Fluorescence Spectroscopic Methods Research Articles

Spectroscopic, electrochemical, and molecular docking studies of the interaction between the antihistamine drug desloratadine and dsDNA

Through the utilization of fluorescence spectroscopy, electrochemical, and molecular docking methods, this research investigates the interaction between the antihistamine drug desloratadine and calf thymus double-stranded DNA (ct-dsDNA). Deoxyguanosine (dGuo) and deoxyadenosine (dAdo) oxidation signals were diminished by incubation with varying concentrations of desloratadine, as determined by differential pulse voltammetry (DPV). This change was ascribed to desloratadine's binding mechanism to ct-dsDNA. The binding constant (Kb) between desloratadine and ct-dsDNA was determined to be 2.2 × 105 M-1 throughout electrochemical experiments. In order to further develop our comprehension of the interaction mechanism between desloratadine and ct-dsDNA, a series of spectroscopic experiments and molecular docking simulations were conducted. The Kb value was found to be 8.85 × 104 M-1 at a temperature of 25 °C by the use of fluorescence spectroscopic techniques. In summary, the utilization of electrochemical and spectroscopic techniques, alongside molecular docking investigations, has led to the prediction that desloratadine has the capability to interact with ct-dsDNA by groove binding.

Antibacterial and cytotoxicity studies of pyrrolo-based organic scaffolds and their binding interaction with bovine serum albumin.

Two pyrrolo-based compounds, 1H-pyrrolo[3,2-b]pyridine-3-carboxylic acid (L1) and 1H-pyrrolo[3,2-c]pyridine-4-carboxylic acid (L2), were employed for the detection of bovine serum albumin (BSA) by UV-Vis and fluorescence spectroscopic methods in phosphate buffer solution (pH = 7). In the presence of L1 and L2, the fluorescence emission of BSA at 340 nm was quenched and concomitantly a red-shifted emission band appeared at 420 nm (L1)/450 nm (L2). The fluorescence spectral changes indicate the protein-ligand complex formation between BSA and L1/L2. An isothermal titration calorimetry (ITC) experiment was conducted to determine the binding ability between BSA and L1/L2. The binding constants are found to be 4.45 ± 0.22 × 104 M-1 for L1 and 2.29 ± 0.11 × 104 M-1 for L2, respectively. The thermodynamic parameters were calculated from ITC measurements (i.e. ∆rH = -40 ± 2 kcal/mol, ∆rG = -4.57 ± 0.22 kcal/mol and -T∆rS = 35.4 ± 1.77 kcal/mol), which indicated that the protein-ligand complex formation between L1/L2 with BSA is mainly due to the electrostatic interactions. The protein-ligand interactions were studied by performing molecular docking. Further, the antibacterial assay of L1 and L2 was conducted against gram-positive and gram-negative bacterial strains in an effort to address the difficulties caused by the co-occurrence of antimicrobial and multidrug-resistant bacteria. E. coli and S. aureus were significantly inhibited by L1 and L2. The L1 exhibits 13, 12 and 15 mm, whereas L2 exhibits a 2, 3 and 5 mm zone of inhibition against S. aureus, S. pyogenesand E. coli, respectively. In silico molecular docking of L1 and L2 was performed with bacterial DNA gyrase to establish the intermolecular interactions. Finally, the in vitro cytotoxicity activities of the ligands L1 and L2 have been carried out using drosophila.

Methodological Considerations Regarding the Quantification of DNA Impurities in the COVID-19 mRNA Vaccine Comirnaty®.

DNA impurities can impact the safety of genetically engineered pharmaceuticals; thus, a specific limit value must be set for them during marketing authorisation. This particularly applies to mRNA vaccines, as large quantities of DNA templates are used for their production. Furthermore, when quantifying the total DNA content in the final product, we must observe that, in addition to the mRNA active ingredient, DNA impurities are also encased in lipid nanoparticles and are therefore difficult to quantify. In fact, the manufacturer of the mRNA vaccine Comirnaty (BioNTech/Pfizer) only measures DNA impurities in the active substance by means of a quantitative polymerase chain reaction (qPCR), whose DNA target sequence is less than just 1% of the originally added DNA template. This means that no direct DNA quantification takes place, and compliance with the limit value for DNA contamination is only estimated from the qPCR data using mathematical extrapolation methods. However, it is also possible to dissolve the lipid nanoparticles with a detergent to directly measure DNA contamination in the final product by using fluorescence spectroscopic methods. Experimental testing of this approach confirms that reliable values can be obtained in this way.

Protein Interaction and Molecular Docking Analysis by Schiff Base Derived from 2,4-Dinitro Phenyl Hydrazine

A novel and cost-effective 2,4-dinitrophenyl hydrazine derived from Schiff base 1-benzylidine-2-(2,4-dinitrophenyl) hydrazine ( L) was designed and characterized using various spectroscopic techniques. The interaction between L and bovine serum albumin (BSA) has been carried out using UV–Vis and fluorescence spectroscopy, DSC, SEM, and molecular docking methods. The phosphate buffer ([Formula: see text]) solution of BSA showed fluorescence emission maxima at 342[Formula: see text]nm. Upon addition of L to the BSA solution, it quenched the fluorescence emission at 342[Formula: see text]nm. The quenching of the fluorescence emission is due to the formation of a complex between L and BSA. The binding constant was calculated from the fluorescence titrations and found to be [Formula: see text][Formula: see text]M[Formula: see text]. Further, molecular docking analysis was carried out to establish the binding between L and BSA.

Synthesis, Characterization and Photophysical Properties of 2-Quinolone-Based Compounds

2-Quinolone (1,2-dihydroquinoline) and 1-aza coumarin derivatives are quinoline class pharmacophore structures known for their versatile bioactive and stable photophysical properties. In the present study, N-amino (2) and N-acetamido (3) derivatives of 2-quinolone-based 1-aza Coumarin-3-carboxylic acid were synthesized. Structure characterizations of the synthesized compounds were performed using 1H NMR, IR, 13C NMR spectral techniques. The synthesized compounds are thought to be precursor structures for the development of new bioactive agents because of their structural similarity. The photophysical sensitivities of compounds (2 and 3), which have the 1-Aza coumarin skeleton, in different solvents were examined by ultraviolet−visible (UV−Vis) absorption spectroscopy and fluorescence spectroscopy methods. In addition, the compounds synthesized in this study could serve as fluorophores, fluorescently active and bioactive new Schiff base sensors in different fluorescence studies.

Design, synthesis, and characterization of M(II)-Schiff base complexes containing 3,5-di-tert-butyl salicylaldehyde: DNA binding/cleavage, DPPH radical scavenging activity, cytotoxic activity, and catalytic activity investigation

Two mononuclear Cu(II) and Zn(II) based complexes were synthesized via microwave-assisted method utilizing Schiff base ligand based on 3,5-di-tertbutylsalicylaldehyde. The compounds were characterized using elemental and spectroscopic analysis methods. The ligand posed as an ON-donor ligand, confirmed by spectrum analysis in the complexes. A geometry optimization analysis was also performed using density functional theory to obtain the geometry, stability, and electronic properties of the synthesized compounds. CuL1 has a distorted square planar geometry, whereas ZnL1 has a distorted tetrahedral geometry. Fluorescence and absorbance spectroscopy were utilized to explore the interaction properties of calf thymus-deoxyribonucleic acid (CT-DNA) with the complexes. The CuL1 and ZnL1 are highly sensitive to DNA binding, with binding constant (Kb) in the range of 105 M−1, representing substantial interaction with CT-DNA, combining intercalation and electrostatic interactions. The Stern-Volmer constant (Ksv) obtained from the fluorescence spectroscopy method varied from 3.31 x 104 to 8.42 x 104 M−1, indicating moderate DNA binding. Circular dichroism spectroscopy confirmed the presence of intercalative binding among the DNA and the complexes. The in-vitro DNA cleavage activity revealed that complexes could efficiently break the supercoiled plasmid DNA without using any external agents. The complex CuL1 induced significant cytotoxicity for Dalton’s lymphoma cancer cell lines, having IC50 values of 18.96 ± 0.021 μM. The antioxidant activity of the compounds was also studied, confirming CuL1 to be the most active antioxidant with IC50 = 399.27 µM. A molecular docking simulation was also conducted to comprehend the compounds' interaction mechanism with CT-DNA (1BNA) and cancer cells (BCL-family proteins). Furthermore, the catalytic activity of the zinc metal complex was assessed for multi-component reactions involving substituted benzaldehydes, malononitrile, and resorcinol.

Electrochemical Impedance Spectroscopy for the Sensing of the Kinetic Parameters of Engineered Enzymes.

The study presents a promising approach to enzymatic kinetics using Electrochemical Impedance Spectroscopy (EIS) to assess fundamental parameters of modified enteropeptidases. Traditional methods for determining these parameters, while effective, often lack versatility and convenience, especially under varying environmental conditions. The use of EIS provides a novel approach that overcomes these limitations. The enteropeptidase underwent genetic modification through the introduction of single amino acid modifications to assess their effect on enzyme kinetics. However, according to the one-sample t-test results, the difference between the engineered enzymes and hEKL was not statistically significant by conventional criteria. The kinetic parameters were analyzed using fluorescence spectroscopy and EIS, which was found to be an effective tool for the real-time measurement of enzyme kinetics. The results obtained through EIS were not significantly different from those obtained through traditional fluorescence spectroscopy methods (p value >> 0.05). The study validates the use of EIS for measuring enzyme kinetics and provides insight into the effects of specific amino acid changes on enteropeptidase function. These findings have potential applications in biotechnology and biochemical research, suggesting a new method for rapidly assessing enzymatic activity.

The β2-adrenergic receptor associates with CXCR4 multimers in human cancer cells

While the existence and functional role of class C G-protein-coupled receptors (GPCR) dimers is well established, there is still a lack of consensus regarding class A and B GPCR multimerization. This lack of consensus is largely due to the inherent challenges of demonstrating the presence of multimeric receptor complexes in a physiologically relevant cellular context. The C-X-C motif chemokine receptor 4 (CXCR4) is a class A GPCR that is a promising target of anticancer therapy. Here, we investigated the potential of CXCR4 to form multimeric complexes with other GPCRs and characterized the relative size of the complexes in a live-cell environment. Using a bimolecular fluorescence complementation (BiFC) assay, we identified the β2 adrenergic receptor (β2AR) as an interaction partner. To investigate the molecular scale details of CXCR4-β2AR interactions, we used a time-resolved fluorescence spectroscopy method called pulsed-interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS). PIE-FCCS can resolve membrane protein density, diffusion, and multimerization state in live cells at physiological expression levels. We probed CXCR4 and β2AR homo- and heteromultimerization in model cell lines and found that CXCR4 assembles into multimeric complexes larger than dimers in MDA-MB-231 human breast cancer cells and in HCC4006 human lung cancer cells. We also found that β2AR associates with CXCR4 multimers in MDA-MB-231 and HCC4006 cells to a higher degree than in COS-7 and CHO cells and in a ligand-dependent manner. These results suggest that CXCR4-β2AR heteromers are present in human cancer cells and that GPCR multimerization is significantly affected by the plasma membrane environment.

Quantitative assessment whole-rock iron content in magnetite protolith based on terahertz time-domain spectroscopy.

Terahertz time-domain spectroscopy was first used to establish a correlation with the whole-rock iron (TFe) content in different depths of the Bayan Obo protolith. Compared with element content obtained by the traditional method of X-ray fluorescence spectroscopy (XRF), a similar tendency of the absorption coefficient and refractive index is presented. Furthermore, three machine learning algorithms, namely, partial least squares regression (PLSR), random forest (RF), and multi-layer perceptron (MLP), were used to develop a quantitative analytical model for TFe content of the protolith minerals. Among the three algorithms, MLP has the highest detection accuracy, with a model coefficient of determination R 2 reaching up to 0.945. These findings demonstrate that terahertz time-domain spectroscopy can be used to rapidly quantify the TFe elemental content of protolith, providing a method of detecting the content of mineral components.

Synthesis, Spectroscopy, X-ray Structures, DNA Binding and Photocatalytic Properties of Two Ni(II) and Co(II) Complexes of a Pyrazolyl Schiff-base Ligand

Two new nickel(II) and cobalt(II) complexes, [Ni(MPAFA)3](BF4)2 (I) and [Co(MPAFA)3](BF4)2 (II) were synthesized from a pyrazole containing ‘NN’ bidentate Schiff-base ligand, N-(furan-2-ylmethyl)-1-(5-methyl-1H-pyrazol-3-yl)methanimine, (MPAFA) (L). The complexes I and II were characterized by various physico-chemical and spectral parameters. Both I and II were 1:3 (M:L) coordination complexes and behaving as 1:2 electrolytes. Single crystal X-ray diffraction studies revealed that both of them were distorted octahedral in nature with a N6 donor set. The binding interactions of the complexes with CT-DNA were studied by UV-Vis and fluorescence spectroscopic methods. I was found to bind with CT-DNA in a partial intercalative mode, whereas II bound via the groove-like manner in solutions. The ligand and the complexes were shown to have potential photocatalytic activity in degrading methylene-blue (MB) under UV-Vis light irradiation.

Dissolution behavior of chromite mineral impurities in raw materials of glass production using scanning electron microscopy-energy dispersive spectrometer, X-ray fluorescence spectroscopy and Raman spectroscopy methods

Silica sand is an essential raw material for glass production. The specification of silica sand for each type of glass is the most important point, such as chemical purity, grain size, grain shape, and their impurities. Some of the impurities in the sand can be eliminated by processing yet some cannot be avoided. This paper indicates that as an impurity in the sand, chromite minerals dissolve in glass. 0.200 mm and 0.250 mm grain size chromite minerals were observed grain size change at 1350 °C − 1400 °C − 1450 °C. With increasing in temperature, the rate of size change in the grain diameter increased. Because of the chemical composition of chromite mineral, with increasing temperature, first of all, aluminum and magnesium content start to dissolve in soda lime silicate glass. Then, chromium content transforms into chromium oxide. The transformation rate depends on the mineral composition as well as the temperature and the residence time in the furnace. This paper concerns the chemical composition of the chromite by scanning electron microscopy equipped with energy dispersive spectrometer, the compositions of the raw material analyzed with X-ray fluorescence spectroscopy, inductively coupled plasma optical emission spectrometer and chromite characteristics analyzed by Raman Spectroscopy methods.

Development of a highly sensitive and green first-derivative synchronous fluorescence spectroscopic method for the simultaneous quantification of telmisartan and rosuvastatin: Greenness metric assessment and application to a pharmacokinetic study in rats

Hypertension and hyperlipidemia frequently coexist and are correlated with elevated cardiovascular adverse outcomes. Fixed dose combination tablets containing antihypertensive and antihyperlipidemic drugs have the potential to improve patient compliance. Telmisartan and rosuvastatin fixed dose combination tablet has been recently formulated. This study provided the first fluorescence spectroscopic method for simultaneously quantifying telmisartan and rosuvastatin in tablet dosage form and plasma. The native fluorescence spectra of telmisartan and rosuvastatin completely overlapped, making direct measurement unachievable. However, through the implementation of synchronous fluorescence measurements of telmisartan and rosuvastatin at a Δλ = 60, distinct narrow bands were observed at 358 nm and 375 nm, respectively. Regrettably, the challenge of overlapping remained unresolved. Nevertheless, by converting these synchronous spectra into first-order spectra, the problem of overlapping was completely resolved. This conversion also allowed for the selective quantification of telmisartan and rosuvastatin at 374 nm and 358 nm, respectively. The validity of this method was confirmed in accordance with ICH guidelines, yielding satisfactory results in terms of the validation characteristics. The method demonstrated linear relationships between the response and the studied drugs concentrations in working range of 50–1000 ng/mL for telmisartan and 100–2000 ng/mL for rosuvastatin. The described methodology was applied for the pharmacokinetic study of telmisartan and rosuvastatin in rat plasma after a single oral dose of 4 mg/kg telmisartan and 50 mg/kg rosuvastatin. Pharmacokinetic analyses revealed a moderate drug-drug interaction between the two drugs, which was not considered to be clinically significant. Moreover, the described method was assessed in terms of sensitivity and environmental sustainability against three previously documented methods. The comparison effectively underscores the supremacy of the proposed technique over the documented techniques.

Investigating the third-order nonlinear optical properties of a Schiff base (DBAP) and its Co/Cu metal complex using Z-scan and DFT methodology

Utilizing UV-visible, Fluorescence spectroscopic, and Z-scan methods, the optical and structural properties of 2-(4-(dimethyl amino)benzylidene amino) phenol (DBAP) and their Co/Cu metal complexes were studied. The Z-scan method has been used to investigate the nonlinear absorption coefficient (β), nonlinear refractive index (n2), third-order susceptibility (χ(3)), and optical limiting (OL). In dimethyl sulfoxide (DMSO) and methanol (MeOH) solvents, the DBAP and their Co/Cu metal complexes display positive nonlinear absorption and a positive nonlinear refractive index, according to the Z-scan data. Using the Z-scan approach and an 800 nm central wavelength, femtosecond amplified 48 fs pulse, 1kHz repetition rate laser, the compound's third-order nonlinear optical (NLO) properties are measured. According to the Z-scan data, we may modify the structure and bonding of legend with metals to improve the NLO capabilities of metal complexes, making this material a promising choice for upcoming optoelectronic and photonic devices. The geometrical structure of the compound is optimized using theoretical computations at the B3LYP that are functional with 6-31G and the LanL2DZ on a mixed basis, as determined by the density functional theory (DFT) framework. They provide insight into the charge transfer interactions taking place in the molecule through their HOMO-LUMO analysis.

Protective effects of functional Nano-Selenium supplementation on spleen injury through regulation of p38 MAPK and NF-κB protein expression

Selenium (Se) is a trace element necessary for humans to maintain normal physiological activities, and Se deficiency may lead to splenic injury, while Se supplementation can alleviate splenic injury. However, the mechanism is unclear. In this study, we constructed a Se deficiency animal model by feeding Sprague-Dawley (SD) rats with low Se feed. Meanwhile, we observed the repairing effect of Se supplementation on splenic injury with two doses of novel nano-selenium (Nano-Se) supplement by gavage. We measured the Se content in the spleens of the rats by atomic fluorescence spectroscopy (AFS) method and combined the results of hematoxylin-eosin (HE) and Masson staining to observe the splenic injury, comprehensively evaluating the construction of the animal model of low selenium-induced splenic injury. We measured the mRNA and protein expression levels of p38 mitogen-activated protein kinase (p38 MAPK), nuclear factor kappa-B (NF-κB), and interleukin-6 (IL-6) in the spleen by Real-time quantitative polymerase chain reaction (qPCR), western blot (WB), and immunohistochemistry (IHC). We found that the Se deficiency group exhibited lower Se content, splenic fibrosis, and high expression of p38 MAPK, NF-κB, and IL-6 compared to the normal group. The Se supplement groups exhibited higher Se content, attenuated splenic injury, and down-regulated expression of p38 MAPK, NF-κB, and IL-6 relative to the Se deficiency group. This study suggests that Se deficiency leads to splenic injury in rats, and Se supplementation may attenuate splenic injury by inhibiting the expression of p38 MAPK, NF-κB and IL-6.

Study of the kinetics of accumulation and distribution of the photosensitizer photoditazin in the oral mucosa in patients with lichen planus

Was to explore the accumulation and distribution of the photosensitizer Photoditazine in the oral mucosa when applied to pathological lesions in patients with severe forms of lichen planus. A clinical and laboratory examination was carried out in 50 patients with severe forms of lichen planus (bullous and erosive-ulcerative) aged 18 to 70 years, including 6 men and 44 women. For autofluorescent imaging a LED device with a wavelength in the violet region of the spectrum (400±10 nm) was used. Quantitative registration of the kinetics of accumulation and distribution of the photosensitizer was carried out using the method of local fluorescence spectroscopy by measuring the fluorescence spectra. The measurements were made before applying the photosensitizer, 10, 20 and 30 minutes after application. The study showed that in most patients with erosive-ulcerative and bullous forms of lichen planus, the accumulation of the photosensitizer in the lesions on the oral mucosa increased as the exposure time increased from 20 to 30 minutes. The fastest accumulation of the photosensitizer occurred in the areas of mucosal lesions with the most pronounced vascularization, namely, in the area of the tongue and the bottom of the oral cavity. Using the method of local fluorescence spectroscopy, the kinetics of accumulation and destruction of photosensitizer in pathological areas of the oral mucosa was determined, and therefore the optimal time of laser exposure to the lesion was determined.

Studying Macromolecular Interactions of Cellular Machines by the Combined Use of Analytical Ultracentrifugation, Light Scattering, and Fluorescence Spectroscopy Methods.

Cellular machines formed by the interaction and assembly of macromolecules are essential in many processes of the living cell. These assemblies involve homo- and hetero-associations, including protein-protein, protein-DNA, protein-RNA, and protein-polysaccharide associations, most of which are reversible. This chapter describes the use of analytical ultracentrifugation, light scattering, and fluorescence-based methods, well-established biophysical techniques, to characterize interactions leading to the formation of macromolecular complexes and their modulation in response to specific or unspecific factors. We also illustrate, with several examples taken from studies on bacterial processes, the advantages of the combined use of subsets of these techniques as orthogonal analytical methods to analyze protein oligomerization and polymerization, interactions with ligands, hetero-associations involving membrane proteins, and protein-nucleic acid complexes.

Synchronous Fluorescence Spectroscopy Method based on Chemometrics: Authentication of Extra Virgin Olive Oils Harvested in Mut (Mersin) Region and Refined Edible Oils

Bu çalışma, Mut (Mersin) bölgesinden iki farklı hasat döneminde (2019 ve 2020 Ekim) elde edilen ekstra saf sızma zeytinyağı (VOO) ve farklı markalara ait rafine yemeklik yağ numunelerinde tağşiş/sahtecilik durumu hakkında fikir edinmeyi amaçlamaktadır. Araştırmayı gerçekleştirmek için senkron floresans (SyF) spektroskopisine dayalı analitik yaklaşım, PCA ve SIMCA kemometrik veri analiz yöntemi ile kullanılmıştır. SyF verileri 200–800 nm emisyon bölgesinde elde edilmiş ve uyarma/emisyon monokromatörleri senkronize şekilde kullanılmıştır. Saf VOO ve farklı türdeki yağ numuneleri için elde edilen veriler; PCA ve SIMCA çok değişkenli veri modellemeleri ile analiz edilmiştir. Elde edilen PCA skor grafiklerinde; yağ türlerinin ve farklı hasat zamanlarına ait zeytinyağı örneklerinin sınıflandırma yeteneğinin oldukça yüksek olduğu; SIMCA modellemelerinde ise VOO numunelerinin diğer yağ türlerinden %100 farklı bir grupta sınıflandırılabildiği tespit edilmiştir. Sonuç olarak SyF spektroskopisi kemometrik analiz yöntemleri ile birleştirildiğinde hız ve maliyet açısından oldukça avantajlı bir yöntem olup, zahmetli numune ön işlemleri ve kimyasal kullanımını ortadan kaldırarak büyük kolaylık sağlamaktadır.

Modern methods of the diagnostic of pathology of pregnancy and the postpartum period

Postpartum purulent-inflammatory diseases are currently a serious problem. Purpose - to develop and implement of a new modern method of the diagnosis, monitoring and assessment of health of women during pregnancy, before childbirth and in the postpartum period - the method of fluorescence spectroscopy - to ensure the provision of highly qualified medical care, including the effective treatment. Materials and methods. The research material consisted of blood serum samples of 265 patients. There were 40 pregnant women (the Group 1), 40 women with an uncomplicated postpartum period (the Group 2), 170 - with postpartum purulent-inflammatory diseases (the Group 3), 15 patients with sepsis (the Group 4). Diagnostic methods: clinical, laboratory, instrumental, method of fluorescence spectroscopy, statistical (logistic regression and ROC analysis methods). Results. In the Group 1 there is an increase in the intensity of fluorescence to 1.3 r.u. For the Group 2 the intensity of fluorescence was within 0.86-1.0 r.u. For the Group 3, the decrease in fluorescence intensity from 1 to 0.35 r.u. was recorded. For the Group 4 in addition to decreasing the fluorescence intensity, a noticeable shift of the fluorescence spectra of blood serum into the long-wave range was recorded. Conclusions. A reliable prognostic model of the development of postpartum purulent-inflammatory diseases was created. The modern approach for the diagnosis and effective control of treatment within the framework of the method of fluorescent spectroscopy and biomarkers using infusions of donor albumin solutions is proposed. The research was carried out in accordance with the principles of the Helsinki Declaration. The study protocol was approved by the Local Ethics Committee of participating institution. The informed consent of the patient was obtained for conducting the studies. No conflict of interest was declared by the authors.

Vintage identification of sauce-flavor liquor based on fluorescence spectroscopy

The vintage of sauce-flavor liquor represents its collection value and grade, so its identification is essential for collectors and connoisseurs. In this research, a vintage identification model for sauce-flavor liquors was proposed based on the fluorescence spectroscopy method. A fluorescence spectrophotometer was used to measure the fluorescence spectrum of sauce-flavor liquors of different years, and the optimum emission peaks of the spectrum were obtained. By analyzing these optimum emission peaks, it was determined that intensity of the spectrum increased with the vintage of sauce-flavor liquor. A prediction model was established to identify quantitatively the vintage of sauce-flavor liquor according to spectrum intensity, and its coefficient of determination (R2) was 0. 995. The prediction model was verified with an average error of 0.06 years. Moreover, an online testing platform was designed to realize the real-time, rapid, and quantitative vintage identification of sauce-flavor liquors. The model and platform should be helpful for evaluating sauce-flavor liquor.

Determination of tryptophan in milk

Tryptophan or L-tryptophan is one of the essential amino acids for the human body. An important component of the human diet, L-tryptophan is not only involved in protein synthesis in the body, but is also crucial for a number of metabolic functions. One of the important sources of tryptophan for the human body are dairy products, and their feature is the fact that milk itself contains the best ratio of tryptophan/competing amino acids, which is necessary for the synthesis of serotonin. Since tryptophan is thermolabile, one of the factors that can affect its content is heat treatment of milk. The standard and certified method for determining tryptophan in milk is high-performance liquid chromatography with fluorescence detection. Tryptophan belongs to fluorophores and fluoresces most strongly among all amino acids. It absorbs electromagnetic radiation with a wavelength of 290 nm and emits in the range of 300–350 nm. In the presented study, tryptophan was determined by the method of fluorescence spectroscopy without chromatographic separation of 18 samples of drinking milk from well-known Ukrainian producers of dairy products, which differed in the method of heat treatment and manufacturing technology. Fluorescence spectra were recorded on a Perkin-Elmer LS-55 fluorescence spectrometer; the content of dry skimmed milk residue and lactose in milk samples was determined on an ultrasonic milk analyzer “Ekomilk-Bond” (Bulgaria). Sample preparation of milk samples for the determination of tryptophan was carried out according to DSTU ISO 13904:2008. Research has shown that the content of tryptophan in milk samples from Ukrainian dairy producers ranges from 189.5 to 515.1 mg/l, which is basically consistent with literature data. Dependence of the method of heat treatment of milk on tryptophan content was not found. Obviously, first of all, the tryptophan content in milk will be influenced by the total protein content in the product.