I've so far used Gelatin as the best choice as capping agent when making colloidal silver that is used orally. Gelatin is an animal product, and as lots of people are vegetarians or vegans, there must be options. And I have looked at the following alternatives...
- Pectin
- Carrageenan
- Agar (agar-agar)
- Alginic acid (and its salts - alginates)
Pectin, a polysaccharide that comes from fruits, is actually used as a capping agent ( for instance:
http://www.scopemed.org/?jft=36&ft=36-1422348209 )
Carrageenan is also a polysaccharide, which comes from red seaweed, and is also used as a capping agent ( for instance:
http://eprints.utm.my/33882/ )
Agar is derived from the polysaccharide agarrose, which is extracted from red algae, and is also sometimes used ( for instance:
http://www.sciencedirect.com/science/article/pii/S0960852411017032 )
Alginic acid is an anionic polysaccharide that comes from the cell walls of brown algae. Different alginates seem to be used as capping agents ( for instance:
http://www.sciencedirect.com/science/article/pii/S0925400511000426?np=y )
They all have in common that they consists of polysaccharides (long chain of mono-saccharrides) and are jelly-like when absorbing water (similar to gelatin), so they should also suit as good capping agents like gelatin. The question is how well they withstand the gastric acid compared to gelatin.
I think that this is something that we should investigate and try out.