Opus 7

All photochemical experiments in UHV were performed with a home-built high-intensity UV source in the vicinity of the sample. In brief, we used a high-power LED (Seoul Viosys, CUN6AF4A, 2.35 W), which yields a photon flux density of 1.68 × 10⁻¹⁸ cm^−2.s⁻¹ at a wavelength of 365 nm, corresponding to a power density of 910 mW^.cm⁻². Further information can be found in the literature^{32 (link)}. During all photoconversion experiments, the sample was cooled to 110 K. The UV source was operated by an external power supply (TDK Lambda Z + 200) triggered by the IR spectrometer (Bruker OPUS 7.2) or manually. For each sample, nine illumination steps were applied, such that the total illumination time was increasing exponentially (0.01 s, 0.04 s, 0.16 s, 0.64 s, 2.56 s, 10.24 s, 40.96 s, 163.84 s, 655.36 s). After each illumination step, an IR spectrum was recorded with an acquisition time of 10 min.

ATR-FTIR spectra were recorded by an ATR-FTIR spectrometer (Agilent technologies 4500 series FTIR, Kuala Lumpur, Malaysia). The spectra were obtained in the range of 4000–650 cm⁻¹ and at 4 cm⁻¹ resolution with 256 co-added scans per spectrum. Each spectrum was normalized and integrated by OPUS 7.2 (Bruker, Hanau, Germany). The absorption intensities under the spectra were integrated at wavenumbers of 1695–1596, 1596–1493, and 1189–973 cm⁻¹, which represent the regions of amide I, amide II, and carbohydrate, respectively.
Absorption unit ratios of the integrated results were evaluated for amide I/amide II and carbohydrate/amide II ratios from F1- or F2-treated mucosa with or without niosomes in comparison to the relevant blanks.
From interaction and non-interacted mucosa, samples were analyzed by principal component analysis (PCA). Spectral pre-processing was conducted by taking the second derivative, smoothing with a Savitzky–Golay function (3 polynomials and 15 smoothing points), and correcting the spectral scattering at fingerprint (1780–980 cm⁻¹) by using Extended Multiplicative Scatter Correction of a computer software (Unscrambler X 10.5, (CAMO Software AS, Oslo, Norway).

The Fourier transform infrared spectra were recorded in ATR mode using a Brucker ALPHA (Platinum ATR) FTIR spectrometer (Bruker Optics GmbH, Ettlingen, Germany) equipped with a diamond crystal in the 3100–800 cm⁻¹ region, with a resolution of 4 cm⁻¹, using air as background, and with all spectra representing an average of 30 scans. Three recordings were performed for each sample, and an evaluation was made using the average spectrum obtained from these recordings. The processing of the spectra was carried out with the Bruker software OPUS 7.2 (Bruker Optics GmbH, Germany). Prior to each test, a background spectrum was obtained to compensate for the effect of humidity and the presence of carbon dioxide by spectra subtraction.

IR data was analyzed using OPUS 7.2 (Bruker Corporation) and Matlab R2017b (The MathWorks, Inc.) software. UV/VIS data were analyzed using Matlab R2017b.

ATR–FT–IR measurements were performed using a Bruker Tensor 37 FT-IR spectrometer (Ettlingen, Germany) equipped with a mercury cadmium telluride (MCT) detector (D* = 4 × 10¹⁰ cm Hz^0.5 W⁻¹ at 9.2 μm). The spectrometer was constantly flushed with dry air in order to reduce the influence of water vapor from the atmosphere. One drop of pure milk fat extract was manually placed onto a Platinum ATR single-bounce element (Bruker, Ettlingen, Germany). Measurements were performed with a spectral resolution of 2 cm⁻¹, between 600 and 4000 cm⁻¹ in double-sided, forward–backward acquisition mode. A Blackman–Harris 3-term apodization function and a zero-filling factor of 2 were used to calculate the final spectra. One hundred and twenty-eight scans were averaged per spectrum, leading to an acquisition time of fifty-two seconds. After each spectral acquisition, the ATR surface was cleaned with isopropanol and dichloromethane consecutively until recovery of the baseline signal. Transmission measurements were performed using the same instrument parameters, by injecting homogenized whole milk into a flow cell equipped with two CaF₂ windows and a 37 µm-thick spacer. The software package OPUS 7.2 (Bruker, Ettlingen, Germany) was used for evaluation of the spectral data.

The biochemical composition of the samples was analyzed using SR-FTIR spectroscopy [38 (link)]. Spectral data were collected using the infrared microspectroscopy beamline BL4.1 IR Spectroscopy and Imaging at the Synchrotron Light Research Institute (SLRI, Nakhon Ratchasima, Thailand). Spectra were obtained using a Vertex 70 FTIR spectrometer (Bruker Optics, Ettlingen, Germany) coupled to an IR microscope (Hypersion 2000, Bruker), equipped with a liquid nitrogen cooled MCT detector. The data were collected over the 4000 to 800 cm⁻¹ measurement range. The measurement was performed in mapping mode with an aperture size of 10 µm × 10 µm and acquisition of 64 scans with a spectral resolution of 4 cm⁻¹. The software OPUS 7.2 (Bruker Optics Ltd, Ettilngen, Germany) was used for the derivation of the spectra and instrument control, and the results were analyzed with the CytoSpec software.
Samples from CO and OR (12 samples per group) were used to investigate the changes in the biochemical composition of meat. First, the original spectra were averaged to obtain a total of five spectra, followed by the second derivation at 13 smoothing points, and the vector was normalized using the Savitzky–Golay method in Unscrambler X software (version 10.1, Camo Analytics, Oslo, Norway) to account for the effects of varying sample thickness.