A comparative study on carbohydrates and antioxidants of indigenous crop black jack (Bidens pilosa L.) and selected commercial vegetable crops.

Abstract

The adequate consumption of African leafy vegetables has been closely associated with a strong reduction of chronically disease such as cancer, diabetes and cardiovascular diseases. The health benefits provided by African leafy vegetables are due to the presence of various primary and secondary metabolites. However, most of the epidemiological studies have indicated that very little is known about the antioxidant activity of African leafy vegetables, which is believed to be responsible for their therapeutic effect. In this present study the physiochemical and antioxidant properties were examined, in relation to other Asteraceae, commercial vegetables (lettuce and chicory). Firstly, the study investigated the physicochemical and antioxidant compounds during seed germination in black jack. Secondly examined the non-enzymatic and enzymatic antioxidants in black jack and compared them with lettuce and chicory. In seed germination test, physicochemical seed quality properties for African leafy vegetable, black jack antioxidants accumulation during seed imbibition were reported. The results revealed that soaking of black jack seeds in water before sowing, induces germination. In this study black jack seeds that were soaked for 15 hours before germinating, showed a highest percentage of germination (72 %) in 5 days. The seeds also showed high considerable total antioxidants capacity of antioxidants (DPPH) and phenols (0.69±0.44 mg/g and 56.45±0.08 mg/g DW). The protein content was also high on the seeds (0.328±0.17 mg/g DW). However, there were high amounts of anti-nutritional factors noticed on the seeds, where the total tannins content was (416.36±1.14 mg/g DW). The results further revealed that African leafy vegetable, black jack contained significant amount of non-enzymatic antioxidants at the early stages of growth than other leafy vegetables. The plant biomass per plant increased with the number of harvests. The plant DPPH antioxidant assay recorded black jack (0.73 ± 0.13mg/g DW - 0.29±0.083mg/g DW), lettuce (0.10±0.64mg/g DW - 0.29±0.03mg/g DW) and chicory (0.35±0.72 - 0.20±0.11mg/g DW). The plant phenolic content recorded black jack (155.46±0.07mg/g DW - 73.11±0.02mg/g DW) for lettuce it was found to be (13.24±0.05mg/g DW - 44.92±0.07mg/g DW) and for chicory (97.09±0.37mg/g DW - 17.88±0.22mg/g DW). However, as black jack all of the secondary metabolites were decreasing drastically when it was reaching maturity, while the phenols were increasing. For carbohydrates, black jack had the lowest concentration of the soluble sugars (glucose, sucrose and fructose). The enzymatic antioxidants of black jack were the lowest for most of enzymes, but SOD activity was higher. Although it decreased as the plant approaches maturity. In conclusion, black jack accumulates different types of antioxidants and their concentration varied over plant developmental stages. The key findings of this study are; the African leafy vegetables have different antioxidant production trends compared to exotic vegetables. Depending on leaf positions and leaf stage, preferably young leaves of the ALVs, there might be sequential harvests, increases the food access for extended period for household consumption. The ALVs also experience higher SOD, CAT, POD activities during early growth stage. These plants have also displayed the highest antioxidant capacity during the early plant development, early stage high accumulation of the studied antioxidants most likely contribute to this antioxidant strength. Furthermore there adaptation to wild environment, exposed to various harsh conditions, their tolerance to survive to this condition probably attributed to plants’ antioxidant production characteristics.