Food Microbiology Exam 1

Intrinsic Factors

inherent, not dependent on external conditions. Examples: water content, surface area, pH, salt content, biological structures, nutrient content, antimicrobial constituents, presence of other microbes

Extrinsic Factors

factors that are influenced by external factors. Examples: temperatures, humidity, air composition, packaging

Biological Structures

first line of defense, outer coverings of fruits, shells of nuts or eggs. Can also harbor unintended microbes

pH

most microbes optimally grow at neutral pH, 4.6 is magic number for inhibition

Effects of pH outside of Optimum Growth

stationary-phase bacterial cells are more resistant to low or elevated pH, also more resistant to other stresses (cross-protection)

Moisture Content: a_w

Ratio of the water vapor pressure of a food to the vapor pressure of pure water at the same temperature, measure of available water within food. Pure water is 1.0

Humectants

bind water and lower a_w, examples: NaCl, Sucrose, Glycerol.

Halophiles

Salt-loving, require high-salt for growth (6% to over 30%)

Xerophiles

Dry loving, grow in environments with low a_w (<0.8), halophiles are often xerotolerant (can surive but not grow)

Osmophiles

high osmotic-pressure loving, high sugar content. examples: yeast in juice

Osmotic Stress

Osmotic shock is caused by change in solute concentration around a cell, causing water movement to change across membrane of cell. Usually occurs prior to desiccation

Desiccation

Cell needs to increase the internal osmolarity of the cell:

• selective influx of potassium

• Accumulate osmoprotectants (compatible solutes) in their cytoplasm, nuetral compounds that do not effect metabolism

Compatible Solutes

uptake or synthesis of compatible solutes renders the cell more resistant to stress such as high osmolarity or high temperatures. Also confer cross protection to different stresses such as heat, cold, and oxidation

Eh: Redox potential (measured in millivolts)

• Aerobic bacteria required oxidized conditions (+)

• Anaerobic bacteria require reduced conditions (-)

• microbes can influence Eh conditions 

• Manufacturing: vacuum packaging, modified atmosphere packaging, hot-filling, 10% CO2 in fruits, vegetables, and meats

Antimicrobials

spices may contain antimicrobial constituents. milk contains lactoferrin, eggs contain lysozyme. Can be created by bacteria such as bacteriocins (small proteins that poke holes in closely related bacteria)

Presence of other microorganisms

inhibition by natural microflora or added microbes due to competition, inhibitory metabolites, alteration of environment (lowering pH)

Psychrotrophs

<7 to 30C

Mesophiles

20 to 45C

Thermophiles

55 to 65C

Freezing

not lethal step for bacteria and fungi, considered lethal step for parasites

Relative Humidity

%RH of storage environment and aw of food, EXTRINSIC

Hurdle Concept 

use multiple factors to control microbe growth

HACCP

Hazard Analysis Critical Control Points, knowing/predicting/anticipating hazards and controlling them

Three Hazards

Biological, Chemical, Physical

Biological Hazards

foodborne pathogens

Chemical Hazards

Allergens: (9) eggs, dairy, fish, crustaceans (shellfish),  peanuts, tree nuts, wheat, soy, and sesame

Added: pesticides, cleaners, sanitizers

Natural: heavy metals (lead), mycotoxins, shellfish toxins, etc.

Physical Hazards

• may chip teeth, choke, lacerate

• evaluate your ingredients at receiving

• evaluate your process (metal detectors)

Seven Principles of HAACP

1. Conduct a hazard analysis

2. Identify critical control points (CCP)

3. Establish critical limits for each critical control point

4. Establish critical control point monitoring requirements

5. Establish corrective actions

6. Establish procedures for verifying the HACCP system is working as intended

7. establish record keeping procedures. Establish procedures for verifying the HACCP system is working as intended

1. Conduct a hazard analysis 

focus on food and hazards associated with the ingredient, processing, storage, and intended use 

2. Identify Critical Control Points (CCP)

Critical points in the process to take action to control/reduce the likelihood of those hazards

Examples:

1. Biological: cooking, cooling, high pressure processing, formulation

2. Chemical: labeling to warn consumer, cleaning

3. Physical: metal detection, X-ray

3. Establish Critical Limits for each CCP

science-based decision process and data to prove those limits will control/reduce the hazards. Could come from USDA, FDA, scientific publication, metal detector for physical hazards. Example, chicken must be cooked to 165F internal temp

4. Establish CCP Monitoring Requirements (Monitor)

how to ensure that you are meeting CCP. Temperature probes, metal detectors, allergen labels, cleaning procedures

Principle 5: Establish Corrective Actions

When something goes wrong, what do you do?

Product hold procedures, investigations, documentation, training of line workers

Is finished product testing a good CCP?

NOOOO

Principle 6: Establish Procedures for verifying HACCO system is working as intended 

Verification (are you doing what you said you would in HACCP plan)

Validation (is what you said you would do in HACCP plan still controlling the hazard), hazards can evolve

Principle 7: Establish Record-Keeping Procedures

• designate individuals capable of taking recordings of data and corrective actions

• designate record-retention requirements

• make records easy to retrieve in case of emergencies

Preservatives

• slow product spoilage caused by mold, air, bacteria, or yeast

• maintain quality of food

• help control contamination that can cause foodborne illness

• Physical, static, and cidal agents

Physical Strategies for Preservation

• Filtration

  • Microfiltration (0.1uM) great for protozoans and okay for bacteria

  • Ultrafiltration (0.01uM) great for both protozoans, bacteria, and some viruses

  • Nanofiltration (0.001uM) great for everything

• Reverse Osmosis (removal of chemicals and salts while removing all microbes)

• Centrifugation (often done in cheese wheel production)

Static + Cidal Preservatives

• salt is one of the best preservatives

• Organic acids + esters (transport and membrane effected)

Mechanism for Organic Acids in Preservation

• if the pH is LOWER than the pka, then the acid can enter the cell

• Acid must be protonated (uncharged) to go through cell membrane

• the acid will dissociate within the cell

• the cell must spend energy (ATP) pumping the acid out of the cell, and will not be able to grow/thrive

if pH>pka, will organic acid preserve?

• NO

• this means that the RCOO- will be unprotonated

• cannot enter the cell

if pH<pka, will organic acid work as a preservative?

• YES, the RCOOH will enter the cell

• it will deprotonate inside and make the cell pump it out 

pH of food = 5.5; pKa of organic acid = 4.75

DOES NOT CROSS THE MEMBRANE

H of food = 5.5; pKa of organic acid = 6.0

DOES CROSS MEMBRANE

Organic Acids: Acetic and Lactic

inhibit gram-negative and positive bacteria

Organic Acids: Benzoic, Propionoic, and Sorbic

inhibit Yeasts and molds

Natamycin

pka=3.58

• like sorbic acid, used in fermented foods (low pH)

• inhibits yeasts and molds very well

Sulfites 

• effective below pH=4

• inhibit DNA replication, enzymes, protein synthesis, etc. 

• used in wine, fruits, juices, SAUSAGE, shrimp, pickles, and starches 

• some humans are sensitive to sulfites

Sodium Nitrite

• used as curing agent in meats

• primarily inhibits C. botulinum, prevents outgrowth of spores

• Lactic acid bacteria are tolerant of nitrite

• causes pink color in cured meats

• reduces ATP production in C. bot

Preservatives vs. Processing Aids

• Preservatives slow product spoilage caused by mold, air, bacteria, etc.

  • remain in food throughout shelf life (chemicals must be labelled)

• Processing aids are substances used in production of foods and are NOT present in any significant amount in the finished product

Processing Aid 

• substances used in production of foods and are NOT present in any significant amount in the finished product.

• added to food but removed before finished product 

• a wash of the food 

• added but only present in an insignificant level 

• Example: chlorine wash for baby carrots 

Microbial Preservation Methods

• Heat

• Pressure

• Irradiation

• gases, bacteriocins, phage

High Pressure Processing

• “cold pastuerization”

• DONE IN PACKAGING

• microbial control

• Enzyme inactivation

• Cheese ripening (releases lysis enzymes)

• shellfish shucking, removes shell

• Could create tailing effect where subpopulations of resistant microbes survive

• Spore forming bacteria are much more resistant

• can create cross-protectants

Ionizing Radiation

• removes electrons from molecules in cell, free radicals that damage molecules such as DNA

Ultraviolet Light (UV)

• non-ionizing radiation

• excites electrons in molecules, hinders replication

• LIMITING FACTOR IS EXPOSURE TIME

Gamma Rays

• stored in pool of water to absorb radiation from cobalt-60

• consumers don’t appreciate it

Bacteriocins and Phage

• Bacteriocins are peptides produced by microbes to perforate membranes of closely-related microbes

• Phages are specific to certain bacteria, can be used as sanitization step

Sanitation

reduces levels of microorgansims of public health concern to an acceptable level 

Cleaning

removal of soils, minerals, and other deposits

typically use the look test, if it looks clean then it is

Clean-In-Place (CIP)

wet-cleaning water and chemicals are cycled through equipment, typical for juiceries, dairies, and breweries

Biofilm

• complex ecosystem formed by one or more bacteria

• provides attachment, survival, and nutrition

Cleaning Methods: Open Exposure, Low Moisture

• flour, bakeries, peanut butter, etc.

• dry clean

  • vaccums

  • sweeping

  • alcohol

  • limited, out of place, water usage

Cleaning Methods: Open Exposure, High Moisture Foods 

• meats, cheeses, fruits, veggies 

• Disassembling, foaming, scrubbing, etc. 

• need to make sure contact time is long enough, avoid splashback from floors and walls 

Measuring Cleaning Effectiveness

-ATP swabs, tests for living cells

D-Value

reflects the resistance of an organism to a specific temperature (measured in minutes)

• as the decimal reduction time, time required to destroy 90% (or one log) of the organisms at a specific temperature

Z-value

• number of degrees required to change the processing time ten-fold

• provides information on the relative resistance of an organism to different temperatures

• can help calculate equivalent thermal processes at different temperatures

If the current thermal processing time is D-value= 11.6 minutes at 145F and the Z-value=14.4F, what would the processing time be at 130.6F and 159.4F?

• 116 minutes at 130.6

• 1.16 minutes at 159.4

F-value

• process lethality over a range of times and temperatures

• includes heating and cooling

• to find logarithmic reduction, divide F-value by the D-value

Retort

• inactivates spore formers (C. bot, C. perfrigens, Bacillus cereus)

• 12-D process, over a billion cell elimination

• used for canned goods

Pasteurization 

target vegetative forms of bacteria and fungi 

• milk (used to be for tuberculosis)  and juice 

Commercial Sterility

destroys all vegetative and spore-forming pathogens and most spoilage microbes

Ex) retort and ultra-high temp process

Product Recall: Class 1

reasonable probability that use or exposure of product will cause serious adverse health consequences or death (Listeria, allergens, etc.)

Product Recall: Class 2

situation where use or exposure to product may cause temporary or medically reversible adverse health consequences ow where the probabiltiy of seriou adverse health consequences is remote (undeclares sulfites)

Product Recall: Class 3

situation where use or exposure is not likely to cause adverse health effects (flies in food)

Market Withdrawal

product has minor violation that would not be subject to FDA legal action but does not align with the band. Example,

Infection

Microbes are ingested and grow in your body, causing illness.
• Onset times vary but generally day(s).
• Examples: Listeria monocytogenes, Escherchia coli O157:H7, Salmonella spp., Vibrio spp.,Campylobacter jejuni, Hepatitis A, Toxoplasma gondi

Intoxication

Microbes grow in foods and produce toxins.
• You ingest the food with the toxin and become sick.
• Onset times generally hours.
• Watch out with Mycotoxins – years?
• Examples: Staphylococcus aureus, Clostridium botulinum, Bacillus cereus, Mycotoxins

Toxicoinfection

Microbes are ingested, colonize and then produce toxins.
• Examples: C. botulinum (infant botulism), C. perfringens.
rare- can happen in infants who consume honey 

Spoilage Microbes

• lactic acid bacteria

  • facultative anerobes

  • produce gas, slime, milkiness, souring, and discoloration

• Yeasts and molds

  • gas production, visual, odor, taste

Killing Spoilage Microbes

• extend LAG phase as long as possible, AVOID log phase 

• heat processes

• hot-filling

• pausterization

• irradiation

• UV