Statistical optimization of an RP-HPLC method for the determination of selected flavonoids in berry juices and evaluation of their antioxidant activities.

An isocratic RP-HPLC method for the separation and identification of selected flavonoids (quercetin, rutin, luteolin-7-O-glucoside, kaempferol and kaempferol-3-O-glucoside) in commercial berry juices (blackcurrant, blueberry, red raspberry and cherry) was developed with the aid of central composite design and response surface methodology. The optimal separation conditions were a mobile phase of 85:15 (% v/v) water-acetonitrile, pH 2.8 (adjusted with formic acid), flow rate 0.5 mL min-1 and column temperature 35°C. The obtained levels of bioflavonoids (mg per 100 mL of juice) were as follows: for quercetin, ca. 0.21-5.12; for kaempferol, ca. 0.05-1.2; for rutin, ca. 0.4-6.5; for luteolin-7-O-glucoside, ca. 5.6-10.2; and for kaempferol-3-O-glucoside, ca. 0.02-0.12. These are considerably lower than the values in fresh fruits. Total phenolic, flavonoid and anthocyanin contents were determined spectrophotometrically. Total flavonoid content varied as follows: blackcurrant > blueberry > red raspberry > cherry. The antioxidant activity of juice extracts (DPPH and ABTS methods) expressed as IC50 values varied from 8.56 to 14.05 mg L-1 . These values are ~2.5-3 times lower than quercetin, ascorbic acid and Trolox®, but compared with rutin and butylhydroxytoluene, berries show similar or better antioxidant activity by both the DPPH and ABTS methods.

Phenolic compounds and biological activity of Kitaibelia vitifolia.

This study was aimed at evaluating the antioxidant activity and efficacy of the ethanolic extract of the endemic plant species Kitaibelia vitifolia in inhibiting the growth of selected fungi and bacteria. Antimicrobial activity was tested using the broth dilution procedure for determination of minimum inhibitory concentration (MIC). MICs were determined for eight selected indicator strains. The highest susceptibility to K. vitifolia ethanolic extract among the bacteria tested was exhibited by Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 25923, and Klebsiella pneumoniae ATCC 13883 (MIC=15.62 µg/mL), followed by Escherichia coli ATCC 25922 and Proteus mirabilis ATCC 14153 (MIC=31.25 µg/mL), and Proteus vulgaris ATCC 13315 (MIC=62.50 µg/mL). Of the fungi, Candida albicans ATCC 10231 (MIC=15.62 µg/mL) showed the highest susceptibility, and Aspergillus niger ATCC 16404 (MIC=31.25 µg/mL) had the lowest. Results showed that K. vitifolia extract possesses antioxidant activity, with total antioxidant capacity of 75.45±0.68 µg of ascorbic acid/g and 50% inhibition concentration values of 47.45±0.55 µg/mL for 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity, 35.35±0.68 µg/mL for inhibitory activity against lipid peroxidation, 95.25±0.52 µg/mL for hydroxyl radical scavenging activity, and 31.50±0.35 µg/mL for metal chelating activity. Total phenolics, flavonoids, condensed tannins, and gallotannins were 85.25±0.69 mg of gallic acid (GA)/g, 45.32±0.55 mg of rutin/g, 54.25±0.75 mg of GA/g, and 41.74±0.55 mg of GA/g, respectively. The phenolic composition of K. vitifolia extract was determined by high-performance liquid chromatography. Rosmarinic acid was found to be the dominant phenolic compound of the extract.