A colloidal mixture of large polysaccharides consisting chiefly of galacturonic acid residues and typically of molecular mass 10 000 to 40 000 kDa. Pectin is an important constituent of the matrix of plant cell walls and of the middle lamella between adjacent cell walls; it is also found in certain plant juices. Normally present in an insoluble form, in ripening fruits and in tissues affected by certain diseases it changes into a soluble form, which is evidenced by softening of the tissues. It is used in making jam as it forms a gel with sucrose.