Separation of Hydroxycitric Acid Lactone from Fruit Pectins and Polyhydroxyphenols on Polybenzimidazole Weak-Base Resin

Polybenzimidazole (PBI) free-base resin has been used for selective sorption and recovery of hydroxycitric acid lactone (HCAL) from aqueous solutions containing also significant proportions of polyhydroxyphenols and fruit pectins, because the study has relevance to the problem of separation and recovery of HCAL, a potent antiobesity substance, from aqueous extracts of Garcinia cambogia fruits, grown largely in coastal areas of South India. PBI resin has the saturation sorption capacity of 315 mg/g dry resin for HCAL, compared with 131, 138, and 293 for catechol, pyrogallol, and pectin, respectively, in individual sorptions from aqueous solutions. The resin selectivity for HCAL over catechol, pyrogallol, and pectin in binary sorptions varies with pH, the separation factor of HCAL being maximum over catechol and pyrogallol at a pH of 1.7−1.8 and infinite over pectin at pH < 1.8. Under vigorous agitation the initial uptake of HCAL is very fast with 30% of the equilibrium sorption taking place in 10 s, followed by a significantly lower rate, leading to an overall 75% attainment of equilibrium sorption in 30 min. In continuous column operations with PBI resin and influent containing HCAL, polyhydroxyphenols, and fruit pectins, a proper combination of relatively low flow rate, a relatively low substrate pH (1.7−1.8), and "dead-end" stripping with alkali, which involves use of less than the theoretical amount of stripping agent necessary for complete stripping, produces an excellent separation and good yield of HCAL from the mixed influent.