Phenotypic Based Characterization of Nutritional and Bioactive traits of Amaranth Vegetable for Improved Iron Bioavailability and Acceptability

Abstract

The amaranth vegetable has been shown to be rich in micronutrients as well as many bioactive compounds. The crop, however, has different species and varieties which possess different nutritional attributes. Though the vegetable has anti-nutrients which reduces mineral bioavailability, it is tolerant to harsh environmental conditions which may affect nutrient accumulation positively or negatively. Varied cooking methods may also affect nutrient retention and bioavailability. The objective of this study was to determine how varietal differences, environment and cooking affects nutritional composition of amaranth vegetables and also to develop nutritionally improved recipes that enhance nutrient retention and iron bioavailability of these vegetables. The study sought to understand how morphological phenotypes, environmental stress in form of drought and cooking habits relate to the nutrient composition of amaranth. The study involved ten accessions of amaranth from four different species: Amaranthus hypochondriacus, Amaranthus cruentus, Amaranthus blitum and Amaranthus dubius. The seeds were obtained from the World Vegetable Centre in Tanzania and Taiwan. Morphological characterization of the lines was done by precision phenotyping technology using Phenospex field scan. This is a three-dimensional (3D) laser scanning equipment fitted with sensors that are moved on top of the plant canopies, taking plant measurements. Nutritional laboratory analysis was also carried out and the association between the traits determined. The amaranth accessions were also grown in a greenhouse and subjected to drought stress. The effect of drought stress on nutrient accumulation as well as the effect on the transcription of biosynthesis genes of selected components were then determined. Surveys on consumer preference and utilization practices for amaranth vegetables were carried out in Kenya and Tanzania. This was done through focus group discussions and key informant interviews to explore on the knowledge, attitudes and practices around amaranth. Nutrient retention of amaranth vegetable dishes prepared using traditional food preparation methods identified from the survey were evaluated. Iron bioavailability of amaranth dishes prepared by traditional and improved food preparation methods were compared. Recipes were then developed, based on themes that help improve diversity, nutrient retention, mineral bioavailability and other nutritional benefits from the vegetables. The accessions of the A. dubius species showed significantly higher nutritional contents compared to the accessions of other species. Greenness of the leaves was found to be positively correlated with oxalate and vitamin C contents, while the hue of the leaves also correlated with the contents of specific carotenoids. The study on drought stress revealed that oxalates are reduced under stress, while components with anti-oxidative properties including vitamin C, carotenoids, flavonoids and phenolic acids are enhanced under stress. Changes in accumulation of calcium, iron and zinc were not significant. Significant changes in transcription of biosynthetic genes of oxalate, vitamin C and carotenoids was also observed, with a positive correlation between vitamin C change with the level of expression of its biosynthetic gene, GDP-L-galactose phosphorylase (GGP/VTC2). Amaranth utilization survey in Kenya and Tanzania revealed that preference for indigenous vegetables differ with region as well as individuals. A. dubius and A. blitum were the most commonly consumed varieties in Kenya; while A. dubius and A. hypochondriacus were the most common in Tanzania. The consumer preference for species was mostly based on taste and availability. Cooking methods were varied among consumers and included boiling, frying and steaming. Most people considered taste rather than nutrition when cooking. Some cooking methods could lead to reduced nutritional value. The study pointed out some of the commonly used cooking practices such as prolonged cooking, that reduce nutritional value. Three recipes were selected and prepared under controlled conditions in the laboratory. These were then analyzed and the nutrient retentions found to be fairly high, though the iron bioavailability was quite low. Further experiments on the recipes showed that incorporating vitamin C, adding an iron rich vegetable and boiling of the vegetable significantly improved the iron bioavailability and hence the iron uptake by the body. Incorporating lemon juice enhanced dialysable iron of the selected recipe by up to 66%. In order to improve the nutrient uptake, diversity of amaranth dishes and acceptability of vegetable amaranth, 16 recipes were made based on 5 nutritional themes. The themes addressed nutritional and utilization related factors of amaranth, and also applied principles from the iron bioavailability enhancement study to improve nutritional quality of amaranth vegetables. Sensory evaluation in Kenya and Tanzania showed high acceptability of the recipes. This study concludes that varietal differences significantly affect the nutritional contents in amaranth vegetables, and some morphological phenotypes such as hue and greenness of leaves are associated with certain nutritional components. Harsh environmental conditions, specifically drought stress, affects metabolite biosynthesis and accumulation in amaranth. Finally, there exists varied preferences, attitudes and utilization practices of amaranth in Kenya and Tanzania. The study recommends the adoption of improved amaranth cooking methods in order to increase consumption and maximize the nutrition benefits from amaranth vegetables.