introduction to FOOD ANALYSIS by muga.ppt

This module is a very brief overview of common methods of food analysis used in food processing organizations.

1. 1
INTRODUCTION TO FOOD
ANALYSIS
1126
Steven C Seideman
Extension Food Processing Specialist
Cooperative Extension Service
University of Arkansas

2. 2
INTRODUCTION
•This module is a very brief overview of
common methods of food analysis used in
food processing organizations.

3. 3
WHY ANALYZE FOOD?
•Government regulations require it for certain
products with standards of identity (e.g.% fat and
moisture in meat products).
•Nutritional Labeling regulations require it.
•Quality Control- monitor product quality for
consistency.
•Research and Development- for the development
of new products and improving existing products.

4. 4
What Properties are Typically
Analyzed?
•Chemical Composition – water, fat,
carbohydrate, protein etc
•Physical Properties- Rheological or stability
•Sensory Properties- Flavor, mouth-feel,
color, texture etc.

5. 5
References on Analytical
Techniques
•Official Methods;
- Association of the Official Analytical Chemists (AOAC)
- American Oil Chemists Society (AOCS)
- American Association of Cereal Chemists (AACC)

6. 6
Criteria for Selecting an
Analytical Technique
•There are many techniques to analyze foods but
each has drawbacks or compromises.
•You must select the technique that is required or
fits into your system.
•For example, the most accurate techniques
generally take longer to perform and you may not
have the time if the food product you are making
requires “real time” results such as in the
formulation of processed meats.

7. 7
Criteria for Selecting an
Analytical Technique
•Precision
•Accuracy
•Reproducibility
•Simplicity
•Cost
•Speed
•Sensitivity
•Specificity
•Safety
•Destructive/ Non-
destructive
•On-line/off-line
•Official Approval

8. 8
SAMPLING AND SAMPLE
PREPARATION

9. 9
What is the Purpose of the
Analysis
•Official Samples
•Raw Materials
•Process Control Samples
•Finished Products

10. 10
Sampling Plan
•A sampling plan is a predetermined procedure for
the selection, withdrawal, preservation,
transportation and preparation of the portion to be
removed from a lot as samples.
•The sampling plan should be a clearly written
document containing details such as;
- Number of samples selected
- Sample location (s).
- Method of collecting samples

11. 11
Factors Affecting a Sampling
Plan
•Purpose of inspection
-acceptance/rejection, variability/average
•Nature of the product
-homogenous, unit, cost
•Nature of the test method
-Critical/minor, destructive, cost, time
•Nature of the population
-uniformity, sublot

12. 12
Developing a Sampling Plan
•Number of samples selected
-Variation in properties, cost, type of analytical techniques
•Sample location
-random sampling vs systematic sampling vs judgment sampling
•Manner in which the samples are collected
-manual vs mechanical device

13. 13
The Bottom Line in Sampling
•Depending upon the nature of the material
to be analyzed, you must determine a
method of taking small subsamples from a
large lot ( 5,000 lb blender, 20 combos on a
truck etc) that accurately reflect the overall
composition of the whole lot.
•An inaccurate sample of a large lot may
actually be worse than no sample at all.

14. 14
Preparation of Laboratory
Samples
•You may have taken as much as 10 lbs of sub-
samples from a lot that now needs to be further
reduced in size;
-Make the sample homogeneous by mixing and grinding
and then more sub-sampling.
-Be aware of any changes that might occur between sampling and
analysis and take proper action ( e.g. enzymatic action, microbial
growth etc).
-Properly label the final sample with name, date/time, location, person
and other pertinent data.

15. 15
FOOD COMPONENTS
•Food consists primarily of water( moisture),
fat (or oil), carbohydrate, protein and ash
(minerals).
•Since food consists of these 5 components,
it is important that we understand how these
components are measured.

16. 16
COMPOSITION OF FOODS
COMPONENT
Milk
Beef
Chicken
Fish
Cheese
Cereal grains

Potatoes
Carrots
Lettuce
Apple
Melon
% Water %Carbohydrates %Protein % Fat % Min/Vit
87.3 5.0 3.5 3.5 0.7
60.0 0 17..5 22.0 0.9
66.0 0 20.2 12.6 1.0
81.8 0 16.4 0.5 1..3
37.0 2.0 25.0 31.0 5.0
10-14 58-72 8-13 2-5 0.5-3.0
78.0 18.9 2.0 0.1 1.0
88.6 9.1 1.1 0.2 1.0
94.8 2.8 1.3 0.2 0.9
84.0 15.0 0.3 0.4 0.3
92.8 6.0 0.6 0.2 0.4

17. 17
pH DETERMINATION

18. 18
pH Determination
•pH refers to the relative amounts of acid and base
in a product.
•It is scientifically defined as the negative log of
the hydrogen ion concentration.
•pH ranges from 0 to 14 with pH of 7 being
neutral. pH values below 7 are considered acids
and pH values above 7 are basic or alkaline.
•pH is generally determined with a pH meter
although litmus paper can also be used.

19. 19
MOISTURE
DETERMINATION

20. 20
Moisture Determination
•Moisture or water is by far the most
common component in foods ranging in
content from 60 – 95%.
•The two most common moisture
considerations in foods is that of total
moisture content and water activity.

21. 21
Moisture Content
•The total moisture content of foods is
generally determined by some form of
drying method whereby all the moisture is
removed by heat and moisture is
determined as the weight lost.
•% water = wet weight of sample-dry weight of sample
wet weight of sample

22. 22
Methods of Moisture Loss
Measurement
•Convection or forced draft ovens (AOAC)
- Very simple; Most common
•Vacuum Oven
-Sample is placed in oven under reduced pressure thereby
reducing the boiling point of water.
•Microwave Oven
-Uses microwave as a heat source; Very fast method
•Infrared Drying
-Uses infrared lamp as a heat source; Very fast

23. 23
Water Activity (a
w
)
•Water Activity (Aw) is the amount of free
water in a sample that is not bond and
therefore free for microbial growth, enzyme
and vitamin decomposition and can reduce
color, taste and flavor stability.
•Two general types of sensors:
–Capacitance sensor: electrical signal
–Chilled-mirror dew point method (AquaLab):
dew point temperature change due to ERH
change.

24. 24
WATER ACTIVITY
•Aw Microorganism
1.0-0.95 Bacteria
0.95-0.91 Bacteria
0.91-0.87 Yeasts
0.87-0.80 Molds
0.30-0.20 No microorganism
proliferation
•Foods
Meat, fish, sausage, milk
Cheese, cured meat (ham), fruit juice
conc
Fermented sausages (salami), dry
cheeses, margarine
Juice conc, syrups, flour, fruit cakes,
honey, jellies, preserves
Cookies, crackers, bread crusts

25. 25
PROTEIN ANALYSIS

26. 26
PROTEINS
•Proteins are made up of amino acids.
•Amino acids are the building blocks of protein.
•Nitrogen the most distinguishing element versus
other food components (carbohydrates, fats etc)
•Nitrogen ranges in proteins : 13.4 - 19.1%
•Non-protein nitrogen: free amino acids, nucleic
acids, amino sugars, some vitamins, etc.
•Total organic nitrogen = protein + non-protein
nitrogen

27. 27
Types of Protein Analysis
•Kjeldahl – measures the amount of nitrogen
in a sample.
•Lowry- measures the tyrosine/tryptophan
residues of proteins.

28. 28
Total organic nitrogen - Kjeldahl
method
•Crude protein content
•Johan Kjeldahl (1883) developed the basic
process
•Principle: total organic N released from
sample and absorbed by acid
–Digestion: sulfuric acid + catalyst
–Neutralization and distillation; Sodium hydroxide
–Titration; Hydrochloric acid

29. 29
Total organic nitrogen - Kjeldahl
method
Digestion
Protein (NH
4
)
2
SO
4

(ammonium sulfate)
Protein N  NH
4
+
+ H
2
SO
4
 (NH
4
)
2
SO
4
Sulfuric acid
Heat, catalyst

30. 30
Total organic nitrogen - Kjeldahl
method
Neutralization and distillation
(NH
4
)
2
SO
4
+ 2NaOH  2NH
3
+ Na
2
SO
4
+ 2H
2
O
NH
3
+ H
3
BO
3
 NH
4
+
: H
2
BO
3
-
+ H
3
BO
3
(boric acid) (ammonium-borate complex)
excess
Color change

31. 31
Total organic nitrogen - Kjeldahl
method
–Titration (direct titration)
H
2BO
3
-
+ H
+
 H
3BO
3
–Calculation
moles HCl = moles NH
3 = moles N in the sample
%N = N*(HCl)  
%N = N*(HCl) 
N*=Normality of HCl
(HCl)
(mL acid sample-mL acid blank) 14g N
g sample mole1000 
100
(mL acid sample-mL acid blank)
g sample
 1.4

32. 32
Total organic nitrogen - Kjeldahl
method
•Calculation
%Protein = %N  conversion factor
Conversion factor: generally 6.25
–most protein: 16% N
Conversion factor
egg or meat 6.25
milk 6.38
wheat 5.33
soybean 5.52
rice 5.17

33. 33
Kjeldahl Apparatus

34. 34
Total organic nitrogen - Kjeldahl
method
•Advantages:
–applicable to any foods
–simple, inexpensive
–accurate, official method for crude protein content
•Disadvantages:
–measuring total N not just protein N
–time consuming
–corrosive reagents

35. 35
Lowry Method
•Principle: Color formation between tyrosine and
tryptophan residues in protein and Biuret reagent
and Folin-Ciocalteau phenol reagent (750 nm or
500 nm).
•Procedure
protein solution + biuret reagent
room temp10 min
+ Folin reagent
50C 10 min
650 nm
(20-100 g)

36. 36
Lowry Method
•Advantages
–most sensitive (20-200g)
–more specific, relatively rapid
•Disadvantages
–color development not proportional to protein
concentration
–color varying with different proteins
–interference (sugars, lipids, phosphate buffers, etc)

37. 37
Infrared Spectroscopy
•Principle: absorption of radiation of peptide bond at
mid-infrared (MIR) and near-infrared (NIR) bands
•Advantages
–NIR applicable to a wide range of foods
–rapid, nondestructive
–little sample preparation
•Disadvantages
–expensive instruments
–calibration for different samples

38. 38
Crude Fat Analysis

39. 39
Fats
•Fats refers to lipids, fats and oils.
•The most distinguishing feature of fats
versus other components ( carbohydrates,
protein etc) is their solubilty. Fats are
soluble in organic solvents but insoluble in
water.

40. 40
Solvent Extraction Methods
•Sample preparation: Best under nitrogen &
low temperature
–Particle size reduction increases extraction
efficiency
–Predrying sample to remove water is common.

41. 41
Solvent Extraction Methods
•Solvent selection
–Ideal solvent
•high solvent power for lipids
•low solvent for other components
•easy to evaporate
•low boiling point
•nonflammable
•nontoxic
•good penetration into sample
•single component
•inexpensive
•non-hygroscopic

42. 42
Solvent Extraction Methods
•Common Solvents
–Ethyl ether - best solvent for fat extraction,
more expensive, explosion, fire hazard,
hygroscopic
–Petroleum ether - cheaper, more hydrophobic,
less hygroscopic
–Hexane - soybean oil extraction

43. 43
Types of Fat Analysis
•Extraction Methods
Continuous – Goldfinch
Semi-Continuous- Soxhlet
Discontinuous- Mojonnier
•Instrumental Methods
Dielectric
Infrared
Ultrasound

44. 44
Solvent Extraction Methods
•Continuous extraction: Goldfish method
–Principle: Solvent continuously flowing over
the sample with no build-up
–Advantages: fast, efficient.
–Disadvantages: channeling – not complete
extraction.

45. 45
Solvent Extraction Methods
•Semicontinuous extraction:
Soxhlet method
–Principle: Solvent building up in
extraction chamber for 5-10 min
before siphoning back to boiling
flask.
–Advantages: no channeling
–Disadvantages: time consuming

46. 46
Solvent Extraction Methods
•Discontinuous extraction: Mojonnier
method (wet method extraction)
–Principle: a mixture of ethyl ether and
petroleum ether in a Mojonnier flask
–Advantages: no prior removal of moisture
–Disadvantages: constant attention

47. 47
Instrumental Methods
•Dielectric method
–Principle: low electric current from fat
•Infrared method
–Principle: Fat absorbs infrared energy at a
wavelength of 5.73 m
•Ultrasound method
–Principle: sound velocity increases with
increasing fat content

48. 48
CARBOHYDRATE ANALYSIS

49. 49
Introduction
•Next to water, carbohydrates are the most
abundant food component
•%carbohydrate=100% - (H
2
O + ash + fat + protein)
•Types of carbohydrates include;
–monosaccharide: glucose, fructose, galactose
–disaccharide: sucrose, lactose, maltose
–oligosaccharids: raffinose
–polysaccharide: starch, cellulose

50. 50
Ash and Mineral Analysis

51. 51
Definitions
•Ash: total mineral content; inorganic residue
remaining after ignition or complete oxidation of
organic matter
•Minerals:
–Macro minerals (>100 mg/day)
• Ca, P, Na ,K, Mg, Cl, S
–Trace minerals (mg/day)
•Fe, I, Zn, Cu, Cr, Mn, Mo, F, Se, Si
–Ultra trace minerals
•Va, Tn, Ni, Sn, B
–Toxic mineral
•lead, mercury, cadmium, aluminum

52. 52
Ash Contents in Foods
Wheat flour, whole grain1.6%
Macaroni, dry, enriched0.7%
Milk, whole, fluid0.7%
Butter, with salt2.1%
Apple, raw with skin0.3%
Banana, raw0.8%
Egg, whole, raw0.9%
Hamburger, regular, plain1.7%

53. 53
Methods for Determining Ash
–Dry ashing
•high temperature
–Wet ashing
•oxidizing agent and/or acid
–Low-temperature plasma ashing
•dry ashing in partial vacuum at low temperature

54. 54
Dry Ashing
•Principles
–High temperature (>525C) overnight (12-18 hr)
–total mineral content
•Instrumentation
–Muffle furnace
–Crucible
•quartz
•porcelain
•steel
•nickel
•platinum

55. 55
General Procedure for Dry
Ashing
1. 5-10g pretreated sample into a crucible
2. Ignite crucible to constant weight at ~550C
for 12-18 hr
3. Cool in desiccator
4. Weigh cooled crucible
% ash (db) =  100
wt after ashing - crucible wt
Sample wt  solid%/100

56. 56
Dry Ashing
•Advantages
–safe and easy
–no chemical
–many samples handled at one time
–resultant ash for further mineral analysis
•Disadvantages
–loss of volatiles
–interaction
–long time and expensive equipment

57. 57
Ion-Selective Electrodes
•Direct measurement via chemical potential
of cations (Ca, Na, K), anions (Br, Cl, F), or
even dissolved gases (O
2, CO
2)
•Components:
–sensing electrode
–reference electrode
–readout device
•Types: glass membrane, polymer-body,
solid-state

58. 58
Ion-Selective Electrodes
•Activity (A) vs. Concentration (C)
A=C =activity coefficient
A: chemical activity
C: a measure of ions in solution
 is a function of ionic strength; ionic strength is
a function of concentration and charge on all
ions
A  C

59. 59
Ion-Selective Electrodes
•Advantages
–more precise, rapid,
practical
–direct measurement of a
wide range of ions
–inexpensive and simple
•Disadvantages
–inability to measure
below 2-3 ppm
–unreliable at low
concentration (10
-4
M)
•Applications:
–processed meats: salt,
nitrate
–butter and cheese: salt
–milk: Ca
–low-sodium products:
sodium
–soft drink: CO
2
–wine: Na, K
–can vegetable: nitrate

60. 60
Physical Properties of Foods

61. 61
PHYSICAL PROPERTIES
•While chemical properties measures the
chemical components of food such as water,
protein, fat, carbohydrates, the physical
properties determine how the chemical
properties and processing ultimately effect
the color and texture of foods.

62. 62
Physical Properties
•Physical properties include;
Color
Texture
Viscosity (liquids)
Texture analysis machines
Sensory panels
Trained
Consumer

63. 63
COLOR
•Color can be described in terms of hue, value and chroma;
Hue is the aspect of color which we
describe by words like green, blue,
yellow and red
Value or lightness describes the relationship between
reflected and absorbed light, without regard to specific
wavelength.
Chroma describes reflection at a given wavelength and
shows how much a color differs from gray.

64. 64
HUNTER L,a,b
•The Hunter L,a,b
system describes the
color of a food in
terms of L
(100=white; 0= black),
a (green- red) and b
(blue to yellow).

65. 65
COLOR
•More subjective color determination
systems include;
- Paint color match pages
-The Pantone Matching System.
- Actual photos of finished food products

66. 66
TEXTURE
•The methods of measuring the texture of
foods can be roughing divided into those
used for liquids (viscosity) versus those
used for more solid foods.

67. 67
Fluid Viscosity
•Viscosity: a key property of liquids and a measure of the
resistance to flow.
•More energy required to make a viscous fluid flow than a
non-viscous fluid.
•The viscosity of a solution increases non-linearly with
polymer concentration.
•The properties of the solution are conventionally split into
three regions:

68. 68
•Dilute Regime
•The polymers act as isolated "particles" too dilute
to interact with each other. They can be
approximated as spheres of radius r
g (the Stokes
radius - the smallest sphere that can contain the
polymer).
•Semi-Dilute Regime
•The "particles" start to interact significantly
because their total excluded volume approaches
close packing. Further increase in concentration
leads to much greater overlap of polymer coils and
rapid increase in viscosity.
•Concentrated Regime
•The individual polymer molecules overlap in a
tangled mass. The viscosity of concentrated
polymer solutions is very high and as the
concentration increases further starts to show
some solid-like behavior.

69. 69
Brookfield (Rotational) Viscometer
•Viscosity measurement by sensing the torque
required to rotate a spindle at constant speed while
immersed in the sample fluid.

70. 70
Brabender Viscoamylograph and Rapid
Visco Analyzer
l
l
l
l
l
l
l
l
^
^
Scale - linked to
printer
Torsion
device
Spindle
Brabender Cup
(rotates)
Heat-at 1.5
o
C per Minute

71. 71
Brabender Profile

72. 72
Brabender and RVA
Applications
•Starch, flours, baking products, noodle
quality, extrusion, sprouting and enzyme
activity, malting and brewing, storage,
Effect of amount of water added
during extrusion on RVA pasting
curves of corn based extrudates.
Lower water addition causes a
higher degree of cook in the
extrudate and this is reflected in
a progressive change in the RVA
pasting curve.

73. 73
Bostwick Consistometer
•A simple, dependable instrument which determines
sample consistency by measuring the distance which a
sample of material flows under its own weight
•The unit is constructed of stainless steel and is equipped
with two leveling screws and a level. The gate is
spring operated and held by a positive
release mechanism, permitting instantaneous flow
of sample. The trough is graduated in 0.5cm
divisions.
•Used extensively in the food industry for jams,
jellies, tomato paste, ketchup, condensed soup and
other highly viscous products.

74. 74
Bostwick Consistometer
30 sec reading

75. 75
Instron Universal Testing Machine
•A highly accurate and versatile material testing
instrument for the precise measurement of the
properties and behavior of materials in tension,
compression, flexure and torsion.
•The instrument weighing system employs strain
gauge load cells for measuring the load applied to
the specimen under test.
•The output from the load cell is applied to a solid
state load cell signal conditioning amplifier which
provides a wide range of full scale load ranges for
each type of load cell used. The controls provide
for adjustment and calibration of the load
weighing system to obtain accurate and reliable
test data. The load cell amplifier output is in a
signal form suitable for controlling the pen servo
system of the chart recorder.

76. 76
Texture Analyzer

77. 77
Sensory Properties
•Trained Sensory Panels – a few well trained
people that characterize flavor, texture and odor
versus like/dislike,
•Consumer Panels- usually consist of 200 plus
people who determine like/dislike, desirability etc.
•Additional detailed information on sensory panels
can be found in the module “Sensory Evaluation
of Foods; 1213”

78. 78
SUMMARY
•This module has presented the topic of
Food Analysis by discussing why we
analyze food, sampling and preparation, the
components of food generally analyzed for
(water, protein, fat, carbohydrates) and
some general methods of analyzing the
physical properties of food (color, viscosity
and texture).