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Chemistry World

 

Secret of tasty tomatoes revealed


05 May 2006

Vine-ripened tomatoes are officially tastier than gas-ripened supermarket equivalents, and it's all down to their umami.

Chefs and scientists at Heston Blumenthal's triple Michelin-starred restaurant the Fat Duck in Bray, UK, teamed up with Don Mottram at the University of Reading, UK to find out which part of a tomato is the tastiest.

Early results show that different parts of tomato have different amounts of umami content, said Christopher Young, food research manager at the Fat Duck. Tomatoes left to ripen on the vine have more umami content than tomatoes that are picked green and then gas-ripened.

Umami is gaining acceptance as the fifth basic taste (the others being bitter, salty, sour, and sweet). It is often said to be the taste of monosodium glutamate (MSG), and umami  is quantified by measuring the absolute concentrations of MSG and the ribonucleotides IMP, (inosine 5'-monophosphate), and GMP (guanosine monophosphate).

Mottram's group at Reading conducted the preliminary umami measurements using capillary electrophoresis and GCMS. From initial results, Mottram thinks the different factors in tomato growing and different varieties will contribute to the levels of taste compounds. Blumenthal is interested in these compounds because of their behaviour in cooked foods.

The seeds of the tomato, typically discarded by most chefs, have by far the highest MSG and ribonucleotide content, Young told Chemistry World. 'We found an eight-fold difference in the umami content of the seeds versus in the flesh,' said Young.

'It is really interesting from a chef's standpoint. You really want to think very carefully before you start chucking out the centre [of the tomato] because that's one of the most flavourful parts of it.'

The work came about because Blumenthal detected different tastes in the different parts of a tomato, a skill that impressed Mottram: 'not many other people could pick up those differences,' he said. 

The Fat Duck uses air-freighted tomatoes from Sicily, Morocco, Spain and Italy, costing up to 1 each. Young claims that these pricey tomatoes have higher umami content in their seeds, and so are tastier than cheaper varieties. Young noted that the seeds act as the tomato's placental sack. 'What we suspect is as the tomato is developing, that placental tissue is gaining the nutrients, proteins and amino acids, and those are going to be the umami content later on,' he said.

Tomatoes left to ripen naturally could get more of those nutrients and so have greater umami content, Young suggested. 'We suspect there is a real advantage in letting your tomato come to full ripening versus picking it green (which is easier to transport) and then gas ripening.' Katharine Sanderson