Estimation of Total Quercetin and Rutin Content in Malus domestica of Nepalese Origin by HPLC Method and Determination of Their Antioxidative Activity

Malus domestica (Apple) is one of the most widely cultivated cash crops of Nepal. Jumla and Mustang are two major pocket areas for the production of apple. Flavonoids including quercetin and rutin are potent antioxidants present in apples. This study was designed to quantify and compare the presence of quercetin and rutin in different plant parts (peel, leaf, and bark) among various cultivars of Malus domestica from two pocket zones of Nepal. A new HPLC-UV method was developed and validated for the quantification of quercetin and rutin. Polyphenols, flavonoids, and carbohydrate contents were determined by colorimetric methods. 2,2′-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay was carried out to measure in vitro antioxidative activity. Acid hydrolysis of each extract was carried out by the standard method to measure aglycone quercetin content after hydrolysis of its glycosides. The total rutin content ranged from 3.69 ± 1.34 to 374.50 ± 2.35 mg/100g dry extract weight. Before the acidic hydrolysis, the total quercetin content ranged from 2.96 ± 0.13 to 171.05 ± 0.95 mg/100g dry extract weight whereas its amount increased highly after the hydrolysis and it ranged from 80.84 ± 19.65 to 7445.32 ± 29.25 mg/100g dry extract weight. Total polyphenol content ranged from 19.48 ± 0.23 to 123.48 ± 1.84 µg gallic acid equivalent/mg of dry extract weight. Similarly, flavonoid content ranged from 2.21 ± 0.72 µg to 755.54 ± 1.91 µg quercetin equivalent/mg of dry extract weight. Total carbohydrate content ranged from 144.15 ± 3.73 to 484.65 ± 2.63 µg glucose equivalent per 0.5 mg dry extract weight. All the extracts showed the various degrees of antioxidant activity in a dose-dependent manner. Among them, stem bark of the Jonathan Jumla showed potent antioxidant activity with IC₅₀ value of 13.003 µg/mL. The present study provides the information about variation of the phytochemical content among the different cultivars, parts, and geographic locations. Furthermore, it revealed that bark of Malus domestica cultivars had high quercetin and rutin content with high antioxidant activity.