Food Microbiology Unit 3 Flashcards
What are characteristics of spoiled food?
Poor taste, appearance, smell, or texture
organoleptically detectable
What causes finfish to have a high bacterial count?
Trawling, dragging the fish through the water on the ground which kicks up bacterial from the floor. Close proximity of the fish also cause them to poop on each other and contaminate that way.
line fishing is much more sanitary
What determines the quality of shrimp?
Because shrimp are filter feeders the quality of the water that they live in matters substantially.
What is the order in which bacteria will use resources in meat?
Carbohydrates _> Proteins _> Lipids
What is the primary spoilage microorganism in foods that are vacuumed packed or packed in modified atmospheres?
Lactic acid bacteria
What happens to meat from animals that have been stressed when it spoils?
The meat spoils more quickly because there is less glucose which means more lactic acid
-lactic acid makes meat sour
What is the primary spoilage organism for dry (low water activity) foods?
Fungi
Dry=fuzzy
slimy = bacteria
-Fungi tolerate salty and sugary environments
What are three reasons that ground (comminuted) meat spoils
- Higher initial microbe load due to lower quality product for grinding
- contamination during processing
- effect on muscle tissue; introduces more oxygen
Three types of spoilage i processed meats
- formation of slime
- development of SOUR taste
- greening from the production of hydrogen sulfide
What causes cured meats to spoil?
they contain lactobacilli and micrococci, which are both aerobic and tolerate low water activity, that will spoil the meat.
What are the methods used to preserve muscle foods?
GMPs, removal of contaminants from carcasses through rinsing with water (by immersion or by spraying), refrigeration (storage under vacuum or modified atmosphere), and irradiation
Can spoilage organisms utilize the fats and proteins in milk?
Yes, although they cannot use whey. They can use caseins, but not whey because the whey is soluble.
What inhibits the growth of spoilage microorganisms in yogurt and cheeses?
a LOW pH
What causes yogurt and cottage cheese to spoil?
yeasts and molds. The low acid inhibits the bacteria, but not the yeast and molds
What are the primary spoilage bacteria in milk?
Pseudomonas (psychotropic), coliforms, LAB, Bacillus, clostridium
What are a plants defense against spoilage microorganisms?
outer layers including cuticle, epidermis, and cell wall. Waxes
What are the microflora of vegetables?
Bacteria, yeasts, and molds
Why do fruits spoil less readily than vegetables?
fruits have a lower pH, higher sugar content, lower water activity, thicker epidermis, and higher concentration of organic acids
How are grains and grain products preserved?
Low water activity
Are the populations of microbes decreased in processing of grains?
yes, from drying
Origin of microflora: Meat poultry finfish shellfish
- hide, hooves, and hair
- feathers, skin, and feet
- environment, trawling
- environment, filter feed
Proteolytic enzyme activity
- only occurs in populations >10^8 CFU/cm
- digestion of protein, comes before lipolytic
- production of the protease enzyme doesn’t occur until the late log phase
Lipolytic enzyme activity
- oxidative rancidity with unsaturated fatty acids
- rate is influenced by the proportions of unsaturated fatty acids in the fat
- unlikely to occur until all the glucose in the muscle is depleted
Adipose tissue
- insoluble fat, cannot be used until its broken down and emulsified
- low levels of carbs in adipose tissue means that spoilage odors are detected from lower numbers of bacteria .
- spoilage of fat before lean tissue is unlikely
Anaerobic conditions
- lactic acid bacteria
- growth rate is lower is considerably lower than those in aerobic environments
Cooked muscle foods
cause by bacteria that survive the heating process, psychotropic and micrococci species
Prevention of spoilage
prevent the growth or select for less offensive species
- GMPs
- TEMPERATURE
- vacuum and modified atmosphere
Dairy fat
Few microorganisms can utilize fat as an energy source
- fat globules are surrounded by a protective membrane
- must rely on proteolysis or lipolysis to obtain energy
Lactose
many microorganisms cannot utilize lactose
-not sufficient amounts of glucose in milk to be a good growth medium
proteins
two types; casein and whey.
Casein is readily susceptible to proteolysis but why is not as much.
-Lactoferrin binds to iron and inhibits microbial growth
— lactoperoxidase
Liquid milk concentrates
-so not have sufficiently low water activity to inhibit spoilage and so products must be canned or refrigerated
Milk powders
sufficiently low water activity to inhibit spoilage
Butter
unsalted butter is usually made from acidified cream and relies on low pH and refrigeration for preservation.
-growth of psychotropic bacteria only occurs on butters made from sweet cream