Lecture
Preface
Food chemistry is one of the chemical disciplines whose knowledge
is necessary for understanding the complex processes occurring in a food system,
from the study of food raw materials to the production of finished
food products. At the heart of the complex transformations of food raw materials into food
products lie hydrolytic and oxidation-reduction processes,
isomerization phenomena, and the synthesis of more complex compounds from simple ones,
proceeding at different rates under the influence of the most diverse factors:
temperature, pressure, pH of the medium, activators, and inhibitors. To understand the essence
of these processes, knowledge of the structure and properties of both macronutrients
(proteins, carbohydrates, lipids) and micronutrients (vitamins, mineral
substances), water, enzyme systems, and biologically active substances is required. In addition,
a specialist in the field of food production must understand the effect of food on
the course of physiological processes in the human body and know the fundamentals of the biochemistry
of digestion.
Understanding the role of each food component and the specifics of their transformations
enables a food specialist to competently and reliably manage
technological processes and to obtain food products that are wholesome and safe from a
toxicological point of view, fully meeting
the requirements of the science of nutrition - nutritionology.
This textbook presents the knowledge necessary for
the training of highly qualified specialists in the field of production and
quality assessment of food products: the chemical composition of food raw materials and
food products, the importance of macro- and micronutrients in food technology and for
the human body, the fundamentals of nutrition physiology, and the basic concepts of nutrition.
1 Introduction
1.1 The subject of food chemistry
Food products perform three main functions in the human body:
- supplying material for building human tissues;
- providing the energy necessary to sustain vital activity and
to perform muscular and mental work;
- providing substances that play an important role in regulating the metabolism
in the human body.
Food chemistry – is the science:
- of the chemical composition of food raw materials and food
products;
- of the general patterns of chemical transformations that occur during
the production of food products from food raw materials;
- of new technologies for producing food products using
various improvers.
1.2 Nutrition problems. Ways to solve nutrition problems
At present, the following main nutrition problems can be identified.
1. Protein deficiency. More than half of the world's population is in
a state of chronic protein starvation. The daily protein requirement of an adult
is on average 1.1 g per 1 kg of body weight, or 70-90 g per day.
A lack of protein in the diet leads to a sharp lag in a child's
development – growth slows, bone formation is disrupted, and mental
development slows. A protein deficiency in an adult's diet causes significant
health disorders: hematopoiesis is disrupted, as is the metabolism of fats and
vitamins (hypovitaminosis develops, and then avitaminosis); working capacity,
vital activity, and the body's resistance decline
to colds and infectious diseases, and the diseases themselves proceed with
severe complications. A severe protein deficiency in the diet leads to the
onset of the disease «kwashiorkor», from which tens of thousands of people die worldwide
each year.
2. Unbalanced nutrition. Nutrition is called balanced
when the qualitative and quantitative composition of the dietary intake fully
corresponds to the needs of the body.
It has been proven that unbalanced nutrition, poor in protein and vitamins,
can lead to the development of malignant neoplasms, i.e. cancer. In those
regions of the world where protein consumption meets the norms, human
life has become longer. When there is a non-optimal ratio of the
α-amino acids that make up dietary proteins, the proteins are not fully absorbed.
Consequently, the absorption of the food eaten depends primarily on the correct
balance of its composition.
At present, up to 40 thousand nutrients are counted, which are
divided into macro- and micronutrients:
- macronutrients – are food components, the daily requirement for which
is measured in tens and hundreds of grams; these include proteins, carbohydrates,
lipids;
- micronutrients – are food components, the daily requirement for which
is measured in grams, milligrams, micrograms; these include
vitamins and mineral substances.
3. The need to provide the population with quality food in
sufficient quantity. The world's population has reached 7 billion. Each
week the population of our planet increases on average by 1.2 million people.
Meanwhile, it has been established that the rate of agricultural production
somewhat lags behind the rate of population growth, and this trend will
continue in the future. This poses the problem of providing all inhabitants of the planet
with the necessary amount of food. On the other hand, food must meet
certain quality criteria, which is not always fulfilled.
In order to provide the inhabitants of the Earth with a sufficient amount of food,
new food resources are being sought; food products are being created that
differ from traditional ones; food additives are actively used, without
which the modern food industry cannot manage. Unfortunately,
in doing so the quality of food products often suffers. For example, a deficiency of
animal protein has led to its replacement with proteins of plant origin.
Animal and plant proteins differ in biological value.
The amino acid composition of animal proteins is close to the amino acid composition
of human proteins, and therefore animal proteins are complete. Plant
proteins, however, contain a reduced content of essential amino acids.
The biological value of proteins is determined by the degree of their absorption in the human
body. Animal proteins have a higher degree of digestibility than
plant proteins. Of animal proteins, 90 % of the amino acids are absorbed in the body, whereas
of plant proteins, 60-80 % are. It must be remembered that today some
animal proteins are being replaced with soy proteins, which is often genetically
modified. The latest results of scientific research indicate that
food products containing genetically modified components
are dangerous to health.
To eliminate the existing nutrition problems, a wide variety of solutions are
currently proposed:
1. Fostering a culture of nutrition is an important task facing
educational institutions, health authorities, and the mass
media. People must be taught a healthy lifestyle, instilled with
skills of a culture of nutrition, and taught to eat rationally. Food chemistry as
a separate branch of science emerged relatively recently, and it has been taught
in educational institutions to students of food-related specialties for an even shorter period. The introduction into
the educational process of the science of a healthy lifestyle (valeology) also occurred
relatively recently. In the last few years, the mass media
have begun to pay serious attention to food quality. On practically every
television channel there are regular programs telling about food
and nutrition.
2. The introduction in the agricultural sector of the economy of an intensive path of
development in place of an extensive one can serve as a real basis for increasing
the amount of food raw materials. Russian farmers, given certain
conditions, are able to satisfy the needs of Russians for
agricultural raw materials and to displace from the market the food raw materials
imported from abroad. Moreover, imported raw materials often have a low
level of quality.
3. Reducing losses during harvesting, transportation, storage, and processing
makes it possible to preserve an additional amount of raw material.
4. The introduction in the food industry of low-waste and waste-free
technologies makes it possible to obtain a greater amount of finished products from raw materials.
Often the waste of one branch of the food industry can serve as a raw material
source for another branch. For example, the waste generated in the production of
butter – buttermilk, which is a rich source of biologically
active substances, is already a raw material in bread baking.
5. The improvement and introduction of new technologies makes it possible to obtain
products with new organoleptic and physicochemical
characteristics that make them attractive to the consumer.
6. The enrichment of food products with deficient nutrients is currently
regarded as a promising way of solving nutrition problems.
The most widespread are vitaminization, mineralization, enrichment with
essential amino acids and dietary fibers (pectin, cellulose).
7. The application in the food industry of products of
microbiological synthesis is of interest. For example, at present
enzyme preparations of microbial origin are actively used.
1.3 The energy value of food components
The energy that is released from food substances in the process of
biological oxidation is used to support the physiological
functions of the body and determines the energy value of a food product.
On combustion in an atmosphere of oxygen, 1 g of carbohydrates releases on average 4.3 kcal,
1 g of fats – 9.45 kcal, 1 g of proteins – 5.65 kcal. But since food substances
are not fully absorbed by the body, it is customary to consider that 1 g of dietary protein
yields 4 kcal, 1 g of fat – 9 kcal, and carbohydrate – 4 kcal. The energy value
of food products is customarily expressed in kilocalories, with the calculation made per 100 g
of product. When conversion into the SI system is necessary, the conversion
factor 1 kcal = 4.184 kJ is used.
The energy value of food substances is given in Table 1.
Table 1 – The energy value of food components
Food substance
Energy
value
coefficient, kcal/g
Energy
value
coefficient, kJ/g
Proteins 4 16.74
Carbohydrates (by difference*) 4 16.74
Sum of mono- and disaccharides 3.8 15.90
Fiber 0 0
Fats 9 37.66
Acetic acid 3.5 14.64
Malic acid 2.4 10.04
Lactic acid 3.6 15.06
Citric acid 2.5 10.46
Other organic acids 3.0 12.55
Ethyl alcohol 7 29.29
* To determine the carbohydrate content «by difference», the amount of proteins, fats, and ash
substances is subtracted from the dry residue. As a result, not only digestible
carbohydrates but also some indigestible ones are taken into account. Therefore, the calculation of the energy value
1.3 The energy value of food components
The energy that is released from food substances in the process of
biological oxidation is used to support the physiological
functions of the body and determines the energy value of a food product.
On combustion in an atmosphere of oxygen, 1 g of carbohydrates releases on average 4.3 kcal,
1 g of fats – 9.45 kcal, 1 g of proteins – 5.65 kcal. But since food substances
are not fully absorbed by the body, it is customary to consider that 1 g of dietary protein
yields 4 kcal, 1 g of fat – 9 kcal, and carbohydrate – 4 kcal. The energy value
of food products is customarily expressed in kilocalories, with the calculation made per 100 g
of product. When conversion into the SI system is necessary, the conversion
factor 1 kcal = 4.184 kJ is used.
The energy value of food substances is given in Table 1.
Table 1 – The energy value of food components
Food substance
Energy
value
coefficient, kcal/g
Energy
value
coefficient, kJ/g
Proteins 4 16.74
Carbohydrates (by difference*) 4 16.74
Sum of mono- and disaccharides 3.8 15.90
Fiber 0 0
Fats 9 37.66
Acetic acid 3.5 14.64
Malic acid 2.4 10.04
Lactic acid 3.6 15.06
Citric acid 2.5 10.46
Other organic acids 3.0 12.55
Ethyl alcohol 7 29.29
* To determine the carbohydrate content «by difference», the amount of proteins, fats, and ash
substances is subtracted from the dry residue. As a result, not only digestible
carbohydrates but also some indigestible ones are taken into account. Therefore, the calculation of the energy value
10. What are micronutrients?
11. List and substantiate the ways of solving nutrition problems.
12. Give a definition of the concept «energy value of a food
product».
13. What is the energy value of proteins?
14. What is the energy value of carbohydrates?
15. What is the energy value of fats?
16. What data must be known to calculate the energy value of a
food product?
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