INTRODUCTION%20TO%20FOOD%20ANALYSIS%201126

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INTRODUCTION TO FOOD ANALYSIS1126

• 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.

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Criteria for Selecting an Analytical Technique

• Precision
• Accuracy
• Reproducibility
• Simplicity
• Cost
• Speed

• Sensitivity
• Specificity
• Safety
• Destructive/ Non-destructive
• On-line/off-line
• Official Approval

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SAMPLING AND SAMPLE PREPARATION
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What is the Purpose of the Analysis

• Official Samples
• Raw Materials
• Process Control Samples
• Finished Products

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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

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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

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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

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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.

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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.

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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.

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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

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pH DETERMINATION
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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.

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MOISTURE DETERMINATION
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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.

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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

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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.

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WATER ACTIVITY

• 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

• 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

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PROTEIN ANALYSIS
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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

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Types of Protein Analysis

• Kjeldahl measures the amount of nitrogen in a
  sample.
• Lowry- measures the tyrosine/tryptophan residues
  of proteins.

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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

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Total organic nitrogen - Kjeldahl method

• Digestion
• Protein (NH4)2SO4
• 
  (ammonium sulfate)
• Protein N ? NH4 H2SO4 ? (NH4)2SO4

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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
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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) ?
• NNormality of HCl

(HCl)
100
1000 ?
(mL acid sample-mL acid blank)
? 1.4
g sample
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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

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Kjeldahl Apparatus
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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

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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)
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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)

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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

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Crude Fat Analysis
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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.

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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

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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

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Types of Fat Analysis

• Extraction Methods
• Continuous Goldfinch
• Semi-Continuous- Soxhlet
• Discontinuous- Mojonnier
• Instrumental Methods
• Dielectric
• Infrared
• Ultrasound

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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.

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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
• 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

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CARBOHYDRATE ANALYSIS
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Introduction

• Next to water, carbohydrates are the most
  abundant food component
• carbohydrate100 - (H2O ash fat protein)
• Types of carbohydrates include
• monosaccharide glucose, fructose, galactose
• disaccharide sucrose, lactose, maltose
• oligosaccharids raffinose
• polysaccharide starch, cellulose

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Ash and Mineral Analysis
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Definitions

• Ash total mineral content inorganic residue
  remaining after ignition or complete oxidation of
  organic matter
• Minerals
• Macro minerals (gt100 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

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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

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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

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Dry Ashing

• Principles
• High temperature (gt525?C) overnight (12-18 hr)
• total mineral content
• Instrumentation
• Muffle furnace
• Crucible
• quartz
• porcelain
• steel
• nickel
• platinum

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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
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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
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

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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

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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

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Physical Properties of Foods
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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.

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Physical Properties

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

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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.

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HUNTER L,a,b

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

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COLOR

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

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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.

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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

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• 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.

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Brookfield (Rotational) Viscometer

• Viscosity measurement by sensing the torque
  required to rotate a spindle at constant speed
  while immersed in the sample fluid.

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Brabender Viscoamylograph and Rapid Visco Analyzer
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Brabender Profile
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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.
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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.

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Bostwick Consistometer
30 sec reading
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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.

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Texture Analyzer
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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

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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).