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Tomato, TomatOh: Flavour and colour coupled
Wednesday, 28 July, 2021, 16 : 00 PM [IST]
Dr A.P.Jayaraman
Recall the common spectacle of the tomato laden handcart on the roadside and the discerning buyers picking up fruits and visually examining them at three hundred and sixty degrees. That is rugged and rustic quality assessment at its best. They are screening and selecting good tomatoes based on their uncanny hunch  that goodness and  shades of colour are somehow related.

From sheer experience, they have discovered that perfectly coloured tomatoes have finer flavour and  better taste and their every procurement had confirmed their conviction after consumption. Of course, biting for tasting each fruit is obviously unacceptable in the marketplace and colour as indicator is the best nondestructive test applicable on the street.

Pigment profile
Japanese and American plant scientists are trying to unravel that eerie tomato equation between colour and flavour. Tasteful tomatoes have appealing colour and the concealed colour chemistry of flavour is being revealed albeit slowly. It has come to light that pigments controlling the colour of tomatoes  are playing a role in determining their flavour.  Colour and flavour are chemically coupled. The nugget  of native wisdom has been validated by analytical instruments.

Scientists set free their analytical skills and assiduously garnered pigment profiles of no fewer than 150 diverse varieties of tomatoes.   Their research work shows that tomato fruits with high sugar content have more chlorophyll, the green pigment. It was further noted that the carotenoid, prolycopene, is associated with an rich repository of aroma compounds.
  
The evanescent flavour of the  tomato is the result of an  interaction between its taste and aroma. Pigments that impart colour to tomatoes determine its flavour. Scientists at the University of Tsukuba in Japan developed an innovative method to rapidly record the pigment profiles of tomatoes.  Conventional methods of identifying and estimating  pigments are notoriously slow. They used this  technique to unravel  how pigments alter  the taste and aroma of different varieties of tomatoes.

All in Colour
If you ask a biology student,  why is the tomato is red in colour? She will instantly reply something like this, as the tomato ripens, its colour starts to change from green to yellow and then eventually to red. This is due to the breakdown of chlorophyll, which in turn synthesises a red carotenoid (another pigment group), lycopene. But colour chemistry is a lot more murky.

The red colour of the tomato is produced by combinations of numerous pigments, including carotenoids and chlorophylls.  These pigments can affect the accumulation of flavour-related compounds such as sugars, which affect the taste of tomatoes. They also control volatile organic compounds , which determine the aroma. As tomato fruits ripen from green to red, the amounts of pigments and flavour-related compounds change but until now the relationship between colour and flavour has been unclear.

Pigments like carotenoids  by themselves are tasteless but they are the forerunners  of taste making molecules. Carotenoids lead to the production of apocarotenoid-volatile organic compounds written as AC-VOC in chemistry shorthand. They are the movers and shakers of  fruity and floral odour in  tomatoes.  The perception of sweetness is also enhanced making the good tomato irresistibly appealing to the buyer. The results showed that tomato varieties with an abundance of chlorophyll also had a high sugar content, contributing to a sweet taste.

Designer Tomato
The look of the tomato tells a lot about its carotenoid profile which is also a tell-tale mark of AC-VOC levels. They also found that this profile of the fruit reflected the appearance of the fruit, as well as its AC-VOC content. The carotenoid content is influenced by growing conditions, like temperature and amount of light. By looking at the pigment profiles and AC-VOC content of fruits in different environments, it may be possible to find ways of improving AC-VOC production, which is good for both consumers and farmers. Armed with such knowledge, it is possible to change the growing conditions to produce tomatoes of choice flavour.

The pigment profile of an orange-coloured variety commercially popular as  Dixie Golden Giant was interesting. It had very high levels of AC-VOCs, but the carotenoid content was not so high. The red pigment, prolycopene, was plentiful in this variety, which explained the high AC-VOC levels.

Fridge and Flavour
There is heated  debate about the cold storage of tomatoes. The main options are storage in the refrigerator at 7 degrees Celsius or at room temperature 20, degrees Celsius. Food scientists investigated whether there are differences in the flavour of ripe tomatoes depending on how they are stored and found none.  The shorter the storage period, the better it is for the flavour. Short-term storage of ripe tomatoes in the refrigerator did not affect their flavour. The variety of tomato does have an  influence on its flavour. Therefore, the development of new varieties with an appealing flavour can be a step towards improving the flavour quality of tomatoes.

At the end of the day, the kerbside hand cart will still have left over non-good, bad and ugly tomatoes with  all the good and great ones gone!

(The author is nuclear scientist ex BARC and chairman, National Centre for Science Communicators, Prescient STEAM Academy)
 
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