Nutritional Composition and Bioactive Components in Slenderleaf (crotalaria ochroleuca and crotalaria brevidens) Vegetable at Various Growth Stages

Abstract

In Africa, one child out of five suffers from chronic malnutrition. In Kenya, 50% of the children have calcium, iron and zinc deficiency and 30% of children suffer chronic malnutrition. African traditional leafy vegetables have a role in alleviating this malnutrition. Such vegetables include slenderleaf. Though some work has been done on this vegetable, the relationship between growth stages on one side and nutritional, non nutritional, bioactives and antinutrients composition on the other side is not well researched. The objectives of this study were to determine the nutrition composition, the bioactive components and the antinutrient content of 10 accessions of slenderleaf at three different growth stages. Slenderleaf were grown in JKUAT farm between January 2011, and February 2012. Fresh leaves were harvested at 8 weeks, 13 weeks and 16 weeks after planting. The leaves were destalked, weighed, and ground. The proximate analysis (Moisture, protein, and ash) were determined and results were reported on dry matter basis. Vitamin C, β-Carotene and Total carotenoids were determined and results were reported on fresh matter basis. Atomic absorption spectrophotometer was used to determine the minerals (Iron, Zinc and Calcium). Phytates were determined using HPLC. The diPhenyl picryl hydrazyl method was used for the antioxidant determination and for the tannins vanillin-hydrochloric acid was used. For nutrients contents (moisture, protein, ash and mineral), it was noticed significant (p≤0.05) differences in the slenderleaf accessions due to maturity stage. The nutrient content was significantly (p≤0.05) higher during flowering stage than the other two stages (moisture 73.98 %, ash 7.16 %, protein 33.07 %, iron 14.45 mg/100g, zinc 3.88 mg/100g, calcium 9.32 mg/100g). There were significant (p≤0.05) lower values of nutrient content at the after flowering stage. There were significant (p≤0.05) differences in bioactive (vitamin C, β-carotene, total carotenoids, flavonoid and vitamin E) content among the different accessions of slenderleaf. The significant (p≤0.05) highest values were observed during flowering stage compare to the two other stages (vitamin C 25.17 mg/100g, β-carotene 10.08 mg/100g, flavonoid 31.51 mg/100g and vitamin E 3.83 %). There were significant (p≤0.05) differences in the antinutrients (tannins, phytate and oxalate) content of slenderleaf at different maturity stages. For the antinutrients, there was significant (p≤0.05) higher values at the after flowering stage (tannins 70.39 mg/100g, phytate 63.14 mg/100g and oxalate124.73 mg/100g) while the significant (p≤0.05) lowest values were observed at the during flowering stage. For all the samples and the different variables analyzed (nutrients, bioactives and antinutrients) were significantly (p≤0.05) different from each other at the three growth stages. For each of the three growth stages we also noticed some significant (p≤0.05) difference between some accessions which were having significant (p≤0.05) higher level compared to others. Before the flowering growth stage, the nutrients, the bioactives and the antinutrient content of the plants were all at their highest level. During flowering, the nutrients and the bioactive content of the plant were at their highest level while the antinutrient content was at their lowest level. Finally after the flowering growth stage, the anti-nutrients content increased as the nutrients and the bioactive contents decreased to their lowest level. It could then be concluded that the growth stage affected the nutritional value of the plant and also the accession. Therefore for an optimal nutritional value, the plant needs to be harvested before end of the flowering stage.