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5) FDSC 300 > Lecture 6- Water Acticity and mineral > Flashcards

Lecture 6- Water Acticity and mineral Flashcards

1
Q

What is water activity?

A

Ratio of vapour pressure of water in a food and vapor pressure of water at the same temperature

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2
Q

aw=

A

p/p0

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3
Q

Is all water available for micorbial growth. physical properties and chemical/enzymatic reactions?

A

No especially bound water

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4
Q

What is the pathogenic microbial growth cut off point?

A

<0.85

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5
Q

Is water activity linear?

A

No but the higher the Aw the higher the water activity

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6
Q

Lipid oxidation is highest in which range of water activity?

A

0.75-0.85

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7
Q

Maillard Browning is most promenant in which range of water acitivty?

A

0.70

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8
Q

What is the cut off point for gorwth of yeast and molds?

A

0.62

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9
Q

What happens as a food product goes from a dry to intermediate moisture?

A

Powder caking

Loss of Crispness

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10
Q

What happens as food goes from intermediate moisture to dry food?

A

Hardening and dryinh

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11
Q

What happens when you increase the moistuer of a food product?

A

Noticable increse in molecular mobility

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12
Q

What is the range for a dry food?

A

<0.2

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13
Q

Intermediate moisture food?

A

0.2-0.85

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14
Q

How do you measure the water activity using a dessector?

A

Measuring the vapour pressure of the headspace after the close system attains equilibirum

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15
Q

How does the sample reach equilibirum?

A

WAter will migrate out of the sample into the container headspace

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16
Q

What are some detectors to determine when equilibrium has been reached?

A
  • Dew Point
  • Electric Hygrometer sensors
  • Direct measurement pressure
  • Tunable diode laser
  • Freezing point determination
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17
Q

What temperature is the assay normally conducted?

A

25C

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18
Q

What samples require longer duration to attain equilibrium

A

dry and dense

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19
Q

Which detector is more accurate?

A

Electric (capacitance/electrolyte) , can determine more water due to the higjer conductance–> more specific

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20
Q

What are the compoenents of the dew point analyzer?

A

Fan
Infrared thermometer
Temeprature contolled mirror
Sensor that detects condensation on morror

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21
Q

What is the principle of the dew point analyzer?

A

Aw of the sample is the same as the RH of the headspace at eq –> instrument measures the RH in headspace

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22
Q

Why is the mirror cooled in the dew-point?

A

Until condensation from headpsace first appears, determine by a change in reflectance

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23
Q

What is recorded?

A

Temperatures of teh sample and the mirror

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24
Q

What is used to determine the vater vapour pressure P0?

A

Temperature of the sample

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25
Q

What is used to determine the vapour pressure of water (P)?

A

Dew Pount temperature

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26
Q

Why is temperature important for equilibration and aw?

A

Higher temp –> higher Aw reading

Temperature difference betwenen samples and containers could cause water condensation –> error

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27
Q

What is Ash?

A

Inorganic(mineral) residue remaining after combustion or complete acid-facilitated oxidation of organic matter in food

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28
Q

What is the principle of ashing?

A

Minerals are not destroyed by heating, low volatility compared to toehr food compoenents

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29
Q

What is the relevance of ash analysis?

A

Microbiological stability
Nutrition
Processing
Adulteration

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30
Q

Relevance of microbiological stability

A

High mineral content used to retard growth of certain imcroogranisms

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31
Q

Relevance of nutriton

A

Some minerals are essential to a healthy diet whereas some can be toxic

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32
Q

Relevance of Processing

A

Often important to know the mineral content of foods during processing and the amounts of minerals interfere with processing

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33
Q

Relevance of adulteration

A

Ash content can help determine if a certain mineral hs been used to cut costs

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34
Q

Ash content in ___ is very low

A

Oils/fats

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35
Q

What product does not vary in ash content?

A

Animal products

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36
Q

What is the ashing procedure?

A
  • Food sample —(O)——–> Co2+N Oxides +H2O+ grey/white ash
37
Q

What is the importance of pre-ashing?

A

Get ride of moisture and lipids

  • -> evaportate water
  • -> reduce the likelihood of sputter
38
Q

What are the type of crucibles?

A

Quartz
Porcelain
Steel
Platinum

39
Q

Which crucible is better?

A

Quartz

40
Q

Pros and con of Quartz?

A

resistant to acids and halogens butno alkali

Stable unti 900C

41
Q

Pros and cons for procelain crucibles?

A

Inexpensive
Will crack with rapid temperature changes
Most common

42
Q

Pros and cons of steel crucibles

A

Inexpensive
Resistant to both acids and alkalines
Contain chromium and nickel

43
Q

Pros and cons of platinum crucibles?

A

Far to expensive for routine use for large numberof samples

44
Q

What are the four types of analytical procedures used to determine teh as content of foods?

A

Dry ashing
Wet ashing
Microwave
Low temp plasma dry ashing

45
Q

What is the temperature of the frunace for dry ashing

A

Use high temperature furnace (500-600C

46
Q

What are the compounds that are vaporize with dry ashing?

A

Water and volatile materials and organic copounds are burned in the presence of oxygen
–> CO2, H2O and N2

47
Q

What are the minerals converted to in dry ashing?

A

Oxides, sulfates, phosphates, chlorides or silicates

48
Q

What is the gerneral dry ashing protocol?

A
  1. Weigh a 5–10-g sample into a tared crucible. Pre-dryif the sample is very moist.
  2. Place crucibles in a cool muffle furnace. Use tongs, gloves, and protective eyewear if the muffle furnace is warm.
  3. Ignite 12–18 h (or overnight) at about 550OC.
  4. Turn off muffle furnace and wait to cool down to at ~250◦C. Open door carefully to avoid losing ash that may be fluffy.
  5. Using safety tongs, quickly transfer crucibles to a desiccator with a porcelain plate and desiccant.
  6. Cover crucibles, close desiccator, and allow crucibles to cool prior to weighing
49
Q

What can the ash content be expressed as?

A

Either a dry or wet bases

50
Q

How do you calculate the percent ash?

A

Weight after ashin/weight before ashing (dry) x100

51
Q

What are the advantages of dry ashing?

A

Safe, few reagents, many sample can be analyzed simutaneously, not labour intensive
–> can analyze specific mineral content

52
Q

What are the disadvantages of dry ashing?

A

Long time required
Costly (power consumption
Possibility of losing volatile minerals

53
Q

What are black spots?

A

Some CHO traps inorganic materials leading to tiny black spots
- fused salts

54
Q

Black Salts are evidence of what?

A

organic materials

55
Q

How do you resolve black sports?

A

Adding a small amoun tof water or HNO3 and reashing

56
Q

With which type of food is complete combustion hard to obtain?

A

High carbohydrate foods

57
Q

What type of water is themost important in terms or microbiolog and other biological processes?

A

Free water

58
Q

What is total water?

A

Aw + bound water

59
Q

How do you determine bound water?

A

Distillation

60
Q

What is the cut off point for pathogenic bacteria?

A

0.85

61
Q

Does a higher Aw mean a higher moisture content?

A

Yes, becaue there is an increase of water in the system

62
Q

Does a higher moisture content lead to higher Aw?

A

No, the linear relation is no linear

63
Q

What reduces the water acitivity?

A

Adding solute to the water solution

64
Q

Why is it omportant to determine the Aw

A

Quality and safety

65
Q

Whta does an increaseof free water in the system lead to?

A

Distrupt Quality

66
Q

What is at equilibirum in the headpace?

A

Aw of the food and the relative humidity of the headspace

67
Q

How should you do when tou get dew?

A

Bring analyzer to a lower temp

68
Q

Why is it important to handle the crucible with tongs?

A

Oil on you skin can contaminate the crucible

69
Q

Would a dry or wet sample have a lower percentage?

A

Wet sample

70
Q

What is the protocol for dry asking?

A
  1. Weigh a 5–10-g sample into a tared crucible. Pre-dryif the sample is very moist.
  2. Place crucibles in a cool muffle furnace. Use tongs, gloves, and protective eyewear if the muffle furnace is warm.
  3. Ignite 12–18 h (or overnight) at about 550OC.
  4. Turn off muffle furnace and wait to cool down to at ~250◦C. Open door carefully to avoid losing ash that may be fluffy.
  5. Using safety tongs, quickly transfer crucibles to a desiccator with a porcelain plate and desiccant.
  6. Cover crucibles, close desiccator, and allow crucibles to cool prior to weighing
71
Q

What is wet ashing?

A

breaking down and reomival of organic matrix surrounding the minerals so that they are left in acidic solution
–> food sample is weighed into flask containing oxidizing agents and then heated
= oxidation of organic contents by acid and heat

72
Q

What is the primary use for wet ashing?

A

preparation of samples for subsequent analysis of specific minerals

73
Q

How much time does wet ashing take?

A

10mins–> few hours at 120C-300C

74
Q

What is the resulting solution from wet ashing?

A

The solution can be assayed for metal ions using AAs or ICP-MS
–> ppb or ppm

75
Q

Advantages of wet ashing?

A

little loss of volatile minerals due to low temperature
More rapid
Provides solution for determination

76
Q

What are the disadvantages of wet ashing?

A

Labor intensive
Requires fume hood
Low sample

77
Q

Wet ashing peocedure?

A
  1. WeighsampleandaddtoErlenmeyerflask(previouslyacidwashedanddried)
  2. Add3mlofH2SO4followedby5mlofHNO3
  3. Heatthesampleonahotplateat200oC(orboilinginblockheaters)
  4. Oncethebrown-yellowfumesceaseandwhitefumesfromdecomposingH2SO4areobserved,thesamplewillbecomedarker.Removetheflaskfromthehotplate
  5. Slowlyadd3–5mlofHNO3
  6. PuttheflaskbackonthehotplateandallowtheHNO3toboiloff.ProceedtothenextstepwhenalltheHNO3isremovedandthecoloriscleartostrawyellow.Ifthesolutionisstilldarkincolor,addanother3–5mlofHNO3andboil.Repeattheprocessuntilthesolutioniscleartostrawyellow
  7. Reducethevolumeappropriatelytoallowforeaseoffinaltransferanddiluteusingultrapurewater
78
Q

What is microwave wet ashing?

A

Microwave source of heat, nitric acid used as the digestant

79
Q

What are the advatanges of microwave wet ashing?

A

Faster to complete digestion (high temp and pressure

Programmable instrument that handles multiple samples at a time

80
Q

Difference between microwave wet ashing and microwave dry ashin

A

with or without acid

81
Q

What is low temperature plasma ashing?

A

Sample is place in glass chamber which is evacuated using vacuum pump, small amount of O2 pumped into chaber and browken down to nascent oxygen by applicaotnof electromagnetic readio frequency field
–> organic matter is rapidly oxidized and moisture evaporated (temp)

82
Q

Advantages of low temperature plasma ashing?

A

Less chance of losing trace elements by volatilization

83
Q

Disadvantages of low temperature plasma ashing?

A

Relatively expensice equipment and small small sample throughput

84
Q

What are other methods of ashing?

A

Water soluble/insoluble ash: index of fruit content in fruit preserves
Alkalinity of ash: ash of fruits and vegetables
Ash insoluble in acid: index of contamination

85
Q

Which ashis alkaline? acidic?

A

Acidic- meat and some cereals

Alkaline- fruit and vegetables

86
Q

What is water insoluble ash a indication of?

A

Presence of siliceous matter

87
Q

What is a lower water insoluble ash indicate?

A

higher fruit content of jam and jellies (lower % of skin, seed, stem)

88
Q

What is acid insoluble ash indicative of?

A

surface contamination of fruits and vegetables and wheat and rice coatings–> generally silicates

5) FDSC 300 (14 decks)

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