Extraction and purification of glycomacropeptide from whey to be used as a source of protein for phenylketonuria patients

Phenylketonuria (PKU) is a genetic disease. Patients suffering from PKU must adhere to a lifelong low-phenylalanine diet. Glycomacropeptide (GMP) is a unique source of protein for PKU patients, because it contains no phenylalanine. The objective of this study was to extract GMP from whey and purify it in order to obtain a product with a minimum phenylalanine content. The ultrafiltration membrane technology was used to separate GMP from the whey protein concentrate solution at different pH values. Two ultrafilteration disc membranes with 50 and 10 kDa cut-off were used to extract glycomacropeptide from a solution of whey protein concentrtae (10% protein w/v).The experiments in triplicates were performed at the ambient temperature (25±2 °C) and a pH of 3.5, 4 or 4.5. The diafilteration technique was used for purification of glycomacropeptide in both ultrafilteration phases; the protein, phenylalanine, and non-protein nitrogen (NPN) contents were measured. The phenylalanine and NPN contents of the ultrafiltered whey at a pH of 4 were at the lowest and highest level, respectively, indicating the high purity and recovery rate of glycomacropeptide. Sweet whey, the major type of whey produced in the country, is the best alternative available for producing a new food source for phenylketonuria patients.