Introduction to Food Analysis II[1]

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INTRODUCTION TO FOOD ANALYSIS 1126Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas1

INTRODUCTION 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.3

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 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 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.6

Criteria for Selecting an Analytical Technique Precision Accuracy Reproducibility Simplicity Cost Speed Sensitivity Specificity Safety Destructive/ Nondestructive On-line/off-line Official Approval




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


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 samples10

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, sublot11

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 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.13

Preparation of Laboratory Samples You may have taken as much as 10 lbs of subsamples 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.14

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 FOODSCOMPONENTMilk Beef Chicken Fish Cheese Cereal grains Potatoes Carrots Lettuce Apple Melon

% Water87.3 60.0 66.0 81.8 37.0 10-14 78.0 88.6 94.8 84.0 92.8

%Carbohydrates %Protein % Fat % Min/Vit5.0 0 0 0 2.0 58-72 18.9 9.1 2.8 15.0 6.0 3.5 17..5 20.2 16.4 25.0 8-13 2.0 1.1 1.3 0.3 0.6 3.5 22.0 12.6 0.5 31.0 2-5 0.1 0.2 0.2 0.4 0.2 0.7 0.9 1.0 1..3 5.0 0.5-3.0 1.0 1.0 0.9 0.3 0.4




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.18



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 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 sample21

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 (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.23

WATER ACTIVITY Aw 1.0-0.95 0.95-0.91 Microorganism Bacteria Bacteria

Foods Meat, fish, sausage, milkCheese, cured meat (ham), fruit juice conc Fermented sausages (salami), dry cheeses, margarine





Juice conc, syrups, flour, fruit cakes, honey, jellies, preserves


No microorganism proliferation

Cookies, crackers, bread crusts




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 nitrogen26

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


Crude protein content Johan Kjeldahl (1883) developed the basic process Principle: total organic N released from sample and absorbed by acid

Total organic nitrogen - Kjeldahl method

Digestion: sulfuric acid + catalyst Neutralization and distillation; Sodium hydroxide Titration; Hydrochloric acid28

Total organic nitrogen - Kjeldahl methodDigestionSulfuric acid

Protein Heat, catalyst

(NH4)2SO4(ammonium sulfate)

Protein N NH4+ + H2SO4 (NH4)2SO4


Total organic nitrogen - Kjeldahl methodNeutralization and distillation(NH4)2SO4 + 2NaOH 2NH3 + Na2SO4 + 2H2ONH3 + H3BO3 NH4+ : H2BO3 + H3BO3-

(boric acid)

(ammonium-borate complex) excess

Color change30

Total organic nitrogen - Kjeldahl method Titration (direct titration) H2BO3 + H+ H3BO3(HCl)

Calculationmoles HCl = moles NH3 = moles N in the sampleblank) 14g N %N = N*(HCl) (mL acid sample-mL acid 1000 g sample %N = N*(HCl) (mL acid sample-mL acid blank)N*=Normality of HCl



g sample


Total organic nitrogen - Kjeldahl method Calculation%Protein = %N conversion factor Conversion factor: generally 6.25 most protein: 16% N Conversion factor 6.25 6.38 5.33 5.52 5.17

egg or meat milk wheat soybean rice


Kjeldahl Apparatus



Total organic nitrogen - Kjeldahl method applicable to any foods simple, inexpensive accurate, official method for crude protein content

Disadvantages: measuring total N not just protein N time consuming corrosive reagents34

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). Procedureprotein solution + biuret reagent(20-100 g) room temp10 min

+ Folin reagent50C 10 min

650 nm35

Lowry Method Advantages most sensitive (20-200g) 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 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 samples37

Crude Fat Analysis


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