Review Article - (2025) Volume 14, Issue 1
industry due to their effectiveness in removing unwanted proteins under mild conditions, lowering energy use and minimizing harmful by-products. Traditional liming processes, which use large quantities of sodium sulfide and lime to dehair and breakdown interfibular proteins for chemical treatments, significantly contribute to environmental pollution through high levels of Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS). This review examines the potential of Soybean Peroxidase (SBP) and Soybean Amylase (SBA), sourced from soybean hull and dust waste, as sustainable alternatives to the conventional liming step. Combining SBP and SBA in an optimized ratio provides a promising single-step method that may perform better at neutral pH and room temperature compared to other enzymatic treatments. This approach reduces various pollution loads and eliminates the need for the time and chemical-consuming reliming and deliming processes. The review emphasizes the benefits of using soybean enzymes from agro bio-waste to lessen environmental impact while aiming to maintain or enhance leather quality. By exploring the extraction, characterization and effects of SBP and SBA, this paper highlights improvements in leather properties with enzyme treatment compared to conventional methods. The use of soybean enzymes in leather processing represents a step toward a more sustainable and efficient production process, contributing to reduced pollution in tannery wastewater and overall industry sustainability.
Soybean peroxidase • Soybean amylase • Enzymatic dehairing • Single-step process • Leather processing • Pollution abatement
Since 2020, approximately 30% of leather industries in India have adopted enzyme-based processes to enhance sustainability in leather production, reflecting a broader shift away from traditional chemical methods notorious for significant pollution [1]. Studies indicate that the pre-tanning stage alone contributes about 50%-60% of the total pollution load in leather processing, with the liming process responsible for a substantial portion of the Chemical Oxygen Demand (COD) in wastewater, accounting for approximately 60%-70% of the total COD due to chemicals like lime and sodium sulfide, which also pose severe health risks [2]. The sulfides used in liming react with acids in the pickling stage to form hydrogen sulfide, a highly toxic gas that can be lethal at concentrations exceeding 1 ppm. Enzyme-based alternatives, particularly protease enzymes, have shown promising results, with replacing 3%-5% of sodium sulfide and 8-10% lime with 1%-2% protease enzymes leading to an 80%-90% reduction in various pollution load parameters. This enzymatic approach also eliminates the need for reliming and deliming stages, further reducing the use of lime and ammonium salts. Despite these benefits, challenges such as specific pH and temperature requirements, longer processing times, large bioreactor needs and high production costs hinder widespread adoption [3]. In this context, exploring enzymatic alternatives for dehairing and fiber opening using soybean waste has emerged as a promising avenue for achieving sustainability goals in leather production, including reduced chemical usage, waste utilization, lower energy consumption, improved effluent quality and enhanced biodegradability. This approach addresses environmental impacts and overcomes limitations associated with conventional and other alternative dehairing techniques, such as mechanical, supercritical carbon dioxide, bacterial, ozone, electrolytic, urea-based and oxidative dehairing [4]. As the leather industry strives to comply with stricter environmental regulations and meet consumer demand for eco-friendly products, enzymatic dehairing using soybean waste emerges as a pivotal technology.
Enzymatic solutions and industrial challenges in ecofriendly leather processing
Peroxidase enzymes, such as Horseradish Peroxidase (HRP), present an environmentally friendly alternative to traditional chemical methods for dehairing leather by breaking down keratin, the primary protein in hair, under mild conditions [5]. This facilitates hair removal from hides when treated with a 1%-2% solution of peroxidase or hydrogen peroxide on the flesh side, effectively cleaving the disulfide bonds in keratin over 3-5 hours. This process, operating at lower temperatures and neutral pH, minimizes hide damage and potentially enhances leather quality [6]. However, challenges include maintaining enzyme activity under industrial conditions, the high cost of production and purification and ensuring consistent results across different hide types and operation scales. Similarly, amylase plays a crucial role in leather processing by hydrolyzing starch into simpler sugars like maltose and glucose, which helps to loosen collagen fibers within hides. Amylase-treated hides exhibit improved leather properties and optimizing pH (around 7.5-8.0) and temperature (50°C-60°C) is essential for maximizing amylase activity [7]. Despite its benefits, the higher cost of amylase compared to traditional chemicals highlights the need for scale-up and optimization efforts to extract the enzyme from microorganisms, aiming for cost-effectiveness in industrial applications.
Availability of soybean waste: Sources, applications and sustainable solutions
Currently, the major soybean-producing states in India like Madhya Pradesh, Maharashtra, Rajasthan and Andhra Pradesh contribute significantly to the soybean industry, generating around 41 million tons of waste annually [8]. This soybean hull waste is primarily used in animal feed due to its high fiber content and also finds applications in dietary supplements, pet food and particle boards. However, some of this waste may not meet quality standards for these uses, potentially leading to disposal issues or additional processing costs [9]. Improper disposal of soybean hull waste alters soil composition, causes nutrient imbalances and results in soil contamination. It can also lead to runoff that causes eutrophication, depletes oxygen in water bodies and harms aquatic life. Additionally, decomposing waste emits methane, a greenhouse gas, creating unpleasant odors and impacting air quality while disrupting local ecosystems and reducing biodiversity. Effective management through recycling and repurposing can mitigate these environmental impacts. Enzymes like beta-glucosidase, alpha-galactosidase, cellulase and pectinase can be extracted from soybean hulls, while soybean dust may yield a broader range of enzymes, including lipase, protease, amylase, urease, peroxidase, phytase, oxalate oxidase, laccase, sucrose synthase and xylanase, offering valuable raw materials for various industrial purposes. This paper proposes utilizing soybean waste in this manner to benefit the leather industry.
Enzymatic dehairing and fibre-opening using soybean waste
The use of enzymes derived directly from natural sources, such as soybean hulls and dust, enhances sustainability by utilizing agro-bio waste for enzyme production. This approach reduces costs and eliminates the need for microbial cultures, careful handling of inoculation and incubation, fermentation and time-consuming processes, making it a safer and more straightforward method for tanneries to adopt. Peroxidase extracted from soybean hulls and amylase from soybean dust offer versatility in dehairing and fiberopening processes in a single step. This dual enzymatic action of oxidizing the disulfide bonds of the keratin bulb by SBP and breaking down inter-fibular protein by SBA simultaneously not only improves the efficiency of dehairing and fiber opening but also contributes to minimizing environmental impacts throughout the leather production cycle.
Enzyme extraction from soybean waste
The blended soybean hulls in sodium phosphate buffer and soybean dust in sodium acetate buffer undergo a series of steps to facilitate enzyme extraction and obtain crude peroxidase and amylase separately, followed by centrifugation. Peroxidase activity for the dehairing process must be assessed using spectrophotometry to measure the HâOâ-dependent oxidation of guaiacol. Quantifying protein concentration and specific activity in the extracted crude of both peroxidase and amylase using the modified Lowry method, with Bovine Serum Albumin (BSA) as the calibration standard, is necessary to calculate the amount of enzyme to apply in the dehairing and fiber-opening process. Further confirmation of soybean enzyme presence and activity through toluene degradation and DPPH assays ensures the suitability of the enzymes for dehairing and fiber-opening processes in the leather industry. This systematic extraction process will underscore the robustness and reliability of soybean-derived enzymes for sustainable leather processing applications.
Synthesis of SBA+SBP for single-step process
Adjusting the enzyme concentration is necessary to tailor the concentrations of SBP and SBA extracts based on their specific activities and desired ratios for dehairing and fiber-opening applications in leather processing. Once adjusted, the SBP and SBA extracts can be combined in an optimized ratio using a stirring apparatus or vortex mixer to ensure thorough mixing. Quality control checks should be performed on the combined enzyme product, verifying SBP and SBA activity through enzymatic assays and assessing any post-mixing precipitation or aggregation. Characterization of the synthesized SBP+SBA mixture's structure via SEM, TEM, DLS, XRD and XPS and assessment of its thermal stability through DSC and TGA, provide valuable insights into its catalytic mechanism. The combined product must be stored under stable conditions and its stability should be monitored over time, with periodic assessments of enzyme activity to ensure suitability for industrial use. Application testing follows, involving pilot trials to evaluate the effectiveness and efficiency of the combined SBP and SBA enzyme product compared to traditional methods in dehairing and fiber-opening processes.
The mechanism in harnessing SBP+SBA for sustainable leather processing
SBP in the leather industry represents a promising alternative to traditional dehairing agents by efficiently breaking down keratin through the oxidation of disulfide bonds in animal hair within an hour, similar to commercial peroxidase. By removing hair from hides sourced from cows, sheep and goats, SBP offers eco-friendly advantages that reduce the environmental impact of leather production. Similarly, soybean amylase is distinguished among liming methods for its ability to hydrolyze the starch content in hides, facilitating fiber opening and significantly reducing water, time and energy consumption. Soybean amylase not only enhances process efficiency but also improves leather quality by ensuring more uniform fiber opening and minimizing environmental impact compared to conventional methods. SBP+SBA is biodegradable and environmentally safe, aligning with global initiatives for greener manufacturing practices. It offers a sustainable choice compared to chemical alternatives and supports reduced chemical usage and waste generation in the tanning process.
Characterization of SBA+SBP treated leather and SBA +SBP treated liquor
If SBA+SBP-treated pelt is processed into leather, properties such as tensile strength, tear strength, elongation at break, load at grain crack, distention at grain crack, water vapor absorption, water vapor permeability and its coefficient, sweat resistance, color, rub fastness and color measurement must be determined and compared to conventional leather properties and ISO standard norms. Since enzymatic dehaired leather treated with commercial protease has shown better properties than conventional leather, SBA+SBP-treated leather is also expected to yield favorable results. Additionally, the processed dehaired liquor treated with SBA and SBP is analyzed for various environmental pollution parameters such as TS, TSS, TDS, COD, BOD, TKN and HPLC, and compared with conventional dehaired wastewater to determine the extent of pollution reduction.
Practical benefits for tanneries in adopting SBP+SBA
The adoption of soybean enzymes for dehairing represents a significant advancement in the leather industry, offering a sustainable and environmentally friendly alternative to traditional chemical methods. By replacing sodium sulfide and lime, soybean enzymes eliminate the subsequent processes of liming, including reliming and deliming. Reliming, which uses a large amount of lime to open up the fiber, results in a substantial amount of lime sludge, leading to high levels of Total Suspended Solids (TSS). This process is bypassed as SBA effectively opens up the fiber during the enzymatic dehairing process itself. The deliming process, which removes the total lime used previously by adding ammonium salts, involves ammonium chloride reacting with calcium carbonate lime to form Calcium Chloride (CaClâ). This reaction releases calcium chloride as Total Dissolved Solids (TDS) in water bodies. Using soybean enzymes effectively eliminates the need for deliming. Therefore, using SBA+SBP after soaking replaces the conventional dehairing and liming processes, eliminating both reliming and deliming. The SBA+SBP-treated skin can proceed directly to the pickling process. This enzymatic approach not only reduces toxic waste during dehairing but also enhances leather quality, improving characteristics such as elongation at break and tensile strength. Our study confirms the effectiveness of soybean enzymes in producing high-quality leather while minimizing environmental impact, positioning them as a promising paradigm shift in leather processing. Soybean enzymes, derived from soybean hulls, are readily accessible and cost-effective, making them a practical choice for tanneries aiming to reduce their environmental footprint.
This review suggests the potential of soybean-derived enzymes as a sustainable option to dehair and open-up fiber among all other alternatives for the leather industry, supporting environmental responsibility while ensuring high leather quality standards. The application of these enzymes in dehairing and fiber opening delivers substantial benefits, such as reducing Chemical Oxygen Demand (COD) by up to 90% during dehairing and 85% during fiber opening, demonstrating their notable environmental advantages. Additionally, using these enzymes eliminates the need for reliming and deliming steps, simplifying the leather production process without sacrificing quality. Leather processed with soybean enzymes can achieve characteristics comparable to those of conventionally processed leather. Unlike traditional methods that separate liming and reliming stages, the enzymatic approach can integrate these processes into a single step, thus reducing processing time and chemical usage. By replacing harsh chemicals like sodium sulfide and lime, soybean enzymes significantly lessen the environmental impact of leather production. As the industry increasingly seeks eco-friendly alternatives, these advancements offer considerable promise for enhancing sustainability and efficiency in leather manufacturing. Future research should focus on optimizing these enzymatic processes for different leather types and refining their application to address various processing needs.
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
The authors received no financial support for the research, authorship and/or publication of this article
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Received: 29-Jul-2024, Manuscript No. JBTW-23-143642; Editor assigned: 30-Jul-2024, Pre QC No. JBTW-23-143642 (PQ); Reviewed: 13-Aug-2024, QC No. JBTW-23-143642; Revised: 14-Jan-2025, Manuscript No. JBTW-23-143642 (R); Published: 21-Jan-2025, DOI: 10.35248/2322-3308.25.14(1).001
Copyright: © 2025 Rajendran S, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
