Screening of traditional South African leafy vegetables for selected anti-nutrient factors before and after processing

Abstract

The present study investigated the effect of processing on anti-nutritional factors of thirteen traditional leafy vegetables collected in KwaZulu-Natal, South Africa. The purpose of this study was to determine whether processing reduced anti-nutrient levels of the species. Three boiling parameters were used with a ratio of 1:4 vegetable to water for a time period of 0, 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 (0.01–0.14 mg/ml), phytic acid (0.002–0.059 mg/ml), alkaloids (3.6–11%), oxalic acid (85.2–1079.3 mg/ml) and cyanogenic glycoside (17–33 mg/100g). Solanum nigrum was the highest in tannin content (0.14 mg/ml).Ceratotheca triloba was the highest in phytic acid content (0.06 mg/ml). Momordica balsamina (11.1%) and Physalis viscosa (10.3%) ranked the highest overall in alkaloid content. Ceratotheca triloba (1079.3 mg/ml), Amaranthus hybridus (796 mg/ml) and Oxygonum sinuatum (673.9 mg/ml) were the highest in oxalic acid. Asystasia gangetica (33.3 mg/g), Ceratotheca triloba (32.6 mg/g), Momordica balsamina (32.5 mg/g), Physalis viscosa (32.3 mg/g) and Solanum nigrum (32.2 mg/g) were the highest in cyanogenic glycoside. All anti-nutrients were reduced significantly through boiling in all the species. The results of this study provide evidence that the local traditional vegetables upon which the population is so reliant upon, are important contributors in micronutrient malnutrition in developing countries and can be eliminated through common boiling methods for a minimum of 5 and maximum of 15 minutes.