Total Reflection X-Ray Fluorescence (TXRF) in Assessment of Essential Micronutrient Levels in Common Beans (Phaseolus vulgaris) in Kenya.

Author: Nguli,, Magdalene K

Supervisors: Micheal Gatari; Keith Sheperd and Lydia Njenga

In this study, essential micronutrient concentrations in common beans (Phaseolus vulgaris) from Muguga, Kiambu County and Kyevaluki, Machakos County were analysed using Total reflection X-ray Fluorescence (TXRF) and Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES). TXRF as a method of analysis is increasingly becoming of interest in food quality analysis since it is a fast and easy technique. This study shows the effectiveness of TXRF for fast and reliable qualitative and quantitative analysis of micronutrients in beans. Samples of both bean leaves and dry grains were collected where 32 bean leaves and 31 dry grain samples were collected. The results were then assessed for nutritional quality in comparison with sufficiency ranges for high quality yielding bean crops, that is, the comparisons were made from a plant nutrition perspective. A comparison was also made between TXRF and ICP-OES as interchangeable methods of analysis. The TXRF analysed bean leaves from Muguga had mean concentration values of 214 ± 52, 758 ± 219, 2 ± 0.8, 9 ± 1.8 and 65 ± 8.9 mg kg-1 for Mn, Fe, Ni, Cu and Zn respectively. The Mn, Ni and Cu concentrations were within the sufficiency ranges while 6.2% of the samples had higher Zn concentrations. Fe concentrations were consistently high with 97% of the samples having concentrations that were higher than the sufficiency range. Out of those, 50% gave Fe concentrations that were higher than the FAO recommended toxic levels of 800 mg kg-1. To compare TXRF and ICP-OES methods of analysis, the TXRF analysed samples from Muguga were further analysed by ICP-OES. To compare the results obtained by both methods, student t distribution and Analysis of Variance (ANOVA) were used. It was observed that both methods produced results that were similar. This meant that the two methods can be used interchangeably for the analysis of trace elements in plants and especially beans. The bean leaves from Kyevaluki gave mean concentrations of 76 ± 16, 218 ± 65, 1.5 ± 0.2, 8 ± 0.8 and 27 ± 4 mg kg-1 for Mn, Fe, Ni, Cu and Zn respectively and all these samples were found to have concentrations that were within sufficiency ranges. In Kenya, the major form in which beans are consumed is the dry grains with less people using bean leaves as vegetables. From this study however, it was found that the analysed bean leaves had high levels of essential micronutrients and thus can be recommended to be widely used as vegetables.