Methods in food analysis applied to plant products

537 Pages·1950·17.186 MB·English

by  Maynard A Joslyn

METHODS IN FOOD ANALYSIS
APPLIED TO PLANT PRODUCTS
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METHODS IN FOOD ANALYSIS
APPLIED TO PLANT PRODUCTS
BY MAYNARD A. JOSLYN
Professor of Food Technology, University of California
and
Biochemist in the California Agricultural Experiment Station
1950
ACADEMIC PRESS INC., PUBLISHERS
NEW YORK 10, Ν. Y.
COPYRIGHT 1950, BY
ACADEMIC PRESS INC.
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NEW YORK 10, Ν. Y.
NO PART OF THIS BOOK MAY BE REPRODUCED IN ANY FORM, BY PHOTOSTAT,
MICROFILM, OR ANY OTHER MEANS, WITHOUT WRITTEN PERMISSION
FROM THE PUBLISHERS
PRINTED IN THE UNITED STATES OF AMERICA
PREFACE
The lack of a suitable text in food analysis stressing principles rather
than practices, being critical rather than comprehensive, and including dis-
cussion of the recently acquired analytical tools has been felt for some time.
An adequate treatment of the principles and limitations of the available
methods of analysis is not found save in the periodical literature and in
voluminous, comprehensive handbooks of biological chemistry. In a course
on the laboratory examination of commercial fruit and vegetable products
it was found that even the upper division chemistry student, with training
in quantitative analyses, organic and inorganic chemistry, and bacteriology,
failed to grasp the principles of the current methods of analysis. In the at-
tempt to teach the student to apply his training in the fundamentals to food
analysis and to carry out the analytical procedures intelligently rather
than blindly, the author developed during the course of over twenty-odd
years a set of lecture notes and laboratory directions.
This book is the outgrowth of these lectures. In it an attempt has been
made to explain certain of the more important methods of food analysis,
stressing in particular the principles involved. The methods chosen are
for the most part those in common use for the examination and analysis of
fruit and vegetable products. The principles involved, however, are ap-
plicable to other products as well. Greater familiarity with fruit and vege-
table products and a better knowledge of the suitability of the methods of
analysis available for them have prompted their selection.
The procedures discussed have been selected particularly to illustrate
the important methods of analysis and not the methods of examination of
a particular food product. The techniques described are illustrative of those
used in the field, and these are discussed in more detail when the available
information is scattered in the literature. Methods that are comprehensively
discussed and described in recent monographs are referred to in the text
but are not presented in detail. This book is intended as a text and refer-
ence work on the physical and chemical methods used in the laboratory
examination and evaluation of commercial fruit and vegetable products.
Previous training in the principles of qualitative and quantitative analysis
as well as inorganic and organic chemistry is assumed. The author does
not believe it desirable to teach the methods of general quantitative analysis
in food analysis.
In its preparation the standard texts on food chemistry and analysis
and the various laboratory manuals of biochemistry and physiological
chemistry have been consulted, largely as guides to the original literature.
Particularly helpful have been the publications of the Association of Of-
ficial Agricultural Chemists, and of the Committee on Methods of Analysis
of the American Society of Plant Physiologists. The special reports of the
Medical Research Council and of the Department of Scientific and Industrial
Research of England have been useful, also. The author is particularly
grateful to Dr. W. W. Skinner and the other officers of the Association of
Official Agricultural Chemists for granting him permission to make use
of the material in "Methods of Analysis" and the Journal which they
publish; to the editors of the Journal of Biological Chemistry, Analytical
Chemistry and other periodicals; and to his brother, Leo Joslyn, for drawing
the graphs and diagrams used. Due acknowledgment has been made in
the text as to the source of material.
MAYNARD A. JOSLYN
Berkeley, California, September, 1950
CONTENTS
CHAPTER PAGE
I. Introduction 1
Outline of Contents, 4. Sources of Information, 4. References, 12.
II. Statistical Analysis, Errors, Expression of Results . . 13
Statistical Analysis, 13. Errors, 19. Expression of Results, 22. Refer-
ences, 26.
III. Sampling: Preparation of Samples for Analysis, Pres-
ervation of Sample 29
Sampling, 29. Preparation of Sample, 35. Preservation of Samples,
40. References, 42.
IV. Moisture Content and Total Solids 47
Properties of Water, 48. Drying Methods, 55. Vacuum-Oven Method,
57. Other Drying Procedures, 63. Distillation Procedures, 64. Elec-
trical Methods, 69. Other Physical Methods, 73. Chemical Methods,
76. References, 79.
V. Ash Content and Ashing Procedures 87
Total Ash, 88. Soluble and Insoluble Ash, 94. Alkalinity of Ash, 95.
Conductometric Methods for Ash in Sugar Products, 102. Special
Dry Ashing Procedures, 102. Ashing in Closed System in Presence
of Oxygen, 105. Wet Ashing, 107. References, 110.
VI. Extraction Methods and Separation Processes 115
Proximate Chemical Analysis, 118. Extraction Methods, 119. Crude
Fat or Ether Extract, 123. Liquid-Liquid Extraction, 129. Water-
Insoluble Solids and Water-Soluble Solids, 133. Crude Fiber, 137.
Alcohol-Insoluble Solids, 140. Alcohol Precipitate, 141. Clarification
of Sugar Extracts, 145. References, 150.
VII. Densimetric Methods 157
Measurement of Specific Gravity of Liquids, 160. Measurement of
Specific Gravity of Solids, 172. Specific Gravity of Tomato Pulp,
174. Specific Gravity of Oils, 176. Specific Gravity of Sugar
Products, 176. The Grade of Canned Fruit, 177. Rapid Determi-
nation of Total Fat, 178. References, 180.
CHAPTER PAGE
VIII. Refractometric Methods 183
Refractive Index, 183. Refractive Constants, 185. Applications of
Refractive Index Measurements, 185. Refractometers, 186. Abbé
Refractometer, 188. Soluble Solids in Fruit Products, 191. Total
Solids in Tomato Pulp from Index of Refraction of Filtrate, 195.
Refractive Index of Oils and Fats, 197. Oil Content, 197. Refer-
ences, 201.
IX. Polarimetry and Saccharimetry 203
Specific Rotation, 204. Mutarotation, 206. Polarimetry, 206. Sac-
charimeters, 209. References, 216.
χ. Colorimetry and Spectrophotometry 219
Absorption of Light, 220. Emission of Light, 224. Color Measure-
ment: Colorimetry, 224. Photoelectric Colorimetry, 233. Spectro-
photometry, 238. Turbidimetry, 242. Artificial Coloring Matter,
244. References, 247.
XI. Potentiometric and Related Methods 255
Principles of Design and Use of Potentiometers, 256. Oxidation-
Reduction Potentials, 259. Potentiometric Titrations, 269. Polaro-
graphic Methods, 270. Thermometry and Pyrometry, 274. Refer-
ences, 275.
XII. pH and Buffer Capacity 281
Definition of pH, 281. Buffers and Buffer Capacity, 283. Application
of pR and Buffer Capacity in Food Technology, 285. Colorimetric
Measurement of pll, 287. Electrometric Determination of pH,
292. References, 298.
XIII. Viscosimetric and Other Physical Methods 305
Viscosimetry, 305. Plasticity and Plastometers, 314. Gelometers,
315. Tenderometers, 320. Conductivity Measurements and Con-
ductometric Analysis, 322. Gas Analysis, 329. References, 331.
XIV. Acidimetry 337
Organic Acids of Fruits and Vegetables and Other Foods, 339. Total
Organic Acids, 344. Volatile Acids, 351. Separation and Determi-
nation of Acids, 362. Formic Acid, 362. Lactic Acid, 364. Tartaric
Acid, 369. References, 371.
CHAPTER PAGE
XV. Alcoholometry 379
Ethyl Alcohol, 381. Volumetric Dichromate Procedure, 385. Physical
Methods, 389. Methyl Alcohol, 392. Glycerin, 395. References,
400.
XVI. Carbohydrates: Reducing Sugars 405
Occurrence, 406. Chemical Methods for Reducing Sugars, 409. Copper
Reduction Procedures, 411. Ferricyanide Reduction Methods,
422. Direct Iodometric Methods, 426. Identification and Determi-
nation of Sugars by Microorganisms, 429. References, 430.
XVII. Carbohydrates: Sucrose and Starch 437
Sucrose, 437. Starch, 440. References, 449.
XVIII. Pectins and Pentosans 453
General Methods of Determining Pectin Content, 454. Pentosans,
462. References, 467.
XIX. Tannins 471
Methods Available for Analysis of Tannins, 473. Loewenthal Titra-
tion, 474. Colorimetric Procedure, 477. Cinchonine Tannate Pro-
cedure, 479. References, 480.
XX. Organic Nitrogenous Compounds 483
Total Organic Nitrogen, 493. Nitrogen Fractionation, 504. References,
505.
Index 513