Detection of Triphenylmethane Drugs in Fish Muscle by Surface-Enhanced Raman Spectroscopy Coupled with Au-Ag Core-Shell Nanoparticles

Silver-coated gold bimetallic nanoparticles were synthesized and used as substrates for surface-enhanced Raman spectroscopy (SERS) in detecting prohibited triphenylmethane drugs (including crystal violet and malachite green) in fish muscle. The optical properties and physical properties of bimetallic nanospheres were characterized by UV-Vis spectroscopy and transmission electron microscopy. The optimal nanospheres selected had relatively uniform size (diameter: 33 ± 3 nm) with a silver layer coated on the surface of gold seed (diameter: 18 ± 2 nm). For both crystal violet and malachite green, characteristic SERS spectral features could be identified at concentration as low as 0.1 μg/L with these bimetallic nanospheres. Crystal violet and malachite green residues in fish muscle could also be detected at levels as low as 0.1 ng/g, which could meet the most restricted regulatory requirements for the limit of detection in terms of analytical methods for crystal violet or malachite green in fish muscle. This study provides a basis for applying SERS technology with bimetallic nanoparticles to the identification of trace amounts of prohibited substances in aquatic food products, and the methodology could be extended to analyses of other hazardous chemicals in complex food matrices like vegetables and meats

Effect of marination in gravy on the radio frequency and microwave processing properties of beef

Dielectric properties (the dielectric constant (ε′) and the dielectric loss factor (ε ″ )) and the penetration depth of raw eye of round beef Semitendinosus muscle, raw beef marinated in gravy, raw beef cooked in gravy, and gravy alone were determined as a function of the temperature (20–130 °C) and frequency (27–1,800 MHz). Both ε′ and ε ″ values increased as the temperature increased at low frequencies (27 and 40 MHz). At high frequencies (915 and 1,800 MHz), ε′ showed a 50 % decrease while ε″ increased nearly three fold with increasing temperature in the range from 20 to 130 °C. ε′ increased gradually while ε ″ increased five fold when the temperature increased from 20 to 130 °C. Both ε′ and ε ″ of all samples decreased with increase in frequency. Marinating the beef in gravy dramatically increased the ε ″ values, particularly at the lower frequencies. Power penetration depth of all samples decreased with increase temperature and frequency. These results are expected to provide useful data for modeling dielectric heating processes of marinated muscle food

Antimicrobial effect of diallyl sulphide on Campylobacter jejuni biofilms

Bacterial biofilms pose significant food safety risks because of their attachment to fomites and food surfaces, including fresh produce surfaces. The purpose of this study was to systematically investigate the activity of selected antimicrobials on Campylobacter jejuni biofilms. C. jejuni biofilms and planktonic cells were treated with ciprofloxacin, erythromycin and diallyl sulphide and examined using infrared and Raman spectroscopies coupled with imaging analysis. Diallyl sulphide eliminated planktonic cells and sessile cells in biofilms at a concentration that was at least 100-fold less than used for either ciprofloxacin or erythromycin on the basis of molarity. Distinct cell lysis was observed in diallyl sulphide-treated planktonic cells using immunoblot analysis and was confirmed by a rapid decrease in cellular ATP. Two phases of C. jejuni biofilm recalcitrance modes against ciprofloxacin and erythromycin were validated using vibrational spectroscopies: (i) an initial hindered adsorption into biofilm extracellular polymeric substance (EPS) and delivery of antibiotics to sessile cells within biofilms; and (ii) a different interaction between sessile cells in a biofilm compared with their planktonic counterparts. Diallyl sulphide destroyed the EPS structure of the C. jejuni biofilm, after which the sessile cells were killed in a similar manner as planktonic cells. Spectroscopic models can predict the survival of sessile cells within biofilms. Diallyl sulphide elicits strong antimicrobial activity against planktonic and sessile C. jejuni and may have applications for reducing the prevalence of this microbe in foods, biofilm reduction and, potentially, as an alternative chemotherapeutic agent for multidrug-resistant bacterial strains

Formation of free and protein-bound carboxymethyllysine and carboxyethyllysine in meats during commercial sterilization

The effect of commercial sterilization treatments on the levels of advanced glycation endproducts (AGEs) in meats was investigated. The amounts of both free and protein-bound N(ε)-carboxymethyllysine (CML) and N(ε)-carboxyethyllysine (CEL) in beef (rump, ribeye, short plate), pork (hind leg, tenderloin, belly), and chicken (chicken breasts, drumsticks) were determined using an HPLC-MS/MS method. Beef and pork had a small proportion (raw <15%; sterilized <8%) of free AGEs compared to the total AGEs, but raw chicken breasts had very high levels of free CEL (7.12±9.98 mg/kg; n=13) with large biological variation compared to pork (0.19±0.09 mg/kg; n=9) and beef (0.44±0.19 mg/kg; n=9). Commercial sterilization (121°C for 10 min) did not significantly affect the amounts of free CML or CEL, but led to about 0.6- to 3.6-fold increase of protein-bound CML and CEL. The amounts of protein and fat content in beef or pork had very little effect on the formation of protein-bound AGEs during sterilization process

Detection of Prohibited Fish Drugs Using Silver Nanowires as Substrate for Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering or surface-enhanced Raman spectroscopy (SERS) is a promising detection technology, and has captured increasing attention. Silver nanowires were synthesized using a rapid polyol method and optimized through adjustment of the molar ratio of poly(vinyl pyrrolidone) and silver nitrate in a glycerol system. Ultraviolet-visible spectrometry, X-ray diffraction, and transmission electron microscopy were used to characterize the silver nanowires. The optimal silver nanowires were used as a SERS substrate to detect prohibited fish drugs, including malachite green, crystal violet, furazolidone, and chloramphenicol. The SERS spectra of crystal violet could be clearly identified at concentrations as low as 0.01 ng/mL. The minimum detectable concentration for malachite green was 0.05 ng/mL, and for both furazolidone and chloramphenicol were 0.1 μg/mL. The results showed that the as-prepared Ag nanowires SERS substrate exhibits high sensitivity and activity

Examination of nanoparticle inactivation of Campylobacter jejuni biofilms using infrared and Raman spectroscopies

AIMS: To investigate inactivation effect and mechanism of zinc oxide nanoparticles (ZnO NPs) activity against Campylobacter jejuni biofilms. METHODS AND RESULTS: ZnO NPs with concentrations of 0, 0.6, 1.2 and 6 mmol l(−1) were employed in antimicrobial tests against C. jejuni planktonic cells and biofilms. C. jejuni sessile cells in biofilms were more resistant to a low concentration of ZnO NPs when compared to planktonic cells. The ZnO NPs penetrated the extracellular polymeric substance (EPS) without damage to the EPS and directly interacted with the sessile bacterial cells, as determined using infrared spectroscopy and scanning electron microscopy. Raman spectroscopy shows alterations in quinone structures and damage to nucleic acids following C. jejuni treatment with ZnO NPs. The mechanism of DNA damage is most likely due to the generation of reactive oxygen species (ROS). Spectroscopic based partial least squares regression (PLSR) models could predict the number of surviving sessile cell numbers within a bacterial biofilm (≥log 4 CFU, RMSEE <0.36) from Fourier transform infrared (FT-IR) spectral measurements. CONCLUSIONS: ZnO NPs were found to have antimicrobial activity against C. jejuni biofilms. ZnO NPs penetrated the biofilm EPS within 1 hr without damaging it and interacted directly with sessile cells in biofilms. Alterations in the DNA/RNA bases, which are due to the generation of ROS, appear to result in C. jejuni cell death. SIGNIFICANCE AND IMPACT OF THE STUDY: ZnO NPs may offer a realistic strategy to eliminate C. jejuni biofilms in the environment

Investigating antibacterial effects of garlic (Allium sativum) concentrate and garlic-derived organosulfur compounds on Campylobacter jejuni by using Fourier transform infrared spectroscopy, Raman spectroscopy, and electron microscopy

Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy were used to study the cell injury and inactivation of Campylobacter jejuni from exposure to antioxidants from garlic. C. jejuni was treated with various concentrations of garlic concentrate and garlic-derived organosulfur compounds in growth media and saline at 4, 22, and 35°C. The antimicrobial activities of the diallyl sulfides increased with the number of sulfur atoms (diallyl sulfide < diallyl disulfide < diallyl trisulfide). FT-IR spectroscopy confirmed that organosulfur compounds are responsible for the substantial antimicrobial activity of garlic, much greater than those of garlic phenolic compounds, as indicated by changes in the spectral features of proteins, lipids, and polysaccharides in the bacterial cell membranes. Confocal Raman microscopy (532-nm-gold-particle substrate) and Raman mapping of a single bacterium confirmed the intracellular uptake of sulfur and phenolic components. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to verify cell damage. Principal-component analysis (PCA), discriminant function analysis (DFA), and soft independent modeling of class analogs (SIMCA) were performed, and results were cross validated to differentiate bacteria based upon the degree of cell injury. Partial least-squares regression (PLSR) was employed to quantify and predict actual numbers of healthy and injured bacterial cells remaining following treatment. PLSR-based loading plots were investigated to further verify the changes in the cell membrane of C. jejuni treated with organosulfur compounds. We demonstrated that bacterial injury and inactivation could be accurately investigated by complementary infrared and Raman spectroscopies using a chemical-based, "whole-organism fingerprint" with the aid of chemometrics and electron microscopy