Valorisation of immature cereal grains to improve food security in Sub-Saharan Africa:a case study on pepeta in Tanzania

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Wageningen University


Cereals contributes a substantial proportion of the food supply for humans and animals globally, including in the SSA where they form a major source of dietary energy and protein intakes as staple foods. Beside their importance to food supplies and health, they contribute to improved income among the most food‐insecure population groups in SSA countries. However, most of cereals are consumed as refined products (dehusked or polished) to improve their sensory properties. This renders the processed cereal-based products of poor nutritional quality as the refining process also removes important nutrients. On the other hand, there is increasing trend of consumers wanting more cereal-based healthy foods containing specific health-promoting properties. In this sense, immature cereal-based products such as pepeta (a locally processed immature rice flakes from Tanzania), appear to be among the many alternatives to pursue the goal of better cereal-based nutrition due to their nutritional potential benefits. It has been found that immature cereals and their products contain higher amount of numerous nutrients beneficial to health, including dietary fiber, vitamins, minerals and phytochemicals, compared to their mature counterparts. However, the information about the effect of processing on the nutritional and sensory properties and the bioavailability of nutrients in immature cereal grains and their products such as pepeta, is limited. Therefore, it is important to assess the traditional knowledge of pepeta product and its quality to improve the processing conditions and products’ nutritional, sensory, and digestibility properties. In Chapter 2, factors that can affect the pepeta value chain, as well as pepeta processing elements that interact with food and livelihood security such as availability of immature rice, pepeta processing techniques, storage practices, product characteristics, preferred product attributes, as well as pepeta trade supply chain and problems, were surveyed among the key players of pepeta processing chain: rice farmers – producer of sole raw materials, i.e., immature paddy grains used in pepeta processing; processors – local indigenous knowledge practitioner with vast knowledge on pepeta processing; and consumers - pepeta end-users with or without pepeta processing knowledge. Results indicated the potential role of pepeta to reduce food insecurity, especially among the rural poor as hunger breaker, i.e., a source of an early food when the crops are yet to reach maturity, and households’ food supply is inadequate. Moreover, as a traditional processing knowledge, the pepeta processing parameters and conditions were not standardised, affecting consistently production of good quality pepeta products. Since pepeta processing knowledge involve roasting of immature rice grains, it was of paramount importance to investigate changes in nutrients content and digestibility during maturation of rice grains, as well as upon processing into pepeta products (Chapter 3). Generally, immature rice grains destined for pepeta production had a higher amount of most nutrients such as lipids, protein, ash, soluble and insoluble dietary fibre, as well as B group vitamins such as thiamine, nicotinic acid, and nicotinamide compared to mature counterparts. Though pepeta processing improved the nutritional properties of rice, a very high and fast starch digestibility comparable to that of cooked milled and polished rice, diminish the health benefits of the pepeta product. Therefore, these findings necessitate further improvement of pepeta processing techniques and the nutritional quality and functional properties of traditionally processed immature rice- based products such as pepeta. From this point of view, the following chapters of this thesis were designed to optimise the processing conditions that improve the specific nutritional, functional and sensory properties of traditionally processed pepeta products (i.e., maturity and roasting conditions (soaking and temperatures)). In Chapter 4, the laboratory simulation of pepeta processing was employed to investigate the impact of dry-heat processing at different conditions on the nutritional composition and in-vitro starch and protein digestibility of immature rice-based products. The results indicate that the nutritional profile of immature rice products can be modulated by processing conditions, dry heating improves vitamin and mineral content when compared to raw and cooked immature rice. Soaking before roasting greatly increased the iron content compared to zinc, thiamine, riboflavin and nicotinamide, indicates the possibility for processed immature cereal products that were soaked before roasted to combat iron deficiency. Moreover, dry heating reduces both protein and starch digestibility when compared to cooked immature rice, where disulphide bonds play a vital role in heat-induced protein interactions in immature rice. The effect of maturity and different processing practices on rice and immature rice-based products’ visual quality and volatile profile was assessed under laboratory simulation, as well (Chapter 5). It was found that both the maturity and roasting influences the colour and volatile profiles of rice grains, whereas soaking before roasting limits non-enzymatic browning process such as Maillard and caramelisation reaction, and diffusion of bran pigments into rice starchy endosperm. The results are vital towards understanding the sensory properties of immature cereal-based products such as pepeta which are critical for the product’s acceptability by consumers. All the findings of this thesis were integrated and discussed in Chapter 6. The discussion focused on the role of immature cereals and their products towards improving the nutritional and sensory properties of cereal-based food products where most consumed products are based on refined cereal grains known to be nutritionally limited. Furthermore, an overview of the opportunities, challenges, and future developments of the utilisation of immature cereals grains and their products was highlighted.


PhD thesis


Immature cereal grains, Food security, Pepeta, Sub-Saharan Africa, Macronutrients, Cereals, Tanzania