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INTRODUCTION TO FOOD ANALYSIS 1126. Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas. INTRODUCTION. This module is a very brief overview of common methods of food analysis used in food processing organizations. WHY ANALYZE FOOD?.

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introduction to food analysis 1126


Steven C Seideman

Extension Food Processing Specialist

Cooperative Extension Service

University of Arkansas

  • This module is a very brief overview of common methods of food analysis used in food processing organizations.
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.
what properties are typically analyzed
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.
references on analytical techniques
References on Analytical Techniques
  • Official Methods;

- Association of the Official Analytical Chemists (AOAC)

- American Oil Chemists Society (AOCS)

- American Association of Cereal Chemists (AACC)

criteria for selecting an analytical technique
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.
criteria for selecting an analytical technique1









Destructive/ Non-destructive


Official Approval

Criteria for Selecting an Analytical Technique
what is the purpose of the analysis
What is the Purpose of the Analysis
  • Official Samples
  • Raw Materials
  • Process Control Samples
  • Finished Products
sampling plan
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

factors affecting a sampling plan
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

developing a sampling plan
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

the bottom line in sampling
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.
preparation of laboratory samples
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.

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.
composition of foods






Cereal grains






% 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

ph determination1
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.
moisture determination1
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.
moisture content
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

methods of moisture loss measurement
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

water activity a w
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.
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



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

  • 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
types of protein analysis
Types of Protein Analysis
  • Kjeldahl – measures the amount of nitrogen in a sample.
  • Lowry- measures the tyrosine/tryptophan residues of proteins.
total organic nitrogen kjeldahl method
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
total organic nitrogen kjeldahl method1

Sulfuric acid

Heat, catalyst

Total organic nitrogen - Kjeldahl method


Protein (NH4)2SO4

(ammonium sulfate)

Protein N  NH4+ + H2SO4  (NH4)2SO4

total organic nitrogen kjeldahl method2
Total organic nitrogen - Kjeldahl method

Neutralization and distillation

(NH4)2SO4 + 2NaOH  2NH3 + Na2SO4 + 2H2O

NH3 + H3BO3 NH4+ : H2BO3- + H3BO3

(boric acid) (ammonium-borate complex)


Color change

total organic nitrogen kjeldahl method3

(mL acid sample-mL acid blank) 14g N

g sample mole

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



1000 

(mL acid sample-mL acid blank)

 1.4

g sample

total organic nitrogen kjeldahl method4
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

total organic nitrogen kjeldahl method5
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
lowry method
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)

lowry method1
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)
infrared spectroscopy
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
  • 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.
solvent extraction methods
Solvent Extraction Methods
  • Sample preparation: Best under nitrogen & low temperature
    • Particle size reduction increases extraction efficiency
    • Predrying sample to remove water is common.
solvent extraction methods1
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
solvent extraction methods2
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
types of fat analysis
Types of Fat Analysis
  • Extraction Methods

Continuous – Goldfinch

Semi-Continuous- Soxhlet

Discontinuous- Mojonnier

  • Instrumental Methods




solvent extraction methods3
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.
solvent extraction methods4
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
solvent extraction methods5
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
instrumental methods
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
  • 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
  • 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
ash contents in foods
Ash Contents in Foods

Wheat flour, whole grain 1.6%

Macaroni, dry, enriched 0.7%

Milk, whole, fluid 0.7%

Butter, with salt 2.1%

Apple, raw with skin 0.3%

Banana, raw 0.8%

Egg, whole, raw 0.9%

Hamburger, regular, plain 1.7%

methods for determining ash
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
dry ashing
Dry Ashing
  • Principles
    • High temperature (>525C) overnight (12-18 hr)
    • total mineral content
  • Instrumentation
    • Muffle furnace
    • Crucible
      • quartz
      • porcelain
      • steel
      • nickel
      • platinum
general procedure for dry ashing
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

dry ashing1
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
ion selective electrodes
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
ion selective electrodes1
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

ion selective electrodes2

more precise, rapid, practical

direct measurement of a wide range of ions

inexpensive and simple


inability to measure below 2-3 ppm

unreliable at low concentration (10-4M)


processed meats: salt, nitrate

butter and cheese: salt

milk: Ca

low-sodium products: sodium

soft drink: CO2

wine: Na, K

can vegetable: nitrate

Ion-Selective Electrodes
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.
physical properties1
Physical Properties
  • Physical properties include;



Viscosity (liquids)

Texture analysis machines

Sensory panels



  • 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


Chroma describes reflection at a given wavelength and

shows how much a color differs from gray.

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).
  • More subjective color determination systems include;

- Paint color match pages

-The Pantone Matching System.

- Actual photos of finished food products

  • 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.
fluid viscosity
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:
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.
brookfield rotational viscometer
Brookfield (Rotational) Viscometer
  • Viscosity measurement by sensing the torque required to rotate a spindle at constant speed while immersed in the sample fluid.
brabender viscoamylograph and rapid visco analyzer

Scale - linked to printer

Torsion device



Brabender Cup




Heat-at 1.5oC per Minute

Brabender Viscoamylograph and Rapid Visco Analyzer
brabender and rva applications
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.

bostwick consistometer
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.
instron universal testing machine
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.
sensory properties
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”
  • 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).