Mineral composition and bioavailability of calcium and phosphorus from acid whey concentrated by various membrane processes

This study has been undertaken to investigate the effect of different membrane separation processes (nanofiltration, nanofiltration with diafiltration, and ultrafiltration) on the content of macro- and microelements in acid whey from tvarog cheese (white cheese) production and on bioavailability of calcium and phosphorus in rats' diets with 20 or 40% content of spray dried whey. The use of nanofiltration and ultrafiltration processes in whey concentration did not cause differences in the content of Ca, Mg, P, Fe, nor Zn in the end product. Compared to nanofiltration and ultrafiltration, the introduction of diafiltration to the nanofiltration process was observed to reduce the content of Ca from over 14 to less than 10 mg g(-1), and that of phosphorus from 8.3 and 7.4 to 5.9 mg g(-1), although the biggest reduction was noted in the content of monovalent Na and K. The changes in the mineral composition of whey did not affect coefficients of Ca bioavailability in diets for rats. By substituting Ca in a standard mineral mixture with a 20% addition of whey concentrate, coefficients of the apparent absorption of this element were increased from 36.4% to 42.8-44.6%, and coefficients of its apparent retention from 33% to 38.5-41.7%. The 40% addition of whey concentrates lowered Ca bioavailability coefficients compared to the diets with the 20% whey concentrate content, but not in respect of the control diet. The application of nanofiltration with diafiltration for whey concentration deteriorated phosphorus absorption from the diet with 40% of whey, which was indicated by decreased values of the apparent retention coefficient and absolute retention of P in the body of rats within 5 days, i.e. from 35.2 to 18.5% and from 98.8 to 64.5 mg, respectively, compared to the control diet.