Savour
the flavour
In
an increasingly expanding world market for flavours, their production
via biotechnological processes offers a number of advantages, says AS
Gholap
It
is believed that there are four primary taste sensations: salty, sour,
bitter and sweet. Interestingly, olfactory receptors situated at the
root of the nasal passage are responsive to a large variety of odour
sensations and also to much lower concentrations than gustatory receptors
found on the tongue.
Natural
flavour compounds
Natural
flavours are produced by biochemical processes active in plant and animals
during growth, maturity and reproduction. Basic nutrients such as carbohydrates,
proteins and fats are presumed to be essentially involved in the formation
of flavours in fruits and vegetables. During ripening of fruits, polysaccharides
are enzymatically broken down into simple sugars. These sugars not only
impart a sweet taste to the fruits but are also metabolised to pyruvic
acid.
Acquiring
the desirable flavours
The
development of flavours during processing is called ‘break-down’ flavours.
It is known that roasted foods such as coffee, cocoa, peanuts and popcorns
develop flavour during processing. Various changes such as oxidation,
reduction, hydrolysis, esterification, decarboxylation, polymerisation,
saturation and desaturation take place during processing of fruits,
vegetables and other food items.
Character
impact compounds
The
classes of compounds which have been found among fruits volatiles are
not only esters which have generally been considered to possess fruity
aroma notes but also lactones, alcohols, acids, aldehydes, ketones,
and hydrocarbons. The aroma note of a particular food varies according
to the nature of compounds present and their relative concentrations.
On the other hand, it is a combination of several organic compounds
in specific proportions that give rise to a characteristic aroma effect.
Amongst these compounds, however, one or a few components are known
to influence significantly the characteristic aroma note(s). Such compounds
are called character impact compounds without which the concerned food
item is difficult to characterise or recognise.
Microbial
flavours
The
formation of aroma compounds is a result of microbial yeast, bacterial
fungi-action and thermal or ageing process, but the sequence of reactions
varies with the product. For example, in bread the compounds formed
by the fermentative effect of yeast are modified by the baking process
resulting in a mixture of hundreds of volatile compounds with definitive
freshly baked aroma. The flavour associated with dairy products such
as cheese, butter and ghee has been attributed to microbiological degradation
of natural precursors. Specific bacterial species have been identified
for the generation of typical flavour components and of these ceratocystis
moniliformis has been reported as a potential source of fruit-like essences.
The fungus ceratocystis variospora produces a series of monoterpenes
like neral, geranial and linalol having a rose-like aroma.
Isolation
of aroma compounds
It
has been mentioned that flavour or aroma notes arise from a complex
mixture of chemical compounds, which are present in extremely small
amounts in various kinds of matter. Therefore the isolation procedures
to be used must be precise and free from artifacts. There are a large
number of techniques such as distillation, extraction, freezing, absorption
and derivation developed so far for the isolation and concentration
of volatile flavour compounds from foods. All of them are more or less
selective depending upon the nature of foods and their flavour principles.
The methods that are frequently in use are:
Extraction
techniques
Distillation:
Distillation has been used for the isolation and concentration of volatile
flavour compounds from food materials. Various distillation techniques
have been used in food flavour research and one of them being steam
distillation.
.....CONTD
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