Blueberry (Vaccinium spp.) is a widely consumed fruit worldwide. Anthocyanins, phenolic acids, and flavonoids are the main bioactive compounds of blueberry. However, little information is available about the changes in phenolic profiles of blueberries during fruit maturation. The aim of this work was to assess the effects of genotype and maturity on phenolic compounds and antioxidant ability of four rabbiteye blueberry cultivars grown in Guizhou, China. The total phenolics, total flavonoid and individual phenolic compound in the rabbiteye blueberries were investigated at five ripening stages based on color. Derivatives of phenolic compounds (gallic acid, epicatechin, rutin, p-coumaric acid, quercetin, catechin, ellagic acid, chlorogenic acid, and ferulic acid) were determined by HLPC and quantified using calibration curves. Antioxidant capacity was evaluated by total reducing power assay (TRPA), 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric ion reducing antioxidant power (FRAP), and 2,2ʹ-Azinobis-(3-ethylbenzthiazoline-6-sulfonate (ABTS) assay. Gallic acid, ellagic acid, and ferulic acid were the main phenolic compounds in rabbiteye blueberries, and phenolic compound contents of different rabbiteye blueberries cultivars changed with ripening stage. The gallic acid content of all cultivars increased at first and then decreased. The ferulic acid contents of 'Powderblue' and 'Gardenblue' cultivars gradually increased during ripening. The ellagic acid content of 'Powderblue' blueberries increased with ripening but decreased in 'Baldwin' blueberries. The total phenolics, total flavonoid, and antioxidant capacity of all cultivars increased nonlinearly with ripening. Phenolic compounds were the main antioxidants found in rabbiteye blueberries. Notably, 'Gardenblue' had exceptionally higher phenolics compound and antioxidant activity compared with other cultivars. ARTICLE HISTORY

This study presents an efficient strategy based on liquid-liquid extraction, high-speed counter-current chromatography, and preparative HPLC for the rapid enrichment, separation, and purification of four anthraquinones from Rheum tanguticum. A new solvent system composed of petroleum ether/ethyl acetate/water (4:2:1, v/v/v) was developed for the liquid-liquid extraction of the crude extract from R. tanguticum. As a result, emodin, aloe-emodin, physcion, and chrysophanol were greatly enriched in the organic layer. In addition, an efficient method was successfully established to separate and purify the above anthraquinones by high-speed counter-current chromatography and preparative HPLC. This study supplies a new alternative method for the rapid enrichment, separation, and purification of emodin, aloe-emodin, physcione, and chrysophanol.

Anthraquinone glycosides, such as chrysophanol 1-O-β-d-glucoside, chrysophanol 8-O-β-d-glucoside, and physion 8-O-β-d-glucoside, are the accepted important active components of Rheum tanguticum Maxim. ex Balf. due to their pharmacological properties: antifungal, antimicrobial, cytotoxic, and antioxidant activities. However, an effective method for the separation of the above-mentioned anthraquinone glycosides from this herb is not currently available. Especially, greater difficulty existed in the separation of the two isomers chrysophanol 1-O-β-d-glucoside and chrysophanol 8-O-β-d-glucoside. This study demonstrated an efficient strategy based on preparative high-performance liquid chromatography and high-speed countercurrent chromatography for the separation of the above-mentioned anthraquinone glycosides from Rheum tanguticum Maxim.ex Balf.