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

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

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. 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. 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. 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. 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. SAMPLING AND SAMPLE PREPARATION

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

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. 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. 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. 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. 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. 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. COMPOSITION OF FOODS COMPONENT Milk Beef 60.0 0 17..5 22.0 0.9 Chicken
Fish
Cheese
Cereal grains
Potatoes
Carrots
Lettuce
Apple
Melon
% Water %Carbohydrates %Protein % Fat % Min/Vit

17. pH DETERMINATION

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. MOISTURE DETERMINATION

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. 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. 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. Water Activity (aw)
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. WATER ACTIVITY Foods Aw Microorganism Meat, fish, sausage, milk
Bacteria
Bacteria
Yeasts
Molds
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
Read the slide

25. PROTEIN ANALYSIS

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 : %
Non-protein nitrogen: free amino acids, nucleic acids, amino sugars, some vitamins, etc.
Total organic nitrogen = protein + non-protein nitrogen

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

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. Total organic nitrogen - Kjeldahl method
Digestion
Protein (NH4)2SO4
(ammonium sulfate)
Protein N  NH4+ + H2SO4  (NH4)2SO4
Sulfuric acid
Heat, catalyst

30. Total organic nitrogen - Kjeldahl method
Neutralization and distillation
(NH4)2SO4 + 2NaOH  2NH3 + Na2SO4 + 2H2O
NH3 + H3BO3  NH4+ : H2BO3- + H3BO3
(boric acid) (ammonium-borate complex)
excess
Color change

31. Total organic nitrogen - Kjeldahl method
Titration (direct titration)
H2BO3- + H+  H3BO3
Calculation
moles HCl = moles NH3 = moles N in the sample
%N = N*(HCl)  
%N = N*(HCl) 
N*=Normality of HCl
(HCl)
(mL acid sample-mL acid blank) g N
g sample mole
100
1000 
(mL acid sample-mL acid blank)
 1.4
g sample

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
milk
wheat
soybean
rice

33. Kjeldahl Apparatus

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. 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
( g)

36. Lowry Method Advantages Disadvantages 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. 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. Crude Fat Analysis

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

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

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. 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. 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. Instrumental Methods Dielectric method Infrared 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. CARBOHYDRATE ANALYSIS

49. Introduction
Next to water, carbohydrates are the most abundant food component
%carbohydrate=100% - (H2O + ash + fat + protein)
Types of carbohydrates include;
monosaccharide: glucose, fructose, galactose
disaccharide: sucrose, lactose, maltose
oligosaccharids: raffinose
polysaccharide: starch, cellulose

50. Ash and Mineral Analysis

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. Ash Contents in Foods Wheat flour, whole grain 1.6%
Macaroni, dry, enriched 0.7%
Milk, whole, fluid %
Butter, with salt %
Apple, raw with skin 0.3%
Banana, raw %
Egg, whole, raw %
Hamburger, regular, plain 1.7%

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

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

56. Dry Ashing Advantages Disadvantages 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. Ion-Selective Electrodes
Direct measurement via chemical potential of cations (Ca, Na, K), anions (Br, Cl, F), or even dissolved gases (O2, CO2)
Components:
sensing electrode
reference electrode
readout device
Types: glass membrane, polymer-body, solid-state

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. 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 (10-4M)
Applications:
processed meats: salt, nitrate
butter and cheese: salt
milk: Ca
low-sodium products: sodium
soft drink: CO2
wine: Na, K
can vegetable: nitrate

60. Physical Properties of Foods

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

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

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. 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. Dilute Regime
The polymers act as isolated "particles" too dilute to interact with each other. They can be approximated as spheres of radius rg (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. Brookfield (Rotational) Viscometer
Viscosity measurement by sensing the torque required to rotate a spindle at constant speed while immersed in the sample fluid.

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

71. Brabender Profile

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. 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 cm divisions.
Used extensively in the food industry for jams, jellies, tomato paste, ketchup, condensed soup and other highly viscous products.

74. Bostwick Consistometer
30 sec reading

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. Texture Analyzer

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. 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).