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for production essential oils and flavors
Various applications of biotechnological methods for the production of volatile compounds useful to the food and pharmaceutical industries are discussed
The yields obtained from intact or genetically modified plants are compared to those achieved by microbial methods. Plant yields are too low for the products to compete commercially to those synthesized chemically
Still lower yields are obtained with in vitro?cultured plant tissues
. However, the most spectacular yields were observed with biotransformations catalysed by microorganisms. Kluyveromyces marxianus, produces over 26?g/l 2?phenylethanol from phenyalanine, whereas Candida sorbophilcan produce 5–40?g/l ??decalactone from ricinoleic acid.with
Amycolatopsis and Streptomyces species. Vanillin can be produced at 5?g/l by Escherichia coli and amorphadiene yields of 37?g/l have been observed with Saccharomyces cerevisiae, both with the genetically overexpressed methyl–erythritol path. Genetically engineered ??oxidation genes result in yields of 10?g/l ??decalactone by Yarrowia lipolytica and up to 80?g/l dicaboxylic acids by various yeasts.
There are hundreds of thousands of different secondary metabolites produced by plants, four times more than the number produced by microorganisms. This number is estimated to represent only 10% of the secondary metabolites existing in plants and still waiting to be isolated and identified
Members of the 10?carbon terpenoids, the monoterpenoids, are constituents of essential oils produced by plants. The essential oil monoterpenoids are volatile
. Essential oils can also contain sesquiterpenoids, phenypropanoids and benzenoids. In addition, plant tissues can produce volatile aldehydes and their corresponding alcohols, and acids as well as volatile ketones. These compounds are occasionally found in essential oils, but are usually formed in specific plant tissues and under specific physiological conditions that favour catabolic reactions
The commercial interest on volatiles stems from their aromatic and flavour qualities. Several of them, have significant antimicrobial and antineoplastic activity. Others act as messengers in communication between plants themselves or with other organisms. Volatiles are obtained from plants by distillation at or by extraction with ethanol or other organic solvents
Unfortunately, volatiles, like most secondary metabolites, are present in plant tissues in limited quantities. Plant seeds, flowers, stem and roots
Even so, a single compound can constitute 40–90% of the oil and usually is not the most useful one. The most desirable volatiles are often present in the essential oil at concentrations

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