Phytochemical, Antioxidant, Functional and Pasting Properties of Composite Flour Developed from Wheat, Soursop Pulp (Annona muricata) and African Walnut (Tetracarpidium conophorum) Flours

Refined wheat flour is deficient in dietary fibre and several bioactive micronutrients, while the underutilised tropical fruit soursop (Annona muricata) and the indigenous oilseed African walnut (Tetracarpidium conophorum) are comparatively rich in these constituents. This study evaluated the effect of replacing wheat flour (WF) with soursop pulp flour (SPF) and African walnut flour (AWF) on the proximate, mineral, phytochemical, antioxidant, functional, pasting, microbial, and sensory properties of composite flours and their cakes. Five blends were formulated: ROA (100% WF, control), RAO (5% SPF + 5% AWF), AFO (7.5% SPF + 7.5% AWF), FOA (10% SPF + 10% AWF) and OFA (15% SPF + 15% AWF), all on a wheat-substitution basis. Substitution significantly (p ≤ 0.05) increased total phenolic content from 621.80 to 1181.04 mg GAE/100g, total flavonoid from 10.25 to 20.22 mgQE/100g and antioxidant activity improved correspondingly (DPPH: 41.99 - 54.26%; FRAP: 0.159 - 0.352 mg/g), while water absorption, oil absorption and foaming capacities rose from 0.97 to 1.20 g/g, 0.64 to 1.97 g/g, 10.15 to 20.22 % respectively, and pasting viscosities declined progressively. Oxalate, phytate, tannin, alkaloid contents and microbial loads of all blends increased with substitution but remained within Codex and JECFA safety limits. The findings establish FOA as the most nutritionally balanced and consumer-acceptable formulation, with RAO recommended where nutrient density for vulnerable groups is prioritised, supporting SPF and AWF as viable functional ingredients for wheat-based bakery products.