Factors affecting growth of microorganisms in food pdf

Therefore, food with highly positive value of O-R potential e. Similarly, food with -ve value of O-R potential e. Ability of food to resist change in O-R potential is called poising capacity. O-R potential is changed by processing technique like heating, grinding etc.

This is the reason why fresh solid cut of meat undergoes anaerobic spoilage by bacteria but ground meat undergoes aerobic spoilage by mold. Nutrient content: Mos utilize various nutrients and growth factor present in food for their growth.

Therefore, food which are rich in nutrients or which contain all essential nutrients e. On the other hand, food which lack particular nutrients or growth factors or are poor in nutrients e. All mos utilize glucose or other mono-saccharides as source of carbon and energy. Very few microbes can utilize complex polysaccharides such as starch, pectin etc. If monosaccharides are not available, therefore only very few species of mold and bacteria that can hydrolyse pectin, can grow in skin of fruits and cause its spoilage.

Proteolytic bacteria like Clostridium, Bacillus etc. Therefore, food which are deficient in carbohydrate and rich in protein e. Some organism also requires various vitamins and growth factors in food for their growth. Biotin present in egg is made unavailable by avidin. Therefore, microorganisms that require biotin cannot grow in egg. Similarly, microorganisms that require vitamin B complex usually cannot grow in fruits because vitamin B is deficient in fruits.

Antimicrobial constituents: Some food contains various antimicrobial components that inhibit growth of many micro-organism. Therefore, food which contain one or more of these anti-microbial agents alcoholic beverages are microbiologically more stable. In some food antimicrobial constituents are present naturally and in others. They are developed antimicrobial constituents include ethanol present in alcoholic beverages and propionic acid present in cheese that inhibit growth of mold.

For e. Furthermore, some plant products like tea and coffee contain caffein, caffeic acid etc which are antimicrobial. Biological structure Some foods have natural covering on their surface that prevent entry of spoilage organisms into inner tissue of food and prevent microbial spoilage. Some such natural covering of some food includes shell of egg, skin of fruits, testa of seed, hide of animal etc.

Nowadays, fruits are covered by artificial covering to protect them from microbial spoilage. Extrinsic parameters: Characteristic of storage environment that affects growth of micro-organism on food are called extrinsic parameters. Some such examples include: i. Therefore, RH of storage environment affects microbial growth on food and determine microbial spoilage.

When relatively moist food is placed in dry environment, food loss water and its A w value decreases. Similarly, when relative dry food is placed in humid atmosphere food absorbs moisture and its A w value increase that facilitate growth of many spoilage organism.

Suppose A w value of food is 0. But when these food is stored in humid atmosphere, its A w value gradually increase and food undergoes microbial spoilage. RH of storage atmosphere mainly affects surface od food. Therefore, food that undergo surface spoilage can be controlled by controlling RH of storage environment. Microorganisms in food products are basically affected by two distinct factors:. Extrinsic factors and 2. Intrinsic factors. This are factors in the environment external to the food, which affect both the microorganisms and the food itself during processing and storage.

Extrinsic factors include Temperature, humidity , and oxygen. Different microorganisms grow over a wide range of temperatures.

There basically three temperature types: Mesophiles, Psychrophiles, Thermophiles. Psychrophiles are microorganisms that grow at low temperatures. Example; Bacillus, Pschrophilus etc. Psychrophiles are the major course of refrigerated food spoilage.

Mesophiles grow best at room temperature. Most human pathogens fall under this group because of the normal C body temperature. Temperature is of paramount importance in food safety because if the growth temperature ranges for dangerous microorganisms are known, it helps in employing appropriate production temperature and time for foods that require heating. It also aids in selecting the proper temperature for food storage to make them less able to grow and reproduce.

An important factor for the growth of microorganisms at the food surfaces is the humidity of the storage environment. Dry conditions are devoid of water for microbial activities referred to as water activity and thus better for food storage than moist conditions. Foods stored in a dry atmosphere, therefore, have a longer shelf life than foods stored in a humid environment. Some microorganisms require oxygen in order to grow and multiply. Sulphur: Forms proteins and some vitamins thiamin and biotin.

Potassium, magnesium, and calcium are often required as enzyme cofactors. Calcium is required for cell wall synthesis in Gram-positive bacteria. Organisms that use molecular oxygen O 2 produce more energy from nutrients than anaerobes. We can classify microorganisms based on their oxygen requirements:. Obligate Aerobes: Require oxygen to live. Example: Pseudomonas , a common nosocomial pathogen.

Facultative Anaerobes: Can use oxygen but can grow in its absence. Have a complex set of enzymes. Examples: E. Obligate Anaerobes: Cannot use oxygen and are harmed by the presence of toxic forms of oxygen. Example: Clostridium bacteria that cause tetanus and botulism. Aerotolerant Anaerobes: Cannot use oxygen but tolerate its presence. Can break down toxic forms of oxygen. Example: Lactobacillus carries out fermentation regardless of oxygen presence.

Microaerophiles: Require oxygen, but at low concentrations. Sensitive to toxic forms of oxygen. Example: Campylobacter. These elements include:. The temperature of the environment has an impact on enzyme processes and microbiological development.

Every bacterial species has distinct temperature requirements for growth, which are mostly governed by the temperature requirements of its enzymes. Each creature will have the following characteristics:. Microorganisms are a diverse group of generally minute simple life-forms that include bacteria, archaea, algae, fungi, protozoa, and viruses.

The pH, Availability of oxygen, Poising capacity or buffering capacity, Nutrient composition such as protein, ascorbic acid, reducing sugars are required in different quantities for various microbes to grow.

Microorganisms can survive in a wide variety of temperatures, having colonised various natural settings and adapted to extremes.