Separation of hydroxycitric acid lactone from fruit pectins and polyhydroxyphenols on poly(4-vinylpyridine) weak-base resin

Poly(4-vinylpyridine) (PVP) has been used for the separation of hydroxycitr ic acid lactone (HCAL) from polyhydroxyphenols and fruit pectins, as the st udy has relevance to the problem of extraction of the antiobesity substance hydroxycitric acid from Garcinia cambogia fruits, a rich source of the aci d. PVP has been used both in free-base form and in protonated or salt form as a sorbent, while catechol and pyrogallol have been used as representativ e polyhydroxyphenols. Though the protonated form, used as PVP(HCl), has a l ow sorption capacity (96 mg/g dry resin) and low selectivity for pectin (at pH 8), its higher, but comparable, sorptions (at pH 8) of HCAL, catechol, and pyrogallol, with respective saturation values of 354, 349, and 366 mg/g dry resin, coupled with high selectivity for the hydroxyphenols, make the sorbent unsuitable for the desired separation of HCAL. On the other hand, P VP free-base resin has significantly high sorption of HCAL as compared to c atechol and pyrogallol in mildly acidic media (pH 1.8-2.8), the respective saturation values being 576, 206, and 303 mg/g dry resin, but the free-base resin also shows high saturation capacity (500 mg/g dry resin) for pectin. However, at low substrate concentrations (<1 g/L) or relatively low pH (<2 ), pectin has an order of magnitude lower sorption than HCAL, making separa tion of the latter possible on PVP Free-base resin. Column operation using PVP free-base resin with influent maintained at pH 1.8, followed by strippi ng with less than the theoretical amount of alkali, produces good separatio n and high yield of HCAL from the mixed influent. Reillex HP, a macroporous PVP resin, used in free-base form, has relatively fast kinetics for HCAL s orption, with a t(1/2) value of about 5 minutes and diffusivity of the orde r of 10(-6) cm(2)/s.