Qualitative and quantitative composition variability of phenolic compounds in pear (Pyrus communis L.) fruits and evaluation of antioxidant activity of their extracts

The aim of the research: to determine the qualitative and quantitative composition of phenolic compounds of fruits of pear cultivars, which grow in Lithuanian climatic conditions and to evaluate the antiradical and reductive activity in vitro of their extracts. The objectives of the research: to choose the extraction conditions of phenolic compounds from the samples of pear fruits. To determine total phenolic compounds, total hidroxycinnamic acid derivatives and total flavonoids content variation in the samples of fruits of pear cultivars 'Patten', 'Concorde', 'Conference', 'Grabova'. To develop and validate HPLC methodology. To determine the qualitative and quantitative composition of phenolic compounds in samples of pear fruits. To determine the antioxidant activity in vitro of pear fruits extracts and to evaluate the correlation between the phenolic compounds content in the samples of pear fruits and the antioxidant activity in vitro of their extracts. The results and conclusions of the research: the highest amounts of total phenolic compounds (10,05 ± 0,17 mg GAE/g, p < 0,05) and total hidroxycinnamic acid derivatives (5,98 ± 0,15 mg CAE/g, p < 0,05) were determined in the samples of pear fruits of cultivar 'Grabova'. The highest amount of total flavonoids (1,05 ± 0,02 mg RE/g, p < 0,05) was determined in the samples of pear fruits of cultivar 'Concorde'. The eight phenolic compounds were identified and quantified by HPLC method. The strongest ABTS free radical binding activity was determined in extracts of the samples of pear fruits of cultivar 'Concorde' (109,96 ± 3,82 µmol TE/g, p < 0,05). The strongest DPPH free radical binding activity was determined in extracts of the samples of pear fruits of cultivar 'Grabova' (40,38 ± 1,53 µmol TE/g, p < 0,05). The strongest reductive activity was determined in extracts of the samples of pear fruits of cultivar 'Grabova' (42,38 ± 0,96 µmol TE/g, p < 0,05). The strongest correlation was determined between the total amount of hidroxycinnamic acid derivatives in the samples of pear fruits and their extracts antioxidant activity in vitro, which was measured by DPPH method (0,976, p < 0,05)

Determination of the Phenolic Composition and Antioxidant Activity of Pear Extracts

The specific HPLC analytical procedure was developed and validated for the determination of phenolic compounds in pear samples of different popular cultivars “Conference,” “Concordia,” “Grabova,” and “Patten.” HPLC mobile phase consisted of 0.05% (v/v) trifluoroacetic acid in water and 100% (v/v) acetonitrile. The HPLC method was used to identify and confirm the specificity of 8 analytes: chlorogenic acid, rutin, hyperoside, isoquercitrin, isorhamnetin rutinoside, quercitrin, quercitrin malonyl glucoside, and isorhamnetin glucoside. Repeatability % RSD did not exceed 3.87%, and intermediate precision did not exceed 4.63%. The total content of phenolic compounds varied from 0.51±0.001 mg/g (cv. “Concordia”) to 1.11±0.013 mg/g (cv. “Patten”). Chlorogenic acid was the major component in all the tested pear cultivars. The highest amount of chlorogenic acid (0.69±0.033 mg/g) was found in pear samples of the cultivar “Grabova,” and the highest amount of flavonol compounds (1.11±0.013 mg/g) was found in pear samples of the cultivar “Concordia.