Abstract
Moringa stenopetala is a socioeconomic valued tree that is widely available and cultivated in Southern part of Ethiopia. The leaves have been traditionally used as a food source with high nutritional and medicinal values. The present work was carried out to evaluate the effect of thermal treatment on the total phenolic content, total flavonoid content, antioxidant activities and α-amylase inhibition of aqueous leaf extracts obtained from M. stenopetala during maceration and different decoction time interval (5, 10 and 15 min). The total phenolic and flavonoid contents were determined by the Folin-ciocalteu and aluminum chloride methods, respectively whereas antioxidant activities were determined by 2,2-diphenyl-1-picryl-hydrazyl(DPPH) radical scavenging, reducing power, phosphomolybdenum and ferrous ion chelating assays and α-amylase inhibition potential was determined using 3,5-dinitrosalicylic acid method. Total phenolic and total flavonoid contents ranged from 34.35 ± 1.06 to 39.47 ± 1.33 mgGAE/g and 10.44 ± 0.61 to 20.36 ± 0.93 mgQRE/g, respectively. Decoction for 10 min extract showed ferrous ion chelating (92.52 ± 0.17 %), DPPH radical scavenging (91.52± 0.59 %), α-amylase inhibition (69.06 ± 0.14%), ferric reducing power (0.765 ± 0.14) and total antioxidant activity (0.329 ± 0.32), respectively. DPPH, reducing power, total antioxidant and α-amylase inhibition activities showed positive linear correlation (R2=0.853, R2= 0.857 , R2= 0.864 and R2=0.930), respectively with total phenolic content but ferrous ion chelating activity were found to be weakly correlated (R2=0.481). Based on present investigation, it could be concluded that major lose of total phenolic content, antioxidant and α-amylase inhibition activities of the crude leaf extracts of M. stenopetala leaves were observed at decoction time for 15 min. Therefore, to maintain the total phenolic content, antioxidant and α-amylase inhibition activities of leaves, cooking practice should be at the optimum decoction time (5-10 min). Key words: Moringa stenopetala, antioxidant, total phenolic content, α-amylase inhibition.
Highlights
In living systems, free radicals are produced by the normal metabolic processes and quite helpful in many of body’s natural functions
The total phenolic content obtained from decoction for 15 min extract were in accordance with previous studies that prolonged decocting at high temperature can lead to degradation of phenolic compounds (Perva et al, 2006)
The data presented in this study indicated that aqueous leaf extracts of M. stenopetala have special ability for iron chelating activity, which were even greater than the standard BHT
Summary
Free radicals are produced by the normal metabolic processes and quite helpful in many of body’s natural functions. Uncontrolled production of derived free radicals can initiate the oxidation of biomolecules such as protein, lipid, amino acids and DNA and can induce numerous diseases (Hsu et al, 2003). There is a trend to substitute and discover new and effective antioxidant and α-amylase inhibitors from plants with minimal or no side effects (Shai et al, 2010). Several African medicinal plants were reported to have both antioxidant and hypoglycemic activities (Atawodi, 2005). Plant foods rich in polyphenols have been reported to cause effects on insulin in the utilization of glucose and act as good inhibitors of key enzymes like α-amylase associated with type II diabetes and decrease the postprandial blood glucose expedition levels in diabetic patients (FredJaiyesimi et al, 2009)
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