Phytoconstituents utility in ethiopian kale and african cabbage orphan leafy vegetables and potential cultivation of the vegetables as functional foods

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Sokoine University of Agriculture


Various studies have recently highlighted the importance of African leafy vegetables (ALVs), which refer to plants whose leaves are accepted and utilized as vegetables by communities through tradition. Due to their higher concentrations of nutritious and non- nutritive compounds than widely cultivated and consumed "exotic" vegetable species, ALVs constitute an important part of people's diets. Orphan ALVs, such as Cleome gynandra (African cabbage) and Brassica carinata (Ethiopian kale), are indigenous, native species that were introduced centuries ago but are still used locally or regionally, having lots of untapped potential to improve nutritional security. Due to their local benefits, occurrence as wild plants, weeds, or volunteer crops, these vegetables are typically characterized as minor, neglected, underutilized, and/or unimproved; and they are almost entirely ignored by farmers, researchers, crop breeders, and even policymakers. Consumers have recently placed a high value on vegetables as functional foods in their diets, with reports indicating that they are not only nutritionally dense, but also contain high levels of some health-beneficial phytochemicals when compared to commonly consumed staple crops, and that they have a high potential to contribute not only to food security, but also to nutritional security. In this thesis, an extensive study was conducted in order to understand the secondary metabolites present in African cabbage and Ethiopian kale vegetables, their utility in promoting human health, possible strategies to improve the vegetables, and the potential application of these vegetables as functional foods and as a source of natural bioactive compounds in the food and pharmaceutical industries. Firstly, this study involved a systematic review to determine the composition and health beneficial compounds obtainable from leafy vegetables and the possible strategies for improving such compounds during vegetable growth. Then using seeds supplied from a gene bank in Kenya, the Centre for Biodiversity in Kenya Resources Centre for Indigenous Knowledge, National Museums of Kenya (eight accessions for African cabbage and one accession for Ethiopian kale), the vegetables were cultivated in the greenhouse of KIST. Plant materials were collected at different stages and separated into several organs for bioactive component profiling. Target chemicals such as glucosinolates (GLs) and phenolics were detected in the vegetables using chromatographic techniques combined with mass spectrometry, based on their fragmentation patterns and mass to charge ratio. The identified compounds were quantified with commercial pure standards or relative response factors of the compounds using High performance liquid chromatography (HPLC) techniques. Upon identification and quantification of the compounds in the different vegetable parts and accessions, the adaptation of the vegetables for application in a vertical smart farming system was determined by checking the agronomic characteristics/desired traits. Furthermore, the possibility of improving vegetables by accumulating the bioactive secondary metabolites and their associated biological properties was evaluated using elicitors treatment. Different types and concentrations of elicitors and their applicability to vegetables grown in vertical farming system were chosen. In the findings from the review, I obtained crucial data on the major composition of leafy vegetables which include GLs and polyphenols, the type of biological activities associated with these compounds such as anticancer, anti-inflammatory, antioxidant activities as well as the different strategies that can be used to improve vegetables at different stages of growth. For the compositional data, I observed variable components and concentrations of the identified compounds in each vegetable, the accessions under study and the vegetable parts used. During the evaluation of the well adapted vegetable to be used in the vertical farming system, Ethiopian kale vegetables were best suited for this type of farming and the cultivation had positive results in improving not only yield but also the quality of the vegetables and the inherent biological activities attributed to them. This vegetable was the choice for further objectives and analysis in this research and the target development stages were chosen depending on their ability to accumulate the bioactive compounds. Ethiopian kale’s samples extracts were subjected to various chemical and in vitro biological assays including antioxidant and anti-inflammatory potential, chosen depending on the identified compounds and effective activities were attributed to these compounds based on the literature review. The findings on elicitation demonstrate how elicitors could be used as a simple strategy to obtain quality plant functional foods with increased quantities of the health promoting compounds. This study shows the utility of both the edible and non-edible parts of the orphan leafy vegetables. It reduces the gap of unknown compounds in the vegetables and the identification of new compounds and provides a future reference for further studies. The evaluation of potential smart farming techniques to improve both yield and content of essential phytochemicals in the vegetables creates a good opportunity to venture and apply this emerging farming techniques for the production of high-quality functional foods and vegetables with accumulated drug target compounds for use in the pharmaceutical industry. The identification of superior accessions provides potential research targets to be used breeding programs for improving available vegetable varieties while the strategies used in production of quality vegetables are useful in the food industry for the production and processing of functional foods from the orphan leafy vegetables.


Ph.D Dissertations


ethiopian kale, african cabbage, orphan leafy, vegetables, potential cultivation