Proteolytic depilation of lambskins : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of philosophy in Bioprocess Engineering at Massey University, Palmerston North, New Zealand
The processing of lambskins plays an important role in the New Zealand meat industry. The use of enzyme dewooling offers considerable advantages over the conventional
depilation method which generates unpleasant working conditions and poses product
quality risks when not properly handled. Prior to this work it was unclear from the
literature why the practice of enzymatic depilation had not generally been adopted by
industry. The aim of this work was to determine the problems associated with enzymatic depilation and provide a mechanistic understanding of the dewooling and damaging processes of enzyme depilation to provide underpinning knowledge for the design of a successful enzymatic depilation system.
It was found that variability in depilation between different regions of the skin resulted
in either over exposure of the skin to the enzyme regent and subsequent damage or
underexposure of the skin to the enzyme reagent and incomplete depilation. Two
approaches were taken in the work: Firstly an attempt was made for the first time to
understand the variability in enzymatic depilation so that the variability observed in enzymatic depilation could potentially be reduced, thereby allowing a complete depilation process with no overexposure. Secondly an investigation was made for the
first time to understand the cause of damage to skins during the process of enzymatic
depilation so that the enzyme depilation process could potentially be modified to avoid damage.
Experimental work characterising the time course of depilation and damage
development was carried out and compared with the variation of physical properties
across the skin. Correlations between depilation and physical properties such as
thickness, grease content and follicle density were found. Reduction in the variability of these properties would likely improve the evenness of depilation but would not reduce it enough to eliminate damage due to over exposure.
A range of techniques including: immunohistology, 2-dimensional electrophoresis, matrix assisted laser desorption ionisation, and atomic force microscopy were used to probe the structural and biochemical mechanism of enzyme depilation and damage. In this way it was found that the removal of minor collagen components were the likely cause of damage observed. In particular the removal of collagen VI was associated with a disruption of the smooth mesh of fine collagen fibres observed at the surface of the leather.
The key requirement identified for a successful enzyme depilation system was the use of a broad spectrum protease which has no activity against collagen VI. The means to
select a protease with these attributes was also developed by adopting a micro depilation
assay incorporating immunohistology. This knowledge will enable the future development of non damaging enzyme depilatory reagents that could revolutionise the industry.