What Is Food Chemistry

 Food Science deals with the physical, chemical and biological properties of
foods as they relate to stability, quality, processing, safety, nutritive value,
wholesomeness, convenience and cost. Food Science is an inter-disciplinary
subject involving primarily bacteriology, chemistry, biology and engineering.

What Is Food Chemistry

Food chemistry, a major aspect of food science deals with the composition and
properties of food and chemical changes it undergoes during handling,
processing and storage. Food Chemistry is intimately related to chemistry and
biological sciences like biochemistry, botany, zoology and molecular biology. 

The primary interests of biological scientists include reproduction, growth and
physiological and biochemical (morphological) changes that biological
substances undergo under environmental conditions that are compatible with

On the contrary, food chemists are concerned primarily with biological
substances that are dead or dying (post harvest physiology of plants and postmortem physiology of muscle) and changes they undergo when exposed to
very wide range of environmental conditions. That is why a food chemist is
concerned with conditions suitable for sustaining the residual life processes
(post harvest physiology) for example fresh fruits and vegetables during their

Both in home scale food preparation and commercial food processing, food
raw material are converted into convenient forms by pounding or milling of
food grains, pulses, etc., oil extraction, extraction of fruit juices, etc. 

chemists are concerned with the chemical properties of these disrupted food
tissues. In other words, food chemists have much in common with biological
scientists, yet they also have interests that are distinctly different and are of
utmost importance to human kinds.

History Of Food Chemistry

The origin of food chemistry is as old as human civilization and shrouded in
obscurity. Until the 20th Century food chemistry did not have a clear identity
and its early developments were associated with agricultural chemistry.
During the period 1780-1850 many famous scientists made important
discoveries, which laid the foundation of food chemistry.
Carl Wilhelm Scheele (1742-1786) is considered as one of the greatest chemist
of all time who has done pioneering work in food chemistry. He isolated and
studied the properties of lactose from milk, malic acid from apples and citric
acid from lemon juice. 
He also tested a number of fruits for the presence of
citric, malic and tartaric acids as well as various new chemical compounds.
Antoine Laurent Lavoisier (1743-1794) also investigated the organic acid
content a large number of fruits. He was perhaps the first to show that the
process of fermentation could be expressed as a balanced equation. 
de Saussure (1767-1845) studied the CO2 and O2 exchange during plant respiration and determined the mineral contents of plants by ashing. Joseph
Louis Gay-Lussac (1778-1850) and Louis-Jacques Thenard (1777-1857)
devised the first method to determine the percentages of carbon, hydrogen and
nitrogen in vegetables. 
Sir Humphrey Davy (1778-1829) who isolated the
elements K, Na, Ba, Sr, Ca and Mg wrote books on agricultural chemistry. In
his book elements of Agriculture Chemistry (1813) he stated “the most
essential vegetable substances consist of hydrogen, carbon and oxygen in
different proportion, generally alone, but in some few cases combined with
azote (nitrogen).
Jons Jacob Berzelius (1779-1848) determined the elemental composition of
about 2000 compounds there by verifying the law of definite
proportions.Justus von Liebig (1803-1873) classified foods as either
nitrogenous (vegetable fibrin, albumin, casein, and animal flesh and blood) or
nonnitrogenous (fats, carbohydrates, and alcoholic beverages). 
He is also
credited for perfecting methods for the quantitative analysis of organic
substances by combustion. His book “Researches on the Chemistry of Food”
is considered by many as the first book on food chemistry.
By the first half of the twentieth century, most of the essential dietary
substances, namely carbohydrates, proteins, lipids, vitamins, minerals etc. were
discovered and characterised.

Functions Of Food Chemistry

Food chemistry, along with the other discipline of food science and nutrition
play a vital role in ensuring nutritious and safe food to the human being. It is
needless to state that to accomplish these roles, a thorough knowledge of the
detailed chemical (nutritional) composition of foods is of prime importance.

Chemical Composition Of Foods

As already mentioned, food chemistry has enabled us to know the nutrient
composition of most of the common foods. This knowledge on their nutritional
role and importance also accumulated. Nutrition studies showed that the
human system require certain nutrients like carbohydrates, proteins and fats in
large quantities and some others like vitamins and minerals in much smaller
Therefore, the former group of nutrients were termed “major
nutrients” and the latter ‘minor nutrients’. Depending on the composition of
foods, they were classified as ‘carbohydrate rich (starchy) foods (e.g. Cereals,
root crops), protein rich foods (e.g. meat, poultry and marine foods, legumes),
fatty foods (oil seeds, fatty meat and fish) etc, Fruits and vegetables, in general
are good sources of the minor nutrients viz. vitamins and minerals which have
protective roles against certain deficiency diseases. Therefore, fruits and
vegetables were classified as protective foods.
Knowledge on food composition and nutrition has also enabled planning and
designing balanced foods suitable for different age groups, sex, convalescing,
etc. Balanced food is a food formulation, which will provide all the nutrients in
required quantities. Wherever, a food formulation is still deficient in certain
nutrients, this knowledge enabled fortification to supplement them.
Today’s nutrition literate consumers are demanding information on the nutrient
content of the foods they consume. This has resulted in nutrition labelling of
food products, which has become mandatory in some countries. 
Nutrition label
provides information on the nutrient content of a particular food product and
also what percentage of the Recommended Dietary Allowance of the nutrient
is present in one normal serving of the product. The serving size is expressed
in millilitres or grams. It is needless to state that nutrition labelling requires
precise chemical analysis of the products.
In addition to the major and minor nutrients mentioned already, a number of
bioactive compounds have been isolated from foods especially from fruits,
vegetables and herbs. They are collectively termed ‘Nutraceuticals’ or
Some of them include: carotenoids, flavonoids, sulphides and
thiols and phenolic cyclic compounds. Several of them have been shown to
have antioxidative protection of the human body, suppression of cancer
growth, improvement of vascular health, retardation of osteoporosis and
control of cataracts. These developments have revived the old concept of
‘Food as Medicine’.
The knowledge of the chemistry of food constituents has also enabled in
modification of foods and food constituents. Production of fermented foods is
an example of food modification. A large number of traditional fermented
foods have been produced in different countries. 
Improvements in their
processing steps and ensuring consistent quality have been possible due to the knowledge in the chemical (biochemical) reactions. You will be learning more
on this in subsequent units. Production of glucose syrup and high fructose
syrup from starch, protein hydrolysates from proteins are examples of
modification of food constituents.

Quality Changes in Foods

Quality of a food is a complex combination of several sensory and hidden
(intrinsic) attributes. You are familiar with some of the sensory qualities like
colour and appearance, firmness, mouth feel, flavour, taste etc. Alterations in
these qualities of a food material, like for example, fruits results in value
reduction and even rejection by the buyer. 
All these sensory quality changes
are caused by chemical (or biochemical) reactions. For example, loss of the
green colour of spinach on storage or cooking is due to degradation of
chlorophyll. Similarly, browning of cut apples is initiated due to enzymatic
oxidation of phenolic substances. 
Softening of fruits for example is due to the
breakdown of pectins or toughening of meat is due to post mortem chemical
changes resulting in pH reduction and tissue hardening. Flavour changes are
also due to chemical reactions. 
For example, flavour change in fatty foods
called rancidity is due to oxidation of unsaturated fatty acids. You will be
learning more on these in subsequent units. The important point to be
understood is that once you know the chemical cause of quality deterioration, it
is possible to devise methods to control it.
The hidden quality factors of food are the nutrients content, and absence of
adulterants and toxicants. Hidden quality cannot be perceived by sensory
means. They have to be assessed by chemical means only. Among the hidden
quality characteristics, nutritional quality changes are more important in
storage and processing of foods. 
Among the nutrients, some of the vitamins are
sensitive to processing conditions. For example, vitamin C (ascorbic acid) is
very heat labile. Knowledge on the chemical kinetics of the reactions has
enabled development of High Temperature Short Time processing technique
and also non-thermal methods of processing. Breakdown of thiamine (vitamin
B1) is well known. Therefore, sulphites are avoided for preservation of foods
rich in thiamine. Nutritional evaluation of processed foods has been the subject
of intense studies in recent times. 
The quality changes in foods during processing and storage are due to two
major factors namely product factors and environmental factors. Product
factors include the chemical composition of a particular food, its pH, and
available water content. 
Environmental factors of importance are temperature
and time, light, access to microbial and insect attack and gas composition of
the storage atmosphere. Altering the composition of food products to control
quality changes is not easily possible except removal of water (drying) even
though in a few cases it has been done. For example, to prevent browning of
egg powder, glucose is removed from egg by enzymatically oxidising it.
Temperature effect on quality is to a great extent controlled by storage at low
temperatures. One of the major functions of packaging is to prevent or reduce
the effect of light on food quality. The effect of gas atmosphere on quality is
equally important. When a food product is exposed to the atmosphere
(containing about 79% N2 and 21% O2) several oxidative reactions take place. 
Examples are oxidation of fatty acids, oxidation of ascorbic acid, oxidative
changes in flavour and browning reactions. In order to prevent the effect of
oxygen in canned foods, the cans are exhausted (steam heating of cans filled
with the product before sealing) to expel air, fruit juices are deaerated,
antoxidants are added to fatty foods etc. 
You will be learning these techniques
in other units. Another method is to alter the gas atmosphere, especially to eliminate or reduce oxygen content in the gas atmosphere inside a package.
You must have seen pillow packs (bloating pouches) of potato chips. They are
filled with nitrogen to prevent browning and also to avoid physical damage to
the chips. In the case of fresh fruits and vegetables, complete exclusion of
oxygen is harmful. 
Knowledge of the biochemistry of plant respiration shows
that reducing the oxygen concentration and increasing the carbon dioxide
concentration can extend the storage life of these commodities. This has led to
the development of Modified Atmosphere Packaging (MAP) and Controlled
Atmosphere (CA) Storage of fresh fruits and vegetables. In MAP, mostly the
gas composition is modified by the respiring commodities while in CA storage,
the gas composition is modified physically by introducing or removing the
respective gases.
Food adulterants and toxicants in foods have to be monitored to ensure food
safety. This is a growing challenge to the food chemist.

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