Jean Yves Wilmot explains his tomato gels to Gene Bervoets
Making gels with fruits that are high in pectin is not particularily challenging. Addition of sugar promotes pectin gel formation with low methoxyl (LM) pectin, but the drawback is that you need a lot of sugar, typically around 50%. So this is only relevant for jams and marmelades. And if you try to gel tomatoes or carrots you may find this quite challenging, even if you add sugar. The approach chosen by Thomas Duvetter, a post doctoral researcher at Laboratory of Food Technology at Katholieke Universiteit Leuven, was to use the pectin methyl esterase enzymes (PME) naturally present in tomatoes, carrots and oranges. The role of PME is to cleave of methyl groups, hence leaving the pectin more prone to calcium induced gelling. Equipped with this knowledge Jean Yves Wilmot presented a number of gels made with the pectin that’s already there.
In order to achieve this one must consider one important thing: tomatoes have another enzyme as well, a polygalacturonase (PG), which causes some trouble. If I got it right this enzyme degrades the pectin gel (and plays an important role in the ripening of tomatoes). One therefore needs to inactivate the tomato PG enzyme and this is done by heat. Regrettably this also knocks out the PME of tomato, but this is were the carrots and oranges come in – they have PME, but no PG. Hence they hold the key to unlock the gelling properties of tomato. So to sum it up, you can use enzymes present in carrot and orange juice to chemically change the pectin of tomatoes to make it more prone to gelling in the presence of calcium ions. If you’re familiar with traditional pectin, what the enzyme does is to make LM pectin out of HM pectin.
Some scientific papers co-authored by Thomas Duvetter which may be of interest:
Isabel Verlent, Ann Van Loey, Chantal Smout, Thomas Duvetter, Binh Ly Nguyen, Marc E Hendrickx “Changes in purified tomato pectinmethylesterase activity during thermal and high pressure treatment” J. Sci. Food. Agric. 2004, 84 (14), 1839.
Ruben P. Jolie, Thomas Duvetter, Ken Houben, Elke Clynen, Daniel N. Sila, Ann M. Van Loey and Marc E. Hendrickx “Carrot pectin methylesterase and its inhibitor from kiwi fruit: Study of activity, stability and inhibition” Inn. Food Sci. Em. Technol. 2009, 10 (4), 601.
Ilse Fraeye, Thomas Duvetter, Eugénie Doungla, Ann Van Loey and Marc Hendrickx “Fine-tuning the properties of pectin–calcium gels by control of pectin fine structure, gel composition and environmental conditions” Trends Food Sci. Technol. 2010, in press.
This is part 6 of my report from The Flemish Primitives in 2010. Apart from an overview of the event (part 1) there was quite some inspiration from Asia this year (part 2 and 3). You can also read an interview with Bernard Lahousse, the project leader of The Flemish Primitives (part 4) and I’ve also written about a number of gadgets shown (part 5).
I also visited The Flemish Primitives in 2009. You can read more about that in my four posts from last year: The Flemish Primitives: A travel report (part 1), Chocolate surprise (part 2), Heston Blumenthal (part 3) and Glowing lollipops (part 4). Final note to readers: This year my travel expenses were covered by TFP and the tourism bureau of Brugge.