Foods are materials, which in their naturally occurring, processed or cooked
forms, are consumed by human beings for their nourishment, sustenance and
enjoyment. Moreover food items are food grains (cereals: wheat, rice, coarse
cereals like sorghum, millets etc.), legumes (pulses: red gram, black gram,
green gram, beans), horticultural produce (fruits, vegetables, spices,
condiments etc.), livestock produce (meat, egg, milk etc.) and fish (fish,
prawns, crabs etc.). Beverages like tea, coffee, cocoa etc are also part of food.
Food sources in their natural form are cultivated, reared, captured or cultured.
Some foods can be taken in raw form while most need some kind of
processing to introduce desirable characteristics in them to make them
acceptable, edible and digestible.
Food, as is known, is the essence of life. It is an exciting subject to study and
know its importance and values. In earlier days human started experimenting
on various forms and tastes. This led to the development of culinary art. Later
on some people who developed special interest, became expert and earned
name and fame. Much later it became a huge industry with a trade value of
US$ two trillion.
Food Science and Food Technology can be defined as
Food Science: Food Science is the discipline in which the Biological and
Physical Sciences and Engineering are used to study the nature of Foods,
Causes of their deterioration and the principles underlying Food Processing.
Food Technology: It is the application of Food Science to the selection,
preservation, processing, packaging, distribution and use of safe nutritious and
Constituents Of Food, Properties And Their Significance
(hedonic) value. The former is relatively easier to quantify since important
nutrients are limited in number and their effects are more or less defined.
properties of food including visual appeal, smell, taste and texture, which
interact with our senses. These properties are influenced by a large number of
compounds, which in part have not been identified. Besides their nutritional
and hedonic values, foods are increasingly being judged according to
properties, which determine their handling.
Physical Properties of Foods
properties that lend themselves to description and quantification by physical
rather than chemical means.
volume, density and surface area as selected to homogeneous units. The
geometrical characteristics of texture refer to structural geometry and
structurally heterogeneous foodstuffs.
into 13 categories such as round, oblate, oblong, conic, elliptical,
truncated, ribbed etc. the much prevailing method for quantitative shape
description involves sphericity which is
diameter of smallest circumscribing sphere (usually the longest diameter
of the test object).
screen, through which the product will or will not pass and measurement
of diameter or length of product.
liquid foods present no special problem, other than the proper control of
temperature at which measurements are made. Standard volumetric
methods (graduated cylinder) for volume quantification and pycnometer or
commercial density meters for density measurement are simple.
of agricultural products, especially those exhibiting an irregular shape, is
usually determined by water displacement. Density of solids can be
determined by floatation in liquids (usually salt solutions) of different
densities. Density of certain agricultural produce (peas, lima beans,
potatoes) is an indirect measure of their texture also.
in floatation is also used with many agricultural commodities to remove
defective materials and extraneous matter. Density is measured and
defined in various ways like true density, substance density, particle
density, apparent density and bulk density.
have been developed for calculating the surface area of products such as
fruits etc based on shape factor measurement (e.g. areas of axial or
longitudinal cross sections).
quality point are colour and surface appearance (gloss) of the produce.
These works on reflected light along with some spectrophotometer
measuring light in both reflectance and transmittance modes. Transmitted
light may be used for detecting defects such as water cores in apple.
quality produce (such as the golden yellow of a table orange) or can alert
the consumer to a potential psychological danger (such as green processed
meat). It also inferences flavour requirements in produce such as
beverages and dessert gels and it affects consumer perceptions.
demarcations reflectance (lightness), dominant wavelength and purity. In
this Hunter colour lab equipment colour scales L, a and b are used. L
defines the lightness, a, the red-green lines and b the blue-yellow lines.
important physical aspect of food quality detected by human vision.
Typical of products where a shiny surface is valued as apples, cucumbers,
cherries, on the other hand, oranges, green beans etc have dull surface.
Gloss in the psychological attribute of surfaces associated with the
spectrum reflects and can vary from surface to surface
some of the reasons for cataloguing separately the flow behaviour of specific
broad classes. Fundamental tests measure properties that are inherent to the
material and independent on the geometry of sample, the condition of loading
or the apparatus e.g. modulus of elasticity, Poisson ratio, relaxation time, and
geometry, speed of test etc also determine the parameter estimated. The
fundamental tests as applied to solid foods may again be classified into two
essentially different groups: those divided under conditions of static (quasistatic) loading and those considered under dynamic conditions. Because foods
are visco-elastic both time dependants and time independent measurements
be fluid foods. Foods may exist as solids at one temperature and as liquid at
other temperature (like ice-creams), suspension of solid matter is fluid media
foods exhibit flow behaviour ranging from simple Newtonian to time
dependent non-Newtonian and visco-elastic. For example, raw whole egg at
21 C was found to be a Newtonian fluid. However frozen egg was found to be
a shear-thinning fluid.
cooling which foods are often subjected. Variability in composition and
physical characteristics is typical for all food products.
thermal diffusivity and heat transfer coefficient. These are much commonly
used properties in designing a system for heating/ cooling of foods.
several other properties that are thermal in value but are much less important
to most heat transfer applications: melting/freezing point, latent heat, heat of
respiration, heat of adsorption, coefficient of thermal expansion, dielectric
constant, emissivity and absorptivity (radiation heat transfer).
Mass Transfer Properties
processing. It is also involved in several physical, chemical and biological
food processes such as salting, sugaring, oxygen absorption, de-aeration, and
cleaning of process equipment. It is important in food processing and storage,
where transfer of moisture; vapours/ gases and flavours components may
influence food quality.
its distribution within the product. Electrical properties are of most basic
interest in high frequency food processing and their dielectric properties
because these determine a number of related electrical properties, which affect
energy coupling and its distribution within a food product.
acts as heavy insulators i.e. non-ideal capacitors, in terms of their ability to
store and dissipate electrical energy from an applied electromagnetic field by
radiation transfer. These properties result form electric charging and less
current generally related to materials electrical capacitance and resistance and
are defined by fundamental dielectric properties.