March 17/Davis, Cal./Journal of Engineering -- According to recent research from the U.S., "The degree of methylesterification (DM) of the pectins in tomatoes affects the firmness of diced products and the consistency of juices. We examined the changes in DM that occur during commercial production of diced tomatoes packed in tomato juice."

"Ripe processing tomatoes contained low amounts of free methanol (<20mu g g fresh weight(-1)) and had a high degree of pectin methylesterification (60%). During production of diced tomatoes, the level of free methanol increased while the degree of pectin methylesterification decreased. Diced tomatoes canned in tomato juice contained about 200mu g methanol g fresh weight(-1), and had a DM of about 35% in the dice and less than 25% in the juice. Similar results were obtained for aseptically processed bulk packed tomatoes. Low-temperature blanching of canned diced tomatoes caused additional pectin de-esterification in the diced tomatoes and improved firmness," wrote G.E. Anthon and colleagues, University of California.

The researchers concluded, "Heating of the diced tomatoes prior to mixing with topping juice, first to temperatures that maximally activate PME then to temperatures that inactivate PME and other enzymes, is proposed as a way to both improve dice firmness and preserve the consistency of the topping juice."

Anthon and colleagues published their study in the Journal of Food Engineering ("Changes in Pectin Methylesterification and Accumulation of Methanol During Production of Diced Tomatoes." Journal of Food Engineering, 2010;97(3):367-372).

For additional information, contact G.E. Anthon, University of California, Dept. of Food Science & Technol, Davis, Cal.

From the March 29, 2010, Prepared Foods E-dition