Effect of different blanching treatments on the nutritional composition, phytochemical contents and antioxidant activity of dried moringa oleifera lam. leaf flour

Abstract

Moringa oleifera leaf is an exceptional vegetable with excellent nutritional and medicinal properties. Blanching improves nutrients availability in the leaf. This study aimed to investigate the effect of different blanching treatments on the nutritional, phytochemicals, and antioxidant properties of dried M. oleifera leaf. Freshly harvested M. oleifera leaf was divided into five parts. Four parts were blanched using different treatments while the fifth was unblanched. Blanching was done at 100°C for 3 minutes. Each part was dried using an electric dryer at 50°C for 7 hours and analyzed for nutritional content by proximate analysis using Standard Official Methods. HPLC was used to determine Vitamin A and C, Gallic acid for Phenol and flavonoid while antioxidant activities were evaluated with four in-vitro scavenging assays, using ascorbic acid as a standard. There was significant difference between the results for both the blanched and unblanched dried M. oleifera leaf: Moisture content (5.83-8.21%; 5.76%), protein (23.02-26.43%; 23.37%), carbohydrate (32.32-39.22%; 38.37%), crude fat (0.75-2.37%; 1.67%), crude fibre (17.74-29.31%; 23.87%), Vitamin-C (69.08-234.32mg/100g; 78.65mg/100g), Vitamin-A (17.10-25.99IU; 41.96IU), phenol (27.93-59.25mgGAE/g; 59.64mgGAE/g), flavonoid (27.98-51.77mgRE/g; 56.93mgRE/g), total antioxidant (12.00-71.56%; 27.36%), DPPH (18.06-87.52; 11.98-67.72%), FRAP (0.09-0.595%; 0.092-0.556%), and nitric oxide (5.12-82.16%; 19.74-68.79%) respectively (p<0.05). Blanching of M. oleifera leaf before drying should be encouraged to improve its nutritional value and for use as a functional food because of its abundant natural antioxidants. All blanching treatments exhibited loss of Vitamin A and minimal loss of phenol and flavonoid. Steam blanching at 1000C for 3 minutes should be encouraged.