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FDSC 442 > 14 - Physical Methods of Food Preservation > Flashcards

14 - Physical Methods of Food Preservation Flashcards

1
Q

what is the goal of modern preservation

A

extend shelf life; ensure safety by inactivating pathogens/preventing their growth

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2
Q

what is inactivation?

A

destruction of a bacteria judged by its inability to recover on microbiological media

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3
Q

_____ methods of food preservation are the most common

A

physical

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4
Q

what are the physical methods of food preservation?

A
  • high temp treatment
  • low temp preservation
  • decreasing water availability
  • ionizing radiation
  • high pressure processing
  • pulsed electric field
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5
Q

how does high temp inactivate microorgs?

A

going beyond optimal temp slows cell functions (multiplication) and eventually death.
damages membranes, proteins, and ribosomes

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6
Q

benefits of heat treatment? (2)

A
  • eliminates almost any microbial target

- customizable to the product and organism of concern

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7
Q

limitations of heat treatment?

A

overheating can damage the product quality

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8
Q

what factors affect heat transfer? (6)

A
  • product state
  • container material
  • container shape
  • container size
  • agitation
  • temperature of heating medium
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9
Q

do liquids or solids transfer heat faster?

A

liquids

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10
Q

do glass or metal containers transfer heat faster?

A

metal

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11
Q

which shape container transfers heat the fastest?

A

tall and narrow

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12
Q

do large or small containers become thoroughly heated faster?

A

small

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13
Q

does agitation speed up heat transfer?

A

yes

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14
Q

what are the 2 most important parameters in high temp treatment?

A

temp and time

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15
Q

_____ _____ depict the logarithmic nature of population inactivation over time

A

survivor plots

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16
Q

what’s a D value?

A

decimal reduction time; the time it takes for a 10 fold reduction in the number of survivors

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17
Q

the greater the D value for a T, the more (resistant/sensitive) the organism is to heat

A

resistant

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18
Q

define a thermal resistance plot

A

when D value is plotted against temperature

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19
Q

what does a thermal resistance plot enable?

A

comparison of resistances of a microorganism at different temps

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20
Q

what is a z value?

A

change in temp required to change the D value of a microorganism by 10-fold

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21
Q

a larger Z value indicates a more heat (sensitive/resistant) organism

A

resistant

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22
Q

measurements taken to determine the amount of time required to commercially sterilize food at a given temp

A

thermal lethality measurements

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23
Q

what’s an F value

A

time (min) at a specified temp to require a targeted reduction in a homogenous population having a specific z value

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24
Q

differentiate between D and F values

A

D = time to reduce by 1 log

F - time to reduce to specified level (can be until sterile)

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25
Q

which value is the most important in the canning industry? (D, F, Z)

A

F

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26
Q

canning reduces C. botulinum by ___ log

A

12

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27
Q

define sterilization

A

renders a product free of any living organisms

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28
Q

define commercial sterilization

A

renders a product free of:

  • miroorgs that can reproduce in food under normal non-refrigerated storage & distribution temps
  • viable microbial cells or spores of public health significance
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29
Q

true or false: commercially sterilized items are completely free of microoganisms

A

false. they are heated just enough to produce a shelf-stable product

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30
Q

what mechanisms cause bacteria to be resistant to heat?

A
  • protein cross-linking (disulfide bonding)

- DNA structural changes (high GC)

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31
Q

state of _____ is an important factor in heat resistance

A

dormancy

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32
Q

what phase of cells are more resistant to heat than exponential phase cells?

A

stationary phase

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33
Q

spore formation dramatically (increases/decreases) heat resistance

A

increases

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34
Q

can other hurdles (pH, aw) influence heat resistance?

A

yes

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35
Q

what is aseptic processing?

A

you have sterile can
you have sterile food
you put them together in aseptic conditions

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36
Q

what does aseptic processing achieve with regard to heat?

A

less excess heating

37
Q

describe the heating process in aseptic processing

A
  • passed through set of heat exchangers to specified time/temp
  • food is passed through a set of cooling heat exchangers
  • cooled product is placed in pre-sterilized packages & hermetically sealed
38
Q

for what kind of commodities is aseptic processing applied?

A

fruit juices, dairy products, sauces

39
Q

for what kinds of foods is aseptic processing unsuitable?

A

low acid, particulate containing fodos

40
Q

why aren’t microwaves used in processing?

A

distribution of heat is very uneven

41
Q

what does freezing accomplish?

A

stops metabolic activity of most food-borne microorganisms; slows biochemical deterioration (lipid ox, maillard, lysis) can also cause damage to living cells (for both food and microbiota)

42
Q

are toxins affected by freezing?

A

no

43
Q

what kind of microorganisms are resistant to low temperature preservation?

A
  • cryophilic
  • psychrophilic
  • psychrotrophic
  • xerotolerant
44
Q

what does freezing do to aw?

A

decreases

45
Q

are gram positive or negative better at surviving low temp preservation?

A

positive

46
Q

how are parasites affected by freezing?

A

they’re killed

47
Q

microbial cells are more susceptible to injury/death during (fast/slow) freezing

A

slow, like the freezer at home

48
Q

what kind of water is essential for microbial growth and activity?

A

unbound

49
Q

aw = ?

A

P/Po

50
Q

ERH = ?

A

aw*100

51
Q

true or false: there is a linear relationship between aw and moisture content of food

A

false

52
Q

chemical and biological activities are better described using…

A

aw

53
Q

give the aw ranges of high moisture, intermediate moisture, and dry foods

A
  • high moisture foods: >0.9
  • intermediate moisture: 0.65-0.90
  • aw: <0.65
54
Q

are intermediate moisture foods resistant to microbial spoilage?

A

moderately yes

55
Q

what aw category does maple syrup belong in?

A

intermediate

56
Q

spoilage need an aw in what range?

A

> 0.95

57
Q

spore forming bacteria can grow in what aw range?

A

0.91-0.95

58
Q

what aw can S. aureus grow?

A

> 0.86

59
Q

which have a higher aw requirement: yeast or bacteria

A

bacteria

60
Q

what are some spoilage yeasts associated with intermediate moisture foods?

A
  • debaryomyces hansenii
  • Candida pseudotropicalis
  • Zygosaccharomyces bailii
  • zygosaccharomyces rouxii
61
Q

are moldes xerotolerant

A

yeah

62
Q

can mycotoxins be produced under xerophilic conditions?

A

it’s restricted

63
Q

what’s a humectant?

A

holds moisture in food

64
Q

how can humectants microbial growth?

A

ability to permeate membranes and impart inhibitory effects

65
Q

does reducing Aw kill microorganisms?

A

not always. they may go dormant until food is rehydrated

66
Q

define drying

A

mobilizes water in food matrix, brining it to the food’s surface, then removing the water from the surface by evaporation. involves both heat and mass transfer

67
Q

define freeze drying

A
  • product is frozen
  • frozen moisture is removed by sublimation
  • retains original structure and flavor
68
Q

define osmotic dehydration

A

removes water using hypertonic solutions (sucrose, salts, glycerols). relies on selective permeability of food cells to pass water out of food.

69
Q

true or false: osmotic dehydration can remove all the free water

A

false - it will always have to reach equilibrium

70
Q

what wavelengths are used for ionizing radiation

A

shorter (x ray and gamma)

71
Q

what is the target of ionizing radiation?

A

cell’s DNA

72
Q

a smaller genome will result in (greater/lower) resistance to ionizing radiation

A

greater

73
Q

how is DNA damaged by ionizing radiation?

A

rxn of ROS

74
Q

how are x rays produced?

A
  • when electron beam strikes a metal
75
Q

what are x rays good for treating?

A

fresh fruit and veggies for microbial lethality

76
Q

what is the drawback of using x-rays?

A

high power requirement; high requirement ffor cooling treatment

77
Q

how is gamma radiation produced?

A

from sources like Co-60 and Cs-137. it’s emitted by an excited nucleus of a radioisotope trying to go to its lowest energy state

78
Q

advantages of gamma radiation?

A
  • high penetration power

- constant energy

79
Q

define redappertization

A

involves high dose (10-75 kGy) to produce commercial sterility

80
Q

define radicidation

A

medium dose (1-10 kGy) to produce equivalent of thermal pasteurization. good against vegetative bacteria but does not inactivate spores.

81
Q

define radurization

A

low dose (0.05-1 kGy) to control presence of insects in grains or stop the sprouting of potatoes or delay fruit ripening

82
Q

expand HPP and PEF

A 
HPP = high pressure processing
PEF = pulsed electric field
83
Q

define HPP

A

involves treating food w/pressures in the range of 100-600 MPa to inactivate most bacteria, yeasts, mold, and viruses (spores survive)

84
Q

limitations of HPP

A
  • food with air pockets may experience deformation

- appropriate packaging must be considered

85
Q

define PEF

A

applies short burst of high voltage between 2 electrodes

86
Q

what does PEF eliminate?

A

vegetative bacterial cells

87
Q

what does the success of PEF treatment rely on??

A
  • food composition
  • pH
  • electrical conductivity
88
Q

true or false: foods with air bubbles are pumpable foods

A

false. air is not a good conductor.

FDSC 442 (14 decks)

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