Juan José Rodríguez Herrera

Incidence of Staphylococcus aureus and analysis of associated bacterial communities on food industry surfaces.

ABSTRACT Biofilms are a common cause of food contamination with undesirable bacteria, such as pathogenic bacteria. Staphylococcus aureus is one of the major bacteria causing food-borne diseases in humans. A study designed to determine the presence of S. aureus on food contact surfaces in dairy, meat, and seafood environments and to identify coexisting microbiota has therefore been carried out. A total of 442 samples were collected, and the presence of S. aureus was confirmed in 6.1% of samples. Sixty-three S. aureus isolates were recovered and typed by random amplification of polymorphic DNA (RAPD). Profiles were clustered into four groups which were related to specific food environments. All isolates harbored some potential virulence factors such as enterotoxin production genes, biofilm formation-associated genes, antibiotic resistance, or lysogeny. PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprints of bacterial communities coexisting with S. aureus revealed the presence of bacteria either involved in food spoilage or of concern for food safety in all food environments. Food industry surfaces could thus be a reservoir for S. aureus forming complex communities with undesirable bacteria in multispecies biofilms. Uneven microbiological conditions were found in each food sector, which indicates the need to improve hygienic conditions in food processing facilities, particularly the removal of bacterial biofilms, to enhance the safety of food products.

Effect of modified atmosphere packaging on shelf-life of iced fresh hake slices

Shelf-life of hake slices (Merluccius merluccius) stored in the ice state (2 ± 1°C) under modified atmosphere packaging (MAP) conditions was determined by measurements of pH, total volatile bases (TVB) and trimethylamine (TMA) content, mesophilic and psychrophilic bacterial counts, malonaldehyde content, exudation, protein functionality and sensorial analyses (colour and odour). The effect of different gas mixtures were evaluated : (1) 40% CO 2 , 50% N 2 , 10% O 2 ; (2) 60% CO 2 , 30% N 2 , 10% O 2 ; (3) 40% CO 2 , 30% N 2 , 30% O 2 ; (4) 60% CO 2 , 10% N 2 , 30% O 2 and (5) air (control). Important differences were found between MAP-stored and air-stored hake slices. Shelf-life of hake stored under MAP conditions was two-fold extended. Bacterial growth was inhibited, increases of pH, TMA and TVB were reduced, and alterations in protein functionality were delayed, and off-odours were not noted in MAP-stored hake slices after 21 days storage. Significant correlations were found between TMA content and total viable count (TVC), as well as between apparent viscosity and exudation. Hake slices could be stored in the ice state under MAP conditions for about three weeks without an important loss of quality. Fish freshness, handling practices and initial bacterial load have an important influence of shelf-life of hake.

Cryoprotection of frozen-stored actomyosin of farmed rainbow trout (Oncorhynchus mykiss) by some sugars and polyols

A study on the effectiveness of several cryoprotectants (polydextrose, lactitol, glucose syrup and a mixture of sucrose and sorbitol [1:1]) in preventing freeze-induced perturbations of fish proteins was carried out in in vitro systems of natural actomyosin of rainbow trout (Oncorhyncus mykiss) muscle. Adding these cryoprotectants prevented drastic decreases of ATPase activity, as well as a rapid exposure of hydrophobic and sulphydryl groups on the protein surface. Cryoprotectants therefore slowed down the kinetics of aggregation via intermolecular secondary forces and disulphide bonds, thus greatly reducing losses in solubility.

Effect of carbon dioxide atmosphere on microbial growth and quality of salmon slices

Salmon slices (Salmo salar) were packed under CO 2 and stored in a chill room at 2 ± 1°C for 3 weeks. A study was carried out on the effect of CO 2 atmosphere on bacterial growth as well as on chemical deterioration (pH, total volatile bases, (TVB), trimethylamine (TMA), lipid oxidation) and sensory features (exudation, raw fish odour, cooked fish flavour). Results were compared with a control stored in air. Salmon slices stored under CO 2 had a shelf-life of nearly twice as long as those in air, having lower bacterial counts, pH, TMA and TVB, as well as improved sensory features after 18 days at 2 ± 1°C. Exudation was not significantly different between control and CO 2 -stored samples after 10 days ice storage. Exudate values extended from 1 to 2% for CO 2 -stored samples after 10 and 20 days storage, respectively. Salmon slices can be stored under CO 2 at 2 ± 1°C for about 18 days, with no substantial loss of quality. Shelf-life can vary depending upon the state of fish, handling practices, initial bacterial load and storage temperature.

The use of water and ice with bactericide to prevent onboard and onshore spoilage of refrigerated megrim (Lepidorhombus whiffiagonis)

This study investigates the effectiveness of ozonated water and flake ice (combined Petfrost system) to increase the quality and stability of fresh megrim on fishing boats. The captured fish were washed, placed in plastic boxes, covered with flake ice and refrigerated at 2°C for up to 2-weeks onboard and, thereafter, for 11 days onshore. The experiments employed sterile, filtered and ozonated water at a concentration of 2ppm for washing the fish and making the flake ice. The results are compared with samples from a traditional treatment consisting of water and flake ice of marine origin. Fish were caught in four different hauls, which took 14, 12, 8 and 3 days in being landed. Subsequently, fish were stored for 1, 5, 7 and 11 days at 3°C. The different treatments were evaluated using sensory, microbiological and chemical techniques. Fish treated with ozone always showed the best quality. Megrim treated with ozone was still suitable for consumption after 14 days on board, and megrim stored for 12, 8 and 3 days on board could be stored for a further five days in the ice state once landed with an acceptable quality. In contrast, control fish were not suitable for consumption if stored for longer than three days on board.The results indicate that treatment with water and ice flakes made from sterile and ozonated water maintains the quality of fresh megrim onboard fishing boats and upon arrival onshore.

A DSC study on the effects of various maltodextrins and sucrose on protein changes in frozen-stored minced blue whiting muscle

A DSC heat denaturation study on the effects of various maltodextrins and sucrose on protein changes in minced blue whiting muscle during frozen storage at -10 and -20 degrees C was carried out. All maltodextrins slowed down the decreases in the denaturation enthalpies (deltaHd) ascribed to myosin and actin, making evident a noticeable effectiveness against protein denaturation, especially at -20 degrees C. Sucrose was as effective as maltodextrins at -20 degrees C, but was the least effective treatment at -10 degrees C. Significant correlations between both deltaHds and either protein solubility or formaldehyde production were found at each storage temperature. A low protein sensitivity to the small amounts of formaldehyde produced during the first weeks of storage and errors associated with the determination of enthalpies led to poorer correlations at -20 degrees C. Maximum denaturation temperatures (Tmax) correlated with protein solubility only at -20 degrees C. No clear relationship between either Tmax and the effectiveness of cryostabilisation was found, as Tmax also depends on the effectiveness of the treatments against the thermal denaturation of proteins.

A kinetic study on formaldehyde production in cryostabilized water-soluble fish muscle extracts

Abstract Formaldehyde (FA) production in water-soluble fish extracts containing maltodextrins depends on the specific diffusion and freeze-concentration of reactants in the unfrozen water (UFW) phase. A WLF model did not describe the kinetics of FA production when reaction rate was used as the output variable. Methodological limitations in determining T g and C g restricted the use of this equation. The kinetics of FA production were alternatively defined by an exponential model, which, however, would not apply near the freezing point as it does not consider the inflection due to dilution of reactants. Limitations in determining the freeze-concentration of reactants in the UFW phase also prevented the study of whether FA production followed Arrhenius kinetics. However, the use of reaction rate constants for the hydrolysis of nitrophenyl taking place under diffusion-limiting conditions [data from Champion, D., Blond, G., & Simatos, D. (1997) Reaction rates at subzero, temperatures in frozen sucrose solutions: a diffusion-controlled reaction. Cryo-Letters , 18, 251–260] showed that it apparently followed an Arrhenius behavior in the frozen state.

A new and efficient method to obtain benzalkonium chloride adapted cells of Listeria monocytogenes

A new method to obtain benzalkonium chloride (BAC) adapted L. monocytogenes cells was developed. A factorial design was used to assess the effects of the inoculum size and BAC concentration on the adaptation (measured in terms of lethal dose 50 -LD50-) of 6 strains of Listeria monocytogenes after only one exposure. The proposed method could be applied successfully in the L. monocytogenes strains with higher adaptive capacity to BAC. In those cases, a significant empirical equation was obtained showing a positive effect of the inoculum size and a positive interaction between the effects of BAC and inoculum size on the level of adaptation achieved. However, a slight negative effect of BAC, due to the biocide, was also significant. The proposed method improves the classical method based on successive stationary phase cultures in sublethal BAC concentrations because it is less time-consuming and more effective. For the laboratory strain L. monocytogenes 5873, by applying the new procedure it was possible to increase BAC-adaptation 3.69-fold in only 33 h, whereas using the classical procedure 2.61-fold of increase was reached after 5 days. Moreover, with the new method, the maximum level of adaptation was determined for all the strains reaching surprisingly almost the same concentration of BAC (mg/l) for 5 out 6 strains. Thus, a good reference for establishing the effective concentrations of biocides to ensure the maximum level of adaptation was also determined.

Effect of the addition of maltodextrins and sucrose on the ice-melting onset of minced fish muscle

The effects of maltodextrins of various dextrose equivalents (DE) and sucrose added at several proportions on the ice-melting onset temperature (Tm′) of minced fish muscle were studied by differential scanning calorimetry. At high concentrations (200–600 g kg−1), annealing was needed to achieve maximum freeze concentration. Optimum annealing was found to occur at relatively high temperatures, this fact being accounted for in terms of the role of cell membranes as physical barriers to freezing. Maltodextrins increased Tm′ in comparison with an untreated control, but, conversely, sucrose reduced it. The lower the DE, the higher was the increase. The water-compatible fish muscle solutes had a significant effect on Tm′. Accordingly, a linear relationship was found between the amount of cryostabiliser added and Tm′ at low concentrations (up to 200 g kg−1), but it became non-linear and reached a saturation asymptote at higher concentrations. © 2000 Society of Chemical Industry

Changes in lipids of whole and minced rayfish (Raja clavata) muscle during frozen storage

ZusammenfassungDer Einfluß der Gefriertemperatur (−18 °C und −40 °C) und der Zugabe von Butylhydroxytoluene (BHT) auf die verschiedenen Lipoid-Klassen (Phospholipoide, Triacylglyceride, freie Fettsäuren, Sterole und Sterolester bzw. Sterolwachse und die Zusammensetzung der Fettsäuren in ganzem und zerkleinertem (8 und 12 mm) Rochenmuskel wurden nach einem Jahr Gefrierlagerung untersucht. — Der Phospholipoid-Anteil sank deutlich und der Anteil an freien Fettsäuren nahm deutlich zu bei beiden Gefriertemperaturen, besonders bei −18 °C. Deutliche Unterschiede bei beiden Lipoid-Typen wurden zwischen den zerkleinerten und den ganzen Proben gefunden, wobei sich die größten Unterschiede bei −18 °C zeigten. Ein signifikanter Anstieg der häufigsten Fettsäuren (22:6n-3 und 16:0) wurde nach einem Jahr Gefrierhaltung festgestellt, je niedriger die Gefriertemperatur, desto höher ihr Anteil. Der Anteil an polyungesättigten Fettsäuren nahm bei allen Proben deutlich zu, je niedriger die Temperatur, desto höher ihr Anteil. Unerhebliche Unterschiede wurden zwischen den auf 8 mm und 12 mm zerkleinerten Proben gefunden. In keinem der untersuchten Parameter zeigten sich signifikante Unterschiede bei Vorhandensein oder Nicht-Vorhandensein von BHT. Die Zerkleinerung beschleunigte die hydrolytischen und oxidativen Prozesse, die bei niedrigerer Gefriertemperatur langsamer waren, trotzdem wurden keine signifikanten Unterschiede zwischen den beiden Partikel-Größen festgestellt.AbstractThe effects of the storage temperature (−18 °C and −40 °C) and the addition of butylhydroxytoluene (BHT) on the different classes of lipids (phospholipids, triacylglycerides, free fatty acids, sterols and sterol esters plus waxes) and the fatty acid composition of minced (8 and 12 mm) and whole rayfish wing muscle stored for 1 year in the frozen state were studied.The phospholipid content decreased significantly and the free fatty acid content increased significantly at both storage temperatures, but more pronounced, at −18 °C. Significant differences were found between phospholipid and free fatty acid contents of the minced and the whole samples, which again were more pronounced at −18 °C. A significant increase of the major fatty acids (22∶: 6n-3 and 16:0) was observed after 1 year in the frozen state. Significant differences were also obtained between the samples stored at −18 °C and at −40 °C; the lower the storage temperature, the higher their content. The polyunsaturated fatty acid (PUFA) content increased significantly in all the samples. Significant differences were found between the samples stored at −18°C and at −40°C. The lower the temperature, the higher the PUFA content. Nonsignificant differences were observed between the 8-mm and the 12-mm minced samples. Non-significant differences were found between the samples stored in the presence and in the absence of BHT. Mincing hastened hydrolytic and oxidative processes, which were slowed down at the lower storage temperature. Nonetheless, nonsignificant differences were found between both particle sizes.