Pectins are gel-forming compounds that are suitable for use by vegetarians and vegans.
Commercially, pectin is extracted from fruit and you can get apple pectin or citrus pectin for use as a gelling agent in jams.
High methylester pectin High methylester pectin requires a minimum amount of soluble solids (SS) and a pH around 3.0 or lower in order to form a gel. (Geun Pectin Book page 4) This is why you need all that sugar, which is the soluble solids referred to, and lemon juice to lower the pH, added to most traditional jams.
Low methylester pectin requires the presence of a controlled amount of calcium, or other divalent cations, to form a gel. You do not need to worry about the science behind it all. What you do need to know is that low methylester pectin does not need sugar to gel, but instead needs calcium, which usually comes with the pectin when purchasing this product. All my low sugar jam recipes will tell you just how much pectin and how much calcium to use.