Development of the delivery system of an amino acids based protein supplement for the dietary management of phenylketonuria (PKU)

Anders, Simon (2016) Development of the delivery system of an amino acids based protein supplement for the dietary management of phenylketonuria (PKU). Masters by Research thesis (MSc), Manchester Metropolitan University.

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Abstract

Phenylketonuria (PKU) is an inherited metabolic disorder in which the patient cannot metabolise phenylalanine into tyrosine and other metabolites which leads to irreversible brain damage and neurological disorders if left untreated. The majority of the patients are treated using dietary therapy where the patient receives an amino acid based protein supplement. However these supplements exhibit poor organoleptic properties due to the bitter and sulphurous nature of certain amino acids, which can lead to poor patient compliance. In order to reduce the negative organoleptic attributes masking technologies have been previously applied but have only had limited success. Therefore the use of alginate beads was investigated to encapsulate the amino acids. Although the use of alginate beads for encapsulation is well known and are used for pharmaceutical materials, the techniques had not been applied to amino acids. Therefore there was no prior knowledge of how to construct the beads, and the effect of encapsulation on the organoleptic properties and amino acid bioavailability. Experiments were undertaken to firstly develop and refine the method of manufacture utilising laser particle defraction techniques to determine bead size and nitrogen content quantification by Dumas to determine amino acid recovery. Initially the beads manufactured where too large, in excess of 2mm, however by reducing the aperture of the nozzle used to produce the droplet and milling the amino acids to a finer particle size it was possible to produce beads between 1 and 2mm, which was the optimal size for the beads to avoid gastric straining and aid the transit of the beads through the stomach. A design of experiment methodology was then implemented to determine the relationship between the factors; calcium content, alginate content and the time in the gelling solution, and the amino acid recovery (output). The amino acid content remained constant at 10% (w/w) throughout the experiments. It was found that the alginate and time in the gelling solution had a significant effect on the amino acid recovery when the calcium chloride concentration was between 10 and 30% (w/w). The best recovery, of 78%, was produced with a bead containing 10% (w/w) amino acid and 3% (w/w) alginate using a 30% (w/w) calcium chloride gelling solution and a 1 minute residence time. The beads were subjected to an in vitro digestion model and it was found that the amino acids encapsulated in the beads were still bioavailable as there was a reduction in amino acid content of the beads from 10g/100g of bead to 2.95 g/100g of bead after in vitro digestion. To determine if the encapsulation had had an effect on the sensory attributes a triangle test with a maltodextrin containing placebo was carried out. In the test 12 expert panellists trained in tasting amino acid products tasted the beads and only 6 panellists identified the different sample. This was less than the 8 correct identifications needed for significance at 95% and therefore the beads could not be identified from the placebo. Therefore the method applied successfully produced an amino acid alginate bead that masked the flavour but did not compromise the bioavailability.