TOPSIS based comprehensive evaluation of the effect of drying methods on polyphenolic contents and associated antioxidant activities of Moringa oleifera leaves

This study aimed to identify the most suitable drying method for the retention of phenolic content and associated antioxidant activities in Moringa oleifera leaves. The drying methods included: sun drying (SD), shade drying (SHD), oven drying (OD) and freeze drying (FD). The conventional maceration and ultrasonication were used to extract the phenolic components from the dried leaves. A comprehensive non-targeted mass spectrometry was used to determine the major phenolics in the extracts. The leaves dried under shade resulted in higher Total Phenolic Content (9.88 mg Gallic acid equivalent/g) and Total Tannin Content (4.96 mg Tannic acid equivalent/g) when extracted through maceration whereas ultrasonication resulted in higher content of Total Flavonoid Content in SD samples (10.31 mg quercetin equivalent/g). Ultrasonication resulted in higher antioxidant activities (67–70% scavenging) in SHD samples when determined using free radical scavenging assays. The non-targeted UHPLC analysis indicated higher relative quantities of flavonoids (12%), phenolic acid (60%) in SHD samples. The multivariate decision analysis ranked the SHD as the best method for release of higher contents of phenolics and antioxidant activities depending on closeness coefficient.