2nd lecture nutrition and food hygiene
TRANSCRIPT
2The Favourable Conditions for Microbial Growth
By:
Dr. Waleed FoadMSc.Public Health in Nutrition
Clinical Nutrition SpecialistEuropean Society of Gastrointestinal
Endoscopy (ESGE)Member of the American Society of
Nutrition Email: [email protected]
Microbial Growths affecting Food
Most important microbial growths are:1. Bacteria: are single-celled living
micro-organisms. The most common form of food poisoning is bacterial food poisoning.
2. Fungi.A Fungus: is a single-celled or multicellular organism. Fungi can cause infections in humans or only spoil Food.
Microbial Growth Understanding factors that influence microbial
growth is essential to maintaining food quality In production and preservation
Microbial Growth and multiplication is influenced by: 1. Food (nutrients for bacteria). F2. Acidity (Suitable pH) A3. Time. T4. Suitable Temperature. T5. Oxygen (Most of them, but not all). O6. Moisture (Water content) M
Remember: Bacteria need “FAT TOM” to Multiply
Nutrient availability in Food
Nutrients present in a certain food determine the organisms that can grow in these foods
Harmful bacteria and spoilage bacteria grow best in high protein food such as poultry and seafood.
Fungi and moulds need more Carbohydrate
nutrients in food, and cause food spoilage rather than food poisoning. E.g.Dairy products, juices and pastries.
Acidity of FoodImportant in determining which organisms can Live
in specific foodsMany microorganisms are inhibited by acid
conditions Exception include lactic acid bacteriaLactic acid bacteria used in fermentation processAlso prime cause of spoilage of unpasteurized milk
and other foodsFungi are able to survive at relatively low pH
Most acid foods spoil from fungal contamination as opposed to bacteria
pH can determine bacteria’s ability to produce toxin Toxin production of many organisms is inhibited by acid
pH
Chemical Preservatives
•Chemical preservatives are usually derivatives of acids that kill the microorganisms by slightly increasing the acidity of the food. They can be: •Organic: Benzoates; Propionates; Sorbates antimicrobial agents-act vs. mould etc.• Inorganic: Sulfites (SO2
2-); Nitrites/Nitrates(NO2
-/ NO3-)
•Some concerns about safety!!
Microbial Growth: Time Factor
The least time should be given to Raw food till it is processed (e.g.. Cooked, Eaten, Preserved, ..etc.)
Because, under suitable microbial growth conditions, bacteria can multiply by dividing in two every 10-20 minutes.
After 6 hours, 1 bacterium can multiply into 262,144 bacteria, more than enough to cause food poisoning.
Temperature of foodUnder ideal conditions, bacteria multiply rapidly between 5°C and 60°C (the danger zone for food).
Below 5°C, bacteria multiply slower. At freezing temperatures, bacteria stop multiplying and become dormant. Freezing does not kill bacteria. Most bacteria are killed at temperatures above 60°C.
Temperature Danger Zone 5°C and 60°C
Cooking:Can destroy many organismsAlters characteristics of foodIf heat is uneven some organisms may
survive in undercooked portion of food
Refrigeration:Preserves food by slowing growth rate of
spoilage organismsMany organisms unable to multiply in low
temperatures
Home Food Preservation
Food Preservation: Temperature Controlling
1. Pasteurization:Heating foods under controlled conditions at high temperatures
for short periods Reduces number of spoilage organisms Does not alter taste of food significantly
2. Freezing:Stops microbial growth
Water unavailable due to ice formationPortion of organisms remaining can grow when food is thawed
Oxygen availability in Food
Presence or absence of oxygen affects type of microbial population
Obligate aerobes cannot grow under anaerobic conditions (e.g. Staph. A.)
Obligate anaerobes will grow only in anaerobic conditions (e.g. Clostridia)
Food Preservation: Oxygen Deprivation
Examples: Smoked Food, Vaccum and Canning.
MoistureWater availability in Food
Foods vary dramatically in terms of water availabilityFresh meats and milk have high water contentSupports microbial growth
Breads, nuts and dried foods have low water availability
Food Preservation: Water Reduction
Inhibiting Microbial Growth by decreasing water content of Food.
Methods:Drying. (e.g. Fruits, bread, powdered milk)
Salting. (e.g. meat, fish)Preserving in concentrated sugar form(fruit)
Food Preservation: Water Reduction
Drying
Food Preservation: Water Reduction
Salting
Food Preservation: Water Reduction
Concentrated Sugar Preservation.
Preservation using Multiple techniques.
Compined 2 or more techniques for food preservation may be used, Example:Canning: Heating and oxygen
deprivation.Pasteurization: Heating and oxygen
deprivation.Salted Fish Canning: Salting & oxygen
deprivation
Preservation using Multiple techniques.
Freeze Drying
