapour pressure of pure water at the same temperature. The water activity of most fresh food is above 0.99. The minimum value of aw for the growth of the microorganisms in foods should be around 0.86.

Oxidation

The oxygen tension or partial pressure of oxygen around a food and the O-R potential or reducing and oxidizing power of the food itself influence the type of organisms which can grow and the changes produced in the food. The oxidation reduction potential of the food is determined by, The oxidation reduction potential of the original food, The poising capacity, (the resistance to change in potential, of the food.), The oxygen tension of the atmosphere about the food and The access which the atmosphere has to the food.

Nutrient

The kinds and proportions of nutrients in the food are all important in determining what organism is most likely to grow. Consideration must be given to (i) foods for energy (ii) foods for growth and (iii) accessory food substances or vitamins which may be necessary for energy or growth.

Constituents

The stability of foods against attack by microorganism is due to the presence of certain naturally occurring substances that have been shown to have antimicrobial activity. Some species contain essential oils that possess antimicrobial activity. Among these are allicin in garlic, eugenol in cloves and cinnamon.

Extrinsic factors

These extrinsic factors  growth of microorganisms in food those properties of the storage environment that affect both the foods and microorganisms present in them. Storage temperature, pH, presence and concentration of gases in the environment are some of the extrinsic factors that affect the growth of microorganisms.

Further Readings

Reference

  1. https://asm.org/ASM/media/docs/CH02_ASM_Montville_557054.pdf
  2. https://www.canr.msu.edu/smprv/uploads/Factors_that_Influence_Microbial_Growth.pdf