Functionality of gum Arabic and sodium alginate on selected properties of Bambara groundnut tofu and its chunks

Abstract

Bambara groundnut (BGN) (Vigna subterranea [L.] Verdc.) is a source of protein (15-25%), making this legume a suitable alternative to soybean for tofu production. The use of BGN as a main ingredient in tofu is not documented, as most tofu is made from soy milk extracted from soaked soybeans. The texture (Instron texture analyser), colour (HunterLab ColorFlex spectrophotometer), rheology (rheometer), proximate (AOAC methods) and microstructure (scanning electron microscope) of BGN tofu as affected by coagulants (vinegar, lemon juice and gluconolactone (GDL)) and hydrocolloids (gum Arabic and sodium alginate) were established in this study. Factorial design and response surface methodology were used to optimise gum Arabic and sodium alginate concentrations at 0.3, 0.4 and 0.5%. The interaction of gum Arabic and sodium alginate was optimal at 0.5%. The combination of gum Arabic and sodium alginate significantly (p < 0.05) increased the hardness (9.15%) and springiness (11.46%) of tofu and decreased its gumminess (19.72%). The lightness of BGN tofu increased as GDL concentration increased. The coefficient of determination (R2 ) for all measurements using the Power law was >0.9. The consistency coefficient (K) of BGN milk extract prepared using GDL with gum Arabic and sodium alginate was >1, indicating shear thickening behaviour. The entrapped water content of BGN tofu ranged from 45.13 (1% GDL-tofu) to 65.60% (0.6% GDL-tofu + 0.5% GA + 0.5% SA). Adding gum Arabic and sodium alginate to BGN tofu increased the protein, ash and carbohydrate content and decreased the moisture content. Vinegar-tofu exhibited a uniform, smaller particle size network and smooth surface. Gum Arabic and sodium alginate had a significant (p < 0.05) positive effect on the functional and sensory qualities of BGN tofu chunks. Leucine (4.34-4.94%) and phenylalanine (4.61-5.62%) were the most abundant essential amino acids in all BGN tofu chunks samples. There was an increase in the protein content of BGN tofu when gum Arabic and sodium alginate ratio was incorporated. Bambara groundnut tofu chunks with 0.6% GDL with gum Arabic and sodium alginate received the highest in appearance, colour, taste, texture and overall acceptability than tofu chunks coagulated with vinegar and 0.6% GDL. The results of this study highlighted the potential of BGN tofu and its chunks as a nutritious, cholesterol-free protein alternative, with the quality and acceptability influenced by coagulant types and hydrocolloid concentrations.