Caffeine

PREFACE

Caffeine was conceived for a wide range of readers interested in the

effects on human health, nutrition, and physiological function of the

methylxanthine beverages and foods—tea, coffee, maté, cola beverages,

and cocoa and chocolate products. These products supply one or more of

the dietary methylxanthines—caffeine, theobromine and theophylline—

and are an integral part of the diet of many people in many countries. The

interest in the health effects of both the methylxanthines in isolation and

in the products containing them has grown rapidly in recent years.

This comprehensive text gathers in a single volume in-depth informa￾tion on composition, processing, consumption, health effects, and epide￾miological correlations for the methylxanthine beverages and foods and

should serve as a useful tool for anyone interested in the methylxanthine–

containing products. It briefly covers metabolic and physiological aspects.

This design should make this book valuable to physicians, nutritionists,

other health professionals, and food scientists.

Chapters 1 and 2 offer an introductory, concise overview of the chem￾istry and analysis of the methylxanthines. In Chapters 3 through 8, each

natural product (tea, coffee, maté, and cocoa and chocolate products) is

described. Botany, cultivation, processing, composition, and consumption

patterns are covered in detail. The reader can better grasp how the chemi￾cal complexity of the methylxanthines makes it important to carefully

distinguish between the effects of the methylxanthines in isolation and as

part of one of these natural products. The extremely critical and complex

question of consumption is discussed in more than one chapter, but is the

specific focus of Chapter 9. Chapter 10 covers the basic physiology and

biochemistry of caffeine, not with the physiologist or biochemist in mind,

but rather the health professional in need of a concise, easy to read over￾view of these topics. Chapters 11 and 12 focus on the ergogenic, cognitive,

and emotional effects of caffeine, while Chapters 13 through 16 deal

directly with the health effects of methylxanthines, coffee, or tea and their

effects on serum cholesterol, cancer and fibrocystic breast disease, calcium

and bone health, and human reproduction. Appendix I lists the caffeine

content of various popular cola beverages.

©1998 CRC Press LLC

No single book can possibly cover all aspects of the chemistry, con￾sumption, and health effects of the methylxanthines, but I hope that this

volume will help a wide variety of readers to better understand coffee, tea,

maté, cola beverages, and cocoa and chocolate products and their effects

on human health.

Gene A. Spiller, Ph.D.

Los Altos, California

©1998 CRC Press LLC

THE EDITOR

Gene Alan Spiller, Ph.D., D.Sc., is the director of the Health Research

and Studies Center and of the Sphera Foundation in Los Altos, California.

Dr. Spiller received his first doctorate in chemistry from the Univer￾sity of Milan (Italy), and later a Master’s degree and a Ph.D. in nutrition

from the University of California at Berkeley. He did additional studies at

the Stanford University School of Medicine at Stanford, California. He is

a Fellow of the American College of Nutrition, a Certified Nutrition Spe￾cialist, and a member of many professional nutrition societies.

In the 1970s, Dr. Spiller was head of Nutritional Physiology at Syntex

Research in Palo Alto, California, where he did extensive human and

animal research. At the same time he edited many clinical nutrition books.

He continued his work in clinical nutrition research and publishing in the

1980s and 1990s, as a consultant and as the director of the Health Research

and Studies Center and of the Sphera Foundation in Los Altos, California.

Many human clinical studies, reviews, and other publications were the

results of this work. Dr. Spiller has carried out clinical studies on the effect

of complex whole foods, fiber and high fiber foods such as raisins and

whole grains, lipids such as monounsaturated fats, and foods high in fiber

such as nuts. Some of his recent research has focused on antioxidants,

immunity, and bone density in aging. Since the early 1980s, Dr. Spiller has

had a special interest in the health effects of coffee and tea. In addition, he

has been a lecturer in nutrition in the San Francisco Bay Area, first at Mills

College and currently at Foothill College.

Dr. Spiller is the editor of many clinical nutrition books. Among his

multiauthor books are The Methylxanthine Beverages and Foods: Chemistry,

Consumption, and Health Effects (Alan R. Liss, 1984), The Mediterranean Diets

in Health and Disease (Van Nostrand Rheinhold, 1991), CRC Handbook of

Fiber in Human Nutrition 2nd Edition (CRC Press, 1993) and CRC Handbook

of Lipids in Human Nutrition (CRC Press, 1996).

©1998 CRC Press LLC

CONTRIBUTORS

Joan L. Apgar, B.A.

Food Science & Technology

Hershey Foods Corporation

Hershey, PA 17033-0805

Douglas A. Balentine, Ph.D.

Lipton

Englewood Cliffs, NJ 07632

Bonnie Bruce, Dr.P.H., M.P.H., R.D.

Health Research and Studies Center and

Sphera Foundation

Los Altos, CA 94023-0338

Christopher Gardner, Ph.D.

Stanford University Medical School

Center for Research in Disease Prevention

Palo Alto, CA 94304

Harold N. Graham, Ph.D.

Lipton (retired)

Englewood, NJ 07632

Matthew E. Harbowy

Lipton

Englewood, NJ 07632

David Lee Hoffman

Silk Road Teas

Lagunitas, CA 94938

W. Jeffrey Hurst

Food Science & Technology

Hershey Foods Corporation

Hershey, PA 17033-0805

Roland J. Lamarine, H.S.D.

Department of Health and Community

Services

California State University

Chico, CA 95929-0505

Lisbet S. Lundsberg, Ph.D.

Perinatal Epidemiology Unit

Yale University School of Medicine

New Haven, CT 06511

Robert A. Martin, Jr., Ph.D.

Food Science & Technology

Hershey Foods Corporation

Hershey, PA 17033-0805

Barry D. Smith, Ph.D.

Department of Psychology

University of Maryland

College Park, MD 20742

Gene A. Spiller, D.Sc., Ph.D.

Health Research and Studies Center and

Sphera Foundation

Los Altos, CA 94023-0338

Monica Alton Spiller, M.Sc.

Alton Spiller, Inc.

Los Altos, CA 94023-0696

Stanley M. Tarka, Jr., Ph.D.

Food Science & Technology

Hershey Foods Corporation

Hershey, PA 17033-0805

Kenneth Tola

Department of Psychology

University of Maryland

College Park, MD 20742

Myron Winick, M.D.

R. R. Williams Professor of Nutrition

(Emeritus)

Columbia University

College of Physicians and Surgeons

©1998 CRC Press LLC

ACKNOWLEDGMENTS

The editor gratefully acknowledges Mr. William F. Shannon, Con￾tracts Manager at John Wiley & Sons, Inc., whose efforts in obtaining

reversion of the copyright of The Methylxanthine Beverages and Foods (Alan

R. Liss, 1984) from John Wiley & Sons to Dr. Gene Spiller enabled us to

produce this volume. Thanks also to Rosemary Schmele for assistance in

various phases of the editing process and in coordinating the final manu￾script.

©1998 CRC Press LLC

DEDICATION

To Drs. Denis Burkitt and Hugh Trowell, who have given me a unique

perception of the correlation of health and disease with food, and to Drs.

John Farquhar and David Jenkins, who always inspire me with their work

on the relation of diet to chronic diseases.

©1998 CRC Press LLC

TABLE OF CONTENTS

Chapter 1

Introduction to the Chemistry, Isolation, and Biosynthesis

of Methylxanthines

Stanley M. Tarka, Jr. and W. Jeffrey Hurst

Chapter 2

Analytical Methods for Quantitation of Methylxanthines

W. Jeffrey Hurst, Robert A. Martin, Jr., and Stanley M. Tarka, Jr.

Chapter 3

Tea: The Plant and Its Manufacture; Chemistry and Consumption

of the Beverage

Douglas A. Balentine, Matthew E. Harbowy, and Harold N. Graham

Chapter 4

Tea in China

David Lee Hoffman

Chapter 5

The Coffee Plant and Its Processing

Monica Alton Spiller

Chapter 6

The Chemical Components of Coffee

Monica Alton Spiller

Chapter 7

Methylxanthine Composition and Consumption Patterns of

Cocoa and Chocolate Products

Joan L. Apgar and Stanley M. Tarka, Jr.

Chapter 8

Maté

Harold N. Graham

Chapter 9

Caffeine Consumption

Lisbet S. Lundsberg

©1998 CRC Press LLC

Chapter 10

Basic Metabolism and Physiological Effects of the Methylxanthines

Gene A. Spiller

Chapter 11

Caffeine as an Ergogenic Aid

Roland J. Lamarine

Chapter 12

Caffeine: Effects on Psychological Functioning and Performance

Barry D. Smith and Kenneth Tola

Chapter 13

Coffee, Caffeine, and Serum Cholesterol

Christopher Gardner, Bonnie Bruce, and Gene A. Spiller

Chapter 14

Coffee, Tea, Cancer and Fibrocystic Breast Disease

Gene A. Spiller and Bonnie Bruce

Chapter 15

Caffeine, Calcium, and Bone Health

Bonnie Bruce and Gene A. Spiller

Chapter 16

Caffeine and Reproduction

Myron Winick

Appendix I

Caffeine Content of Some Cola Beverages

Gene A. Spiller

©1998 CRC Press LLC

Chapter 1

INTRODUCTION TO THE

CHEMISTRY, ISOLATION, AND

BIOSYNTHESIS OF

METHYLXANTHINES

Stanley M. Tarka, Jr and W. Jeffrey Hurst

CONTENTS

I. Introduction

II. Physical and Chemical Properties of the Methylxanthines

A. Organoleptic Properties

B. Melting and Sublimation Temperatures

C. Solution Formation

D. Ultraviolet and Infrared Absorption

E. Complex Formation

F. Acidic and Basic Equilibria

III. Isolation of the Methylxanthines

IV. Biosynthesis of the Methylxanthines

A. In Coffee

B. In Tea

C. In Cacao

References

©1998 CRC Press LLC

I. INTRODUCTION

The methylxanthines of interest are caffeine (1,3,7-trimethylxanthine),

theophylline (1,3-dimethylxanthine), and theobromine (3,7-

dimethylxanthine) and they occur in coffee, tea, maté, cocoa products, and

cola beverages. This chapter is an introduction to their chemistry, isola￾tion, and biosynthesis. While the class of methylxanthines is large and

comprised of more members than these three, this chapter will essentially

be limited to caffeine, theobromine, and theophylline.

Purine is the parent heterocyclic compound of the methylxanthines,

which are often referred to as the purine alkaloids.1–7 Purine is also the

parent compound of some of the base constituents of the nucleotides,

which in turn are part of the nucleic acids RNA and DNA. Thus, it appears

that the purine alkaloids have similar precursors to nucleic acids.

II. PHYSICAL AND CHEMICAL PROPERTIES OF THE

METHYLXANTHINES

A. Organoleptic Properties

Caffeine, as an example methylxanthine, is a colorless powder at room

temperature; it is odorless but does have a slightly bitter taste.8

B. Melting and Sublimation Temperatures

The trimethylated xanthine, caffeine, sublimes at 1800°C, which is a

lower temperature of sublimation than theobromine.10 Temperatures of

melting and sublimation are given in Table 1.

C. Solution Formation

Solubility values are distinctive for caffeine, theobromine, and theo￾phylline (see Table 2). Caffeine dissolves well in boiling water, but at room

temperature chloroform is one of the best solvents. Theobromine is gen￾erally much less soluble than caffeine but it will dissolve readily in aque￾ous acids and alkalis. Theophylline is intermediate between caffeine and

theobromine in its ability to form solutions. A series of studies were

conducted by Hockfield17 and Gilkey,

18 who, after comparing the solubil￾ity rates of the xanthine alkaloids, determined that the methylxanthines in

which both heterocyclic nitrogen atoms in the ring are methylated (caf￾feine and theophylline) display a much greater solubility in polar solvents

than those with at least one unmethylated nitrogen atom (theobromine).

©1998 CRC Press LLC

TABLE 1

Melting and Sublimation Temperatures for

Methylxanthines

Sublimation

Compound point (°C) Melting point (°C)

Caffeine 1808 236.5 under pressure8

1789 2389

1787 235 anhydrous7

Theobromine 290–2959 3579

2907 330 sealed tube7

Theophylline — 270–2749

269–2727

TABLE 2

Solubility Values for Methylxanthines

Caffeine Theobromine Theophylline

Solvent (%) (%) (%)

Water, 150°C 1.38

Water 2.29 0.005 9 0.839

Water, 400°C 4.68

Water, hot Soluble9

Water, 800°C 18.29

Water, boiling 66.79 0.679

Ether 0.38 Almost insol.9 Sparingly sol.9

0.29

Alcohol 1.28 1.259

1.59

Alcohol, 600°C 4.59

95% Alcohol 0.045 9

Ethyl acetate 2.58

Chloroform 13.08 Almost insol.9 0.919

18.29

Acetone 2.09

Benzene 1.09 Almost insol.9

Benzene, boiling 4.59

Pyrrole Freely sol.9

Tetrahydrofuran Freely sol.9

and 4% water

Petroleum ether Sparingly

sol. 9

Carbon Almost insol.9

tetrachloride

These studies indicate that intermolecular hydrogen bonding between

lactam systems in the nonmethylated alkaloids is responsible for these

differences. The findings indicate a difference between the enthalpies of

theobromine, which would be expected to form a dimer, and those of

©1998 CRC Press LLC

caffeine and theophylline, whose structures would preclude dimerization,

is approximately that of one hydrogen bond per molecule.

D. Ultraviolet and Infrared Absorption

The methylxanthines show useful strong ultraviolet (UV) absorption

between 250 and 280 nm.11 The spectra for the methylxanthines are very

similar and only when one uses techniques such as derivative spectros￾copy can substantial differences be seen. In addition to the UV absorption,

the methylxanthines also exhibit strong infrared (IR) spectra which can

provide critical information about these compounds.

E. Complex Formation

In aqueous solution, caffeine associates to form at least a dimer and

probably a polymer;12 the molecules are arranged in a stack.13 Caffeine will

also associate with purines and pyrimidines either as the free bases or as

their nucleosides.13 Caffeine crystallizes from water as a monohydrate [9].

Chlorogenic acid forms a 1:1 complex with caffeine, which can be

crystallized from aqueous alcohol and yields very little free caffeine on

extraction with chloroform. Other compounds with which caffeine will

complex in this way include isoeugenol, coumarin, indole-acetic acid, and

anthocyanidin. The basis for this selection was the requirement for a

substituted aromatic ring and a conjugated double bond in forming such

a complex. This kind of complex does modify the physiological effects of

caffeine.14 Complex formation will also increase the apparent aqueous

solubility of caffeine in the presence of alkali benzoates, cinnamates, cit￾rates, and salicylates.9

A description of the physical properties and behavior of caffeine in its

aqueous solution was published in 1980 by Both and Commenga.15

Where the complexing agent is phenolic, the pH must be such that the

phenol is undissociated; usually such complexes form at a pH below 6.

Free caffeine concentrations are increased above pH 6.14

The methylxanthines vary in their ability to form certain metal com￾plexes. For example, theophylline will complex with both copper and

silver whereas caffeine will not.16 The interpretation of this is that the metal

ion forms a pentacyclic complex involving the phenolic 0 at C-6 and N at

7.16

F. Acidic and Basic Equilibria

The acidic and basic equilibrium constants Ka and Kb are given in

Table 3.

©1998 CRC Press LLC