Estimation of nutritional postharvest losses along food value chains: A case study of three key food security commodities in sub-Saharan Africa

Postharvest losses (PHLs) amplify food insecurity and reduce the amount of nutrients available to vulnerable populations, especially in the world's Low and Middle Income Countries (LMICs). However, little is known about nutrient loss at the various postharvest stages. The objective of our study was to develop a methodology and a tool to estimate nutritional postharvest losses (NPHLs) along food value chains for three distinct food commodities in sub-Saharan Africa. The study used a combination of literature, laboratory and field data to investigate NPHLs caused by both changes in quantity and quality of food material (quantitative and qualitative NPHLs, respectively). The method can be expanded to various other food value chains. A user-friendly predictive tool was developed for case studies involving maize and cowpea in Zimbabwe, and for sweet potato in Uganda. Quantitative and qualitative NPHLs were combined and converted into predicted nutrient loss and nutritional requirement lost due to postharvest losses. The number of people who may not meet their daily nutritional needs, as a result of the food and nutrient losses at country level, was estimated. The estimates consider nutritionally vulnerable groups such as children under five years and pregnant women. The nutrient density of the harvested food material, the level of food production, the postharvest stages along the food value chain, the levels of pest damage along the value chain, and the susceptibility of the nutrients to degradation e.g. during storage, are all important factors that affect NPHLs. Our modelling work suggests that reducing PHLs along food value chains could significantly improve access to nutritious food for populations in LMICs

The NUTRI-P-LOSS (NUTRItional Postharvest Loss) methodology: a guide for researchers and practitioners

Postharvest losses and food security are important concerns in low- and middle-income countries (LMICs) and research in these areas has become a global priority. Measuring nutritional losses along the crop value chain (VC) can deepen quantitative and qualitative understanding of these losses, which is critical for understanding the contribution of agricultural interventions to nutritional improvement. Nutritional loss estimation methods and metrics can provide crucial information for improving food security strategies at local and global levels. The NUTRI-P-LOSS Project developed a methodology to estimate nutritional postharvest losses (NPHLs) throughout the VCs of key staple food crops (maize, sweet potato and cowpea) in two sub-Saharan African countries (Zimbabwe and Uganda). The project focused on key nutrient losses: energy, macronutrients (protein, lipid, carbohydrate, dietary fibre) and micronutrients, considered the most important in terms of deficiencies (vitamin A, zinc, and iron) in developing countries, especially sub-Saharan Africa. We covered estimation of nutritional losses related to: (1) physical weight losses (building on existing weight loss methodologies) (2) other changes not associated with weight loss (i.e. quality losses). Based on our experience during the NUTRI-P-LOSS Project, we are proposing a methodological approach for model dissemination to other countries and other commodities (i.e. other cereals, pulses and roots and tubers, as well as commodities from any other food group) in a cost-effective and sustainable way (e.g. through an open-line, open access platform such as APHLIS). We describe here the method and lessons learned, including challenges that arose in the development of the tool. A key feature for the success of the NPHL estimate is obtaining reliable data on postharvest loss. A second key facet is managing the combination of the data in a coherent way to produce a reliable model estimate. This requires making choices on the presentation of the data (for example selecting field work data as opposed to laboratory data or vice versa) in order to produce a coherent model. Assumptions must be made carefully and stated clearly to ensure credibility. Lastly, in order to make an impact on nutritional outcomes, the model has to be integrated in an online platform (e.g. APHLIS) that can provide open access to data and enable stakeholders, such as LMIC policy makers, researchers and development partners, to obtain estimates of the nutritional postharvest losses in their focal country, VCs and contexts of interest

Comparative performance of five hermetic bag brands during on-farm smallholder cowpea (Vigna unguiculata L.Walp) storage

Cowpea (Vigna unguiculata L. Walp) grain is an important source of protein for smallholder farmers in developing countries. However, cowpea grains are highly susceptible to bruchid attack, resulting in high quantitative and qualitative postharvest losses (PHLs). We evaluated the performance of five different hermetic bag brands for cowpea grain storage in two contrasting agro-ecological zones of Zimbabwe (Guruve and Mbire districts) for an 8-month storage period during the 2017/18 and 2018/19 storage seasons. The hermetic bag treatments evaluated included: GrainPro Super Grain bags (SGB) IVR™; PICS bags; AgroZ® Ordinary bags; AgroZ® Plus bags; ZeroFly® hermetic bags. These were compared to untreated grain in a polypropylene bag (negative control) and Actellic Gold Dust® (positive chemical control). All treatments were housed in farmers’ stores and were subjected to natural insect infestation. Hermetic bag treatments were significantly superior (p< 0.001) to non-hermetic storage in limiting grain damage, weight loss and insect population development during storage. However, rodent control is recommended, as rodent attack rendered some hermetic bags less effective. Actellic Gold Dust® was as effective as the hermetic bags. Callosobruchus rhodesianus (Pic.) populations increased within eight weeks of storage commencement, causing high damage and losses in both quality and quantity, with highest losses recorded in the untreated control. Cowpea grain stored in Mbire district sustained significantly higher insect population and damage than Guruve district which is ascribed to differences in environmental conditions. The parasitic wasp, Dinarmus basalis (Rondani) was suppressed by Actellic Gold Dust® and all hermetic treatments. All the hermetic bag brands tested are recommended for smallholder farmer use in reducing PHLs while enhancing environmental and worker safety, and food and nutrition security

How different hermetic bag brands and maize varieties affect grain damage and loss during smallholder farmer storage

Smallholder farmers in sub-Saharan Africa store harvested maize to provide food stocks between harvest seasons, which may be up to 12 months apart. Stored maize is highly susceptible to insect pest damage, hence the need for stored grain protection technologies such as hermetic bags. The current study evaluated the efficacy of five brands of hermetic bags in storing three maize varieties under two contrasting agro-ecologies in Guruve and Mbire districts of Zimbabwe, for two storage seasons. The hermetic bag treatments evaluated included: GrainPro Super Grain bag (SGB) IVR™, PICS bag, AgroZ® Ordinary bag, AgroZ® Plus bag and ZeroFly® hermetic bag, which were compared to grain stored in a polypropylene bag either untreated (negative control) or following admixture with a synthetic pesticide treatment, Actellic Gold Dust® (positive control). The maize varieties included a white hybrid, a pro-vitamin A biofortified orange and a local variety. All the hermetic bag treatments out-performed the synthetic pesticide in limiting grain damage and weight loss during storage. No significant difference in grain damage or weight loss was observed among the hermetic bags. However, rodents punctured some hermetic bags; therefore rodent control is recommended. A positive correlation with grain damage and weight loss for all three maize varieties was found for Sitophilus zeamais, Sitotroga cerealella, Tribolium castaneum and Cryptolestes spp adult numbers. Significantly higher insect damage and weight loss (P<0.001) occurred in the white hybrid maize than in the other two varieties. The results confirmed that regardless of brand, all the hermetic bags tested can be recommended for smallholder farmer use to limit postharvest storage losses, avoid 32 pesticide use, and support food and nutrition security

Determinants of smallholder farmers’ maize grain storage protection practices and understanding of the nutritional aspects of grain postharvest losses

Poor storage methods lead to high postharvest losses in maize, an essential staple in sub-Saharan Africa. Smallholder farmers’ knowledge and awareness of postharvest nutritional losses (PHNLs), practices regarding maize grain storage, and factors influencing use of improved storage protection practices were investigated in two districts in Zimbabwe through a cross-sectional field survey of 331 households randomly selected from lists of farmers’ names kept by local extension staff. A multistage sampling technique was used involving purposively selecting the study districts then randomly selecting the study wards, the villages and the households. Twenty eight key informant were purposively selected being officers and stakeholders working or residing in the two districts and involved in postharvest and nutrition issues. The most commonly used storage practices were the admixture of maize grain with synthetic grain protectant pesticides followed by storage of untreated grain in polypropylene bags. Highly toxic pesticides, such as Cabaryl 85 WP and Acetamiprid 20 SP, which are not registered for stored food grain treatment, were being applied by 14.6% of the farmers to protect their grain from insect attack. We developed a PHNL knowledge index that measured farmers’ nutritional knowledge and awareness of PHNL. Level of education and district positively correlated with farmers’ PHNL knowledge (p<0.05), whereas the opposite was found for farmers’ age (p<0.05). Multinomial logistic regression analysis showed that use of grain storage protection practices was positively related to farmers’ age, total maize grain production, education level and PHNL knowledge (p<0.05). Older farmers were less likely to use non-recommended chemicals to protect their maize grain during storage. Farmers’ education level and total maize grain production were positively associated with higher use of synthetic pesticides, while PHNL knowledge was associated with the use of traditional grain protectants (p<0.05). Training on grain storage management, especially safe grain storage protection practices and PHNLs, is essential to contribute towards household food and nutrition security