Sribas Chowdhury, Adamas University, Kolkata
There is a direct correlation between the flavour of tomato and its aroma and taste. From early on, researchers studied how the interaction between the two factors gives rise to such distinct and diverse flavours of different kinds of tomatoes. Interestingly, a team in Japan and the US recently found out that the colour determining pigments present in tomatoes also influence their flavour.
In the study at the University of Tsukuba, researchers developed a new and faster method to analyze the pigment profile of tomatoes. Traditional methods of analysis of pigments are usually time-consuming. Using the development, the team could study the pigments of 157 varieties of tomatoes in a relatively shorter time. They further noticed the effect of different combinations of pigments, comprising chlorophyll and carotenoids, on the flavours of different varieties of tomatoes. The method used was High-Performance Liquid Chromatography (HPLC) along with a multimode microplate reader to study the non-polar pigments.
In tomatoes and other vegetables, the different flavours in different varieties arise as a result of varied combinations of pigments, including chlorophyll and carotenoids. While chlorophyll is responsible for the cumulation of sugars and hence, affects the flavour of tomatoes, carotenoids have a crucial yet underrated function. The carotenoids give rise to something called ApoCarotenoid Volatile Organic Compounds (AC-VOC), mainly responsible for the aroma of the fruit. As the fruit ripens, the AC-VOCs tend to accumulate, giving rise to a different taste. However, the correlation between taste and aroma is still unclear.
The study by the research team revealed that tomatoes having more chlorophyll had a higher sugar content, making the tomato taste sweeter. A gene called SIGLK2 encodes the transcription factor which affects chloroplast production and location. Thus the gene acts as the regulatory link between chlorophyll and sugar production, indicating that more amount of chlorophyll is directly linked to higher sugar content in tomatoes.
On the other hand, different carotenoid levels resulted in varied appearances and AC-VOC contents. It was found that lycopene and derivatives of lycopene like beta-carotene, lutein, and zeaxanthin made up 90% types of carotenoids present. Also, a gene named PSY1 was found to be involved in the regulation of carotenoid content, thereby indicating that levels of carotenoids depend on the PSY1 gene expression. Further, the production of carotenoids was found to be affected by growth factors like sunlight, temperature, season, etc.
One of the varieties called “Dixie Golden Giant” exhibited a different pigment called prolycopene affecting its AC-VOC levels. A study revealed that this variety had a mutation in a gene that was responsible for an enzyme called carotenoid isomerase (CTRISO). This enzyme performs the function of isomerization of prolycopene to lycopene. As a result of this mutation, the levels of prolycopene increased due to the ineffectiveness of the CTRISO enzyme.
As stated earlier, conditions such as temperature and sunlight can affect carotenoid levels. The study gives rise to the possibility of introducing newer and better varieties of tomatoes by growing them in controlled conditions. The researchers believe that there is hope that the new study can help them analyze the pigments profile of other fruits and vegetables too. The study may revolutionize the agriculture methodology as methods to improve AC-VOC levels are developed. It may lead to the growing of crops that are economically feasible and favourable for consumers.
Also read: Role of Gibberellins in panicle architecture of Rice
Source: Aono, Y., et al. (2021) High-Throughput Chlorophyll and Carotenoid Profiling Reveals Positive Associations with Sugar and Apocarotenoid Volatile Content in Fruits of Tomato Varieties in Modern and Wild Accessions. Metabolites.https://doi.org/10.3390/metabo11060398
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