Front-face fluorescence spectroscopy coupled with chemometric tools for monitoring fish freshness stored under different refrigerated conditions

Front-face fluorescence spectroscopy was used as a rapid tool for assessing freshness of whiting fish (Merlangius merlangus) fillets stored at 4 ± 1 °C for up to 12 days under different conditions. Some physicochemical analysis [i.e., water content, pH, peroxide value, thiobarbituric acid reactive substances (TBARS)] were performed. With increasing storage time, the TBARS and pH values increased progressively in all whiting fish fillets, in particular for those exposed to light. Principal component analysis and factorial discriminant analysis applied separately to the tryptophan (excitation: 290 nm, emission: 305–450 nm) and nicotinamide adenine dinucleotide (NADH) (excitation: 340 nm, emission: 360–600 nm) spectra gave only a slight discrimination between the investigated whiting fish fillets. These results were improved when data from all the fluorescence spectra were analyzed jointly, since nearly three-quarters of samples were correctly classified. The best results were obtained by concatenating the fluorescence and physicochemical data sets, giving more than 90% of correct classification.     

High pressure processing extend the shelf life of fresh salmon,cod and mackerel

High pressure processing (HPP) is used on several types of seafood, though its potential for extending the shelf life of fresh fish has not been fully exploited. This study compared the effect of HPP (200 and 500 MPa, 120 s) on salmon, cod and mackerel. Immediately after processing, and during storage up to 26 days different analysis were carried out to evaluate the microbiological shelf life, oxidation, acid phosphatase level and pH of the different fish species during the storage period. For cod and mackerel, HPP at 500 MPa restrained the bacterial flora and it did not reach spoilage level, opposite to the salmon samples exposed to 500 MPa. Analysis of TBARS is often used as a measure of lipid oxidation. The TBARS-level was differently affected by pressure in salmon and cod. HPP at 200 MPa did not have any effect on the oxidation level in salmon during the storage period while this was observed for cod. The TBARS level in mackerel was high, independent of pressure treatment or not. Phosphatase activity in fish has been suggested to be related to freshness. The acid phosphatase (ACP) levels in control samples showed significant differences between salmon and cod. For salmon both control and samples treated at 200 MPa showed a decrease in ACP level at day 11 compared with day 0, whereas the HPP500 values were even throughout the study. This latter observation was also the case for cod treated at 500 MPa. This study have shown that HPP induce different levels of changes in various fish species.     

Preventive effect of tannic acid in combination with modified atmospheric packaging on the quality losses of the refrigerated ground beef

Chemical, microbiological and sensorial changes of ground beef treated without and with tannic acid (200 mg/kg) and stored in air and under modified atmosphere packaging (MAP) (80%O₂/20%CO₂ or 10%O₂/20%CO₂/70%N₂) were monitored during 15 days of storage at 4 °C. During the storage, samples treated with tannic acid and kept under all packaging conditions contained lower peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS) with coincidental lower non-haem iron content, compared with non-treated counterparts (P < 0.05). The sample packed in high oxygen MAP treated without and with tannic acid had the higher oxymyoglobin and a^* values and received the higher likeness scores for colour, whereas the samples stored in air and under low oxygen MAP showed the lower values, regardless of tannic acid treatment. After 15 days of storage, myosin heavy chain (MHC) and actin of all tannic acid treated samples underwent less degradation than those without tannic acid treatment for all packaging conditions. Degradation of MHC was more pronounced in samples kept under MAP with high oxygen. Psychrophilic bacterial count (PBC) of all tannic acid treated samples was lower, compared with that of non-treated samples (P < 0.05), irrespective of packaging condition. Therefore, tannic acid treated samples stored under high oxygen MAP could maintain the red colour and retard lipid oxidation and microbial growth of ground beef during refrigerated storage.     

Construction of an impedimetric immunosensor for label-free detecting carbofuran residual in agricultural and environmental samples

In this paper, a label-free electrochemical impedance immunosensor for the detection of carbofuran was prepared by immobilizing l-cysteine on a gold electrode. The carbofuran antibodies were immobilized on the electrode by the using glutaraldehyde as a cross linker. The stepwise assembly of the electrode surface was confirmed by atomic force microscope (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under the optimized conditions, a linear relationship between the resistance change and the logarithm value of carbofuran concentration was obtained in the carbofuran concentration range of 1.0 × 10⁻¹ – 1.0 × 10³ ng/mL, with a detection limit of 1.0 × 10⁻¹ ng/mL. The immunosensor performed good reproducibility and stability. Additionally, the proposed method can be applied for monitoring carbofuran residual in agricultural and environmental samples.     

Development of Quality Index Method (QIM) scheme for spiny lobster (Panulirus argus,Latreille, 1804) stored in ice

The objective of this study was to evaluate the freshness of spiny lobster (Panulirus argus) stored on ice up to 18 days. Changes during storage were observed with sensory evaluation (Quality Index Method – QIM), pH, total volatile basic nitrogen (TVB-N), trimethylamine nitrogen (TMA-N), and microbiological analyses (total mesophilic and psychrotrophic count). The maximum shelf life of spiny lobster stored in flake ice at 1 ± 0.2 °C was determined with loss of freshness (sensorial, physico-chemical and microbiological evaluations). High correlation R² = 0.922 between Quality Index (QI) and storage time at 1 °C was verified. QI ranged from zero (maximum freshness) to 15 (total loss of freshness) and reached the acceptable limit for consumption (QI = 9.54), which corresponds to a period of 10 days. The microbiological results showed an increase of psychrotrophic count along the storage time. TVB-N ranged from 5.23 to 20.31 mg 100 g⁻¹, TMA-N from 1.07 to 5.72 mg 100⁻¹ and pH from 6.91 to 7.19 in the first and 18th day of storage, respectively. It is suggested that spiny lobster has to be fresh and acceptable for consumption by cooling up to 10 days.     

Measurement of internal quality in chicken eggs using visible transmittance spectroscopy technology

The potential of the ultraviolet and visible (UV/VIS 200–800 nm) transmittance method to inspect the internal quality (freshness) of intact chicken egg was investigated. The nondestructive measurement optical models for egg quality were also studied. Three hundred and fifty chicken egg samples were used for measuring its freshness and spectral collection during egg storage time. Two correlation models between Haugh unit and the storage time, the yolk coefficient and the storage time were developed with the correlation coefficients of 0.994, 0.987, respectively. A relationship between the intact egg transmittance and the storage time was also developed with the correlation coefficients of 0.935 at the sensitive spectral wavelength of 465 nm. It was concluded that: the nondestructive inspection of egg freshness by transmittance properties is feasible in the range of 400–600 nm, while it is impossible to inspect egg freshness in the range of 200–400 nm due to the low transmittance.     

On-package dual sensors label based on pH indicators for real-time monitoring of beef freshness

On-package dual sensors label has been constructed based on two pH indicators, and it has been applied to monitor the beef freshness. The two pH indicators used are methyl red (MR) and bromo cresol purple (BCP). The beef decay could be detected clearly and easily by the dual color indicators, where the MR change from red to yellow, while the BCP change from yellow to purple. The label responses accurately to the beef freshness, in term of its pH change due to the deterioration as shown by both color change at room and chiller temperatures. Similarly with the other parameters, such as the total volatile basic amine (TVBN), total viable count (TVC) and sensory evaluation. These levels were reached at 8 h and 7 days as the threshold of spoilage at room and chiller temperature respectively. Therefore, the label can be used as a simple and practical indicator for freshness monitoring of packaged beef.     

Changes in microbiological,physicochemical and muscle proteins of post mortem large yellow croaker (Pseudosciaena crocea)

This study was devoted to the identification of changes in microbiological, physicochemical and proteins which could be used as freshness indicators in large yellow croaker. The parameters that proved to be most sensitive to variations over storage time were total viable count, Shewanella putrefacents, Photobacterium phosphoreum, TVB-N, PV and K value. They might therefore be considered as good indicators for evaluating spoilage of large yellow croaker during refrigerated storage for 20 days. The proteins including MHC, actin, tropomyosin, protein bands of 14 ～ 15 kDa, 32 ～ 33 kDa, 35 ～ 36 kDa and 41 ～ 42 kDa could be used as the potential freshness markers of large yellow croaker. The results of these analyses indicated optimal quality for large yellow croaker stored under these conditions and established a shelf-life of 12 days.     

Protein changes in post mortem large yellow croaker (Pseudosciaena crocea) monitored by SDS-PAGE and proteome analysis

This study was devoted to the identification of proteins and specific peptides which could be used as indicators of freshness and quality in fish. The post mortem evolution of protein patterns in large yellow croaker muscle was monitored by SDS-PAGE and two-dimensional electrophoresis (2-DE) after cold storage for 0, 5, 10, 15, 20, 25 days. SDS-electrophoresis revealed the gradual degradation of protein bands of 16–17 kDa, 22–23 kDa, 35–36 kDa, 76–78 kDa, as well as the increase of protein bands of 32–34 kDa and 67 kDa. The analysis of 2-DE showed that five spots of interest, including 3 structural proteins, namely myosin heavy chain (MHC), LIM domain-binding protein 3 (LDB3) and troponin T, as well as 2 metabolic proteins α-enolase and glyceraldehyde 3-phosphate dehydrogenase, changed progressively, which could be used as the potential freshness markers of large yellow croaker. Further research is required to evaluate their expression and post mortem evolution in another fish species.     

Effect of nutmeg (Myristica fragrans) essential oil on the oxidative and microbial stability of cooked sausage during refrigerated storage

This paper examines the oxidative and microbial stability of cooked sausages, produced with the addition of 10 ppm (NO1) and 20 ppm (NO2) nutmeg (Myristica fragrans) essential oil. Instrumental parameters of color (CIE L*, CIE a* and CIE b*), Thiobarbituric acid-reactive substance (TBARS) values, microbial profile and sensory properties of aroma have been determined on the 1st, 30th, 45th, and 60th day of storage. Addition of the nutmeg essential oil had no effect on the color of cooked sausages. At the end of the storage, NO2 sausages had the best oxidative and microbial stability. TBARS values of NO1 and NO2 sausages were 1.21 mg MDA/kg and 0.95 mg MDA/kg, respectively, and were significantly lower (P < 0.05) compared to control (1.53 mg MDA/kg). Total number of aerobic mesophilic bacteria was lowest in NO2 sausages (78.3 cfu/g) and highest in control (185 cfu/g). After 45 and 60 days of storage, sensory properties of aroma of NO1 (4.21; 3.92) and NO2 sausages (4.39, 4.28) were better compared to those in control (4.07, 3.25). Hence, the addition of nutmeg essential oil in amount of 20 ppm can be successfully applied in order to extend the shelf life of cooked sausages.     

Development of a novel sensitive molecularly imprinted polymer sensor based on electropolymerization of a microporous-metal-organic framework for tetracycline detection in honey

Electrochemical sensor for the detection of tetracycline, based on a gold electrode surface modified with a molecularly imprinted polymer microporous-metal-organic framework, is described. Imprinted gold nanoparticles composites are assembled on Au surfaces by the electropolymerization of p-aminothiophenol functionalized gold nanoparticles in the presence of the imprint molecule. The electrochemical sensor was characterized by linear sweep voltammetry in the presence of hexacyanoferrate/hexacyanoferrite as redox probe. In order to achieve optimal preconcentration, the influence of various parameters such as extraction and incubation times, washing and eluting solutions was evaluated. The sensor showed a linear range from 224 fM to 22.4 nM and a limit of detection of 0.22 fM. The proposed method was successfully applied to determine tetracycline in honey. The recoveries of tetracycline are in the range of 101.8 %−106.0 % with an RSD ≤8.3%.     

Effect of chitosan–caraway coating on lipid oxidation of traditional dry fermented sausage

Dry fermented sausage (Petrovská klobása) was coated with chitosan–caraway film. Effect of coating on fatty acid profile, lipid oxidation and sensory property of odor and taste were investigated during five months storage.At the end of storage period, sum of unsaturated and polyunsaturated fatty acids was significantly higher (p < 0.05) in coated than in control sausage.Contents of propanal and pentanal were significantly higher in the control sausage, while the rest of aldehydes content (hexanal, heptanal and octanal) did not differ between control and coated sausage.In both coated and control sausage, TBARS values content increased after two months storage and then remained unchanged until the end of storage period. Between examinated groups of sausages no significant difference was observed (p > 0.05).After two months of storage, sensory property of odor and taste did not differ between examinated groups of sausages, but at the end of storage period this value was significantly higher for coated sausage.Chitosan–caraway coated sausage showed lower intensity of lipid oxidative changes and better sensory properties for odor and taste at the end of five months storage in comparison to control.     

Inhibition of Staphylococcus aureus on beef by nisin-containing modified alginate films and beads

Nisin, a bacteriocin, was immobilized into palmitoylated alginate-based films or in activated alginate beads. Sterile beef muscle slices or ground beef were inoculated with Staphylococcus aureus at a level of 10⁴ CFU/g. Sliced beef was then coated with palmitoylated alginate-based films containing 0, 500 or 1000 IU/mL of nisin. Also, ground beef was mixed with 0, 500 or 1000 IU/mL of nisin covalently linked to activated alginate beads in order to evaluate the effect of nisin concentration on S. aureus level. The content of S. aureus in beef was determined during storage at 4 °C. Results demonstrated that after 7 days of storage, a reduction of 0.91 and 1.86 log CFU/cm² was observed on sliced beef covered with film containing 500 or 1000 IU/mL of nisin, respectively. After 14 days of storage, when nisin solution (500 or 1000 IU/g) was mixed with ground beef, 2.2 and 2.81 log CFU/g reductions of S. aureus counts were respectively observed. However, when nisin (500 or 1000 IU/g) was linked into activated alginate beads, 1.77 and 1.93 log CFU/g reductions of S. aureus counts were respectively observed (P ⩽ 0.05). These results suggest that sterile, hydrophobic and biodegradable films or beads incorporating various amounts of nisin could be used efficiently to control the growth of pathogens or microorganisms responsible of spoilage at the surface of round beef or other meat products.     

Quality predictive models of grass carp (Ctenopharyngodon idellus) at different temperatures during storage

To study quality changes in cold chain circulation, kinetic models were developed to predict the freshness changes of grass carp at different temperatures during storage. Sensory assessment, total aerobic count (TAC), K value, total volatile basic nitrogen (TVB-N) and 2-Thiobarbituric acid (TBA) at ?3, 0, 3, 9 and 15 °C were accessed to investigate the relation between the freshness changes and temperature. The kinetic models of sensory assessment, TAC, K value, TVB-N and TBA with respect to storage time and temperature were developed based on Arrhenius equation. The high regression coefficients (R² > 0.9) indicated the acceptability of the first-order reaction and Arrhenius model for predicting the quality changes of grass carp. Activation energies (E_A) of sensory assessment, TAC, K value, TVB-N and TBA are 114.38, 75.88, 57.11, 111.55, 63.09 kJ mol^?1, and corresponding rate constants (k₀) are 2.97 × 10²⁰, 1.12 × 10¹³, 8.30 × 10⁹, 8.34 × 10¹⁹, 9.06 × 10¹⁰ respectively. Relative errors between predicted and observed freshness indictors values of TAC, K value and TVB-N are all within ±10%. Therefore the quality changes of grass carp can be predicted based on the prediction model of TAC, K value and TVB-N within ?3–15 °C.     

Development of a novel method for detecting the integrity of aseptic paperboard laminate packages containing aluminium foil

A method was developed to determine the integrity of aseptic paperboard laminate packages containing aluminium foil using the cyclic voltammetric method. The ability of the method to identify pinholes arising from cracks in the plastic inner layer was demonstrated. When a cyclic voltammetric method was applied, a peak current was observed when the voltage greater than 0.6 V due to the chemical reaction at the exposed aluminium layer. Moreover, in packages with penetrating pinholes, the pinholes formed an ion channel which allowed ions to flow out of the package. This study demonstrates that cyclic voltammetry is applicable to distinguish between the defects of aseptic paperboard laminate packages containing aluminium foil.     

Effect of high pressure treatments on smoked cod quality during refrigerated storage

The effect of high pressure (HP) treatments on microbiological, chemical, textural and sensory characteristics of vacuum-packaged cold-smoked cod refrigerated at 5 °C for 60 d was evaluated. HP at 400, 500 and 600 MPa for 5 and 10 min reduced microbial counts of smoked cod and delayed microbial growth during refrigerated storage. No differences in lipid oxidation estimated as thiobarbituric acid reactive substances (TBARS) were observed after pressurization and during refrigeration. Only tryptamine and spermine at very low levels were detected among biogenic amines in smoked cod. High pressure treatments induced a brighter appearance of smoked cod, with higher values of L∗ and b∗, whereas a∗ values decreased with pressurization. HP affected hardness and shear strength of smoked cod, with higher values after treatment, but differences with untreated smoked cod were attenuated during the storage period. No differences in overall appearance and odor of smoked cod were reported after sensory evaluation. The results obtained in the present work point to the usefulness of pressurization of smoked cod at 400 MPa for 10 min or 500 MPa for 5 min to obtain an acceptable product with extended shelf-life. HP might increase the safety and protect the product against possible pathogen contamination during processing.     

Highly sensitive electrochemical determination of sunset yellow in commercial food products based on CHIT/GO/MWCNTs/AuNPs/GCE

Sunset yellow (SY) belongs to the azo group, commonly used in food industry. Highly consumption of SY may lead toxicity and photogenic to human health. Herein, a simple and highly sensitive electrochemical sensor was developed based on the modified glassy carbon electrode (GCE) with graphene (GO), multiwall carbon nanotubes (MWCNTs), gold nanoparticles (AuNPs) and nanocomposite membrane of chitosan (CHIT) for quantifying the level of SY in commercial food products. The CHIT/GO/MWCNTs/AuNPs were coated onto the GCE surface and analysed by using differential pulse voltammetry (DPV). The surfaces of CHIT/GO/MWCNTs/AuNPs/GCE characteristics were observed under scanning electron microscopy and transmission electron microscope. Under optimal condition, the DPV method was sensitively detected with different concentrations of SY from 10 to 90 mg mL⁻¹. The limits of detection and quantification were obtained to be 0.032 mg mL⁻¹ and 0.096 mg mL⁻¹, respectively. The proposed method was successfully applied to quantify the amount of SY in candy, jelly and soft drinks with good recovery values from 98.11% to 104.03%. Hence, the proposed sensor shows a rapid and sensitive method, low cost and simple, which an appropriate for alternative technique use for the analysis of food colorants in commercial products.     

Application of disinfectant sprays after chilling to reduce the initial microbial load and extend the shelf-life of chilled chicken carcasses

The objective of this study was to evaluate the effects of various disinfectant sprays on initial microbial load and conduct a shelf-life study of chilled chicken carcasses. Chilled chicken carcass samples obtained after chilling were sprayed for 15 s in a purpose-built spray rig with sodium hypochlorite (SH, 50 & 100 mg/L), chlorine dioxide (CD, 50 & 100 mg/L), lactic acid (LA, 1 & 2%), acid electrolyzed oxidizing water (AEOW) and slightly acid electrolyzed oxidizing water (SAEOW). Untreated carcasses were used as the control. Back, leg and breast skin were removed from each carcass after treatment to determine the total viable counts (TVC) and total coliforms. Sprays of 2% LA, AEOW and SAEOW were the most effective treatments with reductions of 0.47–0.83 log CFU/cm² and 0.49–0.96 log MPN/cm² in TVC and total coliforms, respectively. Samples treated with AEOW and SAEOW had 2 days of microbial shelf-life extension compared to the controls, which exceeded the TVC limit of 7 log CFU/cm² at day 6. Even longer extension was obtained for the 2% LA treated samples. The total coliforms, pH and total volatile basic nitrogen (TVBN).TVBN values of the 2% LA, AEOW and SAEOW treated samples were significantly (P < 0.05) lower than those of the controls during storage. Predominantly, the TBARS values of the AEOW and SAEOW treated samples were not statistically different from those of the controls (P > 0.05); however, the 2% LA treatment accelerated lipid oxidization, manifested as the highest TBARS value (2.09 mg MDA/kg) at day 8. Conclusively, this study indicated that the application of AEOW and SAEOW sprays to chilled chicken carcasses after chilling can reduce initial microbial load and maintain quality attributes during refrigerated storage.     

Application of ozone sprays as a strategy to improve the microbial safety and quality of salmon fillets

Ozone research investigating the efficacy of spray application mechanisms for balancing microbial safety with chemical quality attributes of high lipid content fish is lacking. The objectives of this study were to investigate the influence of aqueous spray treatments of 1 mg/L and 1.5 mg/L ozone on the microbial and chemical quality indices of Atlantic salmon fillets inoculated with Listeria innocua as a surrogate species replacing the pathogen Listeria monocytogenes. In order to simulate industry processing parameters, number of passes under spray nozzles (1, 2, and 3) was also investigated.Listeria counts resulting from treatment with three passes of 1 mg/L ozone sprays were significantly lower (p ≤ 0.05) than non-ozonated controls on days 0, 3, 6, and 10 of refrigerated storage at 4 °C. At both ozone concentrations, Listeria counts were significantly influenced (p ≤ 0.05) by the number of passes under spray nozzles with increasing passes resulting in increasing reductions. The residual antimicrobial effectiveness of ozone at both concentrations against aerobic bacterial populations on treated samples was limited to <6 days storage at 4 °C. Lipid oxidation analyses indicate that ozone concentration did not significantly affect (p ≤ 0.05) TBARS but did influence headspace propanal with 1 mg/L ozone treatments yielding approximately 30% higher propanal values than spray treatments of 1.5 mg/L ozone. Both TBARS and propanal levels were significantly influenced (p ≤ 0.05) by storage time, yet the number of spray passes did not significantly affect either measure of lipid oxidation. Our results indicate that ozone sprays at concentrations up to 1.5 mg/L are effective in reducing initial counts of aerobic bacterial populations and in significantly reducing (p ≤ 0.05) counts of L. innocua without causing significant increases in lipid oxidation levels in farmed Atlantic salmon fillets during refrigerated storage at 4 °C.     

Detecting 5-morpholino-3-amino-2-oxazolidone residue in food with label-free electrochemical impedimetric immunosensor

This paper reported a novel label-free electrochemical impedimetric immunosensor for sensitive detection of metabolite of furaltadone, 5-morpholino-3-amino-2-oxazolidone (denoted as AMOZ), based on monoclonal antibody against AMOZ (denoted as AMOZ–McAb) immobilized on gold electrode modified with 1,4-benzenedithiol and gold nanoparticle self-assembled layers. The sensitive steps of surface modification have been characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The immunoreaction between AMOZ and AMOZ–McAb directly triggered a signal via electrochemical impedance spectroscopy measurement. Under the optimized conditions, the relative change in impedance was proportional to the logarithmic value of AMOZ concentrations in the range of 1.0 to 1.0 × 10⁶ ng/mL (r = 0.9991) with the detection limit of 1.0 ng/mL. The advantages of the immunosensor are exhibited in its high sensitivity, wide linear range and better stability. The proposed impedimetric immunosensor was successfully applied to the determination of AMOZ in animal derived food with excellent recoveries.