Physics And Chemistry Basis Of Biotechnology - De Cuyper - tiera.ru

Saskia M. Van Ruth
exploit the advantages offered by biocatalysts in a more specific way. Due to the
advances in microbial fermentation and enzyme technology and consumer demands for
natural products, production of individual flavour compounds or complex flavour
mixtures, are increasingly becoming targets for production on an industrial scale [77-
78]. The exploitation of such techniques is especially attractive, because flavour
compounds obtained via biotechnology are considered to be natural by regulatory
authorities in many countries [79]. The biotechnological processes leading to flavour
production can be divided into two major groups: (1) microbiologically mediated
syntheses and (2) plant production methods [80]. The latter methods will not be
discussed any further as they are beyond the scope of this review.
Flavour-producing microorganisms are primarily fungi, as they are able to carry out
secondary metabolism. Factors, such as media composition, seed culture generation,
pH, fermentation time and temperature, determine the amount and type of flavour
substances produced. The group of flavour compounds produced by fermentation
methods cover a broad flavour area and include acids (dairy flavours), alcohols
(mushroom), lactones (dairy, peach), esters (fruity), aldehydes (fruity), ketones (dairy,
cheese), pyrazines (nutty, roasted green) and terpenoids (citrus, mint flavours) [81].
Currently, the creation of so-called pure aromatic chemicals is one of the major
applications of biotechnology to flavour production. However, simple or complex
mixtures of aroma compounds are also useful. Cheese flavours, dairy-, fruit-,
mushroom- and fish flavours, as well as mixtures of flavour enhancers are produced by
the action of microorganisms or enzymes on substrate materials and are
commercialised as flavours.
Research related to biotechnological flavour synthesis can be divided into three
areas: non-volatile precursors, biotransformations and enzymes.
7.1. BIOTECHNOLOGICAL FLAVOUR SYNTHESIS
7.I.1. Non-volatile precursors
An essential prerequisite for optimum flavour generation by microorganisms and
enzymes is detailed knowledge of the composition and availability of precursors
needed. Many intensive studies have been focused on precursors. Some examples are:
lipids and fatty acids [82], strawberry aroma precursors [83] and passion fruit aroma
precursors [84]. Several studies of other precursors have been published in the book
edited by Teranishi et al. [85]. This type of studies and how enzymatic action releases
characteristic volatiles from precursor compounds has progressed because of the
advance in methods of handling glycosides [65]. Countercurrent chromatographic
techniques have been successfully employed in the isolation of flavour precursors, such
as glycosides. Development of cyclodextrin columns and advances in multidimensional
gas chromatography combined with mass spectrometry has led to progress in analysis
of these desirable flavour compounds. Atmospheric pressure chemical ionisation and
electrospray ionisation, liquid chromatography coupled with mass spectrometry and
tandem mass spectrometry are other techniques, which are tools to provide elucidation
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