Introduction to Food Toxicology (eBook)

Leonard F. Bjeldanes, Takayuki Shibamoto (Autoren)

eBook Download: PDF | EPUB

2012 | 1. Auflage
213 Seiten
Elsevier Science (Verlag)
978-0-08-092577-6 (ISBN)

Infos

The area of food toxicology currently has a high profile of interest in the food industry, universities, and government agencies, and is certainly of great concern to consumers. There are many books which cover selected toxins in foods (such as plant toxins, mycotoxins, pesticides, or heavy metals), but this book represents the first pedagogic treatment of the entire range of toxic compounds found naturally in foods or introduced by industrial contamination or food processing methods. Featuring coverage of areas of vital concern to consumers, such as toxicological implications of food adulteration (as seen in ethylene glycol in wines or the Spanish olive oil disaster) or pesticide residues, Introduction to Food Toxicology will be of interest to students in toxicology, environmental studies, and dietetics as well as anyone interested in food sources and public health issues. The number of students who are interested in toxicology has increased dramatically in the past several years. Issues related to toxic materials have received more and more attention from the public. The issues and potential problems are reported almost daily by the mass media, including television, newspapers, and magazines. Major misunderstandings and confusion raised by those reports are generally due to lack of basic knowledge about toxicology among consumers. This textbook provides the basic principles of food toxicology in order to help the general public better understand the real problems of toxic materials in foods. - Principles of toxicology - Toxicities of chemicals found in foods - Occurrence of natural toxins in plant and animal foodstuffs - Food contamination caused by industry - Toxic chemicals related to food processing - Food additives - Microbial toxins in foods

Inhalt

Front Cover 1
Introduction to Food Toxicology 4
Copyright Page 5
Table of Contents 6
Foreword 12
Preface 14
CHAPTER 1. Principles of Toxicology 16
I. Dose-Response 16
II. Safety 20
III. Absorption 22
IV. Translocation 26
V. Storage 27
VI. Excretion 28
Suggestions for Further Reading 32
CHAPTER 2. Determination of Toxicants in Foods 34
I. Qualitative and Quantitative Analyses of Toxicants in Foods 35
II. Sample Preparations for Determination of Toxicants 36
III. Toxicity Testing 39
Suggestions for Further Reading 48
CHAPTER 3. Biotransformation 50
I. Conversion of Lipid-Soluble Substances 50
II. Phase I Reactions 51
III. Phase II Reactions 52
IV. The Effects of Diet on Biotransformation 58
V. Metabolic Induction 60
Suggestions for Further Reading 62
CHAPTER 4. Natural Toxins in Animal Foodstuffs 64
I. Toxins Occurring in Animal Liver 64
II. Toxins Occurring in Marine Animals 66
Suggestions for Further Reading 79
CHAPTER 5. Natural Toxins in Plant Foodstuffs 82
I. Natural Goitrogens 82
II. Cyanogenic Glycosides 86
III. Favism 89
IV. Lathyrism 90
V. Lecitins (Hemagglutinins) 93
VI. Pyrrolizidine Alkaloids 94
VII. Enzyme Inhibitors 95
VIII. Vasoactive Amines 99
IX. Mutagens in Natural Plants 101
Suggestions for Further Reading 111
CHAPTER 6. Fungal Toxins Occurring in Foods 112
I. Mycotoxins 112
II. Other Mycotoxins 125
III. Mushroom Fungal Toxins 128
Suggestions for Further Reading 131
CHAPTER 7. Toxic Food Contaminants from Industrial Wastes 132
I. Chlorinated Hydrocarbons 132
II. Heavy Metals 141
Suggestions for Further Reading 154
CHAPTER 8. Pesticide Residues in Foods 156
I. History 156
II. Pesticides in the Food Chain 157
III. Regulations 158
IV. Insecticides 160
V. Herbicides 169
VI. Naturally Occurring Pesticides 170
Suggestions for Further Reading 170
CHAPTER 9. Food Additives 172
I. Regulations 174
II. Preservatives 178
III. Antioxidants 184
IV. Sweeteners 188
V. Coloring Agents 190
VI. Flavoring Agents 194
VII. Flavor Enhancers 196
Suggestions for Further Reading 196
CHAPTER 10. Toxicants Formed during Food Processing 198
I. Polycyclic Aromatic Hydrocarbons 199
II. Maillard Reaction Products 203
III. Amino Acid Pyrolysates 204
IV. N-Nitrosamines 206
V. Food Irradiation 212
Suggestions for Further Reading 213
Index 214

Textauszug

Chapter 1

Principles of Toxicology

Toxicology may be defined as the study of the adverse effects of chemicals on living organisms. Its historical origins may be traced to the time when our prehistoric ancestors attempted to eat a variety of substances in order to obtain adequate food. By observing which substances could satisfy hunger without producing illness or death, ancient people developed dietary habits which allowed for the survival and growth of the species. In its modern context, toxicology draws heavily on knowledge in chemical and biological fields and seeks a detailed understanding of toxic effects. Much of toxicology today involves studies of the effects of specific substances on specific biological and chemical mechanisms.

One of the fundamental concepts of toxicology is that the dose determines the toxicity. As noted by Paracelsus (1493–1541), “All substances are poisons; there is none which is not a poison. The right dose differentiates the poison from a remedy.” Thus, the answer to the question, “Is this substance toxic?” must always be, “Yes, if taken in a large enough dose.” Thus, two of the primary objectives of toxicology are to quantitate and to interpret the toxicity of substances.

I Dose–Response

Since there are both toxic and nontoxic doses for any substance, we may also inquire about the effects of intermediate doses. In fact, the intensity of biological response is proportional to the dose of the substance to which the organism is subjected. Thus, as the dose of a substance approaches the toxic level, there is no one point at which all of the organisms in the group will suddenly develop toxic symptoms. Instead, there will be a range of doses to which individuals in the test group respond in similar ways.

Once the response has been properly defined, information from dose–response experiments can be presented in several ways. A frequency–response plot (Figure 1.1) is generated by plotting the percentage of individuals with a specific defined response as a function of the dose. If a range of doses of a particular hypertensive agent is administered to a group of patients, there will be a certain number of low doses where none of the patients will yield a specific response, which in this example could be a blood pressure of 140/100. The highest of these doses without the response is the “no-observed-effect level” (NOEL) indicated in Figure 1.1. As the dose is increased, the percentage of individuals responding with the 140/100 blood pressure will increase until a dose group where the maximum number of individuals within the group responds with this blood pressure. This dose, determined statistically, is the mean dose for eliciting the defined response in the population under study. As the concentration or dose of the hypothetical hypertensive agent is further increased, the individuals previously responding with the defined blood pressure will develop yet higher blood pressures. Eventually a dose will be reached at which all the patients within the test population respond with blood pressures higher than the defined level.

Figure 1.1 A frequency–response plot.

The curve that is generated by these data has the form of the normal Gaussian distribution, and therefore the data are subject to the statistical laws of such distributions. In this model, the numbers of individuals on either side of the mean are equal and the area under the curve represents the total population of individuals tested. The area under the curve bounded by lines from the inflection points (indicated A and A′) include the number of individuals responding to the mean dose plus or minus 2 SD from the mean dose, or 95.5% of the population. This mean value is useful in specifying a dose range over which most individuals respond in the same way.

Frequency–response curves may be generated from any set of toxicological data where a quantifiable response is measured simply by recording the percentage of subjects that responded at each dose minus the percentage that responded at the lower dose. Generally, the frequency–response curve obtained by experiment only approaches the shape of a true Gaussian distribution. Such curves illustrate clearly, however, that there is a mean dose where the greatest percentage of individuals will respond in a specific way. There will always be individuals who require either greater or smaller doses than the mean to elicit the same response. Individuals responding to smaller doses are called hypersensitive and individuals responding to greater doses are called hyposensitive.

Dose–response data and, in particular, information concerning the acute toxicity of substances are often presented as cumulative response vs. dose. In this case, various doses of the substance are administered to groups of individuals and the percentage of individuals responding in a specific way is noted. In the case of a lethal response, the number of individuals that died is noted. In the case of a nonterminal response, such as modification of blood pressure, the number of individuals responding in each group with at least a certain specified blood pressure is noted. Prior experiments establish the broad range of doses over which the response of interest occurs. Data are plotted as a cumulative percentage of individuals responding in the desired manner vs. dose (Figure 1.1). Again, a range of doses too small to elicit a response is administered to establish the NOEL. As the dose increases, the percentage of responding individuals in each test group continues to increase until a dose is reached beyond which 100% of the individuals in the test group will respond.

The shapes of the cumulative–response curves are generally sigmoidal with a nearly linear portion at intermediate dose ranges. The mean toxic dose, or in the case of the lethal effect, the LD50, is established from such curves (Figure 1.2). The LD1 and LD99 are determined in like manner. The slopes of the linear portions of these curves for different substances need not be in the same and the relative toxicities of these substances depend on the dose. These hypothetical compounds have the same LD80 and, therefore, have the same level of toxicity at this dose. However, below this dose compound A produces greater percentages of effect than compound B and in this dose range, therefore, is more toxic than compound B. At higher doses, however, compound B produces higher percentages of toxicity and, therefore, is more toxic than compound A. Based on LD50 information alone, compound A is more toxic than compound B. In comparing the toxicity of two substances the toxic response must be clearly defined, the dose range of toxicity must be indicated, and the slopes of the dose response curves must be compared.

Figure 1.2 A typical cumulative–response curve for two different compounds.

The LD50 is a statistically determined value and represents the best estimation of the dose required to produce death in 50% of the organisms tested. The LD50 value should consequently always be accompanied by some means of estimating the error in the value. The probability range, or p value, which is most commonly used, is generally accepted to be less than 0.05. This value indicates that the same LD50 value would be obtained in 95 out of 100 repetitions of the experiment.

Although every substance will exhibit a lethal dose–response curve, there are wide differences in the LD50’s for various substances. For example, the LD50 of caffeine is estimated to be about 200 mg/kg body weight; the LD50 of botulinum toxin, one of the most toxic substances known, is estimated to be about 100 ng/kg. On the other side of the scale, the LD50 of sodium chloride is estimated to be about 40 g/kg. As a general rule, substances with LD50’s of 1 mg or less are considered extremely toxic. Substances with LD50’s in the range of 1–50 mg/kg are in the highly toxic range. Moderate toxicity is ascribed to substances with LD50’s in the range of 50–500 mg/kg. Substances with higher LD50’s than this are generally considered to be nontoxic since relatively large amounts of material must be consumed in order to produce toxicity. For example, a substance with an LD50 of 2 g/kg requires consumption of about one cup of the material to produce toxicity in an adult human. On the other hand, extremely toxic substances with LD50’s in the 1 mg/kg range require consumption of only drops to produce toxicity in an adult human.

II Safety

Safety is defined as freedom from danger, injury, or damage. Absolute safety of a substance cannot be proven since proof of safety is based on negative evidence, that is, the lack of harm or the lack of damage caused by the substance. A large number of experiments can be run that may build confidence but still not prove the safety of a particular substance. Statistically, there is always the chance that the next experiment might show that the substance is unsafe. Our concept of safety has evolved over the years, and initially a substance was probably considered safe if it could be consumed without causing immediate death or acute injury. Our knowledge of toxic effects and our ability to test them have increased to the point where we now consider a substance relatively safe if it causes no adverse effects on specific biological systems. Today, certain substances are considered unsafe (or at least suspect) if they do nothing more than cause...

Produkt-Details

• Erscheint lt. Verlag: 2.12.2012
• Mitarbeit: Herausgeber (Serie): Steve Taylor
• Sprache: englisch
• Themenwelt: Medizin / Pharmazie ► Gesundheitsfachberufe ► Diätassistenz / Ernährungsberatung
• Themenwelt: Medizin / Pharmazie ► Medizinische Fachgebiete ► Pharmakologie / Pharmakotherapie
• Themenwelt: Studium ► 2. Studienabschnitt (Klinik) ► Pharmakologie / Toxikologie
• Themenwelt: Technik ► Lebensmitteltechnologie
• ISBN-10: 0-08-092577-4 / 0080925774
• ISBN-13: 978-0-08-092577-6 / 9780080925776