Quality and Nutritional Impacts of Extrusion on Pearl Millet and Nutrient Dense Native Plant Blends

Cheikh Ndiaye, Purdue University


Significant efforts have been placed on the development of strategies to address micronutrient deficiencies in Sub-Saharan parts of Africa. Improving the nutritional value of staple foods, including cereals, is a key component of such strategies as traditional cereals such as millet and sorghum are mostly consumed in these areas. Of micronutrient deficiencies, iron, zinc and vitamin A are most critical, and mostly deficient in staple cereal foods. One option to improve the nutrient density of cereal foods is to leverage natural micronutrient dense plant materials that exist locally, and can be formulated into cereals products. Such products can be combined with processing strategies to produce a diverse array of locally produced consumer products that can be adopted by at risk populations. Success of such strategies requires significant insights into the compatibility of traditional cereal and local plant products with processing strategies. This includes new and novel drying and cereal processing strategies currently being implemented in Africa, such as solar drying and extrusion. With this in mind, the objective of the current studies was to address both the development of knowledge related to the impact of a novel solar drying system on micronutrient rich plants. The same objective was oriented toward establishing insights into the impact of extrusion conditions on product quality and the stability and bioaccessibility of provitamin A carotenoids from blended millet instant thin and thick porridges. The initial studies focused on assessing a novel solar drying system as a mode to generate high quality nutrient dense plant ingredients. Our specific focus was on stability of provitamin A carotenoids from carrot and mango fruit, two products commonly available in Africa and that suffer from high post-harvest losses. With final moistures between 7 to 11%, solar dried sliced mango showed dark off color formation as a result of extended drying times compared to carrot. Grated carrot samples, showed lower content of provitamin A carotenoids (p<0.05) when subjected to extended drying as compared to sliced carrot sample. However, grated carrot samples had higher content of provitamin A carotenoids than sliced carrot samples compared to standard drying (thin layer electric and dehydrator) methods suggesting the suitability of solar drying for the development of carrot and mango powders to be used as ingredients in processed foods targeting delivery of provitamin A carotenoids. The second and third studies assessed the impact of micronutrient rich plant ingredients selected based on their content of iron, and vitamin A on quality of extruded cereal products. Formulation of blends were accomplished with whole grain (WG) millet (80%), dried carrot (Carrot-15%), Adansiona digitata (Baobab-5%) or Moringa oleifera (Moringa-5%). Blends were extruded on a Technochem mini-extruder currently being commercialized in rural and urban markets in Africa. As fully gelatinized flours, water absorption indexes were significantly increased with addition of Carrot and Baobab. Addition of Baobab and Moringa decreased product final viscosities, storage (G') and loss modulus (G"). Pooling results from all added plant materials in extruded WG millet, Moringa exhibited high enthalpy and Cinfinity or C ∞ (45.7 %) values, however, starch digestion was not significantly impacted by presence of these ingredients. Regarding provitamin A carotenoid stability, high recoveries (69–90%) were obtained with inclusion of Baobab and Moringa compared to WG millet Carrot blends, (~60% recovery). Results suggest that production of naturally fortified millet blends can be achieved without significant compromise to product quality and recovery of provitamin A carotenoids. The final study further examined the impact of extrusion on the bioaccessibility of provitamin A carotenoids and chemical changes from blends of millet and plant. Generally, water solubility index was significantly increased by inclusion of CRT and Baobab (P<0.05), while starch digestibility was not altered by formulation. In comparing micronutrient delivery, higher relative provitamin A bioaccessibility (~20%) and higher absolute provitamin A bioaccessibility (707.13 µg/100g porridge) were obtained from extruded WG millet, carrot, and Baobab (WG/CRT/Baobab) compared to others, suggesting potential stabilization of carotenoids by Baobab and the possibility of improving bioavailability through formulation and processing of cereal blends. Taken together, these results suggested that low cost extrusion of WG millet combined with appropriate local nutrient dense plant ingredients generated by solar drying could be used to deliver provitamin A carotenoids to at risk populations. Without altering starch digestibility significantly, extruded blends of WG millet with carotenoid sources and Baobab have potential to stabilize and deliver products with improved provitamin A bioaccessibility. Further applied research focused on solar drying tests in in Africa as well as generation and assessment of consumer product acceptability and efficacy are needed to expand upon these initial findings




Hamaker, Purdue University.

Subject Area

Food Science|Sustainability

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