Analytical chemistry of foods

Analytical Chemistry of Foods Analytical Chemistry of Foods c s JAMES Seale-Hayne Faculty of Agriculture, Food and Land Use Department of Agriculture and Food Studies University of Plymouth SPRINGER-SCIENCE+BUSINESS MEDIA, B.v First edition 1995 © 1995 Springer Science+Business Media Dordrecht Origina\ly published by Chapman & HalI in 1995 Typeset in 10112pt Times by Iulia Stevenson of Hove ISBN 978-1-4613-5905-0 ISBN 978-1-4615-2165-5 (eBook) DOI 10.1007/978-1-4615-2165-5 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored; or transmitted, in any form or by any means, without the prior permission in writing ofthe publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK Enquiries conceming reproduction outside the terms stated here should be sent to the publishers at the Glasgow address printed on this page The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or Iiability for any errors or omissions that may be made A catalogue record for this book is available from the British Library § Printed on acid-free text paper, manufactured in accordance with ANSIINISO Z39,48-1992 (permanence ofPaper) Preface Food laws were fIrst introduced in 1860 when an Act for Preventing the Adulteration of Articles of Food or Drink was passed in the UK This was followed by the Sale of Food Act in 1875, also in the UK, and later, in the USA, by the Food and Drugs Act of 1906 These early laws were basically designed to protect consumers against unscrupulous adulteration of foods and to safeguard consumers against the use of chemical preservatives potentially harmful to health Subsequent laws, introduced over the course of the ensuing century by various countries and organisations, have encompassed the features of the early laws but have been far wider reaching to include legislation relating to, for example, specifIc food products, specifIc ingredients and specifIc uses Conforming to the requirements set out in many of these laws and guidelines requires the chemical and physical analysis of foods This may involve qualitative analysis in the detection of illegal food components such as certain colourings or, more commonly, the quantitative estimation of both major and minor food constituents This quantitative analysis of foods plays an important role not only in obtaining the required information for the purposes of nutritional labelling but also in ensuring that foods conform to desired flavour and texture quality attributes This book outlines the range oftechniques available to the food analyst and the theories underlying the more commonly used analytical methods in food studies Details of specifIc procedures for undertaking the routine analysis of the major food constituents are provided and, where appropriate, reference is made to offIcial methods The latter should be referred to in the case of disputes and legislative requirements in order that full details regarding apparatus design, product specifIcations and technical procedures may be obtained C.SJ Contents Abbreviations xi Part Theory 1 Introduction Assessment of analytical methods and data 2.1 2.2 2.3 2.4 7 10 11 Principles of techniques used in food analysis 13 3.1 13 13 16 16 16 17 18 18 26 3.2 Requirements and choice of analytical methods Presentation of data Quality of data 2.3.1 Procedures to improve quality of data Statistical assessment of quality of data 2.4.1 Precision 2.4.2 Reproducibility 2.4.3 Accuracy Classical methods 3.1.1 Titrimetric analysis 3.1.2 Gravimetric procedures 3.1.3 Solvent extraction methods 3.1.4 Refractometry 3.1.5 Polarimetry Instrumental and modem methods 3.2.1 Spectroscopic methods 3.2.2 Chromatography 3.2.3 Electrophoresis 3.2.4 Immunochemical methods Theory of analytical methods for specific food constituents 4.1 4.2 4.3 4.4 4.5 Sampling Moisture and water activity 4.2.1 Methods of measuring moisture Protein 4.3.1 Kjeldahl method 4.3.2 Direct distillation methods 4.3.3 Thermal combustion methods 4.3.4 Dye binding methods 4.3.5 Formol titration 4.3.6 Spectroscopic methods Fats 4.4.1 Gravimetric solvent extraction procedures 4.4.2 Volumetric methods 4.4.3 Instrumental methods 4.4.4 Study of the nature offats and oils Carbohydrates 4.5.1 Determination of available carbohydrates 4.5.2 Estimation of dietary fibre in foods 30 31 37 37 37 38 40 41 43 43 44 45 45 46 46 50 51 51 53 56 59 VIII ANALYTICAL CHEMISTRY OF FOODS 4.6 4.7 4.8 Micronutrients 4.6.1 Mineral elements and ash 4.6.2 Vitamins Food energy Additives 62 62 63 64 66 Part Experimental 69 Experimental procedures - estimation of major food constituents 71 5.1 5.2 5.3 5.4 5.5 71 72 73 75 5.6 5.7 5.8 5.9 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22 5.23 5.24 5.25 5.26 5.27 5.28 5.29 5.30 Laboratory safety Sampling Determination of moisture and total solids Determination of ash content Determination of mineral elements in foods by atomic absorption spectrophotometry (ashing process) Determination of mineral elements in canned food products by atomic absorption spectrophotometry (non-ashing process) Determination of calcium in foods by permanganate titration Determination of phosphorus by the vanadate colorimetric method Determination of phosphorus by the molybdenum blue colorimetric method Determination of iron by the bipyridyl colorimetric method Determination of nitrogen and protein by the Kjeldahl method using the Kjeltec instrument Determination of protein content by the formol titration Determination of fat by the Soxhlet and Soxtec methods Determination of the fat content of dairy products by the Gerber method Determination of fat by the Mojonnier method Determination offat by the Rose-Gottlieb method Determination of fat by the Werner-Schmid method Determination of the fat content of cheese by the modified SBR (Schmid-Bondzynski-Ratzlaft) method Determination of fat by the Weibull-BerntroplWeibull-Stoldt method Determination of dietary fibre in foods by the neutral detergent fibre method Determination of dietary fibre by the Englyst enzymatic instrumental method Determination of dietary fibre in foods by the AOAC enzymatic gravimetric method Volumetric determination of sugars by copper reduction (Lane and Eynon method) Volumetric determination of sugars by copper reduction (Lane and Eynon method - constant volume modification) DNS colorimetric determination of available carbohydrates in foods Determination oflactose in milk by the Chloramine-T method Determination of the lactose content of milk by polarimetry Determination oflactose in cheese by the phenol colorimetric method Identification and determination of sugars in milk products by HPLC Calculation of the calorific value of foods General food studies 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 Determination of ascorbic acid by titration Gas chromatographic study of the fatty acid composition offats Determination of the iodine value of fats and oils Determination of the saponification value offats Determination of sulphur dioxide by iodine titration Determination of total sulphur dioxide (free and combined) using distillation methods Determination of the salt content of dairy products (Volhard method) Determination of the salt content of brine (Mohr titration) 76 78 80 82 84 86 88 90 91 93 96 98 100 102 104 106 108 114 117 120 124 126 128 13 132 135 137 137 140 142 144 146 148 150 152 CONTENTS 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16 6.17 6.18 Titrimetric determination ofthe chloride content of meat products Colorimetric determination of nitrates and nitrites in meat products and brine Spectrophotometric determination of antioxidants Extraction and colorimetric estimation of gallates Determination of alcohol in beverages by gas chromatography Determination of alcohol by the distillation method Titratable acidity of fruit juices Determination of the acetic acid content of vinegar Acidity measurements in dairy products Determination ofL-lactic acid in cheese by an enzymatic method Additional reading material Index 153 155 159 161 162 163 165 167 168 170 173 175 IX Abbreviations AOAC BS BSI FAO FDA GC/GLC HPLC ISO NIR NMR ppm SI TLC Association of Official Analytical Chemists British Standard British Standards Institution Food and Agriculture Organisation Food and Drug Administration (USA) Gas chromatography/gas-liquid chromatography High performance liquid chromatography International Organisation for Standardisation Near infrared Nuclear magnetic resonance spectroscopy parts per million Statutory Instrument, and also Systeme International d'Unites Thin-layer chromatography Part Theory 162 ANALYTICAL CHEMISTRY OF FOODS 6.13 Determination of alcohol in beverages by gas chromatography Principle Alcohol (ethanol) may be estimated in beverages by gas chromatography using propanol as an internal standard A known amount of propanol is added to the beverage and, following separation by gas chromatography, the ratio of the ethanol:propanol peak areas is used to calculate the amount of ethanol Ethanol solutions of known concentrations are used as calibrating standards Apparatus Volumetric flasks Pipettes Gas chromatograph Porapak Q column (or similar) Oven temperature 177°C Reagents Ethanol Propanol Beverage(s) Procedure Prepare, in 100 ml volumetric flasks, solutions of ethanol containing 1.0,2.03.0, 4.0, 6.0, 8.0, and 10.0% ethanol by volume To each flask add 2.0 ml propanol to give a total volume of 102 ml Fill a 100 ml volumetric flask to the mark with the beverage to be analysed and add 2.0 ml propanol to this flask also Mix all the flasks well by inversion Inject samples from each of these above flasks into a gas chromatograph and measure the peak area of each peak obtained (using a computing integrator, where available) Plot a graph of ethanol:propanol area ratio against ethanol content and use this graph, and the ethanol:propanol ratio for the beverage sample(s), to determine the ethanol content of the beverage sample GENERAL FOOD STUDIES Principle Ethanol is detennined by distilling a measured volume of sample and, after making up the distillate to the same volume, the alcohol content is assessed from its gravity by reference to appropriate tables For high levels of alcohol, dilution of the original sample may be necessary and use made of modified tables Proof spirit (100%) has a specific gravity of 0.91702 at 20 De and contains 49.276% ethanol by weight and 57.155% by volume The test is not specific for ethanol and the presence of other water-soluble, volatile compounds such as methanol may cause erroneous results unless a check is made of the refractive index of the distillate against its specific gravity Apparatus Distillation unit (a Kjeltec distillation unit may be used) Volumetric flasks Specific gravity bottles or hydrometers Procedure (a) Wines Fill a 100 ml volumetric flask to the mark with the sample to be analysed Transfer the sample to a distillation flask, rinsing in with water, and distil about 95 ml of distillate into a 100 ml volumetric flask Fill the flask to the mark with distilled water and mix by inversion Detennine the specific gravity of this distillate at 20 D e and read off the alcohol content from Table 6.5 (b) Spirits If the total solids content is small, as for gin and vodka, detennine the specific gravity ofthe sample directly, without distillation, and read the alcohol content from Table 6.5 Where the total solids content is sufficient to raise the gravity of the sample, distil 50 ml of the sample as above into a 50 ml volumetric flask and, from the density of the distillate, obtain the alcohol content from Table 6.5 (c) Beer Distil 100 ml of the sample as in (a) above, having washed the sample into the distillation flask with about 30 ml of water From the density of the distillate obtained the alcohol content from Table 6.5 Calculation The specific gravity of the above samples may be calculated as follows: 6.14 Determination of alcohol by the distillation method 163 164 ANALYTICAL CHEMISTRY OF FOODS x -x Specific gravity = _2_ _1 X3 -Xl where Xl = weight (g) of specific gravity bottle empty, X2 = weight (g) of specific gravity bottle + sample, and x3 = weight (g) of specific gravity bottle + water 'fable 6.5 Relationship between the specific gravity and the proportion of ethanol in alcohol solutions at 20°C Specific gravity 1.0000 0.9995 0.9990 0.9985 0.9980 0.9975 0.9970 0.9965 0.9960 0.9955 0.9950 0.9945 0.9940 0.9935 0.9930 0.9925 0.9920 0.9915 0.9910 0.9905 0.9900 0.9895 0.9890 0.9885 0.9880 0.9875 0.9870 0.9865 0.9860 0.9855 0.9850 0.9845 0.9840 0.9835 0.9830 0.9825 0.9820 0.9815 0.9810 0.9805 0.9800 Proof spirit 0.00 0.58 1.16 1.74 2.33 2.92 3.52 4.12 4.73 5.34 5.96 6.58 7.21 7.84 8.47 9.12 9.77 10.43 11.09 11.76 12.44 13.12 13.80 14.50 15.20 15.92 16.63 17.36 18.09 18.82 19.56 20.31 21.06 21.82 22.58 23.34 24.12 24.90 26.69 26.48 27.27 % Ethanol m/v v/v 0.00 0.26 0.53 0.80 1.06 1.33 1.61 1.88 2.16 2.44 2.72 3.01 3.30 3.59 3.88 4.18 4.48 4.78 5.09 5.40 5.71 6.03 6.35 6.67 7.00 7.33 7.67 8.00 8.34 8.69 9.03 9.38 9.73 10.09 10.44 10.80 11.17 11.53 11.91 12.28 12.65 0.00 0.33 0.67 1.01 1.34 1.68 2.02 2.37 2.72 3.07 3.43 3.75 4.15 4.51 4.88 5.25 5.62 6.00 6.36 6.77 7.16 7.55 7.94 8.34 8.75 9.16 9.57 9.96 10.40 10.83 11.25 11.68 12.11 12.55 12.58 13.42 13.87 14.32 14.87 15.83 15.68 Specific gravity 0.9800 0.9795 0.9790 0.9785 0.9780 0.9775 0.9770 0.9765 0.9760 0.9755 0.9750 0.9745 0.9740 0.9735 0.9730 0.9725 0.9720 0.9715 0.9710 0.9705 0.9700 0.9695 0.9690 0.9685 0.9680 0.9675 0.9670 0.9665 0.9660 0.9655 0.9650 0.9645 0.9640 0.9635 0.9630 0.9625 0.9620 0.9615 0.9610 0.9605 0.9600 Proof spirit 27.27 28.04 28.87 29.68 30.49 31.30 32.11 32.92 33.73 34.54 35.36 36.17 36.97 37.78 38.59 39.39 40.19 40.98 41.77 42.55 43.34 44.12 44.90 45.67 46.44 47.19 47.94 48.69 49.43 50.16 50.89 51.61 52.32 53.02 53.72 54.41 55.06 55.75 56.42 57.06 57.73 % Ethanol mlv v/v 12.65 13.02 13.40 13.78 14.17 14.55 14.93 15.32 15.70 16.09 16.47 16.86 17.24 17.63 18.01 18.39 18.77 19.15 19.53 19.90 20.28 20.66 21.03 21.40 21.77 22.13 22.49 22.85 23.21 23.57 23.92 24.27 24.61 24.95 25.29 25.63 25.96 26.29 26.61 26.93 27.25 15.68 16.13 16.59 17.06 17.53 17.99 18.46 18.92 19.38 19.85 20.31 20.78 21.24 21.70 22.16 22.62 23.06 23.53 23.98 24.43 24.48 25.33 25.77 26.21 26.65 27.06 27.51 27.93 28.36 28.78 29.19 29.60 30.01 30.41 30.80 31.20 31.58 31.97 43.34 32.72 33.09 GENERAL FOOD STUDIES Principle Fruit juices contain a number of fairly simple organic acids such as malic and citric acids which are readily neutralised by strong bases and may thus be titrated against standard bases such as sodium hydroxide The reaction between citric acid and sodium hydroxide is shown by the following equation Apparatus Burettes Pipettes Conical flasks Reagents O.IM Sodium hydroxide solution Phenolphthalein indicator solution Procedure (a) Orange juice and grape juice Filter about 100 ml of the fruit juice into a clean, dry beaker Pipette 10.00 ml of this filtered juice into a conical flask and dilute to about 80 ml with distilled water Add 0.3 ml phenolphthalein by pipette and titrate to a faint pink end-point with O.IM sodium hydroxide solution Repeat to obtain concordant results (b) Lemonjuice Filter about 25 ml of the fruit juice into a clean, dry beaker Pipette 10.00 ml of this filtered juice into a 100 ml volumetric flask and make to the mark with distilled water Pipette 10.00 ml of this diluted juice into a conical flask and dilute to about 80 ml with distilled water Add 0.3 ml phenolphthalein by pipette and titrate to a faint pink end-point with O.IM sodium hydroxide Repeat to obtain concordant results Calculation The acidity of the fruit juices may be expressed as either: (a) The titratable acidity (TA) of the fruitjuice(s) as ml O.1M sodium hydroxide per 100 ml fruit juice, i.e: 165 6.15 Titratable acidity of fruit juices 166 ANALYTICAL CHEMISTRY OF FOODS (i) Orange and grape juice TA= lOx T (ii) Lemon juice TA= 100 x T where T = mean titre (in m1) of O.lM sodium hydroxide solution required to neutralise the acidity in 10.00 ml of the orange and grape juices or 10.00 ml of the diluted lemon juice or: The acidity of the fruit juice expressed as percentage of citric acid, i.e.: (i) Orange and grape juice % Citric acid = Tx 192 - x 1000 (ii) Lemon juice Tx 192 x 10 % Citric acid = - - - - x 1000 where T = mean titre (in ml) of O.lM sodium hydroxide solution require:d to neutralise the acidity in 10.00 ml of the orange or grape juice or 10.00 ml of the diluted lemon juice [192 is the molecular weight (relative molecular mass) of citric acid] GENERAL FOOD STUDIES Principle Vinegars usually contain around 5% acetic acid, and the acidity may be estimated by titration of known aliquots of diluted vinegar with standard sodium hydroxide solution using phenolphthalein as indicator The acidity is then expressed as percentage acetic acid The reaction between acetic acid and sodium hydroxide is shown by the following equation Apparatus Burettes Pipettes Conical flasks Reagents O.IM Sodium hydroxide solution Phenolphthalein indicator solution Procedure Dilute 10.00 ml of vinegar by pipetting 10.00 ml into a 100 ml volumetric flask and diluting to 100 ml with distilled water Mix well by inversion Pipette 10.00 ml of this diluted vinegar into a conical flask, add drops of phenolphthalein and titrate to a faint pink end-point with O.IM sodium hydroxide solution Repeat to obtain concordant results Calculation The acetic acid content of the original vinegar is given by: % Acetic acid (m/v) = Tx 0.6 where T = mean titre (in ml) of O.1M sodium hydroxide solution required to neutralise the acidity in 10.00 ml of the diluted vinegar 167 6.16 Determination of the acetic acid content of vinegar 168 ANALYTICAL CHEMISTRY OF FOODS 6.17 Acidity measurements in dairy products Principle Acidity may be measured in terms of the amount of standard sodium hydroxide solution required to neutralise the acidity of a dairy product to the end point of phenolphthalein, the result being expressed in terms of percentage of lactic acid CH3CH(OH)COOH + NaOH ~ CHFH(OH)COONa + H20 Since the molecular weight (relative molecular mass) oflactic acid is 90, the use of Ml9 sodium hydroxide for the titration allows the calculation of acidity to be obtained simply by dividing the titre value by 10, where 10.00 ml of product has been used for the titration, e.g with milk Apparatus Burettes Pipettes Conical flasks or porcelain basins Reagents Ml9 Sodium hydroxide solution O.IM Sodium hydroxide solution 0.02M Sodium hydroxide solution Phenolphthalein indicator (0.5%) Procedure Milk Pipette 10.00 ml aliquots of a well shaken milk sample into conical flasks, add I ml of 0.5% phenolphthalein solution and titrate to a faint pink colour with Ml9 sodium hydroxide solution Calculate the titratable acidity of the milk sample given that: Titratable acidity (as % lactic acid) = (ml Ml9 NaOH used)110 Cheese Weigh accurately 10-12 g of cheese, fmely divided, into a conical flask Add about 40 ml warm, distilled water and shake well Add another 40 ml warm water and again shake Cool and make up to 100 ml in a volumetric flask Mix well and filter Pipette 25.00 ml aliquots of this solution into conical flasks and titrate with O.IM sodium hydroxide solution using I ml I % phenolphthalein as indicator Calculate the titratable acidity as percentage lactic acid given that: GENERAL FOOD STUDIES (ml NaOH) x 0.9 x % Lactic acid = - - - - - - - - - WeIght of cheese sample (g) Butter and margarine Weigh accurately 18-22 g of food sample into a conical flask Add about 90 ml hot, previously boiled, distilled water and titrate hot with 0.02M sodium hydroxide solution using ml 1% phenolphthalein as indicator Calculate the titratable acidity as: (a) Percentage lactic acid given that: o _ Yo LactIC aCId - (ml NaOH) x 0.02 x W· h f eig to samp e (b) Degree of acidity (ml M NaOH needed to neutralise the acidity in 100 g of butter) 169 170 ANALYTICAL CHEMISTRY OF FOODS 6.18 Determination of L-Iactic acid in cheese by an enzymatic method Principle In the presence ofL-lactate dehydrogenase (L-LHD) L-Lactic acid is oxidised by NAD to pyruvate: L-Lactate + NAD+ L-LDH ~ Pyruvate + NADH + H+ The equilibrium of this reaction lies almost completely on the side of lactate However, by trapping the pyruvate in a subsequent reaction catalysed by the enzyme glutamate-pyruvate transaminase (GTP) in the presence of L-glutamate, the equilibrium can be displaced in favour of pyruvate and NADH: Pyruvate + L-glutamate GPT ~ L-alanine + f3-ketoglutamate The amount of NADH formed in the above reaction is stoichiometric with the concentration ofL-lactic acid The increase in NADH concentration is determined lby means of its absorption at 340nm Reagents Glycylglycine buffer, pH 10 f3-NAD (210 mg in ml distilled water) Glutamate-pyruvate transaminase (1100 units in 0.7 ml) L-Lactate dehydrogenase (about 3800 units in 0.7 ml) (The reagents for this assay are available in kit form from Boehringer Mannheim Company) Apparatus Grinder/homogeniser Volumetric flasks Water bath at 60°C Ice Spectrophotometer cm Quartz cuvettes Procedure (aJ Preparation a/sample Grind about 10 g of cheese and mix Accurately weigh 1.00 g of this cheese sample into a 100 ml volumetric flask Add about 80 ml water and heat for 15 at 60°C in a water bath with occasional shaking Cool to room temperature and make up to volume with distilled water To obtain separation of the fat, place the flask in an ice bath for 15 Filter GENERAL FOOD STUDIES Take 0.1 ml (hard cheese) or 0.5 ml (soft cheese) of the clear filtrate for the assay (b) Assay Pipette into cuvettes solutions as shown in Table 6.6 Mix and read the absorbance of the solutions (AI) after against air (no cuvette in the light path) or water at 340nm Start the reaction by adding 0.02 ml OfL-LDH solution to each cuvette Mix and on completion of the reaction after about 10 read the absorbance of the solution (A ) Table 6.6 Solutions for enzymatic estimation of lactic acid Solution Buffer solution f:I-NAD solution Distilled water GPT suspension Sample solution Blank cuvette (ml) Sample cuvette (ml) 1.00 0.20 1.00 0.02 1.00 0.20 0.90 0.02 0.10 Calculation Calculate the absorbance difference (A - AI) for both blank and sample Substract the difference of the blank from the absorbance difference of the sample: A = Asample - Ablank Calculate the concentration ofL-iactate in the original food sample as follows: (a) Hard cheese % Lactic acid in cheese = (b) A x9x2.24 h f h 6.3 x welg toe eese (g) Soft cheese A x x 2.24 % Lactic acid in cheese = h f h ( ) x welg toe eese g x The molar absorbance coefficient for NADH at 340nm is 6.3 tmmol- I em-I) 171 Additional reading material Birch, G.G (ed.)(1985) Analysis ofFood Carbohydrate Elsevier Applied Science Publishers, London Burns, D.A and Ciurczak, E.W (eds) (1988) Handbook ofNear-Infrared Analysis Marcel Dekker, Inc., New York Complex carbohydrates in Foods The Report ofthe British Nutrition Foundations's Task Force (1990) Published by Chapman and Hall, London, for the British Nutrition Foundation Coultate, T.P (1989) Food: The Chemistry of its Components Royal Society of Chemistry, Cambridge, UK Fennema, O.R (1985) Food Chemistry Marcel Dekker, Inc., New York Hamilton, Rl and Bhati, A (eds) (1980) Fats and Oils: Chemistry and Technology Applied Science Publishers, London Holland, B., Welch, A.A., Unwin, LD., Buss, D.H., Paul, AA and Southgate, D.A.T (1991) McCance and Widdowson's The Composition ofFoods (5th and revised edn) Royal Society of Chemistry and Ministry of Agriculture, Fisheries and Food, Cambridge, UK Holme, D.J and Peck, H (1993) Analytical Biochemistry Longman Scientific & Technical, London Jukes, D.J (1987) Food Legislation of the UK (2nd ed) Butterworths, London Kirk, R.S., and Sawyer, R (1991) Pearson's Composition and Analysis ofFoods (9th edn) Longmans Scientific & Technical, London Morris, B.A and Clifford, M.N (1985) Immunoassays in FoodAnalysis Elsevier Applied Science Publishers, London and New York Southgate, D.A (1976) Determination ofFood Carbohydrates Applied Science Publishers, London Willard, H.H., Merrit, L.L., Dean, lA and Settle, F.A (1988) Instrumental Methods ofAnalysis (7th edn) Wadsworth, Belmont, California Index absorptiometers see colorimeters absorptiometry see colorimetry accuracy 5, 11 acetic acid in vinegar 167 acidity in dairy products 168-9 in fruit juices 165-6 in vinegar 167 additives 66-7 see also specific additive classes adulteration of meat species 34 affinity chromatography 28 atlatoxins 34 alcohol by distillation 163-4 by gas chromatography 162 alcoholic potassium hydroxide 141 amylase 108, 114 amyloglucosidase 114 Angstrom units 18 anthrone reagent 57 antibodies see immunochemical methods antigen see immunochemical methods antioxidants 67 extraction 159, 161 see also specific antioxidants AOAC method of estimation of dietary fibre 60, 114-16 ascorbic acid in fruit juices 137 in fruit and vegetables 137 inmilk 139 by titration 13 see also vitamin C ash 3,62 determination 75 solution of 77 wet oxidation 77 assessment of data atomic absorption spectrophotometry 24,76, 78 instrumentation 26 available carbohydrates 3, 53 Babcock method for fat 51 beer, alcohol in 162, 164 Beer-Lambert law 19 BRA see butylated hydroxyanisole BHT see butylated hydroxytoluene bipyridyl colorimetric method for ion 86 biuret colorimetric method for protein 45 blank analyses Bligh and Dyer method for fat extraction 478 bomb calorimetry 64 boron trifluoride/methanol reagent 140 Btlchi system 41 butanolic potassium hydroxide 141 butylated hydroxyanisole 67 determination 159 butylated hydroxytoluene 67 cadmium for reducing nitrates 155 calcium by atomic absorption spectrophotometry 76, 78 by permanganate titration 80 calibration graphs calorific value calculation 135 carbohydrates classification 53-5 methods of determination 56 see also sugars Carrez reagents 117, 121, 153 cheese acidity in 168 fat by Gerber method 93 lactose by phenol colorimetric method 130-1 salt in 153-4 Chloramine-T method for lactose 58, 126 chloride in brine 152 in meat products 153-4 see also salt chromatography 26 adsorption 27 affinity 28 column 27 gas 29 gel filtration 28 ion-exchange 28 liquid-liquid 27, 29 liquid-solid 27, 29 176 ANALYTICAL CHEMISTRY OF FOODS chromatography contd paper 27 partition 28 planar 27 thin-layer 28 classical methods offood analysis 13 coefficent of variation 10 collaborative testing colorimeters 20 colorimetry 20 instrumentation 21 confirmatory analysis conversion factors for nitrogen to protein 41, 88 copper by atomic absorption spectrophotometry 76, 78 copper reduction method for sugar estimation 58, 117, 120 cream acidity in 168 fat in 93 crude fat crude fibre 3, 60 crude protein determination 88 data assessment of quality 7-8 presentation Dean and Stark method for moisture 38-9 degrees of freedom 11 detergent fibre 60 dextrins 54 2,6-dichlorophenolindophenol 13 dietary fibre 3, 55 AOAC method 60 chemical gravimetric methods 59 determination 59 Englyst method 108-13 enzymatic gravimetric methods 60 enzymatic instrumental methods 61 neutral detergent fibre method 106-7 diffraction gratings 21 dimethyl sulphoxide 110 dinitrosalicylic acid (DNS) reagent 57 for available carbohydrates 123-5 direct distillation method for protein 43 distillation methods alchohol in beverages 163 moisture 38 sulphur dioxide 148 drying methods 73 Dumas principle of nitrogen estimation 43 dye-binding methods for protein 44-5 electromagnetic spectrum 19 electron spin resonance (ESR) 26 electrophoresis 30 capillary 31 isoelectric focusing 31 ELISA immunoassay methods 32 energy conversion factors 65 energy in foods (table) 64 Englyst method for dietary fibre estimation 61, 108-13 enzymatic gravimetric methods for fibre 60 enzymatic instrumental methods for fibre 61 enzymatic methods carbohydrates 58 lactic acid in cheese 170 errors esterification of fatty acids 52 ether extract evaporation methods for moisture 38 Ftest 9, 10 fat Gerber method 93-5 methods of estimation 46-51 Mojonnier method 96-7 Rose-Gottlieb method 98 Schmid-Bondzynski-Ratzlaff method 102-3 SoxhletfSoxtec method 91-2 Weibull-Berntrop method 104-5 Weibul1-Stoldt method 104-5 Werner Schmid method 100-1 fats and oils, study of fatty acid composition 51, 140 fatty acids, methods of esterification 52-3 Fehling's solution 117, 120 fibre see crude fibre; dietary fibre; non-starch polysaccharides flame photometry 24 fluorescence 24 fluorimetry 24 food energy 64 formol titration, milk 45 Foss milko-tester 51 frequency of radiation 18 fruit juices acidity in 165-6 ascorbic acid in 138-9 fruit and vegetables ascorbic acid in 138-9 fundamental vibrations 161 gal1ates 161 gas chromatography (GC) for alcohol determination 162 of fatty acid esters 52, 140-1 Gerber method for fat estimation 50 in cheese 93 in cream 94 in ice-cream 94-5 in milk 93 in yogurt 95 glucose 54, 58 gravimetric procedures 16 Griess diazotisation reaction for nitrites 155 67, INDEX hazards 71 hemicelluloses 54,55 high performance liquid chromatography (HPLC) for lactose 132 for sugar analysis 59 ice cream fatin 94-5 ICP see inductively coupled plasma emission spectroscopy immunochemical methods 31 independent variable inductively coupled plasma emission spectroscopy (ICP) 26 infrared milk analysis 46 infrared spectrophotometry 22 insoluble fibre 108 instrumental methods 18 iodine value 52 estimation 142-3 iron estimation by bipyridyl colorimetric method 86-7 jam, sugars in 118 Karl Fischer titration 40 Kjeldahl method for nitrogen and crude protein 41-2,88 Kjel-Foss instrument for protein estimation 41 Kjeltec method 41-2,88 laboratory safety 71 lactic acid in cheese, enzymatic method 17071 lactose in cheese 130-1 Chloramine-T method 126-7 byHPLC 132 by phenol colorimetric method 130 by polarimetry' 128-9 Lane and Eynon method for sugars 117-22 Leco instrument for nitrogen determination 44 lignin 55 liquid-liquid chromatography 27 loss on drying 3, 38 Lovibond comparator 20 Luff-Schoor! method for reducing sugars 58 MBTH 159 meat, nitrates and nitrites in 155 mercury (II) nitrate 128 methanolic potassium hydroxide 141 methyl esters 140 micronutrients 62 mid infrared spectrophotometry 23 milk acidity in 168 chloride in 150 fat in by Gerber method 93 by Mojonnier method 96 by Rose-Gottlieb method 98 by Werner-Schmid method 100 Millon's reagent 128 mineral elements 3, 62 ashing process 76 in canned food products 78 MINITAB 8,10 Mohr titration for chloride 152 moisture 3,37 methods of estimation 38-40, 73 Monjonnier method offat estimation 49-50 molar absorptivity 19 molybdenum blue method for phosphorus estimation 84-5 near infrared (NIR) 23 NED reagent for nitrite estimation 155 Neusal solution for fat estimation 95 neutral detergent fibre 3, 106 nitrates and nitrites in meat and brine 67, 155 nitrogen, determination by Kjeldahl 41,889 see also protein nitrogen free extractives non-starch polysaccharides 3, 108 nuclear magnetic resonance (NMR) 26 official approval oils see fats and oils, study of fatty acid composition paper chromatography 27 pectins 55 pH measurements 15 phosphorus molybdenum blue colorimetric method 84-5 vanadate colorimetric method 82 picric acid 57 polarimetry 17,56 precision 5, preservatives 66 see also specific additive groups protein methods of determination 40-6 see also nitrogen, determination by Kjeldahl proximate analysis of foods pullulanase 108 radioimmunoassays 32 random errors recovery experiments reducing sugars estimation 56, 117-32 reference samples refractometry 16, 56 Reichert-Polenske-Kirschner values 52 177 178 ANALYTICAL CHEMISTRY OF FOODS replication reproducibility 5, 10 reserve polysaccharides 54 resistant starch 55, 108 Rose-Gottlieb method 47,49-50 saccharimeters 17 salt in brine 152 in dairy products 150-51 sampling 39, 72 saponification value offats and oils 144-5 Schmid-Bondzynski-Ratzlaff (SBR) method for fat estimation 47-8 sensitivity sodium chloride see salt sodium methoxide method for fat esterification 40 soluble fibre 108 solvent extraction methods 16 Southgate method for fibre estimation 61 Soxhlet method for fat extraction 47-8,912 Soxtec fat extraction apparatus 47 specific rotation 17 specificity spectrophotometry 20 instrumentation 22 spectroscopy 18 standard deviation 9-10 standard error of the mean (SEM) 10 starch 53 resistant 108 statistical assessment of quality of data stoichiometric point 15 Student's t test 11 sugars 53 by Fehling's method 117-23 by HPLC 132-3 by polarimetry 128 sulphur dioxide 66 by distillation/iodine titration 148-9 by iodine titration 146-7 systematic errors TBHQ 67,159 Tecator instrumentation for protein estimation 41 thermal combustion methods for protein estimation 43-4 thin layer chromatography 27 titratable acidity in dairy products 168-9 in fruit juices 165-6 titration error 14 titrations 13 acid-base 14 precipitation 16 redox 16 titrimetric analysis 13 total solids 73 trace elements 62 transmittance 19 unavailable carbohydrates 3, 53 uronic acids 55 uv/visible spectrophotometry 20 vanadate method for phosphorus estimation 82-3 variance vinegar, acetic acid in 167 vitamin C in fruit juice 13 inmilk 137 vitamins 62, 63-4 Volhard method for salt 150-1 wavelength 18 wavenumber 19 water 37 see also moisture 37 water activity 37 weak acid preservatives 67 Weibull-Berntrop method for fat estimation 47,49 Weibull-Stoldt method for fat estimation 47, 49 Werner-Schmid method for fat estimation 47-8 wet chemistry techniques 13 wet oxidation 77 yogurt, fat by Gerber method 93 .. .Analytical Chemistry of Foods Analytical Chemistry of Foods c s JAMES Seale-Hayne Faculty of Agriculture, Food and Land Use Department of Agriculture and Food Studies University of Plymouth... methods of gravimetric and titrimetric analysis, on the other hand, may only allow measurements to levels of around 10-3 g 2.1 Requirements and choice of analytical methods ANALYTICAL CHEMISTRY OF FOODS. .. greater body of information being required of particular foods, e.g the degree of saturation of constitutent fats, the levels of individual minerals and vitamins and the amounts of minor constituents