Fonio (Digitaria exilis) in West Africa

Fonio (Digitaria exilis) in West Africa: Towards improving nutrient quality.

Abstract.

Hidden hunger affects a far greater percentage of the world’s population with iron and zinc deficiencies being the most common, particularly affecting women of reproductive age. The primary cause of the mineral and vitamin deficiencies in developing countries is inadequate intakes of multiple and bioavailable micronutrients in common cereal-based diets, emphasizing the need for increased quality of diets. Plant genetic diversity, and also indigenous foods and/ or traditional grains as fonio may play a critical role in reduction of the problem for resource poor populations. Fonio (Digitaria exilis) is the most ancient West African cereal representing a key crop in food supply during crop shortfall periods. However, less is known about its potential to contribute improving nutrition and health. In this context, the thesis investigated whether we could improve the nutrient quality of fonio, especially iron, to potentially contribute to the daily intake of population.

Investigations in this thesis comprised: i) the consumption pattern of fonio and its contribution to nutrient intakes (108 women aged 15‐49 year-old selected from 3‐stage cluster sampling procedure in Bamako, Mali for the purpose of the fonio project); ii) the validation of the Mali food composition database (TACAM) for assessing population level intakes of energy and nutrients (36 women out of 108 previously selected); iii) the genetic diversity, nutrient content especially bioavailable iron and zinc content and the effect of processing on fonio landraces (12 fonio landraces collected from farmers in Mali); iv) the sensory variability among fonio landraces (20 fonio landraces collected from farmers in Mali, Guinea and Burkina Faso); v) improved food processing combining dephytinisation with native phytase and fortification of fonio diet with iron to increase iron absorption (16 women aged 18-30 year-old from simple random sampling in Cotonou, Benin).

The results indicated that i) fonio is consumed one to three times/ month by 68% of our study population. The average daily portion size is 152g when consumed. Only 5% of the study population consumed fonio dishes contributing to 16% of the daily energy intake for the consumed portion size, reflecting the low consumption of fonio related to significant barriers such as availability of cooked fonio in urban markets, lack of consistent supply throughout the year, difficult post- harvest processing, high-quality product demand, hard texture coupled with time consuming cooking process, and high cost of fonio products.

The use of the adjusted TACAM is acceptable for estimating average intake at population level for macronutrients, calcium and zinc in a low intake population, but not for carbohydrate and iron intakes which was underestimated and vitamin A which was overestimated, nor for probability of adequate intakes and nutrient densities. At individual level, significant differences were observed between estimated and analyzed intakes for all the nutrients increasing with higher intakes.

The nutrient content of fonio landraces in Mali and the effect of processing of the nutrient values revealed i) a limited genetic variation of studied landraces, polymorphism level (3.5%) compared to 63% reported for 118 fonio accessions collected in West Africa, three different clusters only for Malians landraces compared to two clusters for Mali, Burkina Faso, Guinea and Benin together; ii) no statistically significant differences between fonio landraces for their iron and zinc content, iii) a high iron and phytate concentration in paddy fonio (35 and 514 mg/100 g dry weight) which reduces considerably with traditional processing, the most important losses occurring during processing from paddy to mid wet fonio (approximately 2 and 129 mg/100 g), 96% reduction for iron and 75% for phytate.

Fonio landraces in West Africa were different for their visual (colour and presence/absence of impurities) and their textural (consistency of cooked grain) charactersitics.

Exploring processing to increase iron biavailability from fonio meals confirm that whole wheat flour could be used as a source of natural phytase to produce low phytic acid containing fonio porridge. It showed also that dephytinisation using intrinsic wheat phytase reduced phytate-to-iron molar ratio from 23.7:1 to 2.7:1 after only 1 hour of incubation at 50ºC with pH of 5.0, and iron fortification decreased the molar ratio to 0.3:1. Dephytinisation with wheat phytase and fortification significantly increased iron absorption ratio from 2.6% to 8.2% in fonio porridges.

From these results, we can conclude that the current contribution of fonio to daily bioavailable iron intake is low due to small portion sizes being consumed in low frequency, to considerable losses during processing to mid-wet fonio, and to a high phytate-iron molar ratio. Fonio landraces from Mali, Guinea and Burkina Faso are variable in visual and textural characteristics (colour, presence of impurity and consistency of the cooked grain, respectively), determining the preference of consumers. Selecting landraces for preferred sensory properties may offer an entry point for processors who intend to promote the consumption of fonio and increase its role in diet. In absence of meaningful genetic diversity and variation in iron content in fonio landraces in Mali, there is little benefit in selecting landraces for natural high iron content. Dephytinisation using intrinsic wheat phytase could be a promising processing practice to improve iron bioavailability and fortification is required to increase the amount of absorbed iron from fonio meals.

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