Non-Thermal Methods for Ensuring the Microbiological Quality and Safety of Seafood

A literature search and systematic review were conducted to present and discuss the most recent research studies for the past twenty years on the application of non-thermal methods for ensuring the microbiological safety and quality of fish and seafood. This review presents the principles and reveals the potential benefits of high hydrostatic pressure processing (HHP), ultrasounds (US), non-thermal atmospheric plasma (NTAP), pulsed electric fields (PEF), and electrolyzed water (EW) as alternative methods to conventional heat treatments. Some of these methods have already been adopted by the seafood industry, while others show promising results in inactivating microbial contaminants or spoilage bacteria from solid or liquid seafood products without affecting the biochemical or sensory quality. The main applications and mechanisms of action for each emerging technology are being discussed. Each of these technologies has a specific mode of microbial inactivation and a specific range of use. Thus, their knowledge is important to design a practical application plan focusing on producing safer, qualitative seafood products with added value following today’s consumers’ needs.

Melanosis and quality changes during refrigerated storage of Pacific white shrimp treated with Chamuang (Garcinia cowa Roxb.) leaf extract with the aid of pulsed electric field

Pacific white shrimp with prior pulsed electric field (PEF) treatment before soaking in Chamuang leaf extract (CLE) at different concentrations (0.5 and 1%) for 30 min were prepared. Sample pre-treated with PEF and soaked with 1% CLE (PEF-1 CLE) showed lower melanosis score than that with 1.25% sodium metabisulfite treatment, PEF treated sample or those soaked in CLE without prior PEF and the control during storage of 10 days (P < 0.05). PEF-1 CLE sample showed lower total volatile base content, peroxide value and thiobarbituric acid reactive substances but high sensory scores than others (P < 0.05). Lower increases in mesophile, psychrophile, Pseudomonas, Enterobacteriaceae and H₂S producing bacterial counts were obtained in PEF-1 CLE, compared to the control and other treated samples. The most abundant compounds from Chamuang leaf extract, including Chrysoeriol 6-C-glucoside-8-C-arabinopyranoside and veranisatin-C were found in PEF-1 CLE sample and were plausibly involved in keeping quality of shrimp.

Pulsed Electric Field Extraction and Antioxidant Activity Determination of Moringa oleifera Dry Leaves: A Comparative Study with Other Extraction Techniques

The scope of this work was to determine the possibility of the application of the pulsed electric field (PEF) technique to the production of extracts from Moringa oleifera plant material (freeze-dried leaves). Various PEF conditions (pulse duration—PD; and pulse interval—PI) were tested. A field strength of 7 kV/cm was used. The total phenols in the extracts were evaluated by the Folin–Ciocalteu method and the antioxidant activity was evaluated by the radical scavenging activity (DPPH•), ferric reducing antioxidant power (FRAP) and Rancimat methods. The results were compared with those of the extracts obtained using other extraction techniques, namely microwave-assisted and ultrasound-assisted extractions, simple boiling water extraction, and plain maceration with water (as the control). The highest extraction of total phenols was achieved by the PEF procedure using 40 min treatment at a PD of 20 msec and a PI of 100 μsec. Additionally, all methods for the determination of the antioxidant activity showed that the activity of the extracts was proportional to the total phenol content. Concerning the PEF procedure, a low pulse duration with a high pulse interval is proposed in order to achieve higher extraction efficiency.

Potential Applications of the Cyclic Peptide Enterocin AS-48 in the Preservation of Vegetable Foods and Beverages

Bacteriocins are antimicrobial peptides produced by bacteria. Among them, the enterococcal bacteriocin (enterocin) AS-48 stands for its peculiar characteristics and broad-spectrum antimicrobial activity. AS-48 belongs to the class of circular bacteriocins and has been studied in depth in several aspects: peptide structure, genetic determinants, and mode of action. Recently, a wealth of knowledge has accumulated on the antibacterial activity of this bacteriocin against foodborne pathogenic and spoilage bacteria in food systems, especially in vegetable foods and drinks. This work provides a general overview on the results from tests carried out with AS-48 in different vegetable food categories (such as fruit juices, ciders, sport and energy drinks, fresh fruits and vegetables, pre-cooked ready to eat foods, canned vegetables, and bakery products). Depending on the food substrate, the bacteriocin has been tested alone or as part of hurdle technology, in combination with physico-chemical treatments (such as mild heat treatments or high-intensity pulsed electric fields) and other antimicrobial substances (such as essential oils, phenolic compounds, and chemical preservatives). Since the work carried out on bacteriocins in preservation of vegetable foods and drinks is much more limited compared to meat and dairy products, the results reported for AS-48 may open new possibilities in the field of bacteriocin applications.

Effect of enterocin AS-48 in combination with high-intensity pulsed-electric field treatment against the spoilage bacterium Lactobacillus diolivorans in apple juice

Enterocin AS-48 was tested in apple juice against the cider-spoilage, exopolysaccharide-producing strain Lactobacillus diolivorans 29 in combination with high-intensity pulsed-electric field (HIPEF) treatment (35 kV/cm, 150 Hz, 4 micros and bipolar mode). A response surface methodology was applied to study the bactericidal effects of the combined treatment, with AS-48 concentration and HIPEF treatment time as process variables. At subinhibitory bacteriocin concentrations, microbial inactivation by the combined treatment increased as the bacteriocin concentration and the HIPEF treatment time increased (from 0.5 to 2.0 microg/ml and from 100 to 1000 micros, respectively). Highest inactivation (4.87 logs) was achieved by 1000 micros HIPEF treatment in combination with 2.0 microg/ml AS-48. While application of treatments separately did not protect juice from survivors during storage, survivors to the combined treatment were inactivated within the following 24 h of storage, and the treated samples remained free from detectable lactobacilli for at least 15 days at temperatures of 4 degrees C as well as 22 degrees C. The combined treatment could be useful for inactivation of exopolysaccharide-producing L. diolivorans in apple juice.

Comparative study of pulsed electric field and thermal processing of apple juice with particular consideration of juice quality and enzyme deactivation

As an alternative to thermal pasteurization, pulsed electric fields (PEF) were applied to apple juices on laboratory and pilot plant scale, investigating the effects on juice quality. PEF application still falls under the EU Novel Food Regulation. Consequently, extensive investigation of quality parameters is a prerequisite to prove substantial equivalence of juices resulting from the novel process and conventional production, respectively. Juice composition was not affected by PEF treatment. However, browning of the juices provided evidence of residual enzyme activities. On laboratory scale, complete deactivation of peroxidase (POD) and polyphenoloxidase (PPO) was achieved when PEF treatment and preheating of the juices to 60 degrees C were combined. Under these conditions, a synergistic effect of heat and PEF was observed. On pilot plant scale, maximum PPO deactivation of 48% was achieved when the juices were preheated to 40 degrees C and PEF-treated at 30 kV/cm (100 kJ/kg). Thus, minimally processed juices resulted from PEF processing, when applied without additional conventional thermal preservation. Since this product type was characterized by residual native enzyme activities and nondetectable levels of 5-hydroxymethylfurfural, also when preheating up to 40 degrees C was included, it ranged between fresh and pasteurized juices regarding consumers' expectation of freshness and shelf life. Consistent with comparable iron contents among all juice samples, no electrode corrosion was observed under the PEF conditions applied.

A test for measuring the effects of enzyme inactivation

In the single-enzyme, single-substrate reaction with non-mechanism-based enzyme inactivation, the formation of the product and inactivation of the enzyme occur independently. For this reaction, we show that the steady-state hypothesis is applicable even when degradation of the enzyme occurs. An equation for the rate of product formation has been derived and it shows Michaelis-Menten kinetics with an apparent Michaelis-Menten constant K(M)(app)=K(M)+K(delta) where K(delta) is the enzyme inactivation constant. Use of a Lineweaver-Burk plot yields values for K(M)(app), which can be used to estimate K(delta) and, consequently, the degree of enzyme inactivation in a particular experiment. We employ this methodology to estimate the inactivation constant for the arsenate reductase catalyzed production of arsenite with appreciable enzyme inactivation.

Modelling inactivation of Listeria monocytogenes by pulsed electric fields in media of different pH

A study of the effect of square-wave pulsed electric fields (PEF) on the inactivation of Listeria monocytogenes in McIlvaine buffer of different pH (3.5-7.0) was conducted. L. monocytoges was more PEF sensitive at higher electric field strengths (E) and in media of low pH. A treatment at 28 kV/cm for 400 mus that inactivated 1.5, 2.3 and 3.0 Log10 cycles at pH 7.0, 6.5 and 5.0 respectively destroyed almost 6.0 Log10 cycles at pH 3.5. The general shape of survival curves of L. monocytogenes PEF treated at different pH was convex/concave upwards. A mathematical model based on the Weibull distribution accurately described these survival curves. At each pH, the shape parameter (n value) did not depend on E. The relationship between n value of the Weibull model and the pH of the treatment medium was described by the Gompertz equation. A multiple linear regression model using three predictor variables (E, E2, pH2) related the Log10 of the scale paramenter (b value) of the Weibull model with E and pH of the treatment medium. A tertiary model developed using McIlvaine buffer as treatment medium predicted satisfactorily the inactivation of L. monocytogenes in apple juice.

Inactivation of Salmonella Typhimurium in orange juice containing antimicrobial agents by pulsed electric field

Combinations of different hurdles, including moderately high temperatures (<60 degrees C), antimicrobial compounds, and pulsed electric field (PEF) treatment, to reduce Salmonella in pasteurized and freshly squeezed orange juices (with and without pulp) were explored. Populations of Salmonella Typhimurium were found to decrease with an increase in pulse number and treatment temperature. At a field strength of 90 kV/cm, a pulse number of 20, and a temperature of 45 degrees C, PEF treatment did not have a notable effect on cell viability or injury. At and above 46 degrees C, however, cell death and injury were greatly increased. Salmonella numbers were reduced by 5.9 log cycles in freshly squeezed orange juice (without pulp) treated at 90 kV/cm, 50 pulses, and 55 degrees C. When PEF treatment was carried out in the presence of nisin (100 U/ml of orange juice), lysozyme (2,400 U/ml), or a mixture of nisin (27.5 U/ml) and lysozyme (690 U/ml), cell viability loss was increased by an additional 0.04 to 2.75 log cycles. The combination of nisin and lysozyme had a more pronounced bactericidal effect than did either nisin or lysozyme alone. An additional Salmonella count reduction of at least 1.37 log cycles was achieved when the two antimicrobial agents were used in combination. No significant difference (P > 0.05) in cell death was attained by lowering the pH value; only cell injury increased. Inactivation by PEF was significantly more extensive (P < 0.05) in pasteurized orange juice than in freshly squeezed orange juice under the same treatment conditions. This increase might be due to the effect of the chemical composition of the juices.

Nutritional improvement of plant foods by non-thermal processing

As a result of the increasing consumer demand for minimally-processed fresh-like food products with high sensory and nutritional qualities, there is a growing interest in non-thermal processes for food processing and preservation. Key advanced technologies such as high-pressure processing, pulsed electric fields, dense gases and ultrasound are being applied to develop gentle but targeted processes to further improve the quality and safety of processed foods. These technologies also offer the potential for improving existing processes as well as for developing new process options. Furthermore, by adding new process dimensions (such as hydrostatic pressure, electric fields, ultrasonics, supercritical CO2) to the conventional process variables of temperature and time, they facilitate enlargement of the availability of unit operations. These operations might be applied effectively in unique combination processes, or as subsequent processing tools in more-targeted and subsequently less-intensive processes for food preservation and modification than the currently-applied processes.