Ca2+-selective electrode: A simple method to measure the phytase-aided release of bound calcium in soymilk

Soymilk is a nutritious beverage widely consumed worldwide. However, the presence of phytic acid hinders the bioavailability of minerals, such as calcium, underscoring the necessity for dephosphorylation. The aim of the study was to develop a quick and simple method to measure the phytase-aided release of bound calcium in soymilk. Freed calcium ion (Ca2+) by the phytase treatment (maximum activity of 48 U/L) at different temperatures (45-65 °C) and pH (4.8-5.6) was analyzed using a calcium ion-selective electrode (ISE) that produced almost a perfect linear relationship between the enzyme activity and the concentration of free calcium (r = 0.98-0.99). The free calcium concentration in untreated soymilk (31 mmol/L) increased up to 77 mmol/L (p < 0.05) with phytase treatment. The entire range of Ca2+ liberation was sensitively quantified with the ISE indicating the feasibility of this simple method for the assessment of the efficacy of phytase to improve the bioavailability of calcium, hence, nutritional value, of soymilk.