Application of response surface methodology for studying the influence of soaking, blanching and sodium hexametaphosphate salt concentration on some biochemical and physical characteristics of cowpeas (Vigna unguiculata) during canning Original Research A

Response surface methodology and central composite design for K = 3 was used to study the combined effect of blanching time (0–12 min), soaking time (0–24 h) and sodium hexametaphosphate [(NaPO3)6] salt concentration (0–1%) on moisture, ash, leached solids, phytates, tannins and hardness (texture) of cowpeas during canning. Regression models were developed to predict the effects of variables on the studied indices. Blanching, soaking and salt concentration all had significant positive effects on moisture content, ash content, leached solids, phytates, tannins and hardness of the canned cowpeas with significant interaction between all the factors with high regression coefficients (72.0–91.4%). The use of blanching and soaking prior to canning led to increasing moisture content and leached solids while significant decreases were observed for phytates, tannins and hardness of the canned cowpeas. Addition of sodium hexametaphosphate salt during soaking also caused significant (p ⩽ 0.05) decreases in phytates, tannins and the hardness of the seeds. The combination of blanching, soaking and sodium hexametaphosphate salt can therefore be used to retain the mineral content of cowpeas during canning while reducing the anti-nutritional factors and the hardness of the canned cowpeas with acceptable product quality characteristics.