Biotechnology for environment-friendly leather production

J.Y. Liu; Geoff Holmes

LASRA research is guiding the application of biotechnology to help the New Zealand leather industry develop environmentally sustainable leather processes. Using 16S rRNA gene sequencing, we have isolated and identified a number of indigenous bacteria from the leather industry environment which are being adopted to develop benign leather processing technologies. We isolated and identified several Bacillus strains from a biofilter used in a leather manufacturing plant which exhibited sulphide oxidation activity, which are being applied in bioremediation of volatile organosulphur compounds emitted by leather products. We also discovered a strain of Stenotrophomonas spp. with significant and beneficial proteolytic activity in a tannery sludge. The identified strain not only displays collagenase activity but also the ability to reduce hexavalent chromium to trivalent chromium, making it an ideal candidate for biodegradation of tanned waste. Recently we revisited the natural autolytic processes of degradation of untreated pelts to guide a natural depilation method without any need for additional chemical treatment. In controlled experiments the wool could be removed completely from follicle after 2 days, without obvious damage and leathers could be processed with mechanical properties comparable to conventionally processed counterparts. The alkaline protease activity of the isolated bacteria is responsible for the observed natural unhairing.

Proceedings of the 35th IULTCS Congress, 2019

Towards a molecular level understanding of chrome tanning

Yi Zhang; Jenna K Buchanan; Geoff Holmes; Sujay Prabakar

Abstract. Synchrotron based small-angle X-ray scattering (SAXS) is a powerful technique that has helped us understand the changes in molecular-level collagen structure during tanning and denaturation (shrinkage). Based on SAXS results from real-time denaturation experiments on leather samples, we established a mechanistic model of chrome tanning indicated by the structural changes of collagen. It suggests that only a low level of chromium is effectively involved in cross-linking with collagen, highlighting the overuse of chrome during conventional tanning processes. Any extra amount of chrome added, however, can support the stabilisation of collagen – possibly via a non-covalent mechanism. Such a mechanism points towards a more environment-friendly tanning method by using suitable supplementary reagents to benefit the tanning effect non-covalently instead of by chrome. Also, by pre-treating with complexing agents such as sodium formate and disodium phthalate, as well as nanoclay (sodium montmorillonite), the uniformity of chrome penetration through the bovine hide collagen matrix can be improved significantly. These pre-treatments effectively reduce the reactivity of chromium during its cross-linking reaction with collagen while retaining bound water. However, collagen pre-treated with a covalent cross-linker (glutaraldehyde) results in a decrease in both the chromium-collagen cross-linking and bound water while improving uniformity. These molecular-level insights can be developed into metrics to guide us towards a more sustainable future for the leather industry. Further, coating on collagen fibrils can provide a pseudo stabilisation effect by increasing the hydrothermal heat resistance of collagen. Overall, synchrotron SAXS provides valuable information about changes in the collagen structure that could lead to more efficient use of chrome (or other tanning agents) in the global leather tanning industry.

Proceedings of the 35th IULTCS Congress, 2019

Strong skin, not always thick: Comparative structural and molecular analysis of deer skin and cow hide

Rafea Naffa; Catherine Maidment; Geoff Holmes; Gill Norris

A comprehensive analysis of the molecular and structural components of deer skin and cow hide was undertaken. These skins are known to be strong. However, they derive their strength from different combinations of molecular and structural properties. Firstly, the physical properties of deer skin and cow hide including tensile strength, tear strength, and denaturation temperature were measured. Secondly, the structure of the collagen fibrils and glycosaminoglycans was investigated using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Finally, the chemical composition of deer skin and cow hide, such as amino acids, crosslinks and glycosaminoglycans, were analyzed. Our results showed that the physical properties of deer skin and cow hide are derived from different combinations of several chemical components, resulting in a different architecture. It was found that the large and “wavy” collagen fibres in deer skin are made up of collagen fibrils with small diameters. Additionally, deer skin fibrils appeared to be linked by regular arrays of filaments of large glycosaminoglycans that are distributed uniformly. Deer skin contained a higher proportion of trivalent collagen crosslinks. In contrast, the collagen fibrils in cow hide were larger, contained a diverse glycosaminoglycan distribution and a higher proportion of tetravalent collagen crosslinks, resulting in straight collagen fibres. This study suggests that although deer skin and cow hide are both strong, they have different structural and molecular features.

Proceedings of the 35th IULTCS Congress, 2019

High-efficiency chrome tanning using pre-treatments: synchrotron SAXS and DSC study

Ethan Zhang, Jenna Buchanan; Geoff Holmes; Sujay Prabakar

Pre-treatments are widely used during tanning processes to improve the performance of the main tannage. Synchrotron small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) were used to study four common types of pre-treatments, viz. a monodentate complexing agent (sodium formate, SF), chelating agent (disodium phthalate, DSP), covalent cross-linker (glutaraldehyde, GA) and nanoclay (sodium montmorillonite, MMT) to learn about their effects on chromium-collagen cross-linking reaction during tanning. Based on the results, the performance of chromium-collagen cross-linking with and without individual pre-treatments was presented based on five parameters: degree of cross-linking, level of hydration, hydrothermal stability, uniformity through the leather cross-section and the relative uptake of chrome. Comparison with ThruBlu chrome tanning, at the same chrome offer levels, on leather pre-treated with SF, DSP and MMT showed improved hydrothermal stability, uniformity and an increased level of hydration, while GA pre-treated leather showed a decreased level of hydration. All of the pre-treatments reduced surface fixation by decreasing the reactivity of chromium with collagen. Changes in the reaction performance can influence both the properties of the leather products as well as the efficiency of the leather manufacturing process. Insights into the structural changes of collagen during tanning with varied reaction conditions can help guide the design of novel, benign tanning processes with reduced environmental impact.

Proceedings of the 35th IULTCS Congress, 2019. Poster Presentation

The 60th John Arthur Wilson Memorial Lecture: A Future for Leather!

by Gustavo Gonzalez-Quijano

Until not so long ago, tanners did not need to promote their leathers particularly, as buyers approached them in search of the sought material. Leather was bought, not sold. Today, things have changed. Leather still exerts its appeal, but tanners have to deploy all their marketing skills and competences for attracting customers.

With the turn of the Millennium leather has entered a new chapter in its long history. And the changes are shaking up longstanding habits. Tanners have started experiencing increasing societal pressures affecting the perception of leather by the general public.

Concerns over social or environmental credentials have impacted the leather trade. Also, the identity of leather is being increasingly challenged. Synthetic or plant-based alternatives shamelessly abuse the name ‘leather’ while they rant and rave about the genuine material. And one can find all over the press, internet and social media pictures and stories of irresponsible leather producers. Moreover, last century failed to put an end to the sector’s most important barriers to trade; export restrictions on raw materials.

What needs to be done for leather looking to the future with confidence?

This paper will review four areas in which leather faces major challenges today and in the coming years. They concern aspects of the trade and industry that affect operators independently of their location. It will examine the leather authenticity challenge in the European Union, illustrate two strategic social policy areas in which European tanners are active, describe the achievement in the area of the environmental footprint of leather, and explain the need for a global sector agreement for the trade in hides, skins and leather.

In the conclusion, this paper will emphasise the importance of sector associations in addressing the challenges of the leather industry and call for more and deeper cooperation between all the sector’s stakeholders for ensuring a bright future for leather.

JALCA July 2019

Leather Species Identification via Mitochondrial DNA Polymerase Chain Reaction

by Xiang Zhang and Steve Lange

Currently the identification of leather species is mainly via a skilled operator using optical microscopy and an extensive visual reference library. However, due to the limitations of optical microscopy and in cases where the leather surface is heavily corrected or finished, it is not always possible to accurately determine the leather species. Therefore, it is crucial to develop a reliable and easy to perform approach to overcome these limitations. In this paper, we used the unique DNA sequence present in every species to identify leather. The conversion process of making leather destroys much of the DNA present but the high copy number of mitochondrial DNA (mtDNA) in relation to nuclear DNA makes some mtDNA likely to survive and be detected via polymerase chain reaction (PCR). However, leather DNA is highly degraded and inhibitors present in the extracted DNA make successful PCR challenging. There are only a few related works reported in the literature attempting to use DNA for leather species identification and they provide limited technical details. In this study, species-specific primers for PCR were designed, conditions for DNA extraction from leather followed by PCR were optimized, and a detailed protocol was also provided. As a proof of concept, our approach demonstrated that the species of leather can be reliably detected via PCR targeting mtDNA.

JALCA July 2019

Limiting Microbial Activity as an Alternative Approach of Bovine Hide Preservation, Part I: Efficacy of Developed Formulations

by Majher I. Sarker, Wilbert Long III and Cheng-Kung Liu

The traditional wet salting technique of bovine hide curing requires 95% or more saturated brine solution which generates a huge amount of pollution and salinity in the form of total dissolved solids (TDS) and chlorides (Cl-) during leather processing. Therefore, much attention is currently placed on tanneries requiring reduction or eliminate the use of sodium chloride as a raw hide/skin preservative. For the preservation of hide it is essential to arrest microbial attack as the collagen-breaking enzymes called collagenase produced by the bacteria can cause serious degradation on hide which leads to the putrefaction of raw hide before converting them into leather. In this research effort, a number of formulas have been developed and evaluated for their efficacy in preserving bovine hide for 30 days or more. This attempt has been made to evolve a least chloride containing curing system for salinity abatement, where 35% saturated brine is used as the base solution. The developed formulations have been evaluated with better efficacy than the conventional technique on limiting bacterial growth, controlling yeast and mold during the storage period of cured hide. The alternative methods also offer quick rehydration of cured hide during leather processing and Airborne Ultrasonic scanning detects no detrimental impact on alternatively cured hides. Therefore, this new development is ideally suited for hide preservation through better protection of hide from microbial degradation and improved conservation of environment in compare to the traditional method.

JALCA July 2019