3.1 Preservation Experiment
Leather preservation methods affect its organoleptic properties. Leather can be made more attractive, durable, and comfortable by proper preservation. However, harsh preservation methods can damage the leather's appearance, texture, and quality, reducing its desirability and longevity. The implementation of effective preservation techniques for hides and skins is of utmost importance in both slaughterhouses and tanneries(Wu et al. 2017).
Table 2 illustrates preliminary goatskin trial findings preserved with cotton seed powder as a source for phyto-based preservation of 5% Powder + 10% Salt (sample A), 7.5% Powder + 10% Salt (sample B), 10% Powder + 10% Salt (sample C), 10% Powder + 12% Salt (sample D), 12% Powder + 10% Salt (sample E) and 15 % Powder (sample F). Various physical changes were noticed over the 28-day preservation period. The preserved goatskin samples were found to be undamaged under all circumstances. Odor, hair slip, fungal growth, and physical feel were assessed to check the preservation. In the case of all the combinations, up to 30 days no hair slip occurred. 15% powder (sample F) smelled some bad odor from the 14th day of the preservation but the other combinations did not exhibit any bad odor in the full period. Besides that, samples showed different physical feel. Sample D, E and, F became fully hard during storage. Sample C exhibited medium hardness whether samples A and B were soft and flexible during storage.
3.2 FTIR Analysis
FTIR analysis gives useful information on the chemical structure and composition of substances, making it an important tool in a variety of scientific and commercial applications(Riaz et al. 2018). From the IR peak of cotton seed powder, it was seen the sharp peak at 3285cm-1 is for the presence of –OH in the phenolic compound (Unsalan, Erdogdu, and Gulluoglu 2009), 2922 cm-1 for –CH stretching, and 2854 cm-1 for -C–H (-CH3, -CH2) stretching. Besides that, peak at 1048 cm-1 for -HC=CH- bending. Moreover, peak at 1745 cm-1 and 1708 cm-1 due to C=O stretching vibrations (Unsalan et al. 2009), peak at 1633 indicates aromatic C=C stretching(Tondi and Petutschnigg 2015). There might be the presence of terpenoids and alkaloids which are responsible for showing antimicrobial effects.
- Evaluation of Preservation Experiment
3.3.1 Moisture Content
One crucial factor is the level of moisture content in many sectors and applications because the presence of water may have a substantial influence on the qualities, quality, and performance of numerous materials (Wu et al. 2017). When assessing the effectiveness of a curing agent, the moisture content is a crucial factor to take into account. Three mechanisms of skin preservation can be successfully followed by a curative agent: antibacterial action, bacteriostatic action, and dehydration action. Dehydration results from the bacterial cell's water content being expelled via the semipermeable cell membrane when it is subjected to hypertonic curative medicines. Dehydration from preserved skin fibers can inhibit the growth of bacteria by lowering moisture content. Conventional salt extracts water from both skin fibers and bacterial cells. Consequently, the curing process takes place. The ability of dry plant powder to absorb water is crucial because of its dryness. Dehydration can therefore only start the curing process. Furthermore, because there is an imbalance between the dry powder and the skin fibers, collagen matrix fibrils can stack together, resulting in extremely hard skin that breaks down before tanning. NaCl, an osmosis generator, effectively preserves the collagen structure during curing by converting it from hypertonic to isotonic solutions. Therefore, if plant powder possesses antibacterial properties, combining less salt with it will be a successful tactic for preserving and lowering moisture content when skin is being preserved. (Hossain et al. 2022).
Fig. 5 displays the results of the moisture content analysis for both the experimental and control samples. On the very first day, the moisture content values were 60%, 59%, 58%, and 57% for Experimental 1, Control 1, Experimental 2, and Control 2 samples respectively. After the 28th day, the moisture content values were 37%, 34%, 36%, and 33% for Experimental 1, Control 1, Experimental 2, and Control 2 samples respectively. It reveals that moisture content gradually decreased in the case of all the samples.
The experimental samples showed slightly higher moisture content than the control samples. Moreover, the moisture content reduction of experimental samples varied by only 2% than the control samples. Therefore, control (40% salt) and experimental samples (5-7.5% powder with 10% salt) showed a similar dehydration effect. This revealed the more hygroscopic effect of cottonseed powder than salt. On the other hand, salt maintains the osmotic balance between cottonseed powder and skin fibers in the experimental samples significantly.
The experimented samples showed less moisture content than the controlled samples. This is due to the higher amount of salt present in the control samples. Salt is less hygroscopic than cotton seed powder. For this reason, salt has a reduced lower amount of moisture content compared to cottonseed powder. In the experimental samples, it seems the moisture content is slightly lower than control samples. This is due to dehydration that occurs for the presence of powder. At the end of the 28th day, the moisture content of the experimental samples was reduced to less than 30%, and in the case of control samples it was less than 35%. The formation of molds that produce proteolytic enzymes and the beneficial effects of bacteria and enzymes are dependent on the moisture content of hides and skins.
3.3.2 Shrinkage Temperature
The impact of leather shrinkage temperature on the quality and performance of leather products is significant (Griyanitasari, Pahlawan, and Kasmudjiastuti 2018). This technology enables manufacturers to systematically adjust processing parameters, attain specific product attributes, and produce leather goods of superior quality that align with customer requirements and expectations.
It is vital to determine the collagen's hydrothermal stability to assess the stability of raw goatskin. Because collagen is hydrothermally stable, any structural degradation of the goatskin protein can be identified. This test, which shows structural integrity as wet heat shrinkage, can start the denaturation transition of collagen. Since the triple helix of skin collagen is made up of 12% -Gly-Pro-Hypro-, 44% -Gly-Pro-Y- or -Gly-X-Hypro-, and 44% -Gly-X-Y-, where X and Y are not specified, it follows that -Gly-Pro-Hypro- is the most common form of collagen (Anthony D Covington 2009). Therefore, the shrinking temperature will be lowered by any process that causes amino acid chains in collagen's triple helix to degrade.
Fig. 6. shows how the temperature changed over the course of the 28-day preservation period for the control and experimental samples. It shows that the experimental and control samples' shrinkage temperatures varied marginally. In the case of both the control and experimental samples, the value increased with time. The values of shrinkage temp on the very first day were 60°C, 60°C, 59°C, and 60°C for Experimental 1, Control 1, Experimental 2, and Control 2 samples respectively. On the 28th day, it increased slightly with time and the values were 66°C, 64°C, 66°C, and 65°C for Experimental 1, Control 1, Experimental 2, and Control 2 samples respectively. Elevation in shrinkage temp is probably for reducing the moisture content (Mohammed et al. 2016).
For any of the experimental skins, there was no significant variation in shrinkage during storage. So, it can be assumed that the above preservation procedures caused no substantial denaturation or disruption of protein connections.
3.3.3 Total Nitrogen Content
Extractable nitrogen content is one of the most crucial indicators for determining whether or not bacteria have damaged the skin(Nur-A-Tomal et al. 2021). Comprehending and regulating the nitrogen content during preservation procedures is of utmost importance in upholding the quality and efficacy of the leather.
The recovered soluble nitrogenous chemicals were used to compute the total Kjeldahl nitrogen (TKN) content. The presence of bacterial deterioration in conserved goatskin samples is best recognized using TKN. Nitrogenous components are produced when goatskin proteins are putrefied. As a result, unpleasant odors are released and hair slip occurs. The values of the nitrogen content are shown in Fig. 7.
The nitrogen content value for the experimental and trial samples was assessed in Fig. 6. In the case of all the samples, the value increased with days. On the very first day, the values of nitrogen content were 0.39, 0.44, 0.48, and 0.54 mg/L for Experimental 1, Control 1, Experimental 2, and Control 2 samples respectively. All the samples showed a gradual increase in nitrogen content with time. On the 28th day, the values were 0.72,0 .92, 0.97, and 1.13 mg/L for Experimental 1, Control 1, Experimental 2, and Control 2 samples respectively. Therefore, the values of the experimental samples were lower than the corresponding control. The changes in TKN for experimental samples was considerable compared to the control samples. In addition, the increment for experimental samples was less than 0.5 mg/L over the preservation time. Hence, it could be said that the experimented combinations could be utilized to preserve goatskin.
3.3.4 Bacterial Count
The quantification of bacterial population (the rate of decomposition of skins) serves as a primary metric for assessing the effectiveness of preservation techniques(Mohammed et al. 2016). The extent of skin deterioration can be inferred from the abundance of bacterial colonies present on the skin during preservation (Nur-A-Tomal et al. 2021).
Fig. 8 represents the value of the bacterial colony count of the control and experiment samples. On the very first day, the values of bacterial count were 1.45×107 and 1.81×107 CFU/g. for Experimental 1 and Experimental 2 respectively. In the case of control samples, the values were 1.62×107 and 1.95×107 CFU/g for Control 1 and Control 2 respectively.
After 4th day, the bacterial load augmented to 3.78×107, 4.23×107, 3.97×107, and 5.21×107 CFU/g for Experimental 1, Control 1, Experimental 2, and Control 2 respectively. During the 8th day of curing the values were decreased to 5.69×106, 5.15×106, 4.87×106 and, 5.76×106 CFU/g for Experimental 1, Control 1, Experimental 2, and Control 2 respectively. Finally, after completing 28th days of preservation, values of bacterial count were reduced to 14.1×104, 12.25×105, 1.95×105, and 2.05×105 CFU/g for Experimental 1, Control 1, Experimental 2, and, Control 2 respectively. Therefore, the bacterial load was increased in the early stage but it started to lessened after 4th day of preservation. Hence, the antimicrobial activity of the studied plant preservative is the key factor for the reduction of bacterial load of experimental samples. Moreover, salt showed bacteriostatic properties during the preservation period. Furthermore, throughout the whole preservation time, the experimental samples' bacterial load matched that of the control samples. In conclusion, cotton seed-based curing agents can protect the goatskin from exponential bacterial growth as well as bacterial degradation.
3.4 Correlation Analysis
The correlation analysis among shrinkage temperature, bacterial count, moisture content, and nitrogen content of control and experimental samples during 28 days of curing was presented in Table 4. It is revealed that the preservation efficacy parameters have a significant correlation. Moisture content and bacterial load is positively correlate (Experimental 1, r= 0.616; Control 1, r= 0.878; Experimental 2, r= 0.734, and Control 2, r= 0.655) to each other while, Control 2 shows a very strong correlation(P<0.01). In addition, Moisture content and Shrinkage temperature show a very strong negative correlation (Experimental 1, r= -0.917; Control 1, r= -0.976; Experimental 2, r= -0.935, and Control 2, r= -0.949) to each other with high significance level (P<0.001). Furthermore, bacterial load and shrinkage temperature show a strong negative correlation for the control sample 1 (r = -0.856) which is statistically significant (P<0.01). Besides, the significant (P<0.01) strong positive correlation between nitrogen content and shrinkage temperature does not make any sense because of the negligible increment of nitrogen content over the preservation period (<0.6 mg/L). There can be a similar conclusion made for the correlation of nitrogen content with bacterial count and moisture content over the preservation period.
3.5 Pollution Load in Soaking Liquor
The soaking process in leather processing can contribute to pollution through the release of various pollutants into the environment. The soaking process is a crucial step in leather production, where raw animal hides are immersed in water to remove impurities, salts, and other substances. While soaking is essential for preparing the hides for tanning, it can also generate significant pollution which is calculated by Checking BOD, COD, TDS, Cl- etc.(Raghava Rao et al. 2003).
After completing skin preservation for up to 28 days, the experimental and the control skin samples were taken into conventional leather processing. After the soaking process, the soaked wastewater was collected and different pollution loads were checked to examine how environmentally friendly the optimized combinations would be.
Table 5. shows the result of BOD, COD, Cl-, and TDS values of the control and experimented samples. Removal capacity was also measured. From the obtained results, it is seen that in all cases, the values of the experimented samples are less than corresponding controls as less salt was used.
For Cl-, experimental 1 sample showed 65.33 % removal capacity and experimental 2 showed 66.91%. In the case of BOD, experimental 1 showed 30.86% better results, and experimental 2 showed 29.15%. The COD values of experimental 1 and experimental 2, were capable of reducing the pollution loads by showing removal capacity 27.15% and 34.28%, respectively. Moreover, the TDS values of controls are also higher than the experimental and removed 41.06% and 35.20% for experimental 1 and experimental 2, respectively, compared to the conventional method. Therefore, it could be said that our optimized combinations for skin preservation could lessen the environmental pollution that occurs from soaking liquor in the conventional method.
Physical Strength of Leather
3.6 SEM Analysis
SEM is essential for studying leather shapes because it allows high-resolution imaging, surface analysis, fiber structure analysis, cross-section analysis, defect detection, and comparison studies (Müller et al. 2004). The effect of preservative materials on the leather sample's fiber orientation, strength, and structure is described in SEM photographs. The fiber structure of the leather samples was evaluated using SEM examination. The fiber orientation of both the control and experimental samples is shown in Fig. 9. It shows that there were no appreciable differences between the samples from the respective controls and trials. There was no breakdown of fibers and the fiber orientation was almost similar. Therefore, it demonstrates that the texture and quality of the goat skin won't be reduced by utilizing this innovative preservation technique.
3.7 Physical Properties of Leather
Physical qualities are important in determining the quality of processed leather since they determine its look, durability, and performance. Leather's physical strength is typically utilized to forecast how well it will function over time. [52]. The physical tests such as tensile strength, elongation at break, distension, and stitch tear strength were determined for the control and experimental samples. The results are shown in Table 6. From the values it is seen that the test results of the experimental samples were compatible with the corresponding controls. All the examined samples have satisfied the standards for upper leather for shoes. So, the used combinations of preservatives do have not any effect in reducing the physical characteristics of the produced leather. It could be said that these combinations could be an effective replacement for the traditional salting method.