Effects of plasma-activated water on microbial growth and storage quality of fresh-cut apple

Fresh-cut ‘Fuji’ apples were immersed for 5 min in plasma-activated water (PAW) generated, by plasma generated with sinusoidal voltages at 7.0 kHz with amplitudes of 6 kV, 8 kV, and 10 kV, designated PAW-6, PAW-8, and PAW-10, respectively. The control group was soaked in distilled water for 5 min instead of PAW. The results indicated that the growth of bacteria, molds, and yeasts was inhibited by PAW treatments during storage at 4 ± 1 °C, especially the microbial inactivation with PAW-8, which was the most efficient. PAW-8 reduced the microbial counts by 1.05 log₁₀CFU g⁻¹, 0.64 log₁₀CFU g⁻¹, 1.04 log₁₀CFU g⁻¹ and 0.86 log₁₀CFU g⁻¹ for aerobic bacteria (aerobic plate counts), molds, yeasts and coliforms on day 12, respectively. In addition, the bacterial counts of fresh-cut apples treated with PAW were <5 log₁₀CFU g⁻¹, which did not exceed to the existing China Shanghai local standard (DB 31/2012–2013) during 12 days of storage. PAW treatments reduced superficial browning of fresh-cut apples without affecting their firmness and titratable acidity. In addition, no significant change was observed in antioxidant content and radical scavenging activity between the PAW-treated and control groups. It is suggested that PAW is a promising method for preservation of fresh-cut fruits and vegetables, which is usually beneficial to the quality maintenance of fresh-cut fruits and vegetables during storage.     

High hydrogen peroxide concentration-low exposure time of plasma-activated water (PAW): A novel approach for shelf-life extension of Asian sea bass (Lates calcarifer) steak

A new method for using plasma-activated water (PAW; 100 ppm H₂O₂) to improve the cold (4 °C) shelf-stability of Asian sea bass steaks (ASBS) was established. Soaking with PAW, created utilizing oxygen and argon, for 30–120 s successfully extended the shelf-life of ASBS by suppressing microbial growths below the permissible level (7 log CFU/g) for 25 days, whereas control reached the microbiological limit after 10 days (p < 0.05). PAW-treated samples had lower accumulation rates of total volatile base nitrogen (< 25 mg/100 g), trimethylamine (< 5 mg/100 g), and propanal (< 400 nmol/g) than control (p < 0.05). PAW improved lipid stability (TBARS <2 mg/kg) but promoted protein oxidation (protein carbonyl ~0.01–0.02 nmol/mg). Hardness and water holding capacity of PAW treatments were better preserved during storage than control as indicated by higher breaking force and lesser expressible moisture drip. Although metmyoglobin tended to stay stable during storage, all treatments' surface total color change tended to increase by 2–5 folds. Overall, argon-produced PAW with 100 ppm H₂O₂ and a short soaking time (30 s) seemed to be a promising method for protecting the quality and safety of ASBS.     

Efficacy optimization of plasma-activated water for food sanitization through two reactor design configurations

The chemistry, antimicrobial efficacy and energy consumption of plasma-activated water (PAW) was optimized by altering the discharge frequency, ground-electrode configuration, gas flow rate and initial water conductivity for two reactor configurations, i.e., air pin-to-liquid discharge and air plasma-bubble discharge in water. The ratio of NO₂⁻ and NO₃⁻ formation was altered to optimise the antimicrobial effects of PAW, tested against two Gram-negative bacteria. An initial solution conductivity of 0.2 S·m⁻¹ and 2000-Hz discharge frequency with the ground electrode positioned inside the pin reactor showed the highest antimicrobial effect resulting in a 3.99 ± 0.13-log₁₀ reduction within 300 s against Escherichia coli and 5.90 ± 0.24-log₁₀ reduction within 240 s for Salmonella Typhimurium. An excellent energy efficiency of reactive oxygen and nitrogen species (RONS) generation of 10.1 ± 0.1 g·kW⁻¹·h⁻¹ was achieved.Industrial relevancePlasma-activated water (PAW) is deemed as an eco-friendly alternative to chemical disinfection because its bactericidal activity is temporary. Optimizing the design and operation of PAW reactors to achieve high inactivation rates of more than 5-log₁₀ reductions, as demonstrated in this work, will support the industrial application of this technology and the scaleup at industrial level.     

Evaluation of pulsed electric field and minimal heat treatments for inactivation of pseudomonads and enhancement of milk shelf-life

Pulsed Electric Field (PEF) treatment of milk provides the opportunity to increase the shelf-life of fresh milk for distribution to distant markets. PEF treatments were evaluated in sterile (UHT) milk to determine the inactivation of added spoilage Pseudomonas isolates and the subsequent gains in microbial shelf-life (time taken to reach 10⁷ CFU mL^− 1). Little inactivation of Pseudomonas was achieved at 15 or 40 °C compared with 50 or 55 °C. The greatest inactivation (> 5 logs) was achieved by processing at 55 °C with 31 kV cm^− 1 (139.4 kJ L^− 1). Heat treatment at the application temperature without PEF treatment caused minimal inactivation of Pseudomonas (only 0.2 logs), demonstrating that the inactivation of the Pseudomonas was due to the PEF treatment rather than the heat applied to the milk. At added Pseudomonas levels of 10³ and 10⁵ CFU mL^− 1, the microbial shelf-life of PEF-treated milk was extended by at least 8 days at 4 °C compared with untreated milk. The total microbial shelf-life of the PEF-treated milk was 13 and 11 days for inoculation levels of 10³ and 10⁵ CFU mL^− 1 respectively. The results indicate that PEF treatment is useful for the reduction of pseudomonads, the major spoilage bacteria of milk.Industrial relevancePseudomonads are the major psychrotrophic spoilage microflora of refrigerated, stored HTST pasteurised milk. Long-life (UHT) products are an important component of milk sales in South-East Asia, but in recent years there has been an increasing demand for less processed milk products with extended shelf-life. The recent practice of shipping fresh bulk milk from Australia to South-East Asian countries has necessitated additional heat treatment prior to export and on arrival, to achieve the required shelf-life. Pulsed electric field treatment of HTST milk, applied alone or in combination with mild heat under optimised conditions, offers the opportunity of shelf-life extension, while limiting the reduction in quality attributes of milk associated with more severe additional heat treatments.     

Evaluating the effects of plasma-activated slightly acidic electrolyzed water on bacterial inactivation and quality attributes of Atlantic salmon fillets

In this study, an intervention non-thermal processing technology plasma-activated slightly acidic electrolyzed water (PASW) was developed to better preserve salmon fillets. Compared to the plasma-activated water (PAW) and slightly acidic electrolyzed water (SAEW), PASW treatment was found to be more effective in inactivating microorganisms. After PAW, SAEW, or PASW treatment for 120 s, the population of Shewanella putrefaciens (S. putrefaciens) was reduced by 2.04, 2.62 and 2.08 Log CFU/mL (P < 0.05) using plate counts, respectively. The test for the leakage of nucleic acids and protein in intracellular contents confirmed that PASW caused serious damage to the microbial cell structural integrity compared to that alone PAW or SAEW. Meanwhile, scanning electron microscopic observations also showed that PASW caused apparent bacterial structural changes. Besides, the PASW treatment did not alter color and textural properties of salmon fillets, and restrained lipid oxidation as compared to the control and SAEW treatments. In all, this study compared the bacterial inactivation mechanisms for PAW, SAEW, and PASW, and suggested that PASW was effective in inactivating S. putrefaciens of salmon fillets.Industrial relevancePlasma-activated slightly acidic electrolyzed water, an emerging technology in food processing, can be a potential green technology for the processing of aquatic food products. PASW treatment had higher disinfection efficacy than that of SAEW or PAW treatment alone, and no adverse effect on the quality of Atlantic salmon fillets. These results boost knowledge in the food preservation field, as well as the application of non-thermal processing in the food industry.     

Preservation effect of plasma-activated water (PAW) treatment on fresh walnut kernels

Fresh walnuts exhibit unique flavor and multiple biological activities, but they are highly perishable due to the lack of practical and cost-effective postharvest preservation technique. In this paper, the quality of fresh walnut kernels treated with deionized water, water containing ClO₂, and plasma-activated water (PAW) for 15 min were monitored during 4 °C storage. Results showed that 100-s PAW treatment reduced the total viable count by 1.15 log CFU/g immediately after treatment. The bactericidal and bacteriostatic effects of PAW was superior to 4 mg/L ClO₂. PAW-treated samples retained their flavor during 12d storage at 4 °C, while other samples generated odor at 6d. Moreover, PAW treatment could prevent nutritional loss, browning, and rancidity. The increases of peroxidase, polyphenol oxidase, and lipase activities were inhibited after PAW treatment. Hence, PAW treatment can be applied for the preservation of fresh walnut kernels due to its effect on microbial inhibition and quality maintenance.Industry relevanceNon-thermal plasma is an emerging non-thermal food processing technology due to its advantages of non-destructive, pollution-free, high efficiency and short treatment periods. In this study, plasma-activated water (PAW) was applied in the preservation of fresh walnut kernels, and inhibited flavor changes, nutritional loss, microbial growth, browning, and oxidation reaction. When approaching food preservation technologies, especially for heat-sensitive materials, PAW treatment as a novel technique appears to have far-reaching implications for increasing markets by antimicrobial properties, and avoiding the negative impacts on quality attributes.     

Preservation of salted,vacuum-packaged,refrigerated sea bream (Sparus aurata) fillets by irradiation: microbiological,chemical and sensory attributes

The effect of gamma irradiation (1 and 3 kGy) on the shelf-life of salted, vacuum-packaged sea bream (Sparus aurata) fillets stored under refrigeration was studied by monitoring the microbiological, chemical and organoleptic changes occurring in fish samples. Non-irradiated, salted, vacuum-packaged fish served as control samples. Irradiation affected populations of bacteria, namely, Pseudomonas spp., H₂S-producing bacteria, Brochothrix thermosphacta, Enterobacteriaceae and lactic acid bacteria. The effect was more pronounced at the higher dose (3 kGy) applied. Of the chemical indicators of spoilage, trimethylamine (TMA) values of non-irradiated, salted sea bream increased slowly to 8.87 mg N (100 g)⁻¹ flesh (whereas for irradiated, salted samples significantly lower values were obtained, reaching a final TMA value of 6.17 and 4.52 mg N (100 g)⁻¹ flesh at 1 and 3 kGy, respectively (day 42). Total volatile base nitrogen values increased slowly attaining a value of 60.52 mg N (100 g)⁻¹ for non-irradiated, salted sea bream during refrigerated storage whereas for irradiated fish, lower values of 48.13 and 37.21 mg N (100 g)⁻¹ muscle were recorded at 1 and 3 kGy, respectively (day 42). Thiobarbituric acid values for irradiated, salted sea bream samples were higher than respective non-irradiated (salted) fish, and increased slowly until day 28 of storage reaching final values of 1.01 (non-irradiated, salted), 2.15 (1 kGy) and 3.26 mg malonaldehyde kg⁻¹ flesh (3 kGy), respectively (day 42). Sensory evaluation (taste) showed a reasonably good correlation with bacterial populations. On the basis of sensorial evaluation, a shelf-life of 27–28 days was obtained for vacuum-packaged, salted sea bream irradiated at 1 or 3 kGy, compared to a shelf-life of 14–15 days for the non-irradiated, salted sample.     

Agar films containing green tea extract and probiotic bacteria for extending fish shelf-life

A bioactive film composed of agar, incorporating green tea extract and probiotic strains (Lactobacillus paracasei L26 and Bifidobacterium lactis B94) was applied on hake fillets in order to evaluate the effect of the films during 15 days of storage. Hake was previously inoculated with Shewanella putrefaciens and Photobacterium phosphoreum (10³–10⁴ CFU/g) to simulate a spoilage process. The green tea and/or probiotic film provoked a reduction, particularly of H₂S-producing bacteria counts and total viable bacteria throughout the storage period. The probiotic strains added to the film could pass to the fish producing an increment of lactic acid bacterial counts, even in the presence of green tea extract. The effect of the films also caused a decrease in the indexes of fish quality (total volatile basic nitrogen (TVB-N), trimethylamine nitrogen (TMA-N) and pH). The total viable counts, H₂S-producing microorganisms and TVB-N were maintained below the limits of acceptability during 15 days for the fillet covered with the green tea + probiotic film, compared to the rest of the samples. Films with green tea and probiotic were able to extend shelf-life of hake at least for a week and increase the beneficial lactic acid bacteria in fish.     

Effects of chilled storage on quality of vacuum packed meagre fillets

The aim of this study was to experimentally assess several quality indices of meagre Argyrosomus regius (Asso, 1801) fillets packed in air (AP) and vacuum (VP) stored chilled (+4 °C) for up to 13 days. Considering our experimental data on concentration of bacterial counts, shelf-life is estimated at ca. 6 days for AP fillets and an additional 3–5 days for VP meagre fillets. Total volatile basic nitrogen (TVB-N) and trimethylamine (TMA-N) did not reach the regulated limits (25–35 mg/100 g chilled fish). The models implemented in the software Seafood Spoilage and Safety Predictor predicted a relatively shorter shelf-life of 4.8–6.9 days for fish stored in air at +4 °C when compared to AP and VP fillets. Empirical data and the models implemented in the software were used to predict the shelf-life of fillets if packaged under different modified atmospheres (MAP). Chilled, MAP fillets are likely to have a longer shelf-life than AP or VP samples if equilibrium CO₂ concentration is substantially high.     

Production,characterization, microbial inhibition,and in vivo toxicity of cold atmospheric plasma activated water

Cold atmospheric plasma activated water (PAW) was produced at various Reactive Nitrogen Oxygen Species (RONS) concentrations. PAW was characterized and in vivo toxicological studies were conducted, using the zebrafish embryo acute toxicity test (OECD 236).Danio rerio (zebrafish), were raised in standard egg PAW of various RONS concentrations and their lethality was monitored. The thresholds for no lethality and simultaneously no obvious morphological phenotypes were determined as approximately 30 mg/L H₂O₂ concentration, while for NO₃⁻ concentration, the values were also correlated to the pH of the solution used. The pH-value of 3.85 was also a measurable threshold for the lethality of the embryos. Toxic and non-toxic PAW were used as medium to assess their inhibitory potential for Escherichia coli and Enterococcus faecium. The results indicated that PAW delayed the recovery time or even resulted in no growth of these microorganisms compared to control samples.     

Cinnamon and nisin in alginate-calcium coating maintain quality of fresh northern snakehead fish fillets

Cinnamon (Cinnamomum zeylanicum) and nisin in alginate-calcium coating were used to maintain quality of northern snakehead fish fillets at refrigeration temperature (4 ± 1 °C). Northern snakehead fish fillets were left untreated (CK), or were treated with alginate-calcium coating (Y0), alginate-calcium coating incorporating 10 μL mL⁻¹ cinnamon (Y1), alginate-calcium coating incorporating 2000 IU mL⁻¹ nisin and 150 μg mL⁻¹ ethylene diamine tetraacetic acid (EDTA) (Y2), or alginate-calcium coating incorporating 10 μL mL⁻¹ cinnamon and 2000 IU mL⁻¹ nisin and 150 μg mL⁻¹ EDTA (Y3). Y1 and Y3 had better effects on inhibiting bacterial growth and maintaining values of pH, total volatile base nitrogen (TVB-N) and thiobarbituric acid (TBA) of northern snakehead fish than CK, Y0 and Y2. Lightness (L*) values of fish fillets of all treatments were higher than CK. Cinnamon in alginate-calcium coating treatments could efficiently maintain quality of northern snakehead fish fillets during storage, but colors of fish fillets of Y1 and Y3 were evidently changed due to the color of cinnamon.     

Inhibition of enzymes and Pseudomonas tolaasii growth on Agaricus bisporus following treatment with surface dielectric barrier discharge plasma

In this study the applicability of cold plasma, produced by surface dielectric barrier discharge (SDBD), to inactivate Pseudomonas tolaasii (P.tolaasii), polyphenol oxidase (PPO) and peroxidase (POD) enzymes, as well as its impact on quality parameters such as, color, texture, pH and weight loss were evaluated. The study evidently shows that treating with combination of 30% hydrogen peroxide vapor)with flow rate of 0.47 mL min⁻¹) and argon (H₂O₂ + Ar) for 180 s is capable of reducing the activity of PPO (0.17 U min⁻¹ g⁻¹ FW) and POD (0.21 U min⁻¹ g⁻¹ FW) and increasing the SOD enzyme (16.29 U g⁻¹ FW) in a 21-day storage period compared to control samples. This is while the quality characteristics of button mushroom are preserved during storage after such treatment.Industrial relevanceThis study provides information of A. bisporus storage during 21-day period after SDBD plasma treatment, which is rarely. Greater inactivation of P. tolaasii after 180 s treatment with combination of hydrogen peroxide vapor and air (H₂O₂ + air) was shown compared to control samples, but this treatment caused also slightly degradation of button mushroom color. A better reduction of PPO and POD enzyme activity as well as further increase of SOD enzyme activity was observed following treatment with 180 s of H₂O₂ + Ar gas in a 21-day storage period. This research work contributes to the understanding SDBD plasma induced effects on the shelf-life of button mushroom and could be a basis for a possible industrial implementation.     

Microbial ecology of Vietnamese Tra fish (Pangasius hypophthalmus) fillets during processing

There are numerous factors that can have an impact on the microbial ecology and quality of frozen Pangasius hypophthalmus fillets during processing in Vietnam. The presence of spoilage bacteria along the processing line can shorten the shelf-life of thawed frozen fish products. Therefore, the spoilage microbiota throughout the processing chain of two companies (BC: large scale factory, chlorine-based process, BW: large scale factory, water-based process and SC: small scale factory, chlorine-based process) was identified by culture-dependent techniques and 16S rRNA gene sequencing. The microbiological counts were observed to be insignificantly different (p > 0.05) between BC and BW. Surprisingly, chlorine treated fillets from the SC line were revealed to have significantly higher microbial counts than potable water treated fillets at BW line. This was determined to be a result of temperature abuse during processing at SC, with temperatures even greater than 10 °C being recorded from skinning onwards. On the contrary, the microbiota related to spoilage for BC and BW lines was determined by 16S rRNA gene sequencing to be more diverse than that on the SC line. A total of 174 isolates, 20 genera and 38 species were identified along the processing chains. The genera Aeromonas, Acinetobacter, Lactococcus and Enterococcus were prevalent at various processing steps on all the processing lines evaluated. A diverse range of isolates belonging to the Enterobacteriaceae such as Providencia, Shigella, Klebsiella, Enterobacter and Wautersiella were isolated from fillets sampled on the SC line whereas Serratia was only observed on fillets sampled on the BC and BW lines. The results can be used to improve Good Manufacturing Practices for processed Pangasius fillets and to select effective measures to prolong the shelf-life of thawed Vietnamese Pangasius fillets products.     

The impact of strawflower and mistletoe extract on quality properties of rainbow trout fillets

Many plants, including strawflower and mistletoe, contain antioxidants and antimicrobials, which can increase the shelf life of seafood. The main aim of this study was to investigate the effect of mistletoe and strawflower extracts at doses of 0.5% (w/v) on the sensory, chemical and microbiological properties of rainbow trout fillets during 27 days of storage at 2 ± 1 °C. The phenolic compounds in these plants have been studied, but their effects on food quality and storage properties have not been reported. We found that extract of mistletoe did not extend the shelf life of the fillets; however, the strawflower extract show high antimicrobial activity in fish fillets. The shelf life of rainbow trout was 20 days for the control and fish treated with mistletoe extract and 23 days for fish treated with strawflower extract. The antioxidant effect of extracts on fish fillets was weak, whereas strawflower extract had high antimicrobial effect. Peroxide value (PV) and thiobarbituric acid (TBA) values fluctuated during storage periods around main values below 14 meq O₂ kg^?1 and 0.6 MA kg^?1, respectively. Putrescine, cadaverine, spermine, spermidine, serotonin, tyramine and dopamine were main amine, whereas histamine accumulated at low levels (<2 mg per 100 g). Strawflower suppressed biogenic amine accumulation in fish fillets. At the limit of acceptability, total viable count (TVC), Enterobacteriaceae and lactic acid bacteria count remained below 7.6, 6.83 and 8.01 log CFU g^?1, respectively. The results of this study show that ethanol extracts of strawflower improve the shelf life of rainbow trout.     

Combination of vaporized ethyl pyruvate and non-thermal atmospheric pressure plasma for the inactivation of bacteria on lettuce surfaces

The effect of vaporized ethyl pyruvate (EP) and atmospheric pressure plasma (APP) treatments on the inactivation of total viable counts of bacteria on fresh lettuce leaves samples after treatment and during storage (1 and 3 days) at 6 and 25 °C was studied. For this purpose, freshly grown B. cereus and Escherichia coli were inoculated on the lettuce leaves prior to treatments. Combination of EP (at a concentration of around 10 μL dm⁻³) with APP was more effective on inactivation of bacteria when compared to EP and APP treatments separately, reducing the total viable counts nearly 5 CFU cm⁻² compared to control. The use of EP and APP together led to around 2.5 more log (CFU cm⁻²) reductions when compared to the sole use of EP and APP separately. B. cereus cells were almost three times more susceptible to APP treatment than E. coli. Growth inhibition increased after storing the treated samples at 25 °C by around 2.5 and 1.5 logs for E. coli and B. cereus, respectively, compared to 6 °C. APP treatment time (30 and 60 s) and storage time (1 and 3 days) did not significantly affect the inactivation levels. E. coli was more effectively inactivated after EP + O₂ treatment followed by storage at 25 °C. The highest level of inactivation was noted as nearly 5 log reductions. Slight differences in the peak intensities of FTIR spectra of treated lettuce samples were observed compared to control, indicating slight modifications on the chemical structure on the lettuce leaves.Industrial relevanceThe microbial load influences the quality, safety, and shelf-life of fresh produce such as lettuce. Current decontamination techniques may cause some unwanted effects such as odor, discoloration, and decreased nutritional value. This study shows that the use of the APP-EP hurdle represents a promising strategy to improve the decontamination efficiency and hence, enhance the shelf-life of freshly cut vegetables. The data obtained contribute to a better understanding of APP-EP-induced effects on the quality and shelf-life of fresh-cut lettuce and provide a scientific basis for industrial implementation.     

Comparison of air freezing,liquid immersion freezing and pressure shift freezing on freezing time and quality of snakehead (Channa Argus) fillets

The objective of this study was to investigate the freezing time and quality differences in Snakehead fillets frozen by pressure shift freezing (PSF), conventional air freezing (AF) and liquid immersion freezing (LIF) at −20 °C, −40 °C and − 60 °C, respectively. The results showed that liquid immersion freezing at −60 °C maintained the quality best, with a freezing time of 3.62 min and the cross sectional area of 209.11 um². Air freezing at −20 °C had the longest freezing time (184.58 min) and the largest cross sectional area (4470.79 um²), and lowest hardness and springiness of the fillets. Pressure shift freezing did not demonstrate the well established advantages of maintaining better product quality found in similar technique with some other foods. The samples of pressure shift freezing also had higher thawing loss and free water ratio after thawing. Therefore, the liquid immersion freezing at lower temperatures was demonstrated to better maintain the quality of frozen products and held significant potential for commercial application.Industrial relevanceFreezing is a widely used method for extending the shelf life of aquatic products, but some freezing methods, especially the slower ones, often lead to the decrease in the quality and commercial value of frozen products during storage. This paper explored the comparison of industrially used freezing techniques (air freezing and liquid immersion freezing) with the novel pressure shift freezing technique. Liquid immersion freezing at −60 °C was found to be the preferred freezing method for Snakehead fillets, which maintained better frozen product quality, with a simple freezing process and low cost.     

Colour changes of fillets of rainbow trout (Oncorhynchus mykiss W.) fed astaxanthin or canthaxanthin during storage under controlled or modified atmosphere

Rainbow trout were fed diets containing two levels of lipids (9 g/100 g and 24 g/100 g) associated with two keto-carotenoid pigments (80 mg of astaxanthin or of canthaxanthin/kg of diet) for 4 months. After slaughter colour stability of fillets was studied during a 4-week storage at +4 °C under controlled (CA) and modified (MA) atmospheres under 100% air, 60:40 N₂-CO₂ mix and 60:40 air-CO₂ mix. Fillets from fish fed high fat level diets showed higher chroma and higher a^* and b^* colour parameters than those from fish fed low fat level diets. Storage time increased lightness and hue angle in CA but only lightness under MA. After storage at +4 °C lightness of fish fillets stored under MA were lower (P<0.05) than those stored under CA. Carotenoid source resulted in differences in chroma and hue angle of fish fillet stored under CA and MA. Dietary lipid levels resulted in differences in chroma under CA. Under CA the lower (P<0.05) differences between stored-initial values was for N₂-CO₂ and the higher (P<0.05) for air. Under MA, air-CO₂ and N₂-CO₂ gave similar results for L^*, C^* and H(°)_ab. Our experiment demonstrated that colour parameters of fish fillets reacted differently according to gas mixture and storage time.     

Probability of growth and toxin production by nonproteolytic Clostridium botulinum in rockfish fillets stored under modified atmospheres

Whether toxin production by Clostridium botulinum precedes or follows spoilage of fish stored under modified atmospheres (MA), remains unclear. In this factorial design study we inoculated a pool of nonproteolytic C. botulinum spores (5 type E, 4 type B, and 4 type F strains) at 6 levels (10⁴ to 10⁻¹) between two rockfish fillets and then incubated the fillets at 4, 8, 12 and 30°C under vacuum, 100% CO₂ and 70% CO₂+30% air for 21 days. The probability of toxigenesis by one spore was significantly affected (P<0.005) by temperature (T) and storage time (S_t), and not (P>0.1) by MA, MA×T or MA×S_t. At the 10° spore/sample level, the earliest time to detect toxin production at 4,8,12 and 30°C under all MAs was >21, 15–21, 6–9 and 2 days, respectively. No toxin production was detected at 4°C. Only type B toxin was present in the toxic samples. At 30°C storage, spoilage of fillets followed toxigenesis. Using linear and logistic regression models, equations were derived that could estimate the lag phase and predict the probability of one spore initiating growth under a particular storage condition.     

High pressure processing on microbial inactivation,quality parameters and nutritional quality indices of mackerel fillets

The objective of this study was to investigate the effect of high pressure processing (HPP) (100, 300 or 500 MPa for 2 or 5 min) on microbial inactivation, quality parameters and nutritional quality indices of mackerel fillets. A significant reduction in TVC and H₂S-producing bacteria was detected at 300 MPa for 5 min and 500 MPa for 2 or 5 min. Lightness (L*) increased and redness (a*) decreased at the highest treatment intensities. Hardness, chewiness and springiness increased with the most intense treatments but neither cohesiveness nor TBARS values were affected by pressurization. HPP significantly decreased levels of EPA, PUFAs, HUFAs, DHA, CLAs and increased MUFAs and SFAs. TI significantly increased at the highest pressurization intensities and AI was affected when HPP was held for 5 min. However, the ratio PUFA/SFA above 0.45 in pressurized mackerel fillets indicated that HPP did not compromise the nutritional value of this pelagic fish.Industrial relevanceThe potential of HPP to inhibit spoilage and increase the shelf-life of mackerel fillets, while maintaining its quality and healthy attributes, could help the fish processing industry to ensure better quality raw material for further processing, thereby enabling the development of new, value-added products with extended shelf- life. The reduction in the processing time with the subsequent saving of energy compared to conventional thermal methods makes HPP a relatively energy efficient and suitable preservation treatment for the fish industry.