Propylene Glycol Alginate (PGA) is produced by reacting alginic acid with propylene oxide, esterifying a portion of the carboxylic acid groups with propylene glycol. The degree of esterification (typically 60–90%) determines its functional properties — higher esterification yields better acid stability and emulsifying capacity, while lower esterification retains more thickening character.
PGA is unique among alginate derivatives in being acid-stable (functional down to pH 2.0) and protein-reactive, forming complexes with milk and soy proteins. It is designated as E405 in the EU and is GRAS (21 CFR 172.858) with a JECFA ADI of 0–70 mg/kg body weight. PGA is the standard stabilizer for beer foam worldwide and a key ingredient in acidified dairy drinks, dressings, and fruit juice beverages.