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    A novel and environmentally friendly method for preserving and depilating sheepskin : comprehensive physical, biochemical and molecular analyses : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biochemistry at Massey University, Manawatu, New Zealand
    (Massey University, 2021) Tu, Yi-Hsuan
    The first step of leather processing, depilation – in other words, removing hair from skins – accounts for one-third of the leather-making industrial waste due to the production of sulfide and alkaline water waste from the process. This study describes a method that preserves and depilates unwashed sheepskins using milk or milk by-products, including whey and permeate. It doesn’t require the use of harsh chemicals or temperature control, and results in skin that is ready to be tanned. In order to evaluate the products of this process, the depilated skin surface was evaluated not only by eye, but with scanning and transmission electron microscopy (SEM and TEM) which showed there was no apparent damage to the grain or fraying of the collagen bundles. The depilated skin was also processed to leather which was subjected to tear, tensile and shrinkage measurements which were shown to be almost identical to leathers made using the traditional process. Quantitative biochemical analyses, including collagen quantitation, collagen crosslink analysis and glycosaminoglycan (GAG) analysis of sheepskins depilated with this process showed no significant differences in both collagen, and collagen crosslink concentrations in contrast to the 10-fold increase seen in the GAG concentration. A quantitative proteomic analysis showed there was a higher retention of proteins found in the basement membrane of the skin, supporting the observation that permeate depilated skins were smoother than their sulfide depilated counterparts and produced leather with a superior surface. It also showed the loss of specific proteins around the hair follicle, hinting at a possible mechanism for depilation. To further investigate this a microbiological survey of the process was conducted. Traditional culturing methods were used to isolate and identify microorganisms present in the depilation solution after the wool had been removed. Two bacterial species (Lactococcus lactis and Lactobacillus plantarum) and two fungal species (Geotrichum candidum and Yarrowia lipolytica), were routinely identified, all of which are known to secrete a number of hydrolytic enzymes and antimicrobial compounds. This was followed by a metagenomic study of changes in the microbial community over the time course of the depilation. Although there were only 13 dominant bacterial genera identified during this study, the biggest change was a concomitant increase in the relative abundance of Lactococcus lactis that matched the decrease in Acinetobacter sp. by the end of the depilation treatment, controlling the proliferation of other putrefying organisms. In conclusion, this preliminary study has paved the way for the development of a depilation process that is kind to the environment, but more research is needed to investigate its potential use with other animal skins.
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    Investigating the molecular building blocks of loose and tight cattle hide : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Biochemistry at Massey University, Manawatu, New Zealand
    (Massey University, 2019) Maidment, Catherine Ann
    Looseness is a defect found in 7% of leather made from cattle hides. It affects the quality of leather, resulting in the leather being downgraded or potentially being discarded altogether. The similarity in appearance between loose leather and wrinkly skin led to the hypothesis that they may share the same causative agent(s). While little to no research has been done to elucidate the molecular basis of loose leather, there are many reports detailing the characteristics and causes of wrinkly skin, especially in ageing humans. Studies have shown that changes in three molecular components of skin are correlated with the appearance of wrinkles; collagen, elastin and glycosaminoglycan’s (GAGs). Cattle hides that produce loose leather were identified by processing half of the selected hides to leather and using the SATRA break scale. Only four hides were suitable for this study with two being loose and two being tight. Although this small sample size limited the statistical significance of the results, it did, however, enable a vast number of analyses on the molecular components of the hides to be carried out. Microscopic techniques were utilised to investigate the localisation and structure of a range of molecular components in loose and tight hides and a series of biochemical assays were used to assess the carbohydrate components, particularly the GAGs. Quantitation of amino acids in the whole hide and different layers of the hide; grain, grain to corium junction and corium provided insight into the total collagen found in loose and tight hides and proteomic analysis using in-gel mass spectrometry (in-gel LC-MS/MS) enabled quantitation of all soluble proteins found in loose and tight hides as well as the extent of collagen glycosylation. Overall loose hides appear to have a decrease in fibrillar collagen, this paired with changes in total crosslinks and glycosylation of collagen potentially result in changes to the structure and organisation of the collagen network. This causes easier extraction of non-collagenous components during leather processing and thus results in loose leather. This study uses a variety of techniques to link differences in the molecular components of hide to the defect looseness. This greater understanding of how the molecular components of raw hide can affect the quality of leather will be of use in developing methods to identify faults in the hide before it is processed to leather and developing methods to produce high quality leather.