Screening of traditional South African leafy vegetables for specific anti-nutritional factors before and after processing

Abstract

This study investigated the effect of processing on anti-nutritional factors of thirteen traditional leafy vegetables collected in Kwa Zulu-Natal, South Africa. The aim was to determine whether processing reduced anti-nutrient levels of leafy vegetables. The vegetables were boiled in a plant-to-distilled water ratio of 1:4 (w/v) at 97 °C for a time period of 5 and 15 min. The vegetables studied were: Amaranthus dubius, Amaranthus hybridus, Asystasia gangetica, Bidens pilosa, Ceratotheca triloba, Chenopodium album, Emex australis, Galinsoga parviflora, Guilleminea densa, Momordica balsamina, Oxygonum sinuatum, Physalis viscosa and Solanum nigrum. From this study, it was determined that non processed samples contained anti-nutrients such as tannins, phytic acid, alkaloids, oxalic acid, and cyanogenic glycoside. Both boiling parameters were effective in reducing the tannin, phytic acid, alkaloid, oxalic acid and cyanogenic glycoside contents of all 13 traditional leafy vegetables. The results of this study provide evidence that the local traditional leafy vegetables which the population is so reliant upon, are important contributors to micronutrient malnutrition in developing countries and can be minimized through common boiling methods for a minimum of 5 and maximum of 15 minutes.

Keywords:
traditional leafy vegetables; tannins; phytic acid; alkaloid; oxalic acid; cyanogenic glycoside