Food Chemistry
FOOD CHEMISTRY
OTHER FOOD ANALYSIS METHODS
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Food Chemistry
OVERVIEW
Food Chemistry
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.
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Food Chemistry
Food Chemistry
LEARNING OBJECTIVES AIMS To give a strong understanding of how to analyse food components such as fibre and carbohydrates, and how to characterize lipids in food.
OBJECTIVES On completion of “Other Food Analysis Methods”, students will be able to demonstrate a sound knowledge of:
(1)
The methods used to analyse food carbohydrates, including the use of standard methods such as AOAC 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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Food Chemistry
CARBOHYDRATE ANALYSIS
Food Chemistry
LEARNING OBJECTIVES – CARBOHYDRATE ANALYSIS AIMS To give an understanding of the chemistry involved in the analysis of carbohydrates in foods, including total soluble 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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Food Chemistry
CARBOHYDRATE ANALYSIS - SUMMARY
Food Chemistry
INTRODUCTION Carbohydrates (including sugars and starch) are in all cases expressed as monosaccharides and the tables of carbohydrate content contain values of available carbohydrate - proximate analysis content. The available carbohydrate consists of the sum of the free sugars (glucose, fructose, sucrose, lactose, maltose and higher maltose homologues), dextrin, starch and glycogen expressed as monosaccharides. These are the carbohydrates 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 with 80% v/v ethanol in a Soxhlet extraction apparatus for three hours or by boiling with 80% v/v ethanol for 20 minutes. The free sugars in the extracts are examined by two reducing sugar methods or by HPLC to give the glucose and fructose concentration. (We look at these in detail later in this module). Sucrose in the extract can be measured by inversion. The residue remaining after extraction of the free sugars is examined for starch and dextrin content. Methods of Quantitative Determination: 1. Reducing Sugars Sugars with a structure containing free aldehyde and ketone groups react as weak reducing agents and are called reducing sugars. 5
Food Chemistry
Food Chemistry
Examples: Reducing Sugars: cellobiose.
all monosaccharides eg: glucose, fructose;
the disaccharides maltose, lactose and
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 when boiled 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 Sugars Disaccharides such as sucrose and raffinose, and higher oligosaccharides.
These sugars are non-reducing because they consist of simple sugars linked through their aldehydic or ketonic groups. There is no hydroxyl group on an anomeric carbon.
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FOOD ANALYSIS EXAMPLES Food products containing a mixture of reducing sugars
Food Chemistry
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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Ion exchange chromatography: an anion-exchange column as part of an autoanalyser is now used to separate and analyse mixtures of sugars.
Food Chemistry
HPLC and Gas Chromatography HPLC is a quick, sensitive and powerful tool for both the qualitative and quantitative analysis of sugars in food 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 as reducing agents. Most are based on the reduction of Cu2+ (cupric ions) to Cu+ (cuprous ions) in alkaline solution to give a red precipitate of cuprous oxide, Cu2O. A number of tests have evolved using different substances for preventing the formation of black cupric oxide when CuSO4 is heated with alkali. 8
Food Chemistry
Food Chemistry
(a)
Fehling’s Solution Test - (simplest qualitative test): Solutions of cupric sulphate (Fehling’s 1) and alkaline sodium potassium tartrate (Fehling’s 2) are mixed together and then with the reducing sugar solution, and finally heated. A positive reaction shows the red precipitate of cuprous oxide or with more dilute solutions of reducing sugar, a green or red, 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 only monosaccharides 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) is further examined for starch and dextrin content. Both are hydrolysed with the selective enzyme glucoamylase to glucose. After filtration of the digest, the liberated glucose is treated with glucose oxidase and estimated colorimetrically at 37 °C in an autoanalyser.
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CARBOHYDRATE ANALYSIS – FURTHER READING
Food Chemistry
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 “Food Analysis” 2nd Edition by S. Suzanne Nielsen (Editor). The material contained in the textbook will not be examined; 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 in food; 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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Food Chemistry
Section 11.1 on Page 169 of the textbook discusses the different types of carbohydrates, including a full list in Table 11-1 on Page 170 of the textbook. Additionally, the analysis of carbohydrates is introduced, and the terms total carbohydrate and other carbohydrate discussed. Total carbohydrate is normally determined by difference with the mass of moisture, total fat, ash, and crude protein subtracted from the mass of the food. The total carbohydrate content of some foods is summarized in Table 11-2 on Page 171 of the textbook. Other (complex) carbohydrate, including starch is determined by subtracting the sum of the mass of 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 carbohydrate analysis, 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 determining the total carbohydrate content of food. The method involves adding an aqueous solution of phenol to an aqueous solution of the carbohydrate, followed by concentrated sulphuric acid (heat generated). A yellow colour results which is then measure spectrophotometrically at 490 nm. Standard sugar solution are then used for quantification. Polysaccharides are broken down to sugars by the acid and heat.
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CHEMICAL ANALYSIS OF INDIVIDUAL SUGARS IN FOOD
Food Chemistry
Total Reducing Sugars Section 11.3.3 on Pages 173-174 of the textbook details wet chemical methods for determining the reducing sugar 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 of copper (II) ions in alkaline solution to copper (I) ions, which then precipitate as brick-red Cu2O. For the Somogyi-Nelson method, the Cu+ ions reduce an arsenomolybdate complex to produce an intense blue colour that is measured spectrophotometrically. For the Munson-Walker method, the Cu2O can be determined: (1) gravimetrically; (2) by titration with sodium thiosulphate; (3) by titration with potassium permanganate; and (4) electrolytically, using AOAC methods. 12
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Munson - Walker Gravimetric Method Fehling’s solution is boiled with a solution of a reducing sugar for six minutes and then filtered hot. The precipitated 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 Method This method involves the determination of reducing sugars by titration with Fehling’s solution using the redox indicator, methylene blue. This is an empirical method and standardized experimental conditions and methods 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 volume technique where the conditions for reduction are standardized by the addition of water to give a constant final volume of 75 ml in the titration flask, and the volume of Fehling’s solution used is calibrated against a standard 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 a dilute solution of the sugar sample.
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Luff-Schoorl Method This method uses an alkaline reagent containing cupric citrate (Cu2+ ion). After boiling this reagent with a solution containing reducing sugars, potassium iodide (KI) and acid (sulphuric acid) are added after cooling. Iodine is liberated from the redox reaction:
Food Chemistry
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, sodium thiosulphate. Thiosulphate equivalent tables can then be used: → II2 coloured colourless
The Luff-Schoorl reagent is less alkaline than Fehling’s solution. Consequently, it is a weaker oxidizing agent 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 another species but are reduced in the process.]
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Nonreducing Sugars
Food Chemistry
Sucrose Determination Remember, sucrose is a non-reducing sugar. Sucrose can be determined in the absence of reducing sugars by inverting a portion of the test solution with acid followed by neutralization with alkali and titration by the Lane 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 after acid inversion. Analysis of Specific Mono-, Di- and Oligosaccharides Section 11.3.4 on Pages 174-178 of the textbook details HPLC, GC and enzymic methods for analysing individual mono-, di- and oligosaccharides. For HPLC analysis, various stationary phases used to analyses sugars are discussed in detail. For GC, sugars need to be converted to derivatives that are volatile and able to be analysed by GC. Extraction of Free Sugars Free sugars must be removed from the food matrix prior to HPLC analysis so that possible interfering components of food are separated from free sugars. This is done by extraction of the dried, lipid-free food with 80% ethanol (AOAC method 922.02, 925.05; 1995). Purification of this extract prior to HPLC analysis is often required. Methods to do this are outlined in Section 11.3.1 on Pages 171-172 of the textbook. After purification of the sugar extract, the aqueous alcohol is removed under reduced pressure using a rotary evaporator at temperatures of 45-50 °C. The dried sample is then dissolved in water and analysed by HPLC. 15
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Food Chemistry
CHEMICAL ANALYSIS OF STARCH IN FOOD Section 11.4.1.1 on Pages 179-180 of the textbook discusses the determination of total starch content. The most reliable method involves the total conversion of the starch to D-glucose by starch specific enzymes such as α-amylase and glucoamylase, and measurement of the D-glucose released by spectrophotometric or HPLC methods. The method involving spectrophotometric analysis (AOAC Method 969.39; 1995) is detailed on Page 180 of the textbook.
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Food Chemistry
FIBRE ANALYSIS
Food Chemistry
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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CONTENT – FIBRE ANALYSIS
Food Chemistry
INTRODUCTION This study examines food fibre and methods used to analyse the different types of fibre, including crude fibre and dietary fibre. The special nature of food fibre analysis has resulted in it being considered separately 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 “Food Analysis” 2nd Edition by S. Suzanne Nielsen (Editor). The material contained in the textbook will not be examined; only the material summarised below is examinable. Chapter 12 is divided into a number of sections covering various aspects of the determination of fibre in food; 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 18
Food Chemistry
IMPORTANCE OF DIETARY FIBRE
Food Chemistry
Section 12.1.1 on Page 191 of the textbook reviews the role dietary fibre plays in human health, and is a good 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 on whether resistant starches are included. Dietary fibre is composed of cell wall polysaccharides, non-cellwall polysaccharides and lignin. Section 12.1.3 on Pages 191-192 of the textbook discusses the composition of 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 their limitations highlighted. The most important section to review is the discussion of the AOAC method for determining the total, insoluble and soluble dietary fibre in food (AOAC Method 991.43; 1995). This is the standard method for determining the dietary fibre content of food. The experimental procedure is well outlined making it easier to implement in the laboratory.
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Food Chemistry
CHEMICAL METHODS OF FIBRE ANALYSIS Section 12.3.4 on Pages 195-196 of the textbook outlines the alternative analysis procedure to the gravimetric methods. Chemical methods for fibre analysis involve determination of all nonstarch monosaccharides and lignin. Monosaccharides are determined colorimetrically or using GC or HPLC. The Englyst-Cummings procedure is an alternative to the gravimetric AOAC method for dietary fibre highlighted above, except lignin is not included in the analysis. The levels of lignin in food is often small and thus the Englyst-Cummings procedure can be used to determine fibre content of such foods. Additionally, resistant starch is not included in this fibre measurement, but a separate analysis is included to determine resistant starch alone.
COMPARISON DIETARY FIBRE ANALYSIS METHODS The merits of the AOAC method and the Englyst-Cummings procedure for dietary fibre determination are discussed in Section 12.4 on Page 197 of the textbook. The points discussed are useful for making a judgement about which methods to use particularly since the Englyst-Cummings procedure requires the least amount 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 of such chromatographic procedures.
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LIPID CHARACTERIZATION
Food Chemistry
LEARNING OBJECTIVES - LIPID CHARACTERIZATION 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 of triglycerides, including the use of fatty acid methyl esters (FAME), and cholesterol composition.
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CONTENT - LIPID CHARACTERIZATION
Food Chemistry
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 “Food Analysis” 2nd Edition by S. Suzanne Nielsen (Editor). The material contained in the textbook will not be examined; only the material summarise below is examinable. Chapter 14 is divided into a number of sections covering various aspects of the characterization of fat in food; 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 highlighted below. 22
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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, why analyses of lipids are important, the standard methods of analyses for lipid characterization, and the lipid content of foods.
Table 14-1 on Page 220 of the textbook summarizes the standard methods to be discussed throughout Chapter 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 standard methods of analysis.
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CHARACTERIZATION METHODS FOR BULK FATS AND OILS Before any analyses can be performed on bulk fats and oils, some form of sampling and sample preparation is required. Sampling procedures such as AOCS Method C 1-47 (AOCS 1996) are available. If drying of the sample is required then the AOAC Method 981.11 is used (AOAC 1995). Any sample storage will need to exclude, heat, light and air to prevent lipid oxidation. A number of chemical and physical methods used to commonly characterize food lipids are summarized in the textbook. Refractive Index Refractive index is used to control hydrogenation and as a purity measurement, and is summarized in Section 14.3.2 on Page 222 of the textbook. Melting Point Many types of melting points (depending on the analysis method used) are possible, each with its own application, often depending on the preference in different countries. The disadvantages and methods of analysis are outlined in Section 14.3.3 on Page 222 of the textbook. Smoke, Flash and Fire Points Section 14.3.4 on Page 222 of the textbook details definitions of each, and how they are measured in the laboratory. These test give an indication of the volatile organic material in fats and oils.
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Cold Test This test measure amount of crystallization at 0 °C, and is a measure of the resistance of the oil to crystallization and, thus is a measure of the winterizing process. Further details are summarized in Section 14.3.5 on Page 222 of the textbook. Cloud Point The temperature at which a cloud forms due to crystallization in a liquid fat is the cloud point. Section 14.3.6 on Pages 222-223 of the textbook details the procedure. Colour The Lovibond (most commonly used method) and spectrophotometric methods for colour measurement are detailed in Section 14.3.7 on Page 223 of the textbook, and are used by the food industry as quality measurements for fats and oils. Solid Fat Index and Solid Fat Content Two methods for determining the amount of solids in a fat are outlined in Section 14.3.11 on Page 225 of the textbook. The proportion of solids to liquids in a fat impact on the functional properties of a food such as mouthfeel, and so is an important measure for a fat. Consistency Consistency is a measure of plasticity, hardness, creaminess and spreadability, and is determined using the penetrometer method. Section 14.3.12 on Page 225 of the textbook summarizes this quality measure.
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Polar Components in Frying Fats and Oils The deterioration of frying fats and oils is monitored by determining the polar components. Polar lipids are separated from the nonpolar compounds using column chromatography, while the composition and quality of the polar lipids are determined using thin later chromatography. Section 14.3.13 on Page 226 of the textbook outlines the importance of polar compounds in frying fats and oils. Iodine Value/Number The iodine value or number measures the degree of unsaturation (number of carbon-carbon double bonds) in a fat or oil. The procedure involves reacting iodine with carbon-carbon double bonds with a mechanism similar to that for the hydrogenation of oils. The procedure is detailed in Section 14.3.8 on Page 223 of the textbook, together with applications. It is particularly important for characterizing oils and for monitoring the hydrogenation process during the refining of oils. See summary of QC tests later in Unit 3. Saponification Value/Number Saponification is the hydrolysis of neutral fats or oils to glycerol and fatty acids. The procedure to determine the saponification value, which is a measure of the amount of saponification, is detailed in Section 14.3.9 on Page 224 of the textbook. See summary of QC tests in Unit 3. Free Fatty Acids and Acid Value Fat acidity is due to free fatty acids and is measured using an acid base titration. Free fatty acids arise from lipolysis of triglycerides. Section 14.3.10 on Pages 224-225 of the textbook outlines the procedure for consideration. This method is also used to analyse food lipids extracts as a means of determining the level of lipolysis and hydrolytic rancidity of a foods with a high oil content. Free fatty acids are monitored in any process that uses bulk oils for cooking and frying such as in the manufacture of potato chip and crisps. See summary of QC tests later in Unit 3. 26
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METHODS FOR ANALYSING LIPID OXIDATION
Food Chemistry
Lipolysis, hydrolytic rancidity, lipid oxidation and oxidative rancidity are briefly discussed. A review of lipid oxidation in Unit 5 is needed prior to studying the analysis methods. A number of measures of lipid oxidation are detailed in Section 14.4 of the textbook. Peroxide Value This is one of the most common tests for lipid oxidation and is detailed in Section 14.4.2 on Page 227 of the textbook. Determining the peroxide value involves a titration of the peroxide or hydroperoxide groups in compounds 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 oxidative stability of foods that have a high oil content, such as nuts. Hexanal Determination Measurement of headspace hexanal using GC is now being used as a measure of lipid oxidation. Section 14.4.4 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) Test This test measures malonaldehyde, the secondary product of lipid oxidation and has been shown to correlate better with the sensory analysis of lipid oxidation than does the peroxide value. TBA reacts with malonaldehyde to produce coloured compounds that are then measured spectrophotometrically. This reaction is not specific to malonaldehyde, with other TBA reactive substances (TBARS) existing. The procedure is discussed in Section 14.4.5 on Page 228 of the textbook. This test is commonly used to measure lipid oxidation in meat products. 27
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METHODS FOR ANALYSING LIPID FRACTIONS FROM FOODS Fatty Acid Composition and Fatty Acid Methyl Esters The fatty acid profile is now a routine indicator used to represent the composition of lipids in foods. The lipid is normally extracted from the food and saponified with alkali. The fatty acids released by this base hydrolysis 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 Pages 230-231 of the textbook, along with applications of the use of the method in food analysis. Cholesterol Analysis Section 14.6.4 on Pages 232-233 of the textbook summarizes the analysis of cholesterol in foods. The AOAC Method 976.26 (AOAC 1995) is outlined and is similar to other methods used. Common to these procedures is an extraction of the lipid from the food, followed by saponification of the lipid. The nonsaponifiable fraction is then derivatized, and the resultant trimethylsilyl (TMS) ethers are quantified using capillary GC. TLC Separation of Lipid Fractions Thin layer chromatography is used to rapidly analyse the various lipid fractions in a food lipid extract. The procedure is outlined in Section 14.6.5 on Page 233 of the textbook.
Food Chemistry Lecture Notes
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