Raman and Atr-Ftir Spectroscopy Towards Classification of Wet Blue Bovine Leather Using Ratiometric and Chemometric Analysis

Abstract

There is a substantial loss of value in bovine leather every year due to a leather quality defect known as "looseness". Data show that 7% of domestic hide production is affected to some degree, with a loss of $35 m in export returns. This investigation is devoted to gaining a better understanding of tight and loose wet blue leather based on vibrational spectroscopy observations of its structural variations caused by physical and chemical changes that also affect the tensile and tear strength. Several regions from the wet blue leather were selected for analysis. Samples of wet blue bovine leather were collected and studied in the sliced form using Raman spectroscopy (using 532 nm excitation laser) and Attenuated Total Reflectance-Fourier Transform InfraRed (ATR-FTIR) spectroscopy. The purpose of this study was to use ATR-FTIR and Raman spectra to classify distal axilla (DA) and official sampling position (OSP) leather samples and then employ univariate or multivariate analysis or both. For univariate analysis, the 1448 cm − 1 (CH 2 deformation) band and the 1669 cm − 1 (Amide I) band were used for evaluating the lipid-to-protein ratio from OSP and DA Raman and IR spectra as indicators of leather quality. Curve-fitting by the sums-of-Gaussians method was used to calculate the peak area ratios of 1448 and 1669 cm − 1 band. The ratio values obtained for DA and OSP are 0.57 ± 0.099, 0.73 ± 0.063 for Raman and 0.40 ± 0.06 and 0.50 ± 0.09 for ATR-FTIR. The results provide significant insight into how these regions can be classified. Further, to identify the spectral changes in the secondary structures of collagen, the Amide I region (1600-1700 cm − 1) was investigated and curve-fitted-area ratios were calculated. The 1648:1681 cm − 1 (non-reducing: reducing collagen types) band area ratios were used for Raman and 1632:1650 cm − 1 (triple helix: α-like helix collagen) for IR. The ratios show a significant difference between the two classes. To support this qualitative analysis, logistic regression was performed on the univariate data to classify the samples quantitatively into one of the two groups. Accuracy for Raman data was 90% and for ATR-FTIR data 100%. Both Raman and ATR-FTIR complemented each other very well in differentiating the two groups. As a comparison, and to reconfirm the classification, multivariate analysis was performed using Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). The results obtained indicate good classification between the two leather groups based on protein and lipid content. Principal component score 2 (PC2) distinguishes OSP and DA by symmetrically grouping samples at positive and negative extremes. The study demonstrates an excellent model for wider research on vibrational spectroscopy for early and rapid diagnosis of leather quality.

Extreme biomineralization: the case of the hypermineralized ear bone of gray whale (Eschrichtius robustus)

“…The registered spectrum confirms that analyzed bone is composed of B-type CO 3 2− substituted hydroxyapatite (CO 3 2− substitutes PO 4 3− in hydroxyapatite) [64,65]. The infrared spectrum registered for organic scaffold isolated by the bone demineralization using Osteosoft® show bands characteristic for collagen [66,67], nevertheless several band or band shifts suggest that this is a collagen-lipid complex [68]. Thus, the peaks at registered 3276 cm −1 and 3030 cm −1 corresponds to Amide A and Amide B bands that are associated with N-H stretching [69] and confirming the existence of hydrogen bonds.…”

“…9 ATR-FTIR spectra of the mineral phase (blue line) in original gray whale tympanic bulla sample and organic matrix isolated after its EDTA-based demineralization (yellow line), collagen standard (red line). The spectra show characteristic spectroscopic features of carbonated (band at 870 cm −1 ) HAP [64] (prior to demineralization) and that of collagenlipid complex [68] in the demineralized specimen Fig. 10 SDS-PAGE analysis of collagen isolated from whale ear bone.…”

Maskless Formation of Conductive Carbon Layer on Leather for Highly Sensitive Flexible Strain Sensors

“…[ 33,34 ] Bands located at 1247 and 1550–1596 cm −1 could be assigned to amide III and amide II of protein. [ 33 ] After the laser irradiation, the bands assigned to pristine leather disappear, while the D and G bands located at ≈1350 and ≈1584 cm −1 , respectively, emerges, indicating that the obtained material by the LDW is mainly carbon. [ 28 ] Figure 2h shows the TEM image of a carbon flake obtained at P L of 0.3 W. Nanoparticles are found on the surface of the carbon flake.…”

“…For the pristine sample without laser irradiation, bands close to 873 and 923 cm −1 is suggested to be originated from the hydroxyproline and proline or the C–C stretching vibrations of collagen amino acids. [ 33,34 ] Bands located at 1247 and 1550–1596 cm −1 could be assigned to amide III and amide II of protein. [ 33 ] After the laser irradiation, the bands assigned to pristine leather disappear, while the D and G bands located at ≈1350 and ≈1584 cm −1 , respectively, emerges, indicating that the obtained material by the LDW is mainly carbon.…”

Vibrational Spectroscopy for Identification of Metabolites in Biologic Samples

“…Although most of the scattered light has the same frequency as the incident light, some of them have different frequencies due to the interaction between the oscillation of light and molecular vibration. This phenomenon is called Raman scattering and, unlike IR spectroscopy, Raman spectroscopy has a very weak water signal and minimal water interference, which is a great advantage for the analysis of the biological samples [ 8 ]. Raman spectroscopy can offer direct measurements from the biofluids, single cells, in vitro, or even in vivo fiber-optic sampling for bladder and prostate, esophagus, and skin, cervix, and arteries [ 4 ].…”