Storage Stability and Sensory Evaluation Of Soy-Fortified Staple Foods in Ghana
The Feed the Future Innovation Lab for Soybean Value Chain Research (SIL) is dedicated to soybean research for economic development and the reduction of poverty and hunger by nurturing improved soybean value chains in Africa. Dr. Juan Andrade, University of Florida, is the principal investigator of the Soybean Nutrition Program and is leading the soy fortification project.
The Soybean Nutrition Program works to promote the consumption of soy to enhance human nutrition, food security and dietary diversity across Sub-Saharan Africa by promoting technologies that produce Delicious Inexpensive Nutritious Environmentally and culturally friendly, and Safe (DINES) soy products.
In sub-Saharan Africa, high poverty rates cause many people to consume diets concentrated on low-cost starchy staples, which are limited in many essential nutrients leading to child malnutrition and stunting. Food fortification has the dual advantage of being able to deliver nutrients to large segments of the population without requiring radical changes in food consumption patternsi. Soybeans represent an inexpensive source of high-quality protein that could be integrated into food items to increase nutritional value.
In Ghana, soymilk is an increasingly popular drink, but is primarily imported. One of the main byproducts from local processing of soymilk is okara, which is commonly used to make wet food for pigs. However, okara is high in protein, carbohydrates, and fiber, making it a potentially attractive nutritional ingredient for food products.
Andrade, in partnership with Dr. Francis Amagloh at the University of Development Studies in Tamale, Ghana, aims to explore fortification of commonly used flours in Ghana – gari (cassava) and tuo zaafi (maize and millet) with dried okara-soy flour and evaluate their stability (i.e. rancidity) under real storage conditions and conduct sensory evaluation.
In this project, the research team evaluated the role of traditional techniques (i.e., soaking, germination, and roasting) on the oxidative stability of full-fat soy flour (FFSF) under commercial and accelerated conditions.
Results from a field study in Ghana and accelerated conditions in the U.S. showed that pretreatment, storage condition, and time alone and together have a defined impact on the oxidative stability (shelf life) of FFSF. The team observed that traditional processing methods such as germination and soaking improve oxidative stability, and therefore, it could expand the useful life of FFSF. Despite its common use and recommendation, roasting promotes oxidation under both accelerated and normal storage conditions.
The study also illustrated that it is technically feasible to replace as much as 10% of maize flour with FFSF to prepare tuo zaafi, a local maize-based dish consumed by most Ghanaians during breakfast. Proportional additions beyond 15% soy flour are discouraged due to changes in flavor.
Upcycling okara, the remaining wet residue from soymilk processing, could result in an important revenue stream for processors. Wet okara contains quality protein and fiber. However, it spoils quickly due to its moisture content and lack of management right after production.
In Tamale, Amagloh’s team evaluated the use of okara as a dry ingredient for incorporation into staple dishes. For this, eight soybean varieties often used to prepare soymilk were evaluated. A low-cost convection oven was used to test temperature and time combinations to obtain a dry okara residue, which was subsequently milled into flour. Okara flour was blended with cassava, as a recipe refinement of gari, a popular cassava-based ready-to-eat food.
The addition of okara flour as a 20 to 50% replacement for cassava resulted in higher total protein, crude fat, and total ash. The okara-enriched gari was equally preferred by consumers, even at 50% replacement. Though drying is an expensive technique, it can directly open opportunities for processors in sub-Saharan Africa to enhance their portfolio of products and bring nutrition at a cost to vulnerable populations.