Differential degradation of pectin may be linked to fruit quality.

The quality of tomato fruit is important to the fresh market and to the tomato processing industry. The consistency of the pectin in the pericarp region is a primary determinant of the fruit's quality. Pectin is a complex polysaccharide found in the cell wall and middle lamella of plant tissue. It's believed to be degraded during the ripening process by pectinmethylesterase and endo-polygalacturonase.

Scientists at Purdue University wanted to determine if differential degradation of the pectin occurs in the pericarp when the tomato ripens. To test their curiosity, the researchers rapidly extracted the pectins from green and ripe tomato fruit. They undertook the differential extraction of pectin from the middle lamella and cell wall regions.

The investigators used size exclusion chromatography analysis, carbohydrate analysis and uronic acid assay profiling of the collected fractions to determine the differences between the middle lamella and cell wall pectin. Ripening had no effect on the molecular size distribution of the cell wall pectin. In contrast, pectin extracted from the middle lamella of ripe tomatoes experienced a significant reduction in molecular size distribution, compared to that of green tomatoes.

Based on these observations, the researchers believe that during early ripening, the middle lamella pectin is degraded by pectinases. But the more tightly bound pectin in the cell wall matrix remains unaffected. Previous studies did not distinguish between the two pectins in the middle lamella and in the cell wall.

Considering the different functions of those pectins, a separate analysis of each type yielded more information on the chemical changes that occur in fruit during the ripening process. The degradation of the middle lamella may be linked to the loss of cell-to-cell adhesion that occurs during ripening, which is related to the quality of the fruit.

Further information. Bradley Reuhs, Whistler Center for Carbohydrate Research, Department of Food Science, 745 Agriculture Mall Dr., Purdue University, West Lafayette, IN 47907; phone: [phone]; fax: [phone]; email: [e-mail].