The science of flavor and fragrances is innately linked to biological sciences. This includes how we recognize the fragrance of a flower, the odor of rotting fish or the smell of a perfume whether it is in the environment, or on our skin, or on our clothing.
There are two aspects to flavor and fragrance biotechnology. They are:
• How we use our olfactory system or biological sensors
• How we can bio-synthetically generate fragrances as for example the smell of roses etc.
How we use our olfactory system or biological sensors
It was Linda Buck and Richard Axel both Nobel Prize winners who identified the genes dealing with olfactory receptors. These were basically proteins that adhere to odorants and therefore responsible for the olfactory sensing mechanism.
How do we actually register the sense of smell?
It's actually a process that's best explained by using biotech concepts. Human beings have about ten million odor detecting neurons with several odor matching proteins on their surface. The role of the proteins is to accept the odor molecules that come its way and generate a neuronal response. So when an odor reaches our nose the molecules constituting the odor binds to a specific protein on the neuronal surface. This generates a neuronal signal to the brain to recognize the smell. The role of the DNA in this process is to give the necessary genetic instruction to make the proteins that enable the sensory mechanism to work.
In order to biosynthetically make flavors and fragrances one must also understand the relationship between an odorant's molecular property and the quality of the odor. This in turn means understanding each and every step from the stimulation of the odor to the perception of the odor. This includes the following:
• Understanding the odorant and olfactory receptor sensitivity and the binding mechanisms
• How the olfactory sensory neurons are activated and how the odor information is processed in the brain.
How we can bio-synthetically generate fragrances
At present natural scents can be recreated by extracting them from harvested plant/animal materials by chemical synthesis. But this entails an expensive process. However if we could identify and categorize the fruit genes which are responsible for the fragrances and flavors in fruits, it could generate new ways in which perfumes are made. This also means that natural fruit aromas can be recreated. By using the process of bio-fermentation and by using the identical genes which the plants themselves use to make the flavor in nature, the target flavor compound can be recreated with identical molecular configuration to the naturally occurring aromas.
Hortresearch has recreated the aroma of green apple by genetically synthesizing alpha-farnesene---the isomeric compound belonging to the class of sesquiterpenes responsible for that flavor.
Importance of natural flavors/fragrances
If supposing a synthetic flavor is added to a nutritional food supplement it diminishes its value as a health food. Instead, bio-fermented natural flavors would be acceptable.
Flavor development in tomatoes
Although we know how a good tomato tastes and a rotten tomato tastes, we do not as yet know what constitutes the taste of an ideal tomato. The taste of a tomato has several attributes. One of them could be sweetness. Which is the volatile that is responsible for the sweetness? Biotechnology can help answer these questions.
The tomato flavor is an intricate mixture of volatile and non-volatile components. There are nearly four hundred different compounds in the volatile portion--of which about thirty are what gives the tomato its distinct smell and flavor. Researchers have established that the smell of ripened tomato is due to the following volatile compounds.
T ra n s-2-hexenal
In general, biotech methods of flavor synthesis could be based on:
• Microbial fermentation
• Bioconversion of natural precursors with the help of microbial cells/enzymes
How flavor volatiles are formed in the tomato
What happens in the tomato is the bioconversion of natural precursors with the help of enzymes through biosynthetic pathways. Specifically these compounds are formed in the tomato by decomposition of fatty acids and amino acids. For example, the precursors for Trans-2-hexenal, 1-pentene-3-one, and Cis-3-hexenal are linoleic acid and linolenic acids (fatty acids). The precursors for3-methylbutanal and 3-methylbutanal are leucine, isoleucine and phenylaniline(amino acids). The precursors for Beta-ionone are geranyl diphosphate, lycopene and beta carotene
The majority of the tomato fruit volatiles are Cis-3-hexanol (an alcohol) and
Cis-3-hexenal (an aldehyde). These are products of fatty acid decomposition that gives the tomato its distinct grassy tomato-like flavor.
Physically how are these flavors formed? Biotechnology explains it.
When the tomato fruit ripens the tissues break up. Thereupon fatty acids interact with catabolic enzymes resulting in the release of volatiles.When lipogenases and hydroperoxide lyases act on lipids the latter degrades to short-chain aldehydes. For example, linoleic acid and linolenic acid gets converted to hexanal and cis-3-hexanal.The effect of alcohol dehydragenases can further reduce the aldehydes to alcohol.
L-Menthol is a terpene alcohol used in toothpastes for giving that refreshing mint flavor. Traditionally it is either made from benzoic acid or extracted from peppermint oil. But the problem is in separating L-Menthol from other constituents. However now proprietary processes are in vogue that uses esterases of Alginomonas and Saccharomyces bacteria that enzymatically solve the problem by first hydrolyzing DL-menthol and thereafter L-Menthol is crystallized and recovered.
In future, identifying the germplasm with the most suitable alleles and evaluating them as to how they have effect on flavor quality is important because that will lead to rapid progress in scientific research and consequent consumer benefits. But the overriding problem with making fruits is that the farmer generally doesn't get paid for the flavor quality of the fruit produce. What gets him better returns is in terms of the size of the fruit and the overall yield, and so breeding techniques generally emphasize this aspect.
At another level, ensuring the stability of enzymes used for making flavor components needs to be further researched. Hopefully in future biotechnology will hopefully address these concerns.
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