Optimisation of experimental conditions for binding of divalent iron to bioactive casein phosphopeptides

Casein phosphopeptides (CPPs) are mineral-binding bioactive peptides derived from enzymatic digestion of casein. They have been shown to increase iron bioavailability due to increasing iron solubility at the alkaline pH of the intestine. Thus, they are potentially applicable as an advantageous preparation for iron fortification of food. This study aimed to characterise a commercially available CPP and determines optimum experimental conditions for binding it with ferrous iron. The effect of three variables - pH (5-7.5), mass ratio of iron to CPP (MR) (0.04-0.16) and holding time (40-80min) - on the CPP's iron content was investigated using the central composite design (CCD) in response surface methodology (RSM), and a quadratic model was developed. The optimisation in this survey was based on the maximum response. Among all the regression's terms, the main and quadratic effects of pH represented the most significant influences on the iron content (P-value <0.05). The obtained optimum conditions were as follows: pH 6.5, MR 0.14 and holding time 72min, resulting in binding 68.66mg iron per gram of the CPP. The quantity of iron bound to the CPP depended considerably on the experimental conditions and proved the importance of optimisation.