Enzymatic Preparation of Low-Phenylalanine Formula Derived from Skim Milk Hydrolysate for Phenyl ketonuric Patients
Background: Phenylketonuria (PKU) is one of the most common inborn errors of amino acids metabolism. WHO guidelines introduced in 1979 and revised 1988 for breast-feeding infants with PKU included a formula containing low amounts of phenylalanine as a part of dietary prescription. Mental retardation can be prevented if PKU is diagnosed in the 1st three weeks of life and diet therapy started straightaway throughout life and especially in the hyper phenylalaninemic mothers before conception and during pregnancy. Aim of the Work: The aim of the present study was to synthesize a lowphenylalanine formula suitable to be taken by PKU children, adolescents and the hyperphenylalaninemic mothers. Materials and Method: This formula should be of high biological value, taken safely by those patients and to be of low cost. The formula was prepared from skim milk hydrolysate using two proteolytic enzymes. The first was the immobilized purified papain enzyme and the second was the modified protease XXIII prepared from Aspergillus oryzae. The skim milk hydrolysate was adsorbed on barium sulphate or activated carbon for removing phenylalanine. They were applied separately for the purpose of debittering and nutritional value comparison. Results: This skim milk hydrolysate had been supplemented with the amino acids tryptophan, tyrosine, methionine and valine. Beside the comprehensive amino acids analysis (Especially for the free amino acids), this formula was then analyzed for protein, fat, lactose and ash contents as well as microbiological and biological testing on mice. Hyperphenylalaninemia was induced in BALB/c mice model then changes in blood phenylalanine level and weight were scored during the periods of mutagenesis as well as the treatment period compared with the control group. Conclusion: The amino acids analysis showed that phenylalanine was 0.71gm/100 gram protein in the skim milk hydrolysate compared to 3.26gm amino acid/100 gram protein in the skim milk. The level of free phenylalanine decreased from 6.34% (In the skim milk) to 0% after adsorption to barium sulphate and compared to 3.41% after adsorption to activated carbon. The formula adsorbed on barium sulphate, although it is more preserving to the nutritional composition; yet, it is less effective in the debittering effect than that adsorbed on activated carbon. This formula, in addition to being of high nutrional value, it is not expensive since it is obtained from skim milk hydrolysate. From the present study, it could be concluded that: The synthesized low-phenylalanine formula was effective in supplying most of the needed dietary intakes for conditions of hyperphenylalaninemia. The use of the immobilized purified Papain and modified protease XXIII from Aspergillus oryzae in enzymatic hydrolysis of skim milk has been proved to be effective in hydrolysis and emulsification.
Keywords: Phenylketonuria, skim milk.
Egypt. J. Hum. Genet Vol. 9 (1) 2008: pp. 51-71