Lecture 16 Flashcards
What is a food preservative
All methods used to prevent spoilage by reducing the growth rate of microbes, and preventing their growth rather than killing them.
Food Spoilage
Enzymological, chemical and physical changes which can cause oxidation, browning, loss of color, or liquefication(converision of solid food to liquid).
What are the 2 groups of antimicrobials? What leads to a synergistic effect of antimicrobials?
1) Bacteriostatic: Reduce the growth rate of microbes
2) Bacteriocidal: Kil bacteria
If you combine different types of anitmicrobials together which target different aspects of bacterial growth the combined effect will be greater than the individual effects of these antimicrobials.
Factors affecting antimicrobial activity:
1) microbial factors/characterisitcs of particular microbe:
- it’s resistance to antimicrobials
- initial amount of cells
- what it’s made of
- how they interact with one another
- the physilogical state of the cell
- is it injured
- It is adapting to intense conditions
- it’s metabolic processes
2)Intrinstic factors: part of food -level of acidity -water activity -what the food is made out of -oxidation-reduction potential of the food
3) Extrinsitc factors
- temperature
- time
- atmospheric conditions
- relative moisture in air/humidity
What two groups do chemical preservative fall under?
1) natural and manufactured chemicals
2) naturally occuring antimicrobials extracted from natural sources
- most consumer friendly
Describe the clean label concept
Consumers prefer preservatives that are considered to be natural and contain recongizable terms
-manufacturers must change formulations or rename ingredients to suit this critieria.
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When are organic acids most useful to delay bacterial growth and why?
They are most useful at a pH below or close to pKa. If below the pka, amount of protonated acids are equal to or greater than 50 percent. Because of this more acids will be able to pass through bacterial cell walls causing them to use up more and more ATP to push out H+ ions that are released in response to the neutral environment of the bacterial cells.
How much acetic acid would you have to add at a pH of 5.5 so there is as much protonated acid as there is at pH 3.5? How would you go about solving this problem?
You would substract the pH of these equations by the pka and you and set it equal to the log of the conjugate base and non dissociated acid. Replace the fraction with an x and raise each side to the power of 10 to get rid of the logarithm and solve for x (X=the amount of conjugate base over 1). Divide what you get for x at pH 5.5 by what you get for x at pH 3.5.
Parabenzoic acids
have pka values of 8.5
-pH values between 3.0-8.0
-as carbon chain length increases, solubility in aqueous solution decreases
-best at reducing growth of mold and yeast but not very consumer label friendly
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Nitrites
- prevent the growth of clostridium botulinum spores and other pathogens in meat products.
- Used to preserve meat
- broken down from nitrates in by oral microbiota
- further broken down with by gut microbiota and stomach acid to produce NO2
Nitric oxide
helps caridovascular system: -relaxes blood vessels for vasodilation -reduces blood pressure -anti inflammotory and acts as a neurotransmitter -
Since green vegetables contain high levels of nitrites why don’t they contribute to nitrosamine forming reactions?
Phytochemical antioxidants located within the vegetables prevent this from happening
What is celery powder used for and why?
Because it is high in nitrates it is used to replace chemically manufactured sodium nitrate and pottassium nitrate in meat to maintain it for longer periods of time. It is used because it is more consumer label friendly than the other options.
What are the roles of nitrates in food preservation and what dosage needs to be added to have effect?
- Nitrates are added to preserve meats
- 100-150ppm of nitrates are added to meats to preserve it
How do polyphosphates preserve food?
Polyphosphates prevent fungi and gram + bacteria from growning by removing the cations or chelating them. Their ability to do this is decreased by the presence of acid because acid protonates these cation sites preventing chelating and removal (how can cations be protonated?).
What are the preservation properties of NaCl?
- This is the oldest method of maintianing foods for longer periods of time
- works by dehydrating bacteria until they die or go into dormant state
- often combined with pasteurization, canning , or drying
- KCl is often used as a substitute but not as effective
- bacteria can combat this by building up enough solute inside their cells to equilbrate with salt solutes outside
How are Disinfectants used to reduce spoilage microbes?
-Can be used as supplemental additives by being already located on surfaces that foods touch.
-Used as antimicrobial wash when:
processing raw meat and poultry
What are some types of disinfectants that can be used to bring down spoilage microbes?
sulfites:
- commonly used in fruit and vegetable products and shrimp
- capable of destroying bacteria more than yeast and mold
- prevents bacterial fermentation in wine
- prevents enzymatic browning
2) chlorine:
- sodium hypochlorite
- powerful electon remove from all microbes
- damages steel
chlorine dioxide
- has no smell
- damages phenol and mercaptin compounds»gets rid of bat tastes
3) Quanternary ammonium compounds:
-don’t have color
-smell
-don’t causes damages to steel
effective in destroying microbes but are expensive
Describe the effects of hydrogen peroxide and peroxyacetic acids
2 most commonly used peroxides
- antimicrobial action comes from free radical oh
- used to sterilize equipment and surfaces
- turns meat white
- vegetables contain catalyzes which get rid of residue when it’s done killing microbes
- can kill all microbes that don’t contain genetic coding for catalysis enzyme activity
Peroxy acids
- much stronger than hydrogen peroxides
- can be used at lower amounts which will not negatively affect meat or poultry
- used to sterilize equipment, surfaces, and reduce microbes in poultry, meat and produce
- cannot be broken down by peroxidases or catylases
Ozone (O3)
- used against a variety of microbes and insects
- used on fruits and vegetables to microbes
Whats the problem with consumer driven natural antimicrobials
can extend shelf life but at the expense of color, flavor, taste and smell which is not a problem in chemically manufactured antimicrobials
Where can natural antimicrobials be taken from
- plants
- bacteria
- animals
- viruses
- alagea
- fungi
what are the animicrobial effects of Lysozyme and what foods does it impact
- antimicrobial enzymes found in bodily secretions which can be used to destroy gram + bacteria along with EDTA.
- Can also bind to calcium and magnesium ions to destablaize lipopolysaccaride membranes to inhibit gram -bacteria (what does this do?)
- brings down bacteria in
- meat
- cheese
- wine
- dietary supplements