Analysis of Phenolic Content and Antioxidant Properties of Selected Cowpea Varieties Tested in Bovine Peripheral Blood

Sarah Adjei-Fremah,Louis En Jackai,Mulumebet Worku

doi:10.3844/ajavsp.2015.235.245

Abstract

Cowpea is an important grain legume with a dual purpose function as a food and feed resource. Cowpea contains phenolic compounds that are beneficial to human and animal health. We evaluated the phenolic content, condensed tannin content and antioxidant capacities of methanol extracts of seed and leaf of seven varieties commonly used in food and animal feed. The total phenolic content and condensed tannins were quantified using the Folin-Ciocalteu and Vanillin-HCL method respectively. The effects of cowpea phenolic extract on total antioxidant capacity, glutathione peroxidase and superoxide dismutase activity was evaluated in vitro in bovine blood. Overall, the methanol extracts of the leaves contained high concentrations (p<0.0001) of total phenolic content (290.51±38.02 mg GAE/g) compared to seed extracts (118.10±71.96 mg GAE/g), although high antioxidant capacity was observed in both extracts. In addition, a positive correlation was found between total phenol and tannins content and antioxidant capacity of the extracts. Treatment with cowpea phenolic extract increased (p<0.0001) the total antioxidant capacity in cow blood (5.33±0.27 mM UAE) relative to controls (1.62±0.10 mM UAE). The enzymatic activities of GSH-Px and SOD were also increased. Our findings, suggest the potential of cowpea polyphenols to reduce oxidative stress in livestock production. Results of the present study showed that leaf and seeds of cowpea possess rich amounts of natural antioxidants and can be further explored for their possible use as a natural additive in food or use in pharmaceutical industries and in animal feed.

Highlights

Cowpea is an important grain legume native to sub Saharan Africa, are typically grown in semi-arid regions in Africa, Asia, Europe, South America and some parts of the United States
The main objectives of this study were to (a) individually evaluate the Total Phenolic Content (TPC), Condensed Tannin content (CT) and antioxidant capacity of the leaves and seed methanol extracts of selected cowpea varieties commonly used in the Unites States and (b) to determine the effect of extracts of Mississippi Silver (MS), a variety commonly grown in the southern U.S on antioxidant status in cow blood
Condensed tannins amounts were high in Mississippi silver seeds (0.22 mg/Catechin Equivalent (CE)/100g) whiles low content was observed in Early scarlet variety (0.22 mg/CE/100g)

Summary

Introduction

Cowpea is an important grain legume native to sub Saharan Africa, are typically grown in semi-arid regions in Africa, Asia, Europe, South America and some parts of the United States. Cowpea is fed to animals as forage, hay or silage. Cowpea forage has high nutritive qualities with crude protein of about. 22% and is highly recommended as a supplementary protein feed for animals on low quality diets (Gwanzura et al, 2012; Paduano et al, 1995). Studies reported that cowpea haulms could be used to sustain animal growth and milk production in lactating dairy cattle during the dry season without health challenges (Anele et al, 2010; 2011). Some cowpea cultivars have dual purpose production for dry seed grains and use as forage. Several crop improvement programs over the past two decades have produced dual purpose cowpea varieties with wider adaptability, drought resistance, insect pest resistance and increase grain and forage yields (Hall, 2004)

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