Ion-exchange chromatographic analysis of soluble cations, anions and sugars in milk whey

Abstract

Three ion-exchange chromatography methods for the separation and quantification of soluble compounds, including cations, anions and carbohydrates in liquid whey were developed. While cations and anions were successfully separated by ion chromatography coupled with electrochemical suppressed conductivity detection, carbohydrate analysis was accomplished by high-pH anion exchange chromatography in conjunction with pulsed amperometric detection. All separations were performed under isocratic elution conditions. With a simple sample preparation, these methods enabled interference-free identification and sensitive quantification of whey soluble ions and compounds: Na+, NH4+, K+, Mg2+ and Ca2+, Cl-, SO42-, PO43-, citrate, isocitrate, and lactose along with some minor sugars, such as galactose, glucose, and N-acetylgalactosamine. Whereas no significant differences were observed between the mean concentrations of Na+, K+ and Mg2+ in wheys deriving from bovine milk of different cheesemaking technologies, the free Ca2+ content in hard cheeses was less than a half of that found in whey from soft cheeses (560±10 mg/l, n=4) as a result of a more favoured solubilization of calcium from the colloidal phase. In spite of an elevated amount of lactose, separation and quantification of minor whey sugars was possible.