Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Food Microbiology > Physical methods of preservation > Flashcards

Physical methods of preservation Flashcards

1
Q

what is modern food preservation aim for

A

Modern preservation methods are designed to extend shelf life, but also to ensure its safety by inactivating pathogens, or in some cases just preventing their growth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the most common preservation methods

A

Physical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is inactivation

A

Inactivation as it refers to bacteria is defined by the destruction of the organism as judged by its inability to recover on microbiological media

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the difference in spoilage between lactose-free milk and normal milk

A

Few bacteria have lactose genes, so lactose-free milk should be more readily spoiled because the lactose has been pre-treated and there is a bunch of available glucose and galactose. BUt lactose-free milk is treated with higher temperature so fewer microorganisms survive resulting in a longer shelf life

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Six physical methods used for food preservation

A

High-Temperature Treatment (cooking)
Low-Temperature Preservation (freezing)
Decreasing Water Availability (i.e. drying, salting)
Ionizing Irradiation
High-Pressure Processing (HPP)
Pulsed Electric Field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the most effective type of physical food preservation and why, why it is not as widely used

A

High temperatures

Heat treatment is effective because it can eliminate almost any microbial target, and it is customizable to the product and organism of concern

However, over heating may damage the product quality so process development and validation is important

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the growth curve of microorganisms destruction under high temperatures looks like why

A

After optimum there is still little phase when it is declining, it balances on the tip of destruction but still menages to control enzymatic reactions

Not a bell curve!!!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Six factors that can affect heat transfer and is critical for high temperature preservation

A
  1. Product Type: Liquids absorb heat faster than solid foods.
  2. Container Material: Glass containers heat more slowly than metal containers
  3. Container Shape: Tall and narrow containers heat more quickly than other shapes
  4. Container Size: The center of small containers get reached more quickly than the center of large containers
  5. Agitation: Agitation and mixing help to increase heat transfer especially in viscous or semi-viscous products

6.Temperature of Heating Medium: The greater the difference in temperature between the heat transfer medium and the product, the more rapid the rate of heat transfer to the product

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is survivol plots?

A

•Survivor plots depict the logarithmic nature of population inactivation over time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is D value

the greater D value what does it mean

A
  • Decimal reduction time (D value) is defined as the time it takes for a 10-fold reduction in the number of survivors at a given temperature
  • The greater the D value at a given temperature, the more resistant that organism is to heat
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Why it isn’t fine as long as you cook it (chicken fingers/ ground beef)

A

Bacterial levels were so high that even cooking can not killing it

Cooking is reducing microbial population by 1 log

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why chocolate is prone to bacterial contamination

A

Because it can be heated only up to 60C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

D value and temperature relationship, and the plot name

A
  • The D value of a microorganism decreases as the processing temperature increases
  • When D value is plotted against temperature, it is known as a thermal resistance plot, it is generally linear, and is also useful for comparing the difference resistances of a microorganism at different temperatures
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

The thermal resistance plot is used to calculate what

A
  • The thermal resistance plot can be used to calculate the z value known as the thermal resistance constant, which is mathematically equal to the negative reciprocal of the slope
  • The z value represents the change in temperature required to change the D value of a microorganism by an order of magnitude (10-fold)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

A large Z value indicates what

A

A more heat resistant organism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why thermal lethality measurements are taken, what is related value to it

A
  • Thermal lethality measurements are taken to determine the amount of time required to commercially sterilize food at a given temperature
  • The F value is the time, in minutes, at a specified temperature, required to achieve a targeted reduction in a homogeneous population having a specific z value
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

The difference between D and F values

A

•The difference between D value, which defines the time it takes to reduce the population by 1 log, F value represents the time it takes to get the population to a specific level (i.e. 101 or sterile)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Where F value is very important

A

F value is important in the commercial canning industry

•It is common for the canning industry to calculate F value with the time at a specific temperature to achieve commercial sterility

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What intial microbial population is assumed in canning industry when calculating F value

A

12 log or 10 ^12

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Why C. botulimun is a thing for canning industry

A

•C. botulinum is the key pathogen of concern for canned low acid foods

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Assume D121C is equal 0.21 and Z =10C, to achieve commercial sterility F how much time is needed

A

F=n*D→ 12*0.21= 2.52 min

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Meat loaf, Green beans in brine, carrots in brine, dog food, creat-style corn: make a table of ascending order of F values

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

The difference between sterilization and commercial sterilization

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is champion or high temperature survival and it is used for what; and does what bad thing in food

A

Geobacilus stearothermophilus is used for autoclave testing, not pathogenic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Make a tale of ascending order for C.botulinum, C.sporogenes, Bacillus coagulans and B.licheniformis→ significance and order their D value

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Why some bacteria are more naturally resistant than others

A

•protein cross-linking (disulfide bonding), DNA structural changes (higher GC), GC- three hydrogen bonds comapred to AT-two

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What bacterial state cna influence their heat resistance factor

A

State of dormancy is an important factor in heat resistance

  • Stationary phase cells are more resistant to heat than exponential phase cells
  • Spore formation dramatically increases heat resistance
28
Q

What characteristic in foods can influence heat resistance

A

•Other characteristics of the food also influence heat resistance (i.e. if the aw, pH, or antimicrobial constituents are already stressing the bacteria out, you’ll need less heat to kill them)

Instead of one method and overcook, you can add more methods and make the product look less processed

29
Q

what is the difference between home canning and aseptic preservation

A
  • Canning involves commercially sterilizing prepackaged food (i.e. like home canning tomatoes)
  • Aseptic processing is used industrially, where foods and cans are sterilized separately and then foods are packaged under aseptic conditions
  • The product is heated by passing through a set of heat exchangers until the holding time and temperature have been reached, then the food is immediately passed through a set of cooling heat exchangers
  • The cooled product is placed in pre-sterilized packages and hermetically sealed
30
Q

Why the products are heated before placing them in cans?

A

•This avoids having to heat the food to excess to ensure that the center of the can reaches temperature, and improves food quality and nutrition

31
Q

Aseptic packaging is sued for what types of products and for what it is not used

A
  • Aseptic processing is generally used for fruit juices, dairy products, and sauces
  • It is not used for low-acid, or particulate-containing foods.
32
Q

•Why aren’t microwaves used in processing, and why aren’t they a good idea for foods that require cooking for safety?

A
  • Microwaves cause rotation of water molecules in foods, and these rotations generate friction and therefore heat. Unlike convectional heat, which penetrates from the outside inward, microwaves generate heat throught out the material leading to faster heating and shorter processing times
  • Distribution of the heat is very uneven, leading to uneven lethality of microorganisms (don’t microwave your chicken fingers)
  • This has hindered the use of the microwave in commercial food processing.
33
Q

How freezing preserves food

A

•Freezing stops the metabolic activity of most food-borne microorganisms, although cryophilic, psychrophilic, and psychrotrophic food microbiota will still alter foods at sub-zero temperatures

•Freezing also decreases the aw therefore, only cold-tolerant and xerotolerant microorganisms can grow, but some yeast and fungi have these characteristics

34
Q

What can damage living cells in freezing

A

•Freezing and thawing cycles can cause damage to living cells (of the food and of the microbiota)

35
Q

What reaction are retarded in freezing? What is not affected by freezing?

A
  • Toxins are generally not affected by freezing
  • Freezing will also retard chemical and biochemical deterioration such as lipid oxidation, Maillard reactions, enzymatic browning, proteolysis, and lipolysis
36
Q

What bacteria survives freezing better?

A

•Gram-positive bacteria survive freezing better than Gram-negative bacteria, Because there are more resistant to cold and little water

37
Q

What microorganisms are readily destroyed by freezing and where it is used

A
  • Parasites are readily destroyed via freezing
  • Trichinella spiralis (pork worm) is eliminated if the raw product is held briefly at -23C
38
Q

Rapid freezing why better for microbial preservation

A

•Rapid freezing produces smaller ice crystals (cells don’t get punctured), and exposes cells to osmotic stress for shorter time periods, therefore, microbial cells are more susceptible to injury and death during slow freezing (like in your home freezer)

38
Q

Types of water

A

•Water can occur in a bound or unbound form

39
Q

Water can be bound by

A
  • Hydroxyl groups
  • Carbonyl and amino acid groups of proteins
  • Salts (image to right)
40
Q

What type of water is essential in microbial preservation

A
  • The amount and form of water influence microbial activity
  • Unbound water is essential for microbial growth and survival
  • Removing or restricting unbound water can preserve the food by suppressing microbial activity and extending the product’s shelf life
41
Q

What is water availability?

A
42
Q

Aw is related to what value

A

equilibrium relative humidity (ERH)

ERH (%) = aw x 100

43
Q

Is Aw and moisture content is the same?

A
  • The relation between aw and the moisture content of food is not linear. There is a clear distinction between aw and moisture content.
  • Chemical and biological activities are better described by the aw than by the water present in the food (moisture content)

That is because of bound water, a food can have high moisture content but low aw if it high salted

44
Q

•Foods can be divided into 3 categories based on their aw : with examples and how prone they are to microbial spoilage

A
45
Q

Maple syrup that is properly cooked aw

A

0.87-0.88

46
Q

How maple syrup is prepared ;what brix; what organism can grow

A
  • Maple syrup is prepared by boiling the sap from sugar maple trees until the boiling temperature is 4.1C higher than that of pure water (which will vary based on air pressure but is around 100C)
  • The Brix of properly prepared maple syrup is 66

at this low aw only mold can grow

47
Q

Why water availability is essential for living cells?

A

•Functionality of living cells relies greatly on water availability for nutrient acquisition, waste removal, and as a medium for metabolic reactions to take place in

48
Q

•Spoilage and pathogenic bacteria tend to need a ____aw for growth

A

•Spoilage and pathogenic bacteria tend to need a very high aw for growth (>0.95)

49
Q

what aw spore forming bacteria need and examples

A

•Spore forming bacteria, L. monocytogenes, and V. parahaemolyticus can grow in the range of 0.91-0.95

50
Q

what bacteria has lowest water requirements, what it can’t do at that level?

A

•S. aureus has the lowest water requirements and can grow with an aw of >0.86. However, it cannot produce toxins at this level

51
Q

What organisms can grow at lower aw than bacteria? What are the common examples of them in intermediate spoilage foods

A
  • Yeasts have aw requirements that are lower than those of bacteria
  • Debaryomyces hansenii,Candida pseudotropicalis, Zygosaccharomyces bailii, andZygosaccharomyces rouxii are spoilage yeasts that are common in intermediate moisture foods where bacterial growth is suppressed
52
Q

Who can grow even lower than yeasts in terms of aw, what si restricted under xerophilic conditions

A
  • Molds are xerotolerant and grow at lower moisture contents than the other types of spoilage microorganism
  • Molds can also produce mycotoxins, but mycotoxin production is restricted under xerophilic conditions
53
Q

Draw a table: what type of bacteria can grow, what type of fungi and product examples

A
54
Q

What else determined bacterial growth in limited aw?

A
  • Growth of microorganisms is restricted not only by the aw but also based on which humectant was used to lower the aw
  • For example, glycerol can permeate the bacterial membrane and may have a different inhibitory effect than that of sodium chloride or sucrose.
55
Q

Does lowering aw inhibits microbial growth permanently ?

A

•Also, lowering aw inhibits microbial growth but may not kill the microorganisms in the food. These microbes may remain dormant until the food is rehydrated and then resume their metabolic activity and multiply (i.e. Salmonella in chocolate bars)

56
Q

What is drying?

A

Drying: is the process of mobilizing water present in a food matrix to its surface and then removing it from the surface by evaporation. It often involves simultaneous heat and mass transfer. Most drying operations involve converting liquid water in the material to vapor and then removing it by passing hot air over the product (i.e. beef jerky).

57
Q

What is freeze-drying

A

Freeze-Drying: During freeze-drying the product is frozen first and the moisture is removed via sublimation. Freeze-drying has a minimal impact on the structure and flavor of the food compared with other drying techniques, but has a relatively high cost, and is therefore used as a value added technique (i.e. camp dinners, instant coffee, infant formulas).

58
Q

What is osmotic drying

A

Osmotic Dehydration: is a procedure that involves removing water from fresh food using a hypertonic solutions (sucrose, salts, glycerol). It relies on the ability of the food cells to selectively permit the passage of water out of the food without allowing surrounding solutes to enter these cells. As a result food is dehydrated. It cannot remove all the moisture from the food, so it is mainly used as a pretreatment to other methods of dehydration. Primarily used for dehydrating fruits and vegetables (apples, blueberries, pineapples, mangoes etc.).

59
Q

On what principle ionizing radiation works on killing microorganisms

A
  • Electromagnetic radiation with shorter wavelengths (gamma radiation) has lethal effects on microorganisms
  • Longer wavelengths (microwaves) just generate heat and are not as effective•Ionizing radiation includes X Rays and gamma radiation
  • The cell’s DNA is the primary target of ionizing radiation, therefore, the smaller the genome, the greater the resistance to ionizing radiation
  • DNA damage is caused by the reaction of reactive oxygen species (ROS) that are generated during radiation
60
Q

Preserving food by X-rays: how, maximum energies allowed, effective on what produce, drawbacks

A
61
Q

How gamma radiation is emitted in food preservation techniques? Advantage and what products it is used on

A
62
Q

Different dosage levels produce different levels of food preservation and are selected based on the end objective for the food:

A

Redappertization. Involves a high dose (10 to 75 kGy) to produce commercial sterility

Radicidation. Involves medium dose (1 to 10 kGy) to produce an equivalent effect to thermal pasteurization – effective against vegetative bacteria but spores are not inactivated

Radurization. Involves low dose irradiation (0.05 to 1 kGy) to control the presence of insects in grains or stop the sprouting of potatoes, or delay fruit ripening

63
Q

What is HPP processing, what should be considered when want to use, principle; what dies and what survives

A
  • High pressure processing (HPP) involves treating food with pressures in the range of 100 to 600 MPa, which will inactivate most bacteria, yeasts, molds, and viruses (spores survive)
  • Food materials containing air pockets may be deformed due to the differences in compressibility between the air and food material
  • Appropriate packaging must also be chosen
64
Q

PEF processing: pricniple, treatment is done to get rid of what; what should be considered before processing

A

Food Microbiology (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions