Effects of dehairing treatment on gelatin yield and quality from bovine hides

Purpose Hides are the by product of slaughter houses which are mostly used for leather production. In Canada, the hides are either disposed of with other slaughter waste or sold at a very low price. Dehairing of hides is a prerequisite for either leather or gelatin production from it. Therefore, the effect of hide dehairing method on subsequent gelatin extraction and quality was investigated.Methods Bovine hides (BH) were dehaired using either 5% acetic acid (AA), 10% calcium hydroxide (CH), 0.02% keratinase (KTN), 2.5% papain (PP), or not at all (control; CT), with control BH subsequently treated with 5% AA (CTAA).Results Mean bovine hide gelatin (BHG) yields (dry basis) were 11.37%, 54.25%, 45.07%, 18.88% and 55.02% for CT, AA, CTAA, CH, and KTN, respectively. Gel strength was highest in AA followed by the CTAA, CT and CH and KTN treatments. The molecular weight (MW) distribution pattern showed that dehairing of BH with enzymes degraded the collagen extensively, increased proportions of low MW peptides that translated into low gel strength.Conclusions Acetic acid, which is extensively using in food industry, can be used to dehair BH as pre-treatment to extracting high quality gelatin.

Collagen: From Waste to Gold

Industrial processing of bovine hides into leather results in many unusable hide off-cuttings, shavings and trimmings. This waste raw material is under-utilised and presents a waste valorisation opportunity to derive a high-value product such as collagen. Collagen is a highly sought-after protein which consists of three polypeptide chains, comprising 30% of the mammalian body’s protein, being the main component of skin, connective tissue and cartilage. The demand for collagen is rising at approximately 20% annually and global collagen-based biomaterials market is predicted to reach US$5 billion by 2025. This chapter presents a waste valorisation opportunity to extract collagen from waste bovine hide off-cuttings. Further, it discusses collagen extraction method optimization and methods used to investigate physicochemical properties of collagen are reviewed.

Screening of additives to reduce grain damage risk on unhairing by proteinase K

Enzymatic unhairing is a cleaner strategy for leather-making. It is a potential alternative to the traditional hair-burning process. However, several shortcomings, such as uncontrolled enzymatic reaction, and risk of grain looseness and damage have restricted the broad application of enzymatic unhairing. In this work, metal ions and organic additives were screened for lessening the hydrolytic activity of proteinase K to collagen fiber. Then, the selected additives were applied to the enzymatic unhairing process for bovine hide. The results showed that a suitable concentration of metal ions (Cu (II), Fe (III) and Al (III)) and organic additives (salicylate, laurate, adipate, gallate and epicatechin (ECG)) could diminish approximately 35% of the hydrolytic activity of proteinase K to collagen fibers. Then, the additives were applied for the bovine hide enzymatic unhairing process. Hydroxyproline determination in the unhairing float shows that applying additives could reduce collagen hydrolysis. The morphology results showed that the grain damage could be significantly reduced with the addition of the screened additives in the proteinase K enzymatic unhairing system, whereas the addition of ECG and gallate significantly slowed down the unhairing speed. This outcome provides new potential to reduce the risk of grain damage in enzymatic unhairing process. Graphical abstract

A Novel Application of Refinery Merox Unit Wastewater for Bovine Hide Unhairing

Unhairing is one of the major steps of the leather tanning process which removes the hairs, epidermis and to some degree inter-fibrillary proteins. This process needs high amounts of chemicals that cause environmental difficulties. On the other hand, these chemicals are available in the wastewater of the Merox unit of Kermanshah Refinery. For reducing chemical consumption and decreasing environment pollution, we used the aforementioned wastewater for bovine unhairing. A unhairing liquor was prepared in order to unhair skins and different parameters such as the concentration of CaCO3 and Na2S, process time, and temperature were considered to evaluate their impact on the unhairing process and to obtain optimum condition. Response surface methodology based on Box-Behnken design was applied to model the unhairing efficiency in terms of four independent variables. A second-order polynomial equation was suggested to predict the response with high certainty. ANOVA revealed the validity and importance of that model by P-value of < 0.0001, large F-values, and, R2 of 98.8. The maximum unhairing efficiency of about 98.5 % was obtained under the optimum condition of 1.7 wt% Na2S, 5.8 wt% CaCO3, 114 min process time and 29.5 ºC.

The Influence of Animal Glue on Mechanical Properties of Painting Canvases

Glues derived from animal products have been used in the preparation and conservation of painting canvas for hundreds of years. However, it is not clear how exactly these adhesives contribute to the mechanical strength of a canvas and how this contribution changes with time. This comparative study looks at the effect of age, thickness, and type of animal glue on the mechanical reinforcement the glues provide to canvas. Isinglass, rabbit skin, bovine hide and bone glue are compared. The mechanical strength of the canvas and glue system have been measured with a tensile test. The influence of glue on the tensile response of canvas has been observed in the slope of the initial region of the stress-strain curve for these samples. This region has been identified as the initial load-bearing region which corresponds to the glue coating. The major contributing factor to change mechanical reinforcement of canvas is found to be the degradation of the glue, however the type of glue used plays a small role as does the thickness of the glue applied.

Limiting Microbial Activity as an Alternative Approach of Bovine Hide Preservation Part II

Wet salting of bovine hide commonly utilizes 95% saturated salt solution or 40-50% salt (w/w) on raw hide weight for preservation. The salt used for the hide preservation ends up being in wastewater and generates enormous environmental pollution. To minimize the environmental pollution problem associated with the traditional method of hide preservation, alternative formulations containing antimicrobial agents and less amount of common salt (35% saturated brine) have been developed. The alternative formulations were found to be more effective in deterring microbial growth than the traditional formulation as demonstrated by the total aerobic bacterial count of the preserved hide soaking liquor. The effect of the newly developed formulations on leather quality was assessed by analyzing the mechanical properties, scanning electron microscopic images, grain pattern and organoleptic properties of the finished leather. The quality analysis of the crust leather revealed that, the leather panels produced from the traditionally and alternatively preserved hides were comparable. The environmental impact of the newly developed formulations was also evaluated by monitoring the leather processing effluents for the pollution indicators such as total solids (TS), total dissolved solids (TDS), chloride content, Chemical oxygen demand (COD) and Bio-Chemical oxygen demand (BOD). Overall, the environmental impact of the newly developed hide preserving formulation was less severe than the traditionally used formulation. Since the newly developed formulations did not affect the quality of the leather produced and their impact on the environments is minimum, they could be considered as viable options for combatting pollution problems associated with the traditional salt curing method.

Determination of Strain Properties of the Leather Semi-Finished Product and Moisture-Removing Materials of Compression Rolls

The paper presents the results of experimental studies to determine the strain properties and characteristics of a chrome leather semi-finished product of middle-weight bovine hide by its topographic sections and the coatings of the processing compression rolls. The strain pressure equations of depend on the topographic sections of a leather semi-finished product are obtained, and the results of experiments on the effect of a number of layers on the amount of pressed moisture are presented. A mathematical dependence of the pressed moisture from the leather semi-finished product is obtained under various pressure values, rates, and the number of skin layers with monchons. The influence of the number of layers of leather semi-finished products with moisture-removing materials (monchons) on the process of moisture extraction at their vertical feed on the base plate is determined. In this paper, the influence of the number of skin layers and moisture-removing materials (monchons) on the technological process of moisture extraction from wet leather semi-finished products at their vertical feed on a base plate is studied as well.