Optimization of Some Physico-Chemical Properties of Predigested Soymilk Fortified with Micronutrients Using Response Surface Methodology

Soymilk extracted from sorted, 12h tap water steeped, 72h sprouted, hand dehulled and bicarbonate boiled TGX 923-2E soybean variety was fortified for complementary feeding with ferric ammonium citrate (Fe), calcium carbonate (Ca) and vitamin C (VC) at 5 levels combinations according to Box-Wilson (1951) experimental design matrix. The fortified soymilk was stored at ambient temperature for 12 weeks for analyses at two weeks intervals. A central composite rotatable response surface design (CCRRSD) was employed to study the linear, quadratic and cross product effects of fortification and preparation methods on some physico-chemical properties of fortified soymilk. A total of 21 experimental runs were generated including six replicates at center point (o, o, o). Data from each run were statistically regressed and analyzed for variance using MINITAB computer software. Results obtained showed that sprouting reduced total solids, and increased visible coagulation time (VCT). Bicarbonate boiling reduced the TS, and increased pH. Filtration contributed to VCT increase while sterilization enhanced stability and shelf-life of soymilk. Besides, calcium fortificant had strongest positive linear significant (P < 0.05) effects by increasing total solids, ash, pH and colour of the fortified soymilk. Estimated regression coefficients developed for the models showed that all the dependent variables were linearly related to their respective independent variables.Keywords: Preparation methods, physico-chemical properties, fortification, complementary feeding, response surface methodology