Food Microbiology and Chemistry

Summarize the chemical and microbiological factors that affect food safety. Objectives هدف

Food Spoilage Six Factors That Affect Growth Potentially Hazardous Foods Food Additives Overview مرور

Food Spoilage Microorganisms are the most important cause of food spoilage. Spoilage microbes: Lactic Acid bacteria - common cause Pseudomonas species of bacteria – commonly causes meat to spoil Fungi – cause moldy bread

Food Spoilage (cont.) Chemical Food Spoilage Chemical reactions can also reduce food quality Exposure to air, light Breakdown of fat in foods form off-flavors and off-orders Reactions caused by enzymes that are naturally present in the food.

Six Factors that Affect Growth There are six main factors that affect microbial growth in food: F- Food A- Acid T- Temperature T- Time O- Oxygen M- Moisture

F (“Food” for the microbes to eat) Nutrients in food affect microbial growth: Sources of energy (e.g., sugars, proteins) Sources of nitrogen (e.g., proteins) Vitamins, Minerals In order for bacteria to grow, the food has to have the right nutrients for the bacteria

A (Acid--pH of the food) pH scale – 0-14 pH range of acids – 0-7 pH range of bases – 7-14 pH 7 is neutral Microorganisms grow best at pH close to neutral If the pH of a food is lowered, pathogens may still grow, but much slower

Acid (cont.) Most pathogens do not grow at pH < 4.6 Some yeast and molds can grow down to pH 1.5

Temperature and Time Heating/cooking foods (to an internal temperature of 74°C), kills pathogens Some toxins/spores are not destroyed by heat Staph aureus Clostridium botulinum, Bacillus cereus

Vegetative and Spore Cells When food is heated (cooked) to 74°C and held <57°C SPORES survive Spores can become vegetative cells again if food is not cooled properly Vegetative cells grow to high numbers and some produce toxins

How Long do Bacteria Need to Grow? Bacteria can double in number every minutes Example: bacteria with a 20 min doubling time: Start 20 Min 40 Min 1 Hour TIME

How Long do Bacteria Need to Grow? Exercise: 1 bacteria on a piece of potentially hazardous food sitting at 90°F, with a 20 minute doubling time: How many bacteria after 1 hr? 4 hrs? 8 hrs? What if there were 10,000 bacteria to start with?

Time Lag Phase Growth Phase Resting Phase Death Phase Bacterial Growth Curve Number of Bacteria (log 10 )

Time Changing the Bacterial Growth Curve *Sub-optimal means lowered: pH, A W, Temperature, etc. Sub-optimal growth conditions* Rapid Bacterial Growth Conditions Much longer Lag Phase Number of Bacteria (log 10 )

Temperature and Time (cont.) If food is held on a hot serving line pathogens can NOT grow Pathogens need time to grow to cause disease Illness is caused by improper cooling of leftover foods Foods cool faster in the refrigerator than on the counter

5°C Danger Zone Keep cold foods cold Keep hot foods hot “Food Safety Thermometer” Temperature range of rapid pathogen growth = Danger Zone Hot Cold 57.2 o C

Oxygen (Oxidation-Reduction Potential) Generally refers to the amount of Oxygen present Most bacterial pathogens can grow with or without Oxygen HOWEVER, some food pathogens can only grow when no Oxygen is present Many spoilage bacteria and molds require Oxygen to grow (obligate aerobic)

Moisture (water) Water is important for growth of bacteria Water in food is present in two forms: BOUNDFREE Bound water is unavailable for bacteria to grow

Moisture (cont.) Water Activity (A W ) A measure of the FREE WATER--water that is available for microbial growth A W can range from: 0.00 (no free water) to 1.00 (all free water) Pathogens do not grow/produce toxins at A w < 0.85 A w < 0.85

Potentially Hazardous Foods (PHF) Definition: A food that supports growth of microorganisms Examples of PHF’s: Raw or cooked foods of animal origin: Meat, Poultry, Waterfoods, Eggs, Dairy Products Some fruit and vegetables

Potentially Hazardous Foods (PHF) Which F&V are PHF’s? Cut melons (like cantaloupe) And the pH of some melons is >4.6 Heated/cooked fruits and vegetables Rice, beans, baked potatoes, etc. after they are cooked Seed sprouts (such as alfalfa sprouts) Garlic in oil mixtures

Food Additives Additive Government approved substances added to food during production or processing Make food taste better, look better, and have a longer shelf life (prevent microbial growth and chemical reactions)

Adulterated food: Adulterated food means one that contains poisonous ingredients, unapproved additives, or is composed of decomposed or unsanitary ingredients to help cover up spoilage Food Additives

SUMMARY Food Spoilage Six Factors That Affect Growth Potentially Hazardous Foods Food Additives

Review Questions What is the most important cause of food spoilage? What can reduce food quality? What forms off flavors and off orders? List the 6 factors that affect growth. At what pH does microorganisms grow best? What pH do most pathogens not grow?

How long do bacteria need to double in growth? What causes illness in leftover foods? What is the temperature range of rapid pathogen growth? Pathogens do not grow/produce toxins at what water level (A w )? What is PHF? Name at least 2 foods considered PHF. What is an additive? Review Questions

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