Process optimization on separation and purification of bound polyphenol in black highland barley bran by macroporous resin

Abstract: Highland barley grows in the Qinghai-Tibet Plateau at an elevation of 1 400～4 700 m, and it is the major crop in the Qinghai-Tibet Plateau region, as well as the main food for farmers and herdsmen in Tibetan areas for sustenance. Black highland barley is a precious germplasm resource. Black highland barley has attracted extensive attention due to its rich nutrition and functional chemical components in the Qinghai-Tibet Plateau region. It has been developed into various types of food. But in the process of black highland barley, lots of brans were produced and wasted. The black barley bran is rich in phenolic compounds including phenolic acids and flavonoids. At present, most of the reports on polyphenols in black highland barley have been about free phenolics. There are few reports about bound phenolics. There have been no reports regarding research on separation and purification of bound phenolic compounds and their antioxidant activities in black highland barley bran from the Qinghai-Tibet Plateau region. This paper focuses on the separation and purification technology of bound polyphenols in barley highland bran and its antioxidant activity. The aim of this study was selecting a resin which has a good adsorption and desorption performance of phenols of black highland barley bran, optimizing the separation process parameters and evaluating its antioxidant activity in vitro, thus improving value of processing and utilization about black highland barley barley bran. The separation and purification process of black highland barley barley bran polyphenol was established by macroporous resin. The static adsorption and desorption performance of ten different polarities macroporous resins (NKA-9, NKA-2, HPD-826, HPD-100, H1020, D101, X-5 and AB-8) to total phenolics and flavonoids of black highland barley barley bran bound extraction were compared to select suitable resin for purification of phenolic compounds. AB-8 macroporous resin exhibited the best capability of adsorption and desorption of total phenolics and total flavonoids in black highland barley bran, it was selected as the best adsorption resin type of separation and purification of bound phenolics. And the macroporous resin reached equilibrium within 4 h. The optimum conditions for adsorption and desorption of bound phenolics were as following: pH value of black highland barley bran bound phenolic extract was adjustment to 3.0, sample concentration was 1.5 mg/mL, the polyphenol was passed through the AB-8 resin at a flow rate of 1.5 mL/min, followed by desorption with 60% ethanol at a flow rate of 1.5 mL/min. Under optimum technology conditions, Ab-8 macroporous resin could significantly increase the content of over 71.43% individual phenolics, the most abundant bound phenolics were ferulic acid, syringic acid, benzoic acid, ellagic acid, myricetin and rutin in the purified black highland barley bran. Among the three antioxidant systems, the crude and purified extracts of bound polyphenols in black highland barley bran both showed a relatively higher capacity to scavenge DPPH( and ABTS(+. It also had a relatively stronger ferric reducing antioxidant power (FRAP). But the antioxidant capacity of the purified bound polyphenol performed was better than crude sample on this study. In conclusion, AB-8 macroporous resin could be applied to purify total phenolics and total flavonoids of bound polyphenol in litchi pulp black highland barley bran. It has potential industrial application prospect.