Pectin is the most complex plant polysaccharides of the plant cell wall. Due to their gelling, thickening and stabilizing properties they are used in a variety of food products and lately their ability to stabilize emulsions and suspensions is utilized in a number of pharmaceutical preparations. Additionally, their use for nanocoating of medical devices is being explored.
Up to now, tailoring pectin for specific applications is done by changing the pectin extraction conditions or modification of the structure of the isolated pectin by chemical or enzymatical means. It seems logical to modify the potato plant to synthesize the desired pectin directly in the tuber during growing. However, to produce tailor made pectin for these applications in planta, in depth knowledge of their biosynthesis is required. The complexity of pectin dictates that a large number of enzymes must be involved in their biosynthesis. The estimated number of genes for enzymes involved in pectin biosynthesis ranges from 53 up to 150 of which only 5 to 10 have been identified until now. The major biosynthetic enzymes required are glycosyltransferases that transfer individual sugar moieties on a growing polysaccharide and decorating enzymes including methyltransferases, acetyltransferases and feruloyl transferases. Several labs are actively working on the characterization of enzymes involved in the biosynthesis of the different cell wall polysaccharides in Arabidopsis, and their focus is on the characterization of different classes of glycosyltransferases. In the project described herein, the main interest is not on the primary biosynthetic steps but we will concentrate mainly on the characterization of pectin decorating enzymes. Experiments in our lab (Cankar et al., in prep.) show that the silencing of different pectin decoration enzymes have an effect on potato quality aspects such as cooking properties (Figure 1).
Pectins are nowadays extracted from fruit press cakes after extraction juice, in particular from apple juice factories. With the technologic advances in the juice extraction process, the amount of pectins remaining in the press cake are reducing dramatically. In the growing pectin market there is a need to look for alternative sources for this polymer and potato is a good candidate. Furthermore, pectins are complex polysaccharides that can be used in different applications both in food, industry and medical applications. For each application there are specific requests concerning pectin properties and structure, thus the tailoring of pectins in the plant would be of great advantage