Carotenoids retention and in vitro iron bioavailability of traditional cowpea leaf dishes of rural Tanzania

Abstract

Food preparation methods play a role in micronutrient retention and ultimately intake. Analyses for carotenoids retention and in vitro iron bioavailability of five cowpea leaf dishes prepared according to the traditional methods of rural Tanzania were carried out. All the five dishes are commonly eaten as relishes for staple meals of maize or rice. Laboratory analyses were carried out at the Nutrition Laboratory of the World Vegetable Centre in Taiwan. Carotenoids were analysed by high-performance liquid chromatography while iron bioavailability was analysed by an in vitro method. Results showed that traditional cowpea leaf dish consisting of sunflower oil, onion, tomatoes and coconut milk cooked for 30 min had the highest retention of β-carotene (40.83 ± 7.00%) and lutein (34.60 ± 3.30%) compared to other traditional recipes (p < 0.05). The highest iron bioavailability (10.04 ± 0.49%) was observed in the traditional recipe which involved boiling fresh cowpea leaves for 15 min. Although recipe variation can affect carotenoids retention and iron bioavailability, simple practices such as reduced cooking time and avoiding direct sun drying also need to be promoted.

Keywords::

• cowpea leaves
• traditional cooking recipes
• carotenoids retention
• in vitro iron bioavailability

Declaration of interest: We acknowledge the financial and material support provided by AVRDC-Taiwan and AVRDC-Arusha through the project ‘Promotion of neglected indigenous vegetable crops for nutritional health in Eastern and Southern Africa (PRONIVA).’ The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.

Notes

Fresh cowpea leaves were dried under direct 6 h sunlight for 3 days time at varying temperatures of the day ranging from averages of 29°C at 10:45 am, 38.5°C at 13:00 pm and 36°C at 16:00 pm.