Optimized Supplementation Ratio of Wheat Flour and African Yam Bean Flour for Best Possible Bread Specific Volume and Crumb Hardness in Nigeria

Bread is the most widely consumed food by all social classes around the world. It represents about 80% of the baked products sub-sector in Nigeria (KPMG, 2016). However, bread is relatively expensive in tropical countries where wheat is imported for bakery industries (Eleazu et. al, 2014). This is because wheat is a temperate crop that will not do well under tropical conditions as a result of unfavourable soil and climatic conditions (Abdelghafor, 2011).Whole-wheat grain consists of the entire grain, and, unlike refined grains, they still contain bran and germ, which are rich in dietary fibre and micronutrients (Kyro and Tjonneland, 2016).Whole-grain foods are associated with reduced risk of several chronic diet-related diseases and it contains a lot of compounds with reputed health benefits (Dalton et al., 2012). The bread industry commands a large market share in Nigeria. According to KPMG (2016), the bread industry is worth ₦122.1 billion and about 72% market share is allocated to the small and medium-sized bakeries. Majority of the bread consumed in Nigeria are baked by small and medium scale bakeries and come indifferent sizes that suit the consumer’sneed, whose standard could be compromised by inadequate quality control. There is a large market for bread in Nigeria with population of over 200 million people with an estimated national population growth rate of 5.7% per annum, and an average economic growth rate of 3.5% per annum in the past 5 years with all social classes consuming it as a staple food. Nigeria, being a tropical country in sub-Saharan Africa, does not have the agronomic variables that support profitable and economical production of wheat. This circumstance causes bakeries to depend highly on imported wheat for bread and other confectionaries. Foreign Agricultural Service (FAS) Lagos under the United States Department of Agriculture forecasts that wheat imports in Marketing Year (MY) 2019/20 is estimated to be 5.6 million metric tons, which is up by almost 4% compared to MY 2018/19. The rise in wheat consumption is attributable to the population growth of about 2.54% (2015-20), with Nigerians increasingly consuming greater amounts of wheat-flour based products (USDA-FAS, 2019). Successive governments in Nigeria, in a bid to reduce the increasing cost of wheat importation, enacted wheat control policies ranging from a complete ban in the years 1987 to 1991, via composite flour approach, which included 5% cassava inclusion from 2007 to 2010, 10% cassava inclusion from 1979 to 2007 and up to 40% cassava inclusion in 2012 (Ohimain, 2015). These policies have not been successful due to the undesired physical quality of wheat-cassava bread.

Though Wheat gluten plays a vital role in the quality and structure of baked bread, a small fraction of the flour matrix can be replaced with other non-wheat flour without affecting its final bread quality.

The use of local and available flours which could produce similar characteristics as gluten or support the available gluten strands during fermentation, proofing and baking would make the applicability of composite flour technology successful. Shittu et al. (2007) defined composite flours as either binary or ternary mixtures of flours from some other crops with or without wheat flour. The reason for considering composite flours in various food products has been to exploit the economic advantage of reducing or even eliminating the cost of imported wheat in bakery and pastry products by partial or complete use of domestically grown products instead of wheat.

African yam bean (AYB) (Sphenostylis sternocarpa L.)is a drought-tolerant legume crop grown primarily as a food in West Africa, especially southern Nigeria. It grows well even on acidic and highly leached sandy soils. It is the second biggest and one of the most economically important within the legume family. Despite its abundant yielding potentials, the crop is still largely under-exploited and under-utilized (IITA, 2010). It is expected that its successful inclusion in bakery products will enhance the value and importance to the crop.

In spite of huge investments made by the Federal Government in the cassava bread initiative over a period of 34 years, the project has not achieved (Punch Newspaper, December 19, 2016). According to Eduardo et al. (Eduardo et al., 2013) commercial production of wheat-cassava bread is still difficult due to the impaired bread structure. Consequently, research has been in progress to enhance the specific volume and texture of wheat-cassava bread by adding bread enhancement substances such as hydrocolloids, enzymes, and emulsifiers (Shittu et al., 2009; Serventi, 2020; Eduardo et al., 2014). Shittu et al., (2007) has shown that bread with improved specific volume and crumb softness can be made from composite cassava-wheat flour with added xanthan gum. But very little has been done by utilizing this native and underutilized crop of Nigerian origin to improve the quality of wheat-cassava bread. Also, utilizing a non-gluten protein may help compensate for some lost protein by substituting more fraction of wheat flour and therefore can help in proper shaping of the bread structure and texture (Ziobro et al., 2016). The specific volume of a loaf is a good indicator of bread quality. It represents the ability of gluten strands to retain enough gas released during fermentation and dough proofing. Higher gas retention ability will lead to a higher specific volume (Nada and Hasan, (2015); (Franco et al., 2020). It has been reported in the literature as a definite measure of loaf size (Shittu et al., 20017; Purna et al., 2011). It is also used by the Standard Organization of Nigeria (SON) as a measure of standard bread quality (NIS, 2004). It is the ratio of loaf volume (cm3) to loaf weigh (g). The objective of this paper therefore to develop an optimized substitution mix ratio of wheat flour and AYB flour production of an acceptable bread quality.