Experiments 1-4 Flashcards
Microbes from Exp 1
Lactobacillus reuteri
Escherichia coli
EC cultured on
LB plates
LR cultured on
MRS plates
Gram stain purpose
Look at morphology
Distinguish gram + and - bacteria
Gram stain protocol
- Heat fix the smear
- Flood with crystal violet for 1 min
- Rinse
- Flood with iodine for 1 min
- Rinse
- Decolorize until colorless
- Flood with counterstain for 30 sec
- Rinse
- Blot dry
Thermal process designed to
Reduce the microbial load
Eliminate one or more spoilage organisms and/or pathogens in the product
Inactivate enzymes
Result of successful heat treatment
More shelf stable product
Increase death rate w/
Salt
Acid
Protective effect on microbes
Decrease in Aw
Increase in fat
Increase in protein
D value
Time (in minutes) to reduce a microbial population by 90% (1 log) in a specified heating medium at a specified temperature
Resistance to a certain temp
Thermal death time
Time (in minutes) to reduce a given number of organisms to 100 (essentially zero) in a specified medium at a specified temperature
Calculate TDT
Extrapolate survival curve
Or
D value x number of cells
Z value
Change in temperature (°F) required to cause the TDT curve to go through one log cycle
Sensitivity of an organism to changes in temp
Preventative techniques for spoilage
Specialized packaging
Use of natural preservatives
Heat treatment
Dehydration
Acidification
Purification of air quality
Decreasing water activity
Irradiation
Refrigeration or freezing
Addition of food additives
Mold growth factors
Oxygen availability
High mositure
Temp
pH
Nutrients
What does refrigeration do
Prolong the shelf life
Does not prevent all growth
Inhibitors
Chemicals or substances added to another substance to slow down or prevent a reaction or change
Amount of inhibitor depends on
Food product
Bacteria or fungi
Shelf life
A guide for consumers showing the period until which food is safe and beyond which it will begin to deteriorate
During shelf life,
a food should
Be safe for consumption
Maintain appearance, odor, texture and color for consumer appeal
Fulfill any nutritional claims made for the product
Factors Affecting Shelf Life
Microbial Spoilage
Non Microbial Spoilage
Microbial spoilage
Growth of bacteria, yeasts and molds
Factors that affect product quality
Aw
pH
Temp of storage
Handling
Non Microbial spoilage
Moisture
Chemical changes
Light induced changes
Physical tampering damage to the product
Rodent and pest damage
Shelf Life Study
A meticulous study that studies all the possible factors affecting the stability and quality of a food product
Direct Shelf Life Study
Pre-selected conditions for time periods longer than expected shelf life
Indirect Shelf Life Study
accelerated study under more harsh conditions/ study using modeling techniques
Milk characteristics
pH close to neutral
highly perishable
lots of nutrients
Spread plating
100 uL
30-300 CFU
Spot Plating
10 uL
3-30 CFU
Gram positive bacteria
Thick layer of peptidoglycan in cell wall
Retain CV
Purple color
Gram negative bacteria
Stain red
Thinner peptidoglycan wall
Don’t retain CV
CFU/mL =
of colonies x dilution factor x uL to mL
TSAYE Agar
Trypticase Soy Agar + Yeast Extract
Nutrient Agar
Total bacterial count
Yeast & Mold agar
Total yeast and mold count
Low temp incubation
Acidified
Pasteurization
Heat process to reduce total bacterial populations to eat food safely
Prepare w/v solution
Prepare a x% solution
Mix x g per 100 mL of the solute
Example
0.85% salt solution
0.85 g salt/100 mL solute
