Utilisation of marama bean [Tylosema esculentum (Burchell) A. Schreiber] flour in gluten-free bread making

Abstract

Interest in gluten-free (GF) bakery products due to wheat allergies and the incidence of coeliac disease, has led to research that continually explores new ingredients and formulations. One aim is to manufacture GF breads as similar as possible to wheat breads. In many African countries the high cost to import wheat particularly into no or low wheat-producing regions, where the climatic conditions do not favour its cultivation, demand that alternative sources of baking flours for bread are required. The cotyledons of marama beans (Tylosema esculentum) and starch from cassava roots (Manihot esculenta Crantz) contain no gluten. Marama bean has great potential as an oilseed legume. The isolated protein from marama flour has high foaming capacity, and produces a dough with high extensibility and good viscoelasticity, while cassava starch has better performance in gluten-free composite bread formulations than other cereal starches commonly available in Africa. Cassava starch is more similar in functional properties to wheat starch than other tropical cereal starches like maize and sorghum considering its high ratio of amylopectin to amylose which gives it good granule expansion at a low temperature.

The dough properties of composites of defatted marama flour (DMF) and cassava starch (CS) were compared with wheat flour dough with the aim of determining the potential of such DMF-CS composites as a functional nutritious gluten-free ingredient in bread. GF breads from DMF and CS combined in different proportions were studied against wheat breads as standards. Freshly produced breads were assessed for colour, height, specific volume and spread ratio. The crumb texture of breads stored at 5 ° C was measured one day and three days after baking by conducting a texture profile analysis using an EZ-L Shimadzu texture analyser. The measured parameters were expressed as crumb firmness (N) and springiness (%). The crumb structures of GF composite breads were visualized using stereomicroscopy and a sensory panel described the sensory properties of the breads using the Flash Profiling method.

DMF-CS doughs with similar strength to wheat flour dough were produced. However, the DMF-CS doughs had much shorter Mixolab development times and stability. Alveography revealed that the DMF-CS doughs could inflate a bubble, with the 33:67 DMF-CS ratio having the most similar bubble size, extensibility and deformation energy as wheat flour dough. With the highest proportion of DMF (57:43 DMF-CS), these parameters were lower possibly because of the highly hydrophilic marama protein which tended to form aggregates rather than distribute homogenously throughout the dough as revealed by confocal laser scanning microscopy. Rheofermentometry showed that similar to wheat flour dough, the DMF-CS composite doughs also held gas produced by yeast fermentation. In this regard, DMF appears to have considerable potential as a functional gluten replacement for making protein- and fibre-rich GF bread.

Indeed, DMF-CS breads with brown crusts and a uniform aerated crumb structure were produced. Higher inclusion of DMF in the formulation led to a higher specific bread volume with a lower spread ratio. The DMF-CS bread crumbs were less soft than wheat bread with a more intense fermented, nutty, bean-like flavour as well as chewier texture. Higher inclusion of DMF in the formulation led to more bitter taste because DMF contains bitter compounds such as saponins, gallic and protocatechuic acids. DMF-CS breads presented different, more intense flavour sensory profiles compared to wheat bread which was blander.

This is the first study to clearly demonstrate the utilisation of DFM in gluten-free formulations for bread making. The research covers an interesting and highly relevant topic, which is the overall food supply in Africa through creation of a new ingredient for the bakery industry and manufacturing of a staple food product such as bread. The findings of this work serve an important purpose. Domestication of marama bean plants and successful processing of the seeds to functional flour may revolutionise the bakery industry and could potentially have significant economic impact. More research is needed to optimise the formulations and baking methods along with the use of effective technologies to mask the bitter taste of the DMF-CS bread flavour to enhance consumer acceptance and potential success on the market. Further research possibilities should also include altering recipes to improve the flavour and adopting alternative processing techniques including sourdough fermentation, frozen storage of dough, and partial baking to accomplish longer shelf life. The findings of this work should contribute to stimulating the development of marama bean as a commercial oilseed legume crop. DMF appears to have considerable potential as a highly functional gluten replacement in the production of “additive-free,” protein- and dietary fibre-rich gluten-free bread or as a partial wheat flour replacement in composite flour breads.