Intrinsic Factors in Microbial Growth

Study Notes

Intrinsic Factors

pH impacts microbial growth by influencing the types of chemical reactions that occur in food
Water Availability: Lower water activity inhibits microbial growth, while higher water activity promotes growth
- Reduced water availability can be achieved through drying, adding salt, or adding sugar
- Osmophilic microorganisms thrive in high osmotic pressure environments
- Xerophilic microorganisms prefer low water activity environments
Physical Structure: Grinding and mixing food increases surface area, exposing more of the food to microbes and promoting microbial growth
- The outer skin of fruits and vegetables acts as a barrier against microbial growth
Antimicrobial Substances: Foods naturally contain substances that inhibit microbial growth
- Coumarins are found in fruits and vegetables
- Lysozyme is present in cow's milk and eggs
- Aldehydic and phenolic compounds are found in herbs and spices
- Polyphenols occur in green and black teas

Extrinsic Factors

Temperature: Lower temperatures generally retard microbial growth
Relative Humidity: High humidity promotes microbial growth
Atmosphere: Presence of oxygen promotes the growth of aerobic microbes
- Modified Atmosphere Packaging (MAP) utilizes shrink wrap and vacuum technologies to control the atmosphere around food and inhibit microbial growth

Microbial Growth and Food Spoilage

Food Spoilage is a result of microbial growth which alters and degrades food, making it unsuitable for consumption
Toxins are sometimes produced by microbes during food spoilage
- Ergotism: a toxic condition caused by fungal growth in grains
- Aflatoxins: carcinogenic toxins produced by fungi in grains and nuts
- Fumonisins: carcinogenic toxins produced by fungi in corn

Controlling Food Spoilage

Removal of Microorganisms: Filtration is commonly used for removing microbes from liquids like water, beer, wine, juices, and soft drinks
Low Temperature: Refrigeration at 5°C significantly slows down but doesn't completely stop microbial growth
- Extended refrigeration periods at 5°C can still lead to spoilage
- Microbial growth has been observed even at temperatures below -10°C
High Temperature: Heating food in a retort (special containers) to 115°C for 25 to 100 minutes eliminates most spoilage microbes
- This process does not necessarily kill all microbes in the food
Spoilage of Canned Goods: Spoilage of canned goods can occur due to underprocessing, leakage of contaminated water during cooling or contamination before canning
Pasteurization: Kills pathogens and significantly reduces the number of spoilage organisms while preserving flavor
- Different pasteurization methods vary in heat duration and intensity
Water Availability: Reducing water availability inhibits microbial growth
- Methods include lyophilisation (freeze drying), spray drying, and adding solutes (salt or sugar) to decrease water activity
Chemical-Based Preservation: Chemical preservatives are used to prevent microbial growth and spoilage
- GRAS (Generally Recognized as Safe) refers to chemical agents considered safe for use in food
- The pH of the food affects the effectiveness of chemical preservatives
Radiation: Ultraviolet (UV) radiation is used to sanitize food-handling equipment surfaces but does not effectively penetrate food
- Radappertisation: Uses gamma radiation to extend shelf life significantly by killing microbes
- Irradiation: Uses ionizing radiation to control microbial growth and improve the safety of food