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
wholesome food.
Constituents Of Food, Properties And Their Significance
There are two important properties of food: nutritional value and taste
(hedonic) value. The former is relatively easier to quantify since important
nutrients are limited in number and their effects are more or less defined.
(hedonic) value. The former is relatively easier to quantify since important
nutrients are limited in number and their effects are more or less defined.
Defining the taste is more difficult because it must take into account all those
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.
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
In broad sense, the physical properties of foods may be defined as those
properties that lend themselves to description and quantification by physical
rather than chemical means.
properties that lend themselves to description and quantification by physical
rather than chemical means.
a) Geometrical properties: These encompass the properties of size, shape,
volume, density and surface area as selected to homogeneous units. The
geometrical characteristics of texture refer to structural geometry and
structurally heterogeneous foodstuffs.
volume, density and surface area as selected to homogeneous units. The
geometrical characteristics of texture refer to structural geometry and
structurally heterogeneous foodstuffs.
Size and shape: The shapes of fruits and vegetables have been classified
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
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
Sphericity = de/dc
Where, de is the diameter of a shape of same as the test object and dc is its
diameter of smallest circumscribing sphere (usually the longest diameter
of the test object).
diameter of smallest circumscribing sphere (usually the longest diameter
of the test object).
Size is usually characterized by determining the opening, as in sieve or
screen, through which the product will or will not pass and measurement
of diameter or length of product.
screen, through which the product will or will not pass and measurement
of diameter or length of product.
Volume, density and surface area: Volume and density measurement of
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.
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.
Volume
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.
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.
Separation by density
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.
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.
Surface area values have a meaning in heat transfer. A number of methods
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).
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).
b) Optical properties: The most important optical properties from the
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 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.
Colour: It is one of the most important attributes and can separate a high
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.
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.
Spectrophotometric method for colour description is based on three
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.
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.
Gloss: The appearance of a surface, whether it is glossy or dull, is an
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
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
Rheological Properties
The complex nature of foods their variability and their diverse behaviour are
some of the reasons for cataloguing separately the flow behaviour of specific
foods.
some of the reasons for cataloguing separately the flow behaviour of specific
foods.
The evaluation of rheological properties of solid foods can be divided into two
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
shear modulus.
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
shear modulus.
Empirical or imitator tests are used to determine properties such as puncture force and extrusion energy where the mass of the sample,
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
are required.
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
are required.
Foods that flow under gravity and do not retain their shape are considered to
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
or emulsions.
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
or emulsions.
Because of wide varieties of their structure and composition,
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.
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.
Thermal Properties
Thermal properties are required to understand heat transfer during heating or
cooling which foods are often subjected. Variability in composition and
physical characteristics is typical for all food products.
cooling which foods are often subjected. Variability in composition and
physical characteristics is typical for all food products.
The major thermal properties are specific heat, enthalpy, thermal conductivity,
thermal diffusivity and heat transfer coefficient. These are much commonly
used properties in designing a system for heating/ cooling of foods.
thermal diffusivity and heat transfer coefficient. These are much commonly
used properties in designing a system for heating/ cooling of foods.
These are
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).
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
Mass transfer plays a very important role in basic unit operations of food
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.
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.
Electrical Properties
These properties determine the amount of energy coupled by a food product,
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.
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.
Biological material
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.
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.