Monitoring the mode of action of synthetic and natural biocides against Aeromonas hydrophila by Raman spectroscopy and chemometrics

We have investigated the mode of action of synthetic biocides,(2-(thiocyanomethylthio)benzothiazole(TCMTB),dichlorophen,(commonly used in leather industry for preservation)and natural biocides,oregano and eucalyptus oils,on Aeromonas hydrophila using Raman spectroscopy in collaboration with multivariate analysis and 2D correlation spectroscopy to evaluate whether Raman spectra acquired contained valuable information to study the action of biocides on bacterial cells.The growth of A.hydrophila in clear and outer edge zone of inhibition differ in their reaction with different biocides,which allows us to highlight the differences as a characteristic of two kinds of bacteria.Such classification helps identify oregano oil as the most effective biocide by altering clear and outer edge zone of bacteria.Standard disk diffusion assay method was used for screening biocide bacteria interactions and later analysed by Raman spectroscopy.The paper also presents the introduction of TCMTB and oregano oil into leather processing stages to examine and determine the antimicrobial effect as an application to real-world setting.Therefore,we conclude that Raman spectroscopy with appropriate computational tools constitutes a powerful approach for screening biocides,which provide solutions to all the industries using biocides including leather industry,considering the potentially harmful effect of biocides to humans and the environment.

RAMAN AND ATR-FTIR SPECTROSCOPY TOWARDS CLASSIFICATION OF WET BLUE BOVINE LEATHER USING RATIOMETRIC AND CHEMOMETRIC ANALYSIS

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$35m 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.