Factors Afecting Microbial Growth in Food Flashcards
Microbial growth phase :
- lag
- log
- Staionary
- Death
Bacteria becoming adapt to new environment (pH, temperature, moisture, Nutrients). what phase?
Lag
bacteria increase rapidly, growth rate increases with time , condiions are opimal with growth. What phase?
Log: Exponenial growth phase
Exhausion of nutrients and build-up of waste and 2nd metabolic products.
growth rate = death rate.
Staionary phase
No more growth cells are dying. If less than opimum condiions: lag is longer, log is more lat, and staionary is lower.
Death Phase
Coliforms Deiniion
all aerobic and facultaive anaerobic,
Gram-negaive,
non-spore forming bacilli ferment lactose with acid and gas within 48 h at 35°C.
Coliforms They are a commonly used
- indicator of sanitary quality of foods and water.
- indicate that pathogenic organisms of fecal origin may be present.
Coliforms are easy to
culture
Factors that afect growth
Intrinsic Parameters
(properies of food)
• pH: Lower then 4.6 grow best at neutral pH
• Water acivity Aw,
lower preferred
• Oxidaion-reducion potenial
Eh of substance is deined as the ease with which a substance loses or
gains electrons
• Nutrient content
Water, carbon, nitrogen, vitamin and minerals
• Animicrobial content
Eggs contain lysozyme, lavor compounds, milk contains lactoferrin
• Biological structures
Egg shell, skin on fruits, nuts have shells
Factors that afect growth Extrinsic Parameters (properies outside food)
• Temperature
Efects growth: refrigeraion or freezing, kills: heating
• Gases
Modiied atmosphere storage in 10% CO2
• ERH Equilibrium
relaive humidity, store foods at a humidity that will prevent up take of moisture
• Compeing microbes Microbes that produce baciocins
• Food packaging films
Vacuum package, edible ilms
bacteria uilized Nitrogen to
to produce cellular proteins and enzymes
bacteria uilized Nitrate and ammonia to
produce amino acids that can be used to make proteins
Growth factors – some bacteria require vitamins and minerals.
• Magnesium
(enzyme cofactor especially for ATP reacions)
• Calcium
(cofactor for enzymaic acivity)
• Phosphorous
(nucleic acid, cofactor for enzymes)
• Sulfur
(amino acids and co-factor for enzymes)
• Iron (cofactor for enzymes)
• Cobalt
(consituent of B12, cofactor for enzymes)
• Potassium
(inorganic cat ion needed for osmoic balance of the cell)
Water acivity ranges
from 0 to 1.0
Microorganisms have …aw for growth
maximum, opimum, minimum
Bacteria can’t grow
pure wate
Bacteria the maximum aw is always
0.99
Bacteria require higher aw’s than
yeast and molds
Need to know minimum aw of microorganisms in order to
prevent their growth and spoilage of food
Reduce water acivity by
dissolving compounds to bind moisture, such as Salt and Sugar ; also physical drying
Cl.botulinum and Salmonella
required for Aw
0.93 aw
Most Bacteria required for Aw
0.099 aw
Most Yeasts required for Aw
0.88 aw
Halophilippic Bacteria required for Aw
0.75 aw
Extreme Osmophiles eg.molds&yeast required for Aw
0.61 aw
Bacteria optimal pH
6 to 8 ph
Yeast optimal pH
4.5 to 6.0 ph
Fungi optimal pH
3.5 to 4.0 ph
Once inside the bacterial cytoplasm the acid dissociates because
cell cytoplasm has a higher pH
Bacteria maintain internal pH near neutral to
to prevent conformaional changes to proteins, enzymes, nucleic acid and phospholipids
when the organic acids dissociate in the bacterial
cytoplasm
That are generated
Protons
The protons are extruded by using energy in the form of ATP this causes
depleion of the cellular energy and death of the cell.
There are two ways to measure acidity of a food:
• By “itratable acidity”
Measure HA “acive form”
• By “pH”
Measure free protons
ionize
completely in aqueous systems
Strong acids such as
- HCl (Hydrochloric acid),
- H 2SO4(sulfuric acid),
- H 3PO4(phosphoric acid)
What Factors afecing the selecion of animicrobial agents?
- Antimicrobial activity
- pH of the food product
- Food composition
- Processing and storage conditions
- Solubility
- Flavor
- Cost
- Markeing impact
Frist chemical preservaive permited by FDA
Sodium benzoate
pH of Foods:
Food may be naturally
acidic
Most active against yeast and molds
Major uses in beverages, juices, and buter
Benzoic Acid
- Major usage in salad dressings, fruit juices, and cotage cheese
- Potassium salt is the most widely used form
Sorbic acid
Aceic acid
- Usage level limited by taste
- More efecive against yeast and bacteria
- Major usage in Pickled foods and natural bread
- Sodium diacetate used in some breads
Propionic acid
- Efecive against molds, but no efect on yeast
- Major usage baked goods
- Calcium salt most used form
- Efecive against molds, yeast, bacteria
* Flavor problems and hypersensiivity
Sulfites
- Efecive against C. botulinum
- Used in cured meat products
- Reacts with myoglobin to give cured meat color
Nitrite
• Efecive against yeast and molds, Gram posiive bacteria
• Used in ariicial sweeteners, baked goods, and few salad
dressings
• pKa = 8.47
Paraben
Antimicrobial agents in common foods
- Bread: Natures own 100% whole wheat
- Salad dressing: Olive garden Italian
- Beverage: Coke – diet coke
- Margarine: Parkay
proteins act as
buffers
Highest pH in nature,
Egg white
Compounds added to foods primarily for efects other than antimicrobial .
Indirect Animicrobials
Antioxidant used primarily to
prevent auto-oxidation of lipids.
agents used to impart aromas and flavors
Flavoring
Flavoring such as
Diacetyl,Menthol
Diacetyl efecive
against Gram-negaive bacteria and fungi.
Diacetyl prevents the
uilizaion of arginine by reacing with arginine-binding proteins
imparts peppermint like aroma is inhibitory against
Staphylococcus aureus and E. coli
Menthol
are used primarily as lavoring and seasoning agents in foods.
Spices and Essenial Oils
Naturally occurring animicrobials in Milk:
Lactoferrin
Lactoperoxidase
lysozyme
Naturally occurring animicrobials in Egg whites:
Lysozyme
Conalbumin
Animicrobial proteins
Bacteriocins
Bacteriocins are
proteins produced by bacteria
more efecive at an acidic pH
Mainly efecive against Gram-posiive bacteria
Increase aeration of food by grinding or Slicing increases the redox potenial
✅❌
✅
Microaerophilic bacteria:
range
3%-6%
Microaerophilic such as
Campylobacter
Facultaive anaerobes such as
E. coli, Shigella, Salmonella
Lowest temperature microbes can grow
Minimum
Heat treatment (sterilizaion) can be used to
kill all microorganisms in foods to destroy undesirable enzymes to destroy toxins Ready-to-eat foods are heated to destroy Pathogenic bacteria
Factors to consider in heat treatment:
Nature of Food
Aw
ph
Antimicrobial content
the time necessary to kill a given number of organisms at a specific temperature. (Temperature is constant and time needed to kill cells is determined)
Thermal Death Time (TDT)
the decimal reducion ime, ime required too destroy 90% of the organisms or 1 log cycle.
D Value
the degrees Fahrenheit required for the thermal
destrucion curve to traverse one log cycle.
z Value
Time in minutes required to destroy a given number of
the organisms in a speciic food product at 250°F (121°C).
F Value
