The Preparation Of Proanthocyanidins Oligomers

Proanthocyanidins are a large type of natural polyphenol compound polymerized with(+)-catechin,(-)-epicatechin and(-)-epicatechin-3-gallate which widely exist in plant kingdom.Because of their forceful antioxidation activity,proanthocyanidins have been widely used in medicine,health products,food and other fields.The antioxidant activity of proanthocyanidins largely depends on the degree of polymerization.Monomer antioxidant activity is inferior to dimer and polymer antioxidant activity reduces with the rise of degree of polymerization.Proanthocyanidins polymer(PPC)is difficult to be absorbed by human body.In this paper proanthocyanidins are fractionated according to the degree of polymerization and PPC is hydrolysed to preparate proanthocyanidins oligomer(OPC)of high biological activity.The factors of proanthocyanidins molar concentration determination were investigated.H2SO4 was selected as catalyzer.The stable colorimetric condition was obtained as 1 mL aqueous solution of sample mixed with 5 mL 1%vanillin-glacial acetic acid and 5 mL 30%H2SO4-glacial acetic acid.The reaction was carried out at 30 ? for 15 minutes in dark and the absorbency at 500 nm was measured once the reaction finished.The standard curve of catechin was drawn through measuring the absorbency at 500 nm with different molar concentration.The linearity range of the standard curve equation built was 0.025 ?mol·mL-1?0.25 ?mol·mL-1 with well relativity.The average degree of polymerization was calculated combining the molar concentration with quality concentration.The conditions of prussian blue method and salicylic acid method for determination antioxidant activity of proanthocyanidins were studied.The maximum absorption wavelength of prussian blue method and salicylic acid method was respectively 700 nm and 526 nm.The suitable analysis concentration was respectively 10 ?g/mL and 0.3 mg/mL.Vc equivalent concentration was used to express the antioxidant activity of prussian blue method.10%?40%and 60%ethanol were selected to gradiently elute the proanthocvanidins adsorpted in the AB-8 resin at the speed 1 BV·h-1 with 2 BV ethanol.The eluting recovery achieves 98.63%.According to the average degree of polymerization and antioxidant activity of proanthocyanidins in each ethanol eluent,only monomer existed in 0?10%ethanol eluent.12%?32%eluent contained mainly OPC,32%?60%eluent contained PPC.The antioxidation activity of 12%?32%eluent was highest that the free radical clearance rate was 44.85%and Vc equivalent concentration was 19.38 ?g/mL.Using the average degree of polymerization and free radical clearance as indicators,the hydrolyzing process of PPC was explored and optimized.Hydrolysis took place at 60? for 10 min with H2SO3 as hydrolysis medium of 0.1 sample volume.The average degree of polymerization of proanthocyanidins polymer-dropped to 4.02 from 7.06 and the free radical clearance rose up to 43.59%from 8.58%.The proanthocyanidins resource was used fully as antioxidant activity was improved.