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Food Microbiology > Lecture 16 > Flashcards

Lecture 16 Flashcards

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1
Q

What is a food preservative

A

All methods used to prevent spoilage by reducing the growth rate of microbes, and preventing their growth rather than killing them.

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2
Q

Food Spoilage

A

Enzymological, chemical and physical changes which can cause oxidation, browning, loss of color, or liquefication(converision of solid food to liquid).

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3
Q

What are the 2 groups of antimicrobials? What leads to a synergistic effect of antimicrobials?

A

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.

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4
Q

Factors affecting antimicrobial activity:

A

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

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5
Q

What two groups do chemical preservative fall under?

A

1) natural and manufactured chemicals
2) naturally occuring antimicrobials extracted from natural sources
- most consumer friendly

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6
Q

Describe the clean label concept

A

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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7
Q

When are organic acids most useful to delay bacterial growth and why?

A

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.

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8
Q

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?

A

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.

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9
Q

Parabenzoic acids

A

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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10
Q

Nitrites

A
  • 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
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11
Q

Nitric oxide

A 
helps caridovascular system:
-relaxes blood vessels for vasodilation
-reduces blood pressure
-anti inflammotory and acts as a neurotransmitter
-
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12
Q

Since green vegetables contain high levels of nitrites why don’t they contribute to nitrosamine forming reactions?

A

Phytochemical antioxidants located within the vegetables prevent this from happening

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13
Q

What is celery powder used for and why?

A

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.

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14
Q

What are the roles of nitrates in food preservation and what dosage needs to be added to have effect?

A
  • Nitrates are added to preserve meats

- 100-150ppm of nitrates are added to meats to preserve it

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15
Q

How do polyphosphates preserve food?

A

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?).

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16
Q

What are the preservation properties of NaCl?

A
  • 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
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17
Q

How are Disinfectants used to reduce spoilage microbes?

A

-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

18
Q

What are some types of disinfectants that can be used to bring down spoilage microbes?

A

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

19
Q

Describe the effects of hydrogen peroxide and peroxyacetic acids

A

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
20
Q

Peroxy acids

A
  • 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
21
Q

Ozone (O3)

A
  • used against a variety of microbes and insects

- used on fruits and vegetables to microbes

22
Q

Whats the problem with consumer driven natural antimicrobials

A

can extend shelf life but at the expense of color, flavor, taste and smell which is not a problem in chemically manufactured antimicrobials

23
Q

Where can natural antimicrobials be taken from

A
  • plants
  • bacteria
  • animals
  • viruses
  • alagea
  • fungi
24
Q

what are the animicrobial effects of Lysozyme and what foods does it impact

A
  • 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
25
Q

how do iron binding proteins fight microbes

A

Egg white proteins
-lactoferrin, transferrin
-ovatransferrin
bind to iron preventing bacteria from getting to it, inhibits certain bacteria from growning

26
Q

what does Avidin do to fight microbes

A
  • Binds to biotin a water soluble B vitamin that microbes need to sustain metabolic pathways and life
  • also binds to transport proteins preventing them from being transported to different locations in the body
27
Q

what do plants do to fight microbes:

A

-They have thousands of chemicals defenses which can destroy microbes as an evolutionary defense to being stationary
examples:
allicin- found in onion and garlic
cloves- contain eugenol and cinnamon aldehyde
Herbs- oregano, rosemary, sage and essential oils are able to destroy microbes
isothoiocynates-
phenols and cresols-give flavor and fight microbes in smoked foods
polyphenols- secondary compounds used to fight microbes

28
Q

What are examples of biological preservatives and what is their purpose?

A 
They are naturally occuring compounds which fight microbes
-lactic acid bacteria
-builds up acid to kill bacteria
-probiotic bacteira
-
-bacteriolysins
-bacteriophages
29
Q

what is the wisconsin process?

A
  • used to prevent the spoilage of bacon

- bacon is coated with lactic acid and a fermentable carbohydrate to prevent growth c.botilinum and nitrosamines

30
Q

what are microgaurd fermentates

A

antimicrobials which destroy bacteria and these are short chain fatty acids, acetic acid, proprionic acid and low molecular weight proteins. Ex: Microgaurd 300. Can be used to replace other antimicrobial preservatives.

31
Q

What did illyich mechnikov do?

A

-First person to find out that microbes in foods can imopact people’s health. He won the nobel prize for discovering the phagiotic macrophages and the concept of cell mediated immunity. He did this by connecting the health of bulgarian peasants to the consumption of fermented dariy products.He wrote a book where he presented the hypothesis that toxin producing gut bacteria could be replaced with lactic acid bacteria to promote healthier GI Health and make you live longer which led to the development of modern probiotics

32
Q

How do the effects of illyich mechnikov affect our health today?

A

Because his work shows that changing our diets can change the types of microbes that grow in our guts whic in fact has the largest impact on what the microbiome is made of and what it does.

33
Q

What are the probiotic bacteria and how do they help you?

A

Microbes which have healthy results for people who consume them.

34
Q

What requirements are probiotic bacteria exempt from?

A

Don’t have to colonize gut and survive intestinal tract

don’t have to fight microbes or change gut microbiota composition

35
Q

What are fermented foods and what do they do

A

can change food characteristics by increasing the number of vitamins and increasing it’s ability to be digested. Microbes must be added to make foods fermented.

36
Q

Why aren’t fermented foods always probiotic?

A

Because they may not automatically ferment food and may not be able to be reproduced. This makes it impossible to test if a food is fermentable or not.

37
Q

what are Bacteriocins and phage used for

A

Added to food and water which are used to feed animals before the animals are slaughtered» gets rid of spoilage microbes on meat
Also used to kill microbes on equipment by preventing the formation of biofilms
Also used in food packaging to kill spoilage microbes and pathogens

38
Q

Broad spectrum antibiotics:

A
  • used to decrease the amount of microbes on farm animals which could end up on meat
  • particular pathogen of focus is chosen and antibiotic targets particular strain without killing other microbes
39
Q

Bacteriocins

A

-produced by ribosomes made by bacteria which kill other microbes. Two types are
-lactobiotics
-pediocin like bacteriocins( more able to destroy listeria)
added to prevent growth of pathogens and unwanted bacteria in starter cultures, and can help starter culturess out compete other bacteria for nutrients coming from that food.
The only commercially acceptable bacteriocins are nisins A and Z which are added are often combined with other preservatives to prevent the growth of listeria monocytogenes.

40
Q

What are the two ways that fermented foods can be added to another food for a purpose which indicates how that food is controlled?

A

It cannot be considered an additive if the food simply added a an ingredient, but it can be if it is meant to have antimicrobial properties.

Food Microbiology (12 decks)

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