Food Chemistry1

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FOOD CHEMISTRY

OTHER FOOD ANALYSIS METHODS

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yOVERVIEW

The chemistry of methods for the total analysis of the following components are detailed:

Carbohydrates analysis

Fibre analysis

Lipid characterization

The material contained below is summary of various analysis methods. It is all examinable.

Further reading on these topics is found in Chapters 11, 12, and 14 of the textbook “Food Analysis” 2nd

Edition by S. Suzanne Nielsen (Editor). Material in this textbook is not examinable.

Food Chemistry3

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yLEARNING OBJECTIVES

AIMS

To give a strong understanding of how to analyse food components such as fibre and carbohydrates, andhow to characterize lipids in food.

OBJECTIVES

On completion of “Other Food Analysis Methods”, students will be able to demonstrate a soundknowledge of:

(1) The methods used to analyse food carbohydrates, including the use of standard methods such asAOAC and AOCS;

(2) The composition of dietary fibre and the methods used to determine the content of fibre in food,including the use of standard methods such as AOAC;

(3) Lipid characterization procedures used in food analysis to determine lipid quality.

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yCARBOHYDRATE ANALYSIS

LEARNING OBJECTIVES – CARBOHYDRATEANALYSIS

AIMS

To give an understanding of the chemistry involved in the analysis of carbohydrates in foods, including totalsoluble solids, individual sugars, and starch.

OBJECTIVES

On completion of “Carbohydrate Analysis”, students will be able to demonstrate a sound knowledge of:

(1) The chemical method used to determine the total carbohydrate content of food;

(2) The chemical methods used to determine individual sugars in food;

(3) The chemical methods used to determine starch in food.

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yCARBOHYDRATE ANALYSIS - SUMMARY

INTRODUCTION

Carbohydrates (including sugars and starch) are in all cases expressed as monosaccharides and the tables ofcarbohydrate content contain values of available carbohydrate - proximate analysis content. The availablecarbohydrate consists of the sum of the free sugars (glucose, fructose, sucrose, lactose, maltose and highermaltose homologues), dextrin, starch and glycogen expressed as monosaccharides. These are thecarbohydrates that are digested and absorbed by man, and which are glucogenic in man.

METHOD

For quantitative work, the sugars can be extracted from the homogenized foodstuffs either by treatment with80% v/v ethanol in a Soxhlet extraction apparatus for three hours or by boiling with 80% v/v ethanol for 20minutes. The free sugars in the extracts are examined by two reducing sugar methods or by HPLC to givethe glucose and fructose concentration. (We look at these in detail later in this module). Sucrose in theextract can be measured by inversion. The residue remaining after extraction of the free sugars is examinedfor starch and dextrin content.

Methods of Quantitative Determination:

1. Reducing SugarsSugars with a structure containing free aldehyde and ketone groups react as weak reducing agents and arecalled reducing sugars.

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yExamples:Reducing Sugars: all monosaccharides eg: glucose, fructose; the disaccharides maltose, lactose andcellobiose.

These properties are used to estimate sugars by the measurement of the reduction of Cu(II) to Cu(I).Fehling’s solution consists of alkaline cupric tartrate and is converted to insoluble cuprous oxide whenboiled with a solution of a reducing sugar.

This forms the basis of a number of procedures.Note: Fehling’s 1: copper(II) sulfate solution

Fehling’s 2: alkaline sodium potassium tartrate

These are kept separate in the dark and mixed just prior to use, to give an alkaline cupric tartrate solution, ie.Fehling’s solution.

2. Non-Reducing SugarsDisaccharides such as sucrose and raffinose, and higher oligosaccharides.

These sugars are non-reducing because they consist of simple sugars linked through their aldehydic orketonic groups. There is no hydroxyl group on an anomeric carbon.

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yFOOD ANALYSIS EXAMPLES

Food products containing a mixture of reducing sugars

The Cu2+ reducing power is referred to as ‘Dextrose Equivalent’ or ‘D.E.’ or ‘K value’.

eg: glucose syrups prepared by the hydrolysis of starch.

42% reducing sugars expressed as dextrose on the dry basis : DE 42

OTHER METHODS FOR THE QUANTITATIVE DETERMINATION OF

SUGARS IN FOOD:

These are based on the traditional polarimetry, refractometry, hydrometry and the more modern HPLC, GC,ion exchange and enzymatic methods.

Polarimetric Methods - optical rotation

Refractometric Methods - refractive index tables

Hydrometric Methods - specific gravity tables

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yIon exchange chromatography: an anion-exchange column as part of an autoanalyser is now used toseparate and analyse mixtures of sugars.

HPLC and Gas ChromatographyHPLC is a quick, sensitive and powerful tool for both the qualitative and quantitative analysis of sugars infood products.

Enzymic Methods

METHODS OF QUALITATIVE ANALYSIS

1. General Carbohydrate Test

Molisch Reaction:All carbohydrates, when treated with strong acids, yield furfural derivatives which combined with naphthol.Red-violet coloured products result.

2. Tests for Reducing Sugars

As mentioned earlier, carbohydrates containing a free aldehyde (-CHO) or ketone (-C=O) group act asreducing agents. Most are based on the reduction of Cu2+ (cupric ions) to Cu+ (cuprous ions) in alkalinesolution to give a red precipitate of cuprous oxide, Cu2O. A number of tests have evolved using differentsubstances for preventing the formation of black cupric oxide when CuSO4 is heated with alkali.

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y(a) Fehling’s Solution Test - (simplest qualitative test):

Solutions of cupric sulphate (Fehling’s 1) and alkaline sodium potassium tartrate (Fehling’s 2) aremixed together and then with the reducing sugar solution, and finally heated. A positive reactionshows the red precipitate of cuprous oxide or with more dilute solutions of reducing sugar, a green orred, or a red-yellow colour.

(b) Benedict’s Test:Same as above using Benedict’s reagent (CuSO4, sodium citrate and Na2CO3).

(c) Barfoed’s Test:In alkaline solution, all reducing sugars precipitate Cu2O; however, in a slightly acidic solution onlymonosaccharides do so. The cupric acetate reagent is used.

STARCH DETERMINATION

The residue remaining after the extraction of the food samples with ethanol (extraction of free sugars) isfurther examined for starch and dextrin content. Both are hydrolysed with the selective enzymeglucoamylase to glucose. After filtration of the digest, the liberated glucose is treated with glucose oxidaseand estimated colorimetrically at 37 °C in an autoanalyser.

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yCARBOHYDRATE ANALYSIS – FURTHER READING

INTRODUCTION

This study examines chemical and physical methods for analysing various types of carbohydrates in foods.

Further reading on this topic is found in Chapters 11 Carbohydrate Analysis of the supplied textbook “FoodAnalysis” 2nd Edition by S. Suzanne Nielsen (Editor). The material contained in the textbook will not beexamined; only that material listed above and below is examinable.

Chapter 11 is divided into a number of sections covering various aspects of the analysis of carbohydrates infood; however, there are five main themes:

Sample Preparation

Chemical Determination of Total Carbohydrates

Chemical Analysis of Individual Sugars in Food

Chemical Analysis of Starch in Food

Physical Methods for Analysing Soluble Solids in Foods

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ySection 11.1 on Page 169 of the textbook discusses the different types of carbohydrates, including a full listin Table 11-1 on Page 170 of the textbook. Additionally, the analysis of carbohydrates is introduced, andthe terms total carbohydrate and other carbohydrate discussed. Total carbohydrate is normally determinedby difference with the mass of moisture, total fat, ash, and crude protein subtracted from the mass of thefood. The total carbohydrate content of some foods is summarized in Table 11-2 on Page 171 of thetextbook. Other (complex) carbohydrate, including starch is determined by subtracting the sum of the massof dietary fibre, sugars and sugar alcohols from the total carbohydrate.

SAMPLE PREPARATION

Section 11.2 on Pages 169-171 of the textbook discusses sample preparation required prior to carbohydrateanalysis, particularly drying or removal of fat from the food.

CHEMICAL DETERMINATION OF TOTAL CARBOHYDRATES IN FOOD

Section 11.3.2 on Pages 172-173 of the textbook details the phenol-sulphuric acid method for determiningthe total carbohydrate content of food. The method involves adding an aqueous solution of phenol to anaqueous solution of the carbohydrate, followed by concentrated sulphuric acid (heat generated). A yellowcolour results which is then measure spectrophotometrically at 490 nm. Standard sugar solution are thenused for quantification. Polysaccharides are broken down to sugars by the acid and heat.

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yCHEMICAL ANALYSIS OF INDIVIDUAL SUGARS IN FOOD

Total Reducing Sugars

Section 11.3.3 on Pages 173-174 of the textbook details wet chemical methods for determining the reducingsugar content of foods. Methods discussed are:

Somogyi-Nelson method (Section 11.3.3.1)

Munson-Walker method (Section 11.3.3.2)

Lane-Eynon method (Section 11.3.3.2)

Standard AOAC methods for each of these methods are listed. These methods are based on the reduction ofcopper (II) ions in alkaline solution to copper (I) ions, which then precipitate as brick-red Cu2O. For theSomogyi-Nelson method, the Cu+ ions reduce an arsenomolybdate complex to produce an intense bluecolour that is measured spectrophotometrically. For the Munson-Walker method, the Cu2O can bedetermined:

(1) gravimetrically;(2) by titration with sodium thiosulphate;(3) by titration with potassium permanganate; and(4) electrolytically, using AOAC methods.

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yMunson - Walker Gravimetric MethodFehling’s solution is boiled with a solution of a reducing sugar for six minutes and then filtered hot. Theprecipitated cuprous oxide (Cu20) is filtered off and weighed. The sugar content is calculated from the mass

of cuprous oxide by referring to AOAC tables.

Lane-Eynon MethodThis method involves the determination of reducing sugars by titration with Fehling’s solution using theredox indicator, methylene blue. This is an empirical method and standardized experimental conditions andmethods must be rigidly adhered to for satisfactory results.

The classical method uses tables indicating the amounts of invert sugar (mixture of fructose and glucose),dextrose (glucose), fructose, maltose or lactose equivalent to volumes of reduced Fehling’s solution.

The now accepted and official method (AOAC Method 923.09, 920.183b; 1995) is a constant volumetechnique where the conditions for reduction are standardized by the addition of water to give a constantfinal volume of 75 ml in the titration flask, and the volume of Fehling’s solution used is calibrated against astandard reducing sugar solution. This standard solution must be specific for a particular reducing sugar.

The Lane and Eynon method involves the titration of a boiling solution of the Fehling’s solution with adilute solution of the sugar sample.

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yLuff-Schoorl MethodThis method uses an alkaline reagent containing cupric citrate (Cu2+ ion). After boiling this reagent with asolution containing reducing sugars, potassium iodide (KI) and acid (sulphuric acid) are added after cooling.Iodine is liberated from the redox reaction:

2I- + Cu2+ → I2 + Cu+

The liberated iodine is thus equivalent to the unreduced copper (Cu2+) ie:

1 mole I2 from 1 mole Cu2+

The liberated iodine (brown-black colour) is then titrated (to colourless) with the reducing agent, sodiumthiosulphate. Thiosulphate equivalent tables can then be used:

I2 → I-

coloured colourless

The Luff-Schoorl reagent is less alkaline than Fehling’s solution. Consequently, it is a weaker oxidizingagent requiring longer boiling with sample solutions than the Lane and Eynon technique.

[Reducing agents reduce another species but are oxidized in the process. Oxidizing agents oxidize anotherspecies but are reduced in the process.]

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yNonreducing Sugars

Sucrose DeterminationRemember, sucrose is a non-reducing sugar. Sucrose can be determined in the absence of reducing sugarsby inverting a portion of the test solution with acid followed by neutralization with alkali and titration by theLane and Eynon method, using standard invert sugar solution for calibration.

% sucrose = % invert sugar x 0.95

In the presence of reducing sugars, titrations are carried out on portions of the test solution before and afteracid inversion.

Analysis of Specific Mono-, Di- and OligosaccharidesSection 11.3.4 on Pages 174-178 of the textbook details HPLC, GC and enzymic methods for analysingindividual mono-, di- and oligosaccharides. For HPLC analysis, various stationary phases used to analysessugars are discussed in detail. For GC, sugars need to be converted to derivatives that are volatile and ableto be analysed by GC.

Extraction of Free SugarsFree sugars must be removed from the food matrix prior to HPLC analysis so that possible interferingcomponents of food are separated from free sugars. This is done by extraction of the dried, lipid-free foodwith 80% ethanol (AOAC method 922.02, 925.05; 1995). Purification of this extract prior to HPLCanalysis is often required. Methods to do this are outlined in Section 11.3.1 on Pages 171-172 of thetextbook. After purification of the sugar extract, the aqueous alcohol is removed under reduced pressureusing a rotary evaporator at temperatures of 45-50 °C. The dried sample is then dissolved in water andanalysed by HPLC.

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yCHEMICAL ANALYSIS OF STARCH IN FOOD

Section 11.4.1.1 on Pages 179-180 of the textbook discusses the determination of total starch content. Themost reliable method involves the total conversion of the starch to D-glucose by starch specific enzymessuch as α-amylase and glucoamylase, and measurement of the D-glucose released by spectrophotometric orHPLC methods. The method involving spectrophotometric analysis (AOAC Method 969.39; 1995) isdetailed on Page 180 of the textbook.

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yFIBRE ANALYSIS

LEARNING OBJECTIVES – FIBRE ANALYSIS

AIMS

To give an understanding of food fibre, particularly dietary fibre, and the methods used to analyse food fibre.

OBJECTIVES

On completion of “Fibre Analysis”, students will be able to demonstrate a sound knowledge of:

(1) The composition and importance of dietary fibre in food;

(2) Gravimetric methods for determining the fibre content of foods;

(3) Chemical methods for determining the fibre content of foods;

(4) The differences between the methods used to determine dietary fibre.

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yCONTENT – FIBRE ANALYSIS

INTRODUCTION

This study examines food fibre and methods used to analyse the different types of fibre, including crudefibre and dietary fibre. The special nature of food fibre analysis has resulted in it being consideredseparately to the carbohydrate analysis detailed later in this module.

Further reading on this topic is found in Chapters 12 Fibre Analysis of the supplied textbook “FoodAnalysis” 2nd Edition by S. Suzanne Nielsen (Editor). The material contained in the textbook will not beexamined; only the material summarised below is examinable.

Chapter 12 is divided into a number of sections covering various aspects of the determination of fibre infood; however, there are 5 main themes:

Importance of Dietary Fibre

Composition of Dietary Fibre

Gravimetric Methods of Fibre Analysis

Chemical Methods of Fibre Analysis

Comparison Dietary Fibre Analysis Methods

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yIMPORTANCE OF DIETARY FIBRE

Section 12.1.1 on Page 191 of the textbook reviews the role dietary fibre plays in human health, and is agood introduction to dietary fibre.

COMPOSITION OF DIETARY FIBRE

Section 12.1.2 on Page 191 of the textbook outlines the two definitions of dietary fibre depending onwhether resistant starches are included. Dietary fibre is composed of cell wall polysaccharides, non-cell-wall polysaccharides and lignin. Section 12.1.3 on Pages 191-192 of the textbook discusses the compositionof these food components, and should be thoroughly studied.

GRAVIMETRIC METHODS OF FIBRE ANALYSIS

Three gravimetric fibre analysis methods are discussed in Section 12.3.3 on Pages 193-194 of the textbook.Crude fibre analysis, and acid and neutral detergent fibre analysis methods are discussed and theirlimitations highlighted. The most important section to review is the discussion of the AOAC method fordetermining the total, insoluble and soluble dietary fibre in food (AOAC Method 991.43; 1995). This is thestandard method for determining the dietary fibre content of food. The experimental procedure is welloutlined making it easier to implement in the laboratory.

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yCHEMICAL METHODS OF FIBRE ANALYSIS

Section 12.3.4 on Pages 195-196 of the textbook outlines the alternative analysis procedure to thegravimetric methods. Chemical methods for fibre analysis involve determination of all nonstarchmonosaccharides and lignin. Monosaccharides are determined colorimetrically or using GC or HPLC. TheEnglyst-Cummings procedure is an alternative to the gravimetric AOAC method for dietary fibre highlightedabove, except lignin is not included in the analysis. The levels of lignin in food is often small and thus theEnglyst-Cummings procedure can be used to determine fibre content of such foods. Additionally, resistantstarch is not included in this fibre measurement, but a separate analysis is included to determine resistantstarch alone.

COMPARISON DIETARY FIBRE ANALYSIS METHODS

The merits of the AOAC method and the Englyst-Cummings procedure for dietary fibre determination arediscussed in Section 12.4 on Page 197 of the textbook. The points discussed are useful for making ajudgement about which methods to use particularly since the Englyst-Cummings procedure requires the leastamount of time, technical skill and specialized equipment relative to the AOAC and other methods.However, the Englyst-Cummings procedure requires access to GC and HPLC equipment, and knowledge ofsuch chromatographic procedures.

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yLIPID CHARACTERIZATION

LEARNING OBJECTIVES - LIPIDCHARACTERIZATION

AIMS

To give an understanding of the physical and chemical methods used to characterize food lipids.

OBJECTIVES

On completion of “Lipid Characterization”, students will be able to demonstrate a sound knowledge of:

(1) The standard methods used to characterize fats and oils;

(2) The methods used to characterize the quality of bulk fats and oils and extracted lipids;

(3) Selected methods used for measuring lipid oxidation in food;

(4) The methods used to analyse lipid fractions from food, focussing on fatty acid composition oftriglycerides, including the use of fatty acid methyl esters (FAME), and cholesterol composition.

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yCONTENT - LIPID CHARACTERIZATION

INTRODUCTION

This study examines the different analyses and tests used to characterize bulk fats and oils, lipid oxidation,and the composition of lipids in foods.

Further reading on this topic is found in Chapters 14 Fat Characterization of the supplied textbook “FoodAnalysis” 2nd Edition by S. Suzanne Nielsen (Editor). The material contained in the textbook will not beexamined; only the material summarise below is examinable.

Chapter 14 is divided into a number of sections covering various aspects of the characterization of fat infood; however, there are 4 main themes:

Introduction to Methods of Analysis

Characterization Methods for Bulk Fats and Oils

Methods for Analysing Lipid Oxidation

Methods for Analysing Lipid Fractions from Foods

Not all the material in Chapter 14 will be studied in this module. The relevant sections will be highlightedbelow.

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INTRODUCTION TO METHODS OF ANALYSIS

Sections 14.1 and 14.2 on Pages 219-221 of the textbook summarizes the classifications for lipids, whyanalyses of lipids are important, the standard methods of analyses for lipid characterization, and the lipidcontent of foods.

Table 14-1 on Page 220 of the textbook summarizes the standard methods to be discussed throughoutChapter 14 of the textbook as part of Module 7. The three organization with standard methods are:

American Oil Chemist’s Society (AOCS);

AOAC International (AOAC);

International Union of Pure and Applied Chemists (IUPAC).

All the fat characterization analysis methods are controlled by these organizations through their standardmethods of analysis.

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yCHARACTERIZATION METHODS FOR BULK FATS AND OILS

Before any analyses can be performed on bulk fats and oils, some form of sampling and sample preparationis required. Sampling procedures such as AOCS Method C 1-47 (AOCS 1996) are available. If drying ofthe sample is required then the AOAC Method 981.11 is used (AOAC 1995). Any sample storage will needto exclude, heat, light and air to prevent lipid oxidation.

A number of chemical and physical methods used to commonly characterize food lipids are summarized inthe textbook.

Refractive IndexRefractive index is used to control hydrogenation and as a purity measurement, and is summarized inSection 14.3.2 on Page 222 of the textbook.

Melting PointMany types of melting points (depending on the analysis method used) are possible, each with its ownapplication, often depending on the preference in different countries. The disadvantages and methods ofanalysis are outlined in Section 14.3.3 on Page 222 of the textbook.

Smoke, Flash and Fire PointsSection 14.3.4 on Page 222 of the textbook details definitions of each, and how they are measured in thelaboratory. These test give an indication of the volatile organic material in fats and oils.

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yCold TestThis test measure amount of crystallization at 0 °C, and is a measure of the resistance of the oil tocrystallization and, thus is a measure of the winterizing process. Further details are summarized in Section14.3.5 on Page 222 of the textbook.

Cloud PointThe temperature at which a cloud forms due to crystallization in a liquid fat is the cloud point. Section14.3.6 on Pages 222-223 of the textbook details the procedure.

ColourThe Lovibond (most commonly used method) and spectrophotometric methods for colour measurement aredetailed in Section 14.3.7 on Page 223 of the textbook, and are used by the food industry as qualitymeasurements for fats and oils.

Solid Fat Index and Solid Fat ContentTwo methods for determining the amount of solids in a fat are outlined in Section 14.3.11 on Page 225 of thetextbook. The proportion of solids to liquids in a fat impact on the functional properties of a food such asmouthfeel, and so is an important measure for a fat.

ConsistencyConsistency is a measure of plasticity, hardness, creaminess and spreadability, and is determined using thepenetrometer method. Section 14.3.12 on Page 225 of the textbook summarizes this quality measure.

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yPolar Components in Frying Fats and OilsThe deterioration of frying fats and oils is monitored by determining the polar components. Polar lipids areseparated from the nonpolar compounds using column chromatography, while the composition and qualityof the polar lipids are determined using thin later chromatography. Section 14.3.13 on Page 226 of thetextbook outlines the importance of polar compounds in frying fats and oils.

Iodine Value/NumberThe iodine value or number measures the degree of unsaturation (number of carbon-carbon double bonds) ina fat or oil. The procedure involves reacting iodine with carbon-carbon double bonds with a mechanismsimilar to that for the hydrogenation of oils. The procedure is detailed in Section 14.3.8 on Page 223 of thetextbook, together with applications. It is particularly important for characterizing oils and for monitoringthe hydrogenation process during the refining of oils. See summary of QC tests later in Unit 3.

Saponification Value/NumberSaponification is the hydrolysis of neutral fats or oils to glycerol and fatty acids. The procedure to determinethe saponification value, which is a measure of the amount of saponification, is detailed in Section 14.3.9 onPage 224 of the textbook. See summary of QC tests in Unit 3.

Free Fatty Acids and Acid ValueFat acidity is due to free fatty acids and is measured using an acid base titration. Free fatty acids arise fromlipolysis of triglycerides. Section 14.3.10 on Pages 224-225 of the textbook outlines the procedure forconsideration. This method is also used to analyse food lipids extracts as a means of determining the levelof lipolysis and hydrolytic rancidity of a foods with a high oil content. Free fatty acids are monitored in anyprocess that uses bulk oils for cooking and frying such as in the manufacture of potato chip and crisps. Seesummary of QC tests later in Unit 3.

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yMETHODS FOR ANALYSING LIPID OXIDATION

Lipolysis, hydrolytic rancidity, lipid oxidation and oxidative rancidity are briefly discussed. A review oflipid oxidation in Unit 5 is needed prior to studying the analysis methods. A number of measures of lipidoxidation are detailed in Section 14.4 of the textbook.

Peroxide ValueThis is one of the most common tests for lipid oxidation and is detailed in Section 14.4.2 on Page 227 of thetextbook. Determining the peroxide value involves a titration of the peroxide or hydroperoxide groups incompounds present in the lipid component of food, which are the initial products of lipid oxidation.Additionally, this method is used to analyses food lipid extracts as a means for determining the oxidativestability of foods that have a high oil content, such as nuts.

Hexanal DeterminationMeasurement of headspace hexanal using GC is now being used as a measure of lipid oxidation. Section14.4.4 on Pages 227-228 of the textbook summarizes the procedure. It is being used in meat analysis.Hexanal together with pentanal may be correlated with sensory analysis of lipid oxidation.

Thiobarbituric Acid (TBA) TestThis test measures malonaldehyde, the secondary product of lipid oxidation and has been shown to correlatebetter with the sensory analysis of lipid oxidation than does the peroxide value. TBA reacts withmalonaldehyde to produce coloured compounds that are then measured spectrophotometrically. Thisreaction is not specific to malonaldehyde, with other TBA reactive substances (TBARS) existing. Theprocedure is discussed in Section 14.4.5 on Page 228 of the textbook. This test is commonly used tomeasure lipid oxidation in meat products.

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yMETHODS FOR ANALYSING LIPID FRACTIONS FROM FOODS

Fatty Acid Composition and Fatty Acid Methyl EstersThe fatty acid profile is now a routine indicator used to represent the composition of lipids in foods. Thelipid is normally extracted from the food and saponified with alkali. The fatty acids released by this basehydrolysis are not volatile enough to be analysed by GC, so derivatization to their fatty acid methyl esters(FAME) is done prior to GC analysis. There are various methods for methylating the released fatty acids,with the standard method involving methanol and boron trifluoride summarized in Section 14.6.1 on Pages230-231 of the textbook, along with applications of the use of the method in food analysis.

Cholesterol AnalysisSection 14.6.4 on Pages 232-233 of the textbook summarizes the analysis of cholesterol in foods. TheAOAC Method 976.26 (AOAC 1995) is outlined and is similar to other methods used. Common to theseprocedures is an extraction of the lipid from the food, followed by saponification of the lipid. Thenonsaponifiable fraction is then derivatized, and the resultant trimethylsilyl (TMS) ethers are quantifiedusing capillary GC.

TLC Separation of Lipid FractionsThin layer chromatography is used to rapidly analyse the various lipid fractions in a food lipid extract. Theprocedure is outlined in Section 14.6.5 on Page 233 of the textbook.

Food Chemistry Lecture Notes