Quantification of isoorientin in Passiflora edulis rinds by HPTLC-densitometry and HPLC/DAD methods and evaluation of radical scavenging capacity of the extracts

Passiflora edulis fo. flavicarpa O. Degener (Passifloraceae) is widely cultivated in Brazil mainly for industrial juice production and is also consumed in natura. Passion fruit rinds represent about half of the fruit's mass, and are a major waste product. The purpose of this study was to develop analytical methods based on HPTLC-densitometry and HPLC/DAD for the determination of isoorientin in P. edulis rinds. Preliminary tests indicated isoorientin as the major flavonoid and the only relevant compound of the rinds with availability of commercial analytical standards. In addition, the antioxidant capacity (radical scavenging) of passion fruit extracts was evaluated by the DPPH· (2,2-diphenyl-1-picrylhydrazyl radical) method, in view of the potential use of passion fruit rind by-products. The content of isoorientin in rinds found by HPTLC (0.206 ± 0,001 mmol L^-1) was higher than the result obtained by HPLC/DAD (0.101 ± 0,001 mmol L^-1). This discrepancy may be explained by the possible overlapping bands (compounds) or also due to the matrix effect in HPTLC. The total volume of organic solvent employed in the HPTLC method was eight times lower compared to the HPLC/DAD method, and the duration of HPTLC analyses was six times shorter than the HPLC/DAD method, indicating the potential of the former as a “green” alternative technique to HPLC in routine qualitative and quantitative analyses of P. edulis foods and extracts, with smaller consumption of solvents and reagents. Besides, the antioxidant capacity of passion fruit rinds (EC50 = 25.93 ± 1.80 g L^-1) was found to be considerably higher than in other foods such as sugarcane juice (EC50 = 100.80 ± 2.56 g L^-1) and passion fruit pulp (EC50 = 38.50 ± 2.28 g L^-1), suggesting a direct correlation between antioxidant capacity and isoorientin content in P. edulis rinds, according with previous studies. These results suggest the relevance of in-depth research into passion fruit rind as a potential source of natural antioxidants.