Endogenous Fluorescence Spectra Research Articles

Annual variation in thermal and structural properties of yesso scallops (Mizuhopecten yessoensis) adductor muscle

The annual changes of the scallop’s adductor muscle in Ca2+-ATPase activity, chymotryptic digestion, endogenous fluorescence spectra, sulfhydryl content, and surface hydrophobicity were studied. Ca2+-ATPase activity peaked in February and reached its minimum in August for males and in July for females. However, no significant differences were observed between males and females throughout the year. The inactivation rate of Ca2+-ATPase activity increased by 17- to 36-fold when the temperature rose from 38°C to 45°C. The ratio of free myosin to bound myosin was approximately 5:4 at 0.5 M KCl and changed to 5:1 at 1.0 M, as determined by modeling. Chymotryptic digestion demonstrated that scallop myosin could be cleaved into S-1/rod portions at 0.1 M and HMM/LMM at 0.5 M KCl. Furthermore, no significant seasonal variations were observed in chymotryptic digestion patterns, endogenous fluorescence, surface hydrophobicity, or sulfhydryl content. In conclusion, the structure and thermal stability of both male and female scallops remained stable throughout the year, making them suitable for processing and preservation.

Synthesis and Characterization of Emulsifiers Based on the Maillard Reaction and Its Application in Stabilized DHA Algal Oil Nanoemulsions.

The aim of this study was to optimize the formation of sodium caseinate (CS) and gum arabic (GA) complexes through the Maillard reaction and to evaluate their effectiveness in improving the emulsification properties and stability of docosahexaenoic acid (DHA) nanoemulsions. First, the best target polysaccharides were selected, and the best modification conditions were determined using orthogonal experiments. Secondly, the response surface experiments were used to optimize the preparation process of the emulsion. The stability, in vitro digestion characteristics, and rheological characteristics of the emulsion prepared by means of CS-GA were compared with the emulsion prepared using a whey protein isolate (WPI). After the orthogonal test, the optimal modification conditions were determined to be a reaction time of 96 h, a CS-GA mass ratio of 1:2, a reaction temperature of 60 °C, and a degree of grafting of 44.91%. Changes in the infrared (IR), Raman, ultraviolet (UV), and endogenous fluorescence spectra also indicated that the complex structure was modified. The response surface test identified the optimal preparation process as follows: an emulsifier concentration of 5 g/L, an oil-phase concentration of 5 g/L, and a homogenization frequency of five, and the emulsion showed good stability. Therefore, the use of a nanoemulsion as a nanoscale DHA algal oil delivery system is very promising for extending the shelf life and improving the stability of food.

Formation, structure and functional characteristics of amyloid fibrils formed based on soy protein isolates

Food protein-derived amyloid fibrils possess great untapped potential applications in food and other biomaterials. The objective of this report was to investigate the formation mechanism, structure and functional characterization of soy protein amyloid fibrils (SPF) through hydrolysis and heating (pH 2.0, 85 °C, 0–24 h) of soy protein isolate (SPI). Fibrillation growth analysis indicated polypeptide hydrolysis upon hydrolytic heating, and the amyloid fibrils were basically formed 8 h later. The microstructure of SPF was monitored by transmission electron microscopy and scanning electron microscopy, exhibiting change from an irregular spherical structure to a coiled, intertwined thread-like polymer. The secondary structures of SPI all changed drastically during the fibrillation process was characterized by Fourier transform infrared spectroscopy, which the α-helical and β-turned content decreasing by 12.67 % and 5.07 %, respectively, and the content of ordered β-folded structures increasing with heating time, finally increasing to 53.61 % at 24 h. The fluorescence intensity of the endogenous fluorescence spectra decreased and the maximum emission wavelength was red-shifted, suggesting that the fibrillation unfolded the protein structure, hydrolyzed and self-assembled into amyloid fibrils aggregates obscuring the aromatic amino acid residues. The emulsification activity, emulsion stability and viscosity of SPF improved with the increase in protein fibrillation.

Effect of NaCl concentration on the formation of high internal phase emulsion based on whey protein isolate microgel particles

At present, the effect of structural modification of microgel particles on high internal phase emulsions (HIPEs) is less studied. In this study, the structural modification effect of NaCl on whey protein isolate microgels (WPIMPs) was comprehensively characterized and applied to the construction of HIPEs. WPIMPs were prepared with NaCl (0–150 mM) and the structural changes were analyzed by measuring the particle size, Zeta-potential, and endogenous fluorescence spectra. The results showed that inducing WPIMPs by NaCl enhanced the surface hydrophobicity, decreased the Zeta potential, and elevated the degree of cross-linking. The interfacial behavior of WPIMPs was characterized by measuring interfacial tensions and adsorbed layer properties. The results showed that NaCl induction decreased the interfacial tension, increased the thickness of the adsorbed layer, and improved the viscoelasticity. The HIPEs were analyzed for micromorphology and particle sizes. The results indicated that NaCl-induced WPIMPs favored the formation of HIPEs with small particle sizes and provided HIPEs with superior environmental stability. This study provides a new idea for the structural modification of microgels and a new theoretical basis for the construction conditions of HIPE.

Effect of Phosphorylation on the Structure and Emulsification Properties of Different Fish Scale Gelatins.

This study aimed to investigate the effect of phosphorylation on the structure and emulsification of Coregonus peled, Esox lucius and Grass carp scale gelatin. Fourier transform infrared spectroscopy (FTIR) and endogenous fluorescence spectra showed that the structures of the three fish scale gelatins changed. Additionally, the surface hydrophobicity index of the three fish scale gelatins increased by 36.72, 31.42 and 111.67, respectively, after 1 h of phosphorylation, and the surface tension decreased by 17.27, 32.58 and 18.7 mN/m, respectively. The emulsification activity index increased by 115.86, 155.22 and 45.52 m2/g, and the emulsification stability index increased by 98.37, 256.77 and 169.61 min, respectively. The structure of fish scale gelatin changed after phosphorylation, which resulted in the improvement of emulsification. This work will provide useful information to understand the relationship between the structure and function of gelatin.

Insights from alpha-Lactoalbumin and beta-Lactoglobulin into mechanisms of nanoliposome-whey protein interactions

The complexation between nanoliposomes and two dominant monomers in whey proteins, i.e. alpha-Lactoalbumin (α-La) and beta-Lactoglobulin (β-Lg), were investigated to reveal the mechanisms of nanoliposome-whey protein interactions. The UV–vis spectra showed that nanoliposomes could significantly interact with the two monomeric proteins. The red shift phenomenon and intensity decrease were observed in the endogenous fluorescence spectra. It indicated that the exposure of hydrophobic groups in α-La/β-Lg increased, and the endogenous fluorescence was quenched. Synchronous fluorescence results showed that Trp fluorescence intensity decreased more significantly than that of Tyr, and more powerful interactions between monomeric proteins and nanoliposomes occurred in the regions around Trp residues. CD spectra showed an increase of β-sheet secondary structures of α-La and β-Lg in content at the cost of a decrease in α-helix and random coil in the two monomeric proteins after complexation. FTIR results indicated that the secondary structures of monomeric proteins altered, and the main interaction forces were hydrogen bond and hydrophobic forces. Surface hydrophobicity and free sulfhydryl content of monomeric proteins enhanced after complexation with nanoliposomes. Molecular docking theoretically demonstrated that the main interaction forces between nanoliposomes and monomeric proteins were hydrogen bond and hydrophobic forces. The interaction between nanoliposomes and α-La was more strong than that between nanoliposomes and β-Lg. The natural properties, such as amino acid composition, advanced structure and surface hydrophobicity, could play a critical role in the interaction between nanoliposomes and monomeric proteins. These findings could deepen the understanding of the interaction mechanisms between nanoliposomes and whey proteins.

Aggregation and deaggregation: The effect of high-pressure homogenization cycles on myofibrillar proteins aqueous solution

Myofibrillar proteins (MPs) have not been fully used for a long time due to its poor solubility in low ionic strength solutions. The study explored the effect of high pressure homogenization (HPH) cycles under two pressures on the solubility of MPs. The MPs solubility increased with HPH cycles (p < 0.05), the results of turbidity, appearance, droplet size indicated that the increase of solubility was due to MPs depolymerization, excessive HPH cycles (25k psi for 11 cycles) would lead to protein re-aggregation but does not affect solubility (p>0.05). SDS-PAGE suggested that myosin formed soluble polymers with different molecular weights through disulfide bonds during HPH cycles, the polymer consisted of myosin subunits of different molecular weights. Endogenous fluorescence spectra, intermolecular chemical forces, isoelectric point analysis and free amino acids (FAAs) indicated that the dissolution of polymers in low ionic strength media was dominated by polar environment and intermolecular steric hindrance, but not to FAAs.

Structural characteristics and foaming properties of ovalbumin - Caffeic acid complex

In this study, we investigated the effects of different caffeic acid (CA) concentrations on the ovalbumin structure and foaming properties. When the concentration of CA was 0.18 mg/mL, the surface hydrophobicity of ovalbumin decreased from 705.37 to 542.79, the sulfhydryl content decreased from 4.15 μmol/g to 2.26 μmol/g, and the foaming ability and stability increased by 72% and 71%, respectively. We observed that hydrophobic interactions represented the main binding force between CA and ovalbumin. Using circular dichroism spectroscopy (α-Helix increased from 7.2% to 13.9%) and endogenous fluorescence spectra (Reduction of fluorescence intensity and redshift), it showed that CA affected the secondary and tertiary ovalbumin structure, thus increasing the flexible structure. The increase in particle size Increased from 10.26 nm to 65.97 nm indicated that CA acted as a crosslinking agent between the ovalbumin molecules and increased the viscosity of the system through hydrophobic interactions. Although the increase in ovalbumin aggregation and the decrease in hydrophobicity were not conducive to the foaming properties of ovalbumin solutions, the increase in solubility, absolute potential, and flexible molecular structure contributed to the improvement of the foaming properties. All results showed that CA could improve the foaming properties of ovalbumin, a potential food-grade foaming agent.

Optical Biopsy of the Upper GI Tract Using Fluorescence Lifetime and Spectra.

Screening and surveillance for gastrointestinal (GI) cancers by endoscope guided biopsy is invasive, time consuming, and has the potential for sampling error. Tissue endogenous fluorescence spectra contain biochemical and physiological information, which may enable real-time, objective diagnosis. We first briefly reviewed optical biopsy modalities for GI cancer diagnosis with a focus on fluorescence-based techniques. In an ex vivo pilot clinical study, we measured fluorescence spectra and lifetime on fresh biopsy specimens obtained during routine upper GI screening procedures. Our results demonstrated the feasibility of rapid acquisition of time-resolved fluorescence (TRF) spectra from fresh GI mucosal specimens. We also identified spectroscopic signatures that can differentiate between normal mucosal samples obtained from the esophagus, stomach, and duodenum.

Endogenous Fluorescence Dissimilarity Assessment of Four Potential Biomarkers of Early Liver Fibrosis by Preservation Media Effect.

Build-up of extracellular matrix in liver fibrosis results in changes on endogenous molecules expression that may be studied through the fluorescence characterization of ex vivo liver samples. To the best of our knowledge, no investigations have provided in-depth evidence and discussion on the changes of the endogenous fluorescence in ex vivo tissue due to the effects of the preservation media. In this work, we contrast and analyze the endogenous fluorescence from tryptophan, vitamin A, hydroxyproline and elastin cross-links potential biomarkers of the liver fibrosis, in in vivo measurements and liver samples preserved on formaldehyde, and two standard preservation media. As it is known, chemical changes in tissue, caused by formaldehyde fixation, alter the endogenous fluorescence spectra. We propose the use of phosphate-buffered saline (PBS), and Iscove's Modified Dulbecco's Medium (IMDM) to elude the fluorescence changes. PBS and IMDM showed to maintain the endogenous fluorescence characteristics similar to in vivo conditions. The results of this work point the way for a more reliable assessment of endogenous fluorescence in ex vivo hepatic studies.

Study of Methionine Choline Deficient Diet-Induced Steatosis in Mice Using Endogenous Fluorescence Spectroscopy.

Non-alcoholic fatty liver disease is a highly prevalent condition worldwide that increases the risk to develop liver fibrosis, cirrhosis, and hepatocellular carcinoma. Thus, it is imperative to develop novel diagnostic tools that together with liver biopsy help to differentiate mild and advanced degrees of steatosis. Ex-vivo liver samples were collected from mice fed a methionine-choline deficient diet for two or eight weeks, and from a control group. The degree of hepatic steatosis was histologically evaluated, and fat content was assessed by Oil-Red O staining. On the other hand, fluorescence spectroscopy was used for the assessment of the steatosis progression. Fluorescence spectra were recorded at excitation wavelengths of 330, 365, 385, 405, and 415 nm by establishing surface contact of the fiber optic probe with the liver specimens. A multi-variate statistical approach based on principal component analysis followed by quadratic discriminant analysis was applied to spectral data to obtain classifiers able to distinguish mild and moderate stages of steatosis at the different excitation wavelengths. Receiver Operating Characteristic (ROC) curves were computed to compare classifier’s performances for each one of the five excitation wavelengths and steatosis stages. Optimal sensitivity and specificity were calculated from the corresponding ROC curves using the Youden index. Intensity in the endogenous fluorescence spectra at the given wavelengths progressively increased according to the time of exposure to diet. The area under the curve of the spectra was able to discriminate control liver samples from those with steatosis and differentiate among the time of exposure to the diet for most of the used excitation wavelengths. High specificities and sensitivities were obtained for every case; however, fluorescence spectra obtained by exciting with 405 nm yielded the best results distinguishing between the mentioned classes with a total classification error of 1.5% and optimal sensitivities and specificities better than 98.6% and 99.3%, respectively.

Optical diagnosis approach for the early detection of tissue transformation in DMBA induced oral carcinogenesis using fluorescence spectroscopy coupled with multivariate analysis

Autofluorescence spectroscopy is a powerful non-invasive diagnostic tool to detect various cancers in real time based on the emissions of endogenous fluorophores. The goal of this study is to estimate the concentration of endogenous fluorophores using autofluorescence spectroscopy in the discrimination of control and DMBA-induced different transformation lesions such as hyperplasia, dysplasia and well differentiated squamous cell carcinoma (WDSCC) tissues. Significant differences in the autofluorescence spectral signatures have been noticed at 410nm excitation wavelength. In the emission spectrum, the endogenous porphyrin (PpIX) emissions was elevated at ∼630nm, ∼665nm and ∼700nm during different transformation lesions compared to control tissues. However, the contribution of the 700-nm peak is substantial, particularly in WDSCC tissues, whereas in dysplastic lesions a broadening of only the 693-nm peak is seen, showing higher garnering of PpIX in WDSCC tissues. The results indicated the intensity of the porphyrin emission increased with the progress of the lesions and it can be exposed by endogenous fluorescence spectra analysis. PC-LDA yields overall classification efficiency 81%. This exploratory work further demonstrates that fluorescence spectroscopy in conjunction with PC-LDA has potential for improving discrimination of control from neoplastic oral tissues.

Optical spectroscopy detects histological hallmarks of pancreatic cancer

An empirical model was developed to interpret differences in the experimentally measured reflectance and fluorescence spectra of freshly excised human pancreatic tissues: normal, adenocarcinoma, and pancreatitis (inflammation). The model provided the first quantitative links between spectroscopic measurements and histological characteristics in the human pancreas. The reflectance model enabled the first (to our knowledge) extraction of wavelength resolved absorption and reduced scattering coefficients for normal and diseased human pancreatic tissues. The fluorescence model employed reflectance information to extract attenuation free "intrinsic" endogenous fluorescence spectra from normal pancreatic tissue, pancreatic adenocarcinoma, and pancreatitis. The method developed is simple, intuitive, and potentially useful for a range of applications in optical tissue diagnostics. This approach is potentially applicable to in vivo studies, because it can account for the absorptive effects of blood in tissues.

Biochemical characterization of exoribonuclease encoded by SARS coronavirus.

The nsp14 protein is an exoribonuclease that is encoded by severe acute respiratory syndrome coronavirus (SARS-CoV). We have cloned and expressed the nsp14 protein in Escherichia coli, and characterized the nature and the role(s) of the metal ions in the reaction chemistry. The purified recombinant nsp14 protein digested a 5'-labeled RNA molecule, but failed to digest the RNA substrate that is modified with fluorescein group at the 3'-hydroxyl group, suggesting a 3'-to-5' exoribonuclease activity. The exoribonuclease activity requires Mg2+ as a cofactor. Isothermal titration calorimetry (ITC) analysis indicated a two-metal binding mode for divalent cations by nsp14. Endogenous tryptophan fluorescence and circular dichroism (CD) spectra measurements showed that there was a structural change of nsp14 when binding with metal ions. We propose that the conformational change induced by metal ions may be a prerequisite for catalytic activity by correctly positioning the side chains of the residues located in the active site of the enzyme.

Evaluation of in vivo endoscopic autofluorescence spectroscopy in gastric cancer

Background The aim of this study was to evaluate light-induced autofluorescence spectroscopy for the in vivo diagnosis of gastric cancer. Methods A total of 344 endogenous fluorescence spectra were obtained from normal (164) and cancerous gastric mucosa (180) in 15 patients with pure adenocarcinoma and in 16 patients with gastric cancer containing signet-ring cells. A special light source capable of delivering either white or violet-blue light for the excitation of tissue autofluorescence via the endoscope was used. Endogenous fluorescence spectra emitted by the tissue were collected with a fiberoptic probe and analyzed with a spectrograph. Results Gastric adenocarcinoma exhibits specific changes in the emitted fluorescence spectra as compared with normal gastric mucosa. By algorithmic classification of the spectra, a sensitivity of 84%, specificity of 87%, a likelihood ratio for a positive test of 6.5 and for a negative test of 0.18 were obtained for the diagnosis of pure adenocarcinoma of the stomach. However, gastric cancer with signet-ring cells exhibits great variation in emitted autofluorescence spectra as compared with normal mucosa. The sensitivity for the diagnosis of all carcinomas containing signet-ring cells was 55%, specificity 85%, the likelihood ratio for a positive test was 3.7 and for a negative test, 0.53. The diagnostic value decreases with increasing numbers of signet-ring cells and tumor grade. Conclusions Light-induced autofluorescence spectroscopy is a new and promising bio-optical technique for the endoscopic in vivo diagnosis of gastric adenocarcinoma. The poor diagnostic accuracy for signet-ring cell carcinoma may be explained by the diffuse and frequent submucosal growth of this tumor and the presence of collagen fibers.

Endoscopic light-induced autofluorescence spectroscopy for the diagnosis of colorectal cancer and adenoma

To evaluate the new, bio-optical method of light-induced autofluorescence spectroscopy for the endoscopic in-vivo diagnosis of (pre)-cancerous lesions of the colorectum, 311 endogenous fluorescence spectra were obtained from normal, adenomatous and cancerous colorectal tissue in 11 patients with cancer, six patients with familial adenomatous polyposis, and six patients with multiple adenomatous polyps. A light source delivered either white or violet–blue light for excitation of tissue autofluorescence via a flexible endoscope. Endogenous fluorescence spectra emitted by the tissue were picked up with a fiberoptic probe and analysed with a spectrograph. Biopsies were taken for definitive classification of the spectra. Rectal cancer ( n=11) as well as adenomas with severe dysplasia ( n=19) showed specific differences between the emitted fluorescence spectra as compared with normal mucosa and hyperplastic polyps. Having applied a mathematical algorithm to the spectra, a sensitivity of 96% and a specificity of 93% were obtained for the diagnosis of rectal cancer. The equivalent values for the diagnosis of dysplastic ademomas were 98 and 89%, respectively. Light-induced autofluorescence spectroscopy is a new and promising bio-optical procedure for the endoscopic in-vivo diagnosis of colorectal cancer and dysplasia.

Endoscopic fluorescence spectroscopy in the upper GI tract for the detection of GI cancer: initial experience

OBJECTIVE: The aim of this study was to investigate autofluorescence spectroscopy using violet-blue excitation light for the in vivo diagnosis of GI cancer during routine endoscopy. METHODS: Fluorescence spectra were obtained from normal mucosa and cancerous lesions of the esophagus and stomach. The spectroscopic system used comprised a special light source capable of delivering either white or violet-blue light to induce autofluorescence of tissue via the endoscope. Endogenous fluorescence spectra emitted by the tissue were recorded with a fiberoptic probe and analyzed with a spectrographic detector system consisting of a polychromator with a photodiode array and an optical multichannel analyzer. The data of each spectrum were sampled within the range of 450–700 nm and stored in a personal computer. RESULTS: Esophageal squamous cell cancer, adenocarcinoma of the esophagus, and adenocarcinoma of the stomach show specific differences in the emitted fluorescence spectra compared with normal mucosa. CONCLUSIONS: Light-induced fluorescence spectroscopy might be a useful tool for the endoscopic in vivo detection of dysplasia and early carcinoma in the upper GI tract. Further trials are needed to test the validity of this new optical detection system.

Endoscopic fluorescence spectroscopy in the upper GI tract for the detection of GI cancer: initial experience.

The aim of this study was to investigate autofluorescence spectroscopy using violet-blue excitation light for the in vivo diagnosis of GI cancer during routine endoscopy. Fluorescence spectra were obtained from normal mucosa and cancerous lesions of the esophagus and stomach. The spectroscopic system used comprised a special light source capable of delivering either white or violet-blue light to induce autofluorescence of tissue via the endoscope. Endogenous fluorescence spectra emitted by the tissue were recorded with a fiberoptic probe and analyzed with a spectrographic detector system consisting of a polychromator with a photodiode array and an optical multichannel analyzer. The data of each spectrum were sampled within the range of 450-700 nm and stored in a personal computer. Esophageal squamous cell cancer, adenocarcinoma of the esophagus, and adenocarcinoma of the stomach show specific differences in the emitted fluorescence spectra compared with normal mucosa. Light-induced fluorescence spectroscopy might be a useful tool for the endoscopic in vivo detection of dysplasia and early carcinoma in the upper GI tract. Further trials are needed to test the validity of this new optical detection system.

Light-induced autofluorescence spectroscopy for the endoscopic detection of esophageal cancer

Background: Any innovative optical system that facilitates the early endoscopic detection of neoplastic change in the GI mucosa has the potential to greatly improve survival and quality of life for patients prone to have GI malignancies develop. The present article describes light-induced autofluorescence spectroscopy with violet-blue excitation light for in vivo diagnosis of cancerous tissue of the esophagus during routine endoscopy. Methods: One hundred twenty-nine endogenous fluorescence spectra were obtained from normal mucosa and malignant lesions in 9 patients with squamous cell cancer and 4 with adenocarcinoma of the esophagus. Following spectrographic measurements, biopsy specimens were obtained for definitive classification of the spectra. A special light source capable of delivering either white or violet-blue light for excitation of tissue autofluorescence by means of an endoscope was used. Endogenous fluorescence spectra emitted by tissues were detected with a fiberoptic probe and analyzed with a spectrograph. Results: Squamous cell cancer and adenocarcinoma of the esophagus exhibit specific changes in the emitted fluorescence spectra as compared with normal mucosa. Based on the results obtained in earlier studies, malignant and benign spectra were differentiated with the aid of a mathematical algorithm. By using this algorithm, a sensitivity of 97% and specificity of 95% were obtained for the diagnosis of esophageal carcinoma. Conclusions: Light-induced fluorescence spectroscopy is useful for the endoscopic detection of squamous cell cancer and adenocarcinoma of the esophagus. This spectroscopic study provides a basis for the design of a simplified autofluorescence imaging system for detection of esophageal neoplasms. (Gastrointest Endosc 2001;54:195-201.)

Light-induced autofluorescence spectroscopy for tissue diagnosis of GI lesions

Background: The present article describes light-induced autofluorescence spectroscopy using violet-blue excitation light for endoscopic in vivo measurements in the upper GI tract. The spectra of normal mucosa, cancer, and dysplastic lesions of the esophagus and stomach are presented and compared. Methods: Over 120 spectra were obtained in 11 patients of normal mucosa and malignant lesions in the esophagus and stomach during routine endoscopy. A special light source capable of delivering either white or violet-blue light was used for the excitation of tissue auto-fluorescence via the endoscope. Endogenous fluorescence spectra emitted by the tissue were collected with a fiberoptic probe and analyzed with a spectrograph. After spectrographic measurements biopsies were taken for definitive classification of histopathologic status. Results: As compared with normal mucosa, (pre) cancerous lesions were associated with special changes in the emitted fluorescence spectra.The spectrographic records were influenced by the intensity of the illumination and on the position of the probe (distance and angle). Conclusion: Fluorescence spectroscopy with a slightly modified conventional light source might be useful for the endoscopic detection of dysplasia and early-stage carcinoma in the upper GI tract. Prospective trials need to determine the sensitivity and specificity of this new method.