Although the pectin content of tomatoes is relatively low in comparison with other fruits (Money & Christian, 1950), the activity of pectinesterase (pectin pectyl-hydrolase, EC 3.1.1.11) is particularly high (Kertesz, 1938). Softening of the fruit takes place relatively rapidly during ripening (Hobson, 1959), and the classical mechanism by which the effect is usually explained assumes the solub...