**1. Introduction**

Protein-energy malnutrition is a major public health concern in sub-Saharan Africa (SSA) [1,2]. Beside food insufficiency, it is because diets in SSA are predominantly starchy with low levels of proteins. Maize (*Zea mays* L.), a cereal with low protein content (10%), is the key staple crop in SSA which is largely consumed as a main dish during lunch and dinner in the form of a stiff porridge. The stiff porridge is usually prepared using flour made from whole maize, non-fermented degermed-dehulled maize or fermented degermed-dehulled maize and is called *nsima* in *Malawi*, *nshima* in Zambia, *sadza* in Zimbabwe, *ugali* in Kenya and Tanzania, *mielie pap* in South Africa, and many other names across SSA. Unfortunately, the majority of the population in SSA lack resources for the purchase of high

protein animal source foods such as meat, milk, eggs, and fish protein [3]. Consequently, they consume this protein-deficient staple along with vegetable relish, thus exacerbating protein malnutrition in the region [4].

Legumes are nutritionally valuable protein sources (20–45%) that offer a cheap option for upgrading the nutritive value of cereal-based foods. Owing to the high protein content, soybeans are the most popular legume used to enrich porridge served as breakfast for the whole family, and as a complementary food for infants and young children in SSA [5,6]. The soybeans are usually roasted or are extruded together with the maize to take care of anti-nutritional factors, off-beany flavor, and reduce the porridge preparation time. However, the roasted and extruded soybean products cannot be used to enrich stiff porridge due to the formation of flavor compounds. Consumers in sub-Saharan Africa are very accustomed to a maize-based stiff porridge that is essentially flat and flavorless, and any deviations from this norm are likely to be objectionable [7–10]. Likewise, it is also impractical to use raw maize-soybean flour mixture as it takes so long to cook and besides, the stiff porridge prepared in this manner retains objectionable off-beany flavors.

Off-beany flavors in soybeans described as "painty, bean, green, and unpleasant" are an activity of endogenous lipoxygenase enzymes which catalyze the insertion of oxygen into polyunsaturated fatty acids producing hydroperoxides, which subsequently participate in autoxidation process leading to the production of off-flavor compounds—particularly hexanal and heptanal [11]. Lipoxygenase works almost instantaneously during the grinding of soybeans in an ambient environment [12]. However, soymilk research has proven that it is possible to hydrothermally deactivate lipoxygenase before it catalyzes the oxidation of polyunsaturated fatty acids at 80 ◦C or higher and produce acceptable milk [12–14].

Despite the feasibility and widespread application of hydrothermal deactivation of lipoxygenase in soymilk industry, no report is available about the evaluation of this technique in the preparation of odorless products for the enrichment of protein-deficient maize stiff porridge. Therefore, the objective of this study was to investigate the effect enriching maize-based stiff porridge with flour made from hydrothermally treated soybeans on consumer acceptability. In this study, the effect of soybean proportion and the maize flour type are investigated, and the nutrition implication of soybean enrichment is discussed.
