Comparative Proteomic Study on the Effect of Heat Stress on Protein Extracts from Seed, Leaf, Stem and Root of Moringa oleifera

The Moringa tree, Moringa oleifera is planted around the world and it is naturalized in many locales. A lot of medicinal and therapeutic properties have been attributed to several part of this multipurpose tree, mostly as a result of its protein content. Heat treatment was carried out on the protein extracts of the leaf, seed, root and stem of Moringa oleifera. Protein extract was divided into three batches, out of which two were subjected to heating at 75 °C and 100 °C, and the remaining one served as control. Comparative UV absorption spectra analysis was carried out on the control protein extracts and heat-treated protein extracts of the leaf, seed, root and stem of Moringa oleifera. A plot of absorbance values at 280 nm against concentrations of the standard produced highly significant (p≤0.01) standard linear curve. The standard linear equation y = 0.0197x + 0.0005 was generated from the plot, where y and x represents absorbance values at 280 nm and protein concentration respectively. The standard linear equation was used to deduce the concentration of the control protein extracts and heat-treated protein extracts of the leaf, seed, root and stem of Moringa oleifera. The protein concentration was highest in the leaf control protein extracts (43.7 %) and was the lowest in the 100 °C heat treated stem protein extract (17.1%). Due to the effect of heat, the comparison of absorbance spectra of the control protein extracts and heat-treated protein extracts were different, having several peaks at different wavelengths. Cluster analysis of absorbance spectra optical density values revealed four clusters (cluster 1, cluster 2, cluster 3, cluster 4) among the control protein extracts and heat-treated protein extracts. Cluster 1 and cluster 2 were made up of closely related protein extracts, cluster 3 consisted of protein extract from seed, root and stem that served as control, heated at 75 °C and 100 °C, while cluster 4 consisted of root protein extract heated at 75 °C and stem protein extract that served as control. The variations in the cluster grouping among the control protein extracts and heat-treated protein extracts obtained in this study could possibly as a result of different levels of heat tolerance among different Moringa oleifera proteomic compositions.