Information on food composition including types and contents of nutrients and anti-nutrients is important for food and nutrition research. There is satisfactory information on established nutritive elements for various food groups. However, literature on anti-nutrient component generally scattered and scanty on few major food groups and commonly consumed plant parts. A better understanding of both the positive and negative qualities of vegetable component would help develop better evidence-based promotion and appropriate dietary strategies. This paper reviews seven types of anti-nutrient elements in vegetables: oxalates, phytates, nitrates, tannins, glucosinolates, saponins and alkaloids and their effects, mechanisms, content and processing methods. A total of 360 research papers were systematically identified and 123 were selected with acceptable anti-nutrient data. Vegetable families and plant parts with highest content of each anti-nutrient were identified, with the Leguiminosae family having highest content of phytate, tannins and saponins, and leafy vegetables having high oxalate. The simplest food processing methods to reduce anti-nutrients in vegetables are boiling and removal of certain plant parts. While consumption of vegetables with anti-nutrients do not normally cause adverse effects in the general population, future research to determine nutrient bioavailability based on diets will help increase awareness and improve recommendations on plant food intake.

Amaranth (Amaranthus spp.) is an underutilized crop increasing in popularity as a grain and as a leafy vegetable. It is rich in protein, minerals, and vitamins, and adapts well to a range of production systems. Currently, the lack of improved cultivars limits the use of the crop. Breeding‐improved cultivars requires access to large collections of amaranth biodiversity stored in genebanks. The task of searching such vast collections for traits of interest can be eased by generating core collections, which display the diversity of large collections in a much smaller germplasm set. The World Vegetable Center amaranth collection contains around 1,000 accessions of 13 species; among them, there are 281 accessions of four species important for use as vegetable amaranth in Africa (A. cruentus, A. hypochondriacus, A. caudatus, and A. dubius). Based on single nucleotide polymorphism (SNP) marker genotype diversity, a core collection (CC) of 76 accessions, cultivars, and selections was assembled. To a large extent, it represents the diversity of the whole collection. The CC was evaluated for yield and nutritional parameters during the cool and warm seasons in Tanzania and Taiwan and a pretest for variation of drought tolerance in the CC has been performed. Cultivar Madiira 2, an improved cultivar developed for vegetable production in Africa, outperformed all other tested cultivars in terms of yield stability, but several CC accessions had higher yield, lower wilting score, and higher nutrient content than Madiira 2. This indicates the core collection can be used for further improvement of amaranth cultivars.

The effects of different protective structures on horticultural and nutritional yield of amaranth and water spinach were studied in three seasons of 2020–2021 in Taiwan. The number of people that can receive recommended dietary intake of iron and β-Carotene from vegetables grown under different production conditions was also estimated. The yield of white and red amaranths was consistently better (7.68–19.70 t/ha) under pink poly-net house in all the seasons, but the yield of water spinach was consistently better under white poly-net house (16.25–20.88 t/ha). Spider mite (fall & spring) and aphid (winter) infestation was mostly observed on all crops under poly-net houses. Neoxanthin, lutein and β-carotene were almost two-fold higher in red amaranth harvested from poly-net houses than open field. Based on the RDI values, β-Carotene supply to both men and women (14+) was consistently higher in all crops produced under pink ploy-net houses in all seasons, except for white amaranth produced under white poly-net house during winter. Its supply to 64,788 more men and 83,298 more women was estimated for red amaranth harvested from pink poly-net house than other production conditions. α-carotene was 2–3 fold higher in amaranths and water spinach harvested from poly-net houses than open field. The iron content of the amaranths was lower in poly-net houses (234.50–574.04 g/ha) than open field (645.42–881.67 g/ha) in the fall, but its supply from pink poly-net house was comparable with open field in the winter. However, pink poly-net house was the highest iron supplier from water spinach (323.90 g/ha) in the winter, which was estimated to provide iron to 19,450–22,939 more men and women than other production conditions. Both poly-net houses were the sole supplier of iron through amaranths in the spring, with pink poly-net house supplying iron to 2,000–5,000 more men and women. Thus, protected cultivation not only leads to more marketable yields but also results in higher quantities of health promoting nutrients. Hence, pink poly-net house may be considered to produce more nutritious vegetables, especially during the off-season to bridge the gaps in the seasonal variations in vegetable consumption, besides providing better income opportunities to the smallholder farmers.

Food preparation methods applied to African traditional vegetables vary greatly depending on preferences of various consumers. Vegetable amaranth is one of the most preferred vegetable, with high nutritional quality. The bioaccessibility of some minerals such as iron is, however, low since it is non-heme, and is also bound by anti-nutrients such as oxalates. This study aimed at evaluating the nutrient retention of amaranth vegetable dishes prepared using selected Kenyan traditional recipes, and to enhance the iron bioavailability of amaranth dishes using food preparation methods. Nutrient retentions of amaranth prepared by three common food methods were analyzed. In-vitro iron bioavailability of amaranth dishes with or without bioavailability enhancers as well as an amaranth meal incorporating a common maize meal staple food was also studied. The nutrient retentions of the various dishes used in this study was fairly high with at least 85% retention of minerals and an increase of up to 45% in three carotenoids. It can be concluded that incorporating vitamin C, adding an iron rich vegetable and boiling of the vegetable significantly improves the iron bioavailability and hence improves the iron uptake by the body. Incorporating lemon juice enhanced dialysable iron of the selected recipe by up to 66%. There was no significant (P≤0.05) effect by the amaranth components on the iron bioavailability of ugali. These methods could therefore be incorporated into household recipes to increase micronutrient intake.