Fish Fillets Research Articles

High-strength collagen/delphinidin film incorporated with Vaccinium oxycoccus pigment for active and intelligent food packaging

This study developed an active and intelligent collagen-based packaging film with high strength for visually monitoring the freshness of fish. The results of scanning electron microscopy and atomic force microscopy showed that the film based on cross-linked collagen/delphinidin catalyzed by laccase exhibited a denser layer structure and a rougher surface. The dry and wet tensile strengths of the laccase-catalyzed collagen/delphinidin film (Col/Dp-LA film) increased by 41.74 MPa and 13.13 MPa in comparison with that of the pure collagen film, respectively. Moreover, the Col/Dp-LA film presented good antioxidant and barrier properties demonstrated by the results of free radical scavenging rate, light transmission rate, and water vapor permeability. The intelligent collagen-based film was obtained by incorporating Vaccinium oxycoccus pigment into the Col/Dp-LA film, which could change color under different pH values. When applied to the preservation of fish fillets, the film could release Dp to minimize oxidative rancidity and prolong the shelf life of the fish for 2 days. Meanwhile, the film showed visual color changes from purplish-red to greyish-blue after the fish spoilage. These results indicated that the collagen film treated with delphinidin, laccase, and Vaccinium oxycoccus pigment has potential application value in the field of active and intelligent food packaging.Graphical

Edible film based on corn zein containing dill extract and essential oil/β-cyclodextrin inclusion complex: Shelf life enhancement of common carp fillet.

The aim of this study was to examine the impacts of corn zein edible film (Z) fortified with dill leaves extract (DE) and encapsulated dill essential oil with β-cyclodextrin (nDEO) on the quality of refrigerated common carp fillet. Gas chromatography/mass spectrometry (GC/MS) analysis showed that the most frequent substances of DEO were apiol (35.1%) and carvone (31.4%), respectively. Designated treatments were as follows: (1) Control (C), (2) Z, (3) Z-DE, (4) Z-DEO, (5) Z-nDEO, (6) Z-DE-DEO, and (7) Z-DE-nDEO. The physicochemical properties (thickness, moisture percent, tensile strength, elongation at break, Young's modulus, color, morphology, functional groups, and thermal resistance) of the activated films significantly improved (p ≤ .05). The total viable counts, lactic acid bacteria, Enterobacteriaceae, and psychrotrophic bacteria significantly decreased in all wrapped fillets compared to the unwrapped ones (p ≤ .05). Throughout storage period, the wrapped fillets exhibited lower changes in pH, thiobarbituric acid reactive substances, and total volatile-based nitrogen values than the unwrapped fillets. According to the sensory findings, incorporating DE and nDEO in the zein films created significantly desirable aroma and flavor in the wrapped samples during storage time (p ≤ .05). Encapsulation of DEO with β-cyclodextrin significantly fortified preservative effects of the films in fish fillets during storage period (p ≤ .05). In conclusion, the designated composite zein edible film containing DE and nDEO can be introduced as an active edible packaging in the shelf life improvement of common carp fillets during cold storage.

Halochromic (pH-Responsive) Indicators Based on Natural Anthocyanins for Monitoring Fish Freshness/Spoilage

Today, smart indicators especially based on pigments and natural biopolymers have developed significantly in laboratory and industrial scale. In addition to tracking the freshness and spoilage of the product, these intelligent systems inform the consumer about the quality of the packaged product without opening the package. On the other hand, they reduce food waste and minimize food poisoning. In this study, two halochromic smart indicators were constructed by encapsulating saffron petal and barberry anthocyanins in gelatin/chitin nanofiber films for indication of the freshness/spoilage of fish fillets. Insights into the molecular, structural, and optical properties of these indicators were obtained using X-ray diffraction, scanning electron microscopy, and infrared spectroscopy, and colorimetry analyses. The results showed that the indicators had smooth surfaces and that the pigments were evenly distributed throughout the biopolymer network. The barberry and saffron anthocyanin solutions underwent color changes from reddish to yellow for barberry and reddish to pink to violet to greenish and yellow for saffron anthocyanin after being exposed to different pH values (1–14). The change in appearance of halochromic indicators was quantified by measuring their color coordinates (L*, a*, b*). When applied for estimating fish spoilage, the color of the G/ChNF/BA and G/ChNF/SPA indicators turned from pink to yellow and from violet to green, respectively. After 3 days of storage, the pH and total volatile basic nitrogen of fish fillets reached 8.0 and 49.06 mg N/100 g, respectively. Therefore, a direct relationship between the increase in pH values, the increase in volatile nitrogen bases content, and the changes in the color of the smart indicator applied to monitor the fish was observed. The simulation tests showed that pH-responsive smart indicators can reveal visually fish fillets freshness in real time prior to the point of consumption.

Nonmigrating Active Antibacterial Packaging: Antimicrobial Mechanism against Staphylococcus Aureus and Its Application in Large Yellow Croaker

In this study, chitosan (CS) was grafted onto the surface of polylactic acid (PLA) film by covalent immobilization to prepare four kinds of CS-grafted PLA (CS-g-PLA) films with different molecular weights. The properties of the films were characterized, and their antibacterial effect and mechanism of action against Staphylococcus aureus (S. aureus) were explored. After being treated with CS-g-PLA films, the cell morphology was destroyed, the permeability of the cell membrane changed, and malate dehydrogenase (MDH) activity decreased. Furthermore, the large yellow croaker fillets were packaged by the films mentioned above and stored at 4 °C, the physicochemical changes and microbial counts were measured. The results showed that the CS-g-PLA films could effectively delay the decay of fish fillets for 1–4 days. Overall, this study demonstrated that grafted films showed great application potential in aquatic product packaging and preservation.

Salting and slight drying as combination pretreatments to alleviate quality alteration of raw grass carp fillets after high pressure processing

ABSTRACT High pressure can induce significant sensory quality changes in fish. Considering the important role of raw attributes in ready-to-eat aquatic products, our study thus focused on combination treatments prior to pressurization, to maintain grass carp quality. Fish fillets with or without salting and/or slight drying were pressurized under 0.1, 300, 400, and 500 MPa for 10 min. Microbiological, sensorial, and chemical analyses were performed to assess fish quality. The salting and slight drying combination have synergistic impacts on alleviation of fish quality changes after pressurization, e.g. muscle semi-transparency, lower lightness, and stronger water-holding capacity. This could be associated with enhanced fibrous interconnection and protein structure (less decrease of α-helix contents, less amino acid residue exposures). By contrast, fillets without pretreatments, or after single salting or drying process, had unfavorable quality alterations after pressurization. Therefore, appropriate means for developing novel ready-to-eat products can be carried out by targeting pressure-sensitive aquatic foods.

The fabrication of films based on polymer and containing nanoclay, sodium diacetate, and tert‐butyl hydroquinone for packaging rainbow trout

This study investigates the fabrication of films based on a polymer containing nanoclay, sodium diacetate (SDA), and tert-butyl hydroquinone (TBHQ) for packaging rainbow trout fillets. The films were prepared by the addition of 2% SDA (SDA film), 2% TBHQ (TBHQ film), and a combination of both (1% SDA+1% TBHQ) into polyethylene polymer (93.00%) and montmorillonite nanoclay (5.00%). A film lack of nanoclay, SDA, and TBHQ was prepared and considered a control film. A film was also prepared by the addition of 95g polyethylene+5g nanoclay (Nanoclay). Morphological properties of the films were investigated by a scanning electron microscope (SEM). In vitro antioxidant properties and antibacterial activities of the films and their effects as the coating on fish samples were evaluated against Listeria monocytogenes, Salmonella typhimurium, and Escherichia coli. The effects of films on oxidative stability, antibacterial activity, pH, total volatile basic nitrogen (TVBN), and total viable count (TVC) of fish samples were assessed. The SEM results showed the homogenous dispersion of SDA and TBHQ into films. The SDA, TBHQ, and ST films showed antibacterial activity against L. monocytogenes, S. typhimurium, and E. coli compared with the control film as the coating and under in vitro conditions (p<0.05). The TBHQ and ST films exhibited higher antioxidant activity and prevented the oxidation as the coating. The films prepared from the SDA, TBHQ, and ST prevented an increase in TVC and TVBN (p<0.05). The ST films can prevent spoilage in fish samples and can be utilized in the food industry. PRACTICAL APPLICATION: We successfully prepared films with the help of nanoclay, sodium diacetate (SDA), and tert-butyl hydroquinone (TBHQ) on polyethylene for packaging fish fillets. Films containing SDA, TBHQ, and nanoclay showed antibacterial activity and prevented spoilage. The films can be used for packaging fish fillets.

Emulsifier free fish gelatin based films with excellent antioxidative and antibacterial activity: Preparation, characterization and application in coating preservation of fish fillets

Emulsifier free fish gelatin based films with excellent antioxidative and antibacterial activity: Preparation, characterization and application in coating preservation of fish fillets

Algal oil gives control of long‐chain omega‐3 levels in full‐cycle production of Atlantic salmon, without detriment to zootechnical performance and sensory characteristics

AbstractThe levels of eicosapentaenoic (EPA) and docosahexaenoic (DHA) in salmon fillets have decreased because of the progressive replacement of fish oil (FO). This study contributes to enabling the sustainable growth of aquaculture by confirming the effects of partially or fully replacing FO with microalgal oil (AO) on growth, muscle fatty acid profiles, and muscle quality of farmed Atlantic salmon. Crucially, this is now done throughout the entire post‐smolt production cycle and up to a harvest weight of 3 kg. Three experiments were performed using fish ranging from 145 g to 3 kg and testing different diets, replacing FO up to 100%. Zootechnical performance was similar among treatments in all experiments. Changing the lipid source in the diet resulted in EPA and DHA digestibility of greater than 96%. Sensory characteristics of raw fish fillets were similar among treatments, supporting a similar sensorial experience with the replacement of FO with no impact on consumers. Overall, results confirm that the AO tested here enables the sustainable growth of Atlantic salmon aquaculture by helping to maintain a level of EPA and DHA in the fish fillets, without detriment to zootechnical performance and sensory characteristics, while simultaneously contributing to a reduced marine footprint for aquafeeds.

Effect of coating with chitosan enriched with different borates on the shelf life of fish fillet.

In this study, the effects of biofilm coatings obtained by immobilization of different borates - namely borax (BX), colemanite (COL), and ulexite (UX) - with chitosan (Ch) on the shelf life of rainbow trout fillets were investigated. The immobilization and characterization of borates in Ch were confirmed by scanning electron microscopy, Fourier transform infrared spectroscopy, and zeta potential analysis. In determining the shelf life of fillets that were covered by immersion and stored for 15 days, microbiological (total aerobic mesophilic, psychrotrophic, lactic acid, Pseudomonas, and Enterobacteriaceae bacteria counts) and chemical analyses (total volatile basic nitrogen, thiobarbituric acid reactive substance, and pH levels) were performed at 3day periodic intervals. In addition, the biodegradation of borates was determined using inductively coupled plasma mass spectrometry in biofilm-coated fillets on the 1st, 8th, and 15th storage days. The microbial results of the coatings enriched with borates (BX, COL, and UX) at different levels (0, 0.03, and 0.06 mg L-1 ) (due to the immobilization with Ch) show the shelf life was extended by 3-6 days in all of the treatment groups compared with the control. It was concluded that BX, COL, and UX coatings enriched by immobilization with Ch increase shelf life and improve fillet quality. In addition, the enrichment of BX, COL, and UX with Ch showed explicit natural protective effects. This study demonstrates that Ch-enriched coatings of BX, COL, and UX can be used as natural bioactive nanocarriers to provide bioactive food ingredients in the seafood processing industry. © 2023 Society of Chemical Industry.

High Pressure Processing under Mild Conditions for Bacterial Mitigation and Shelf Life Extension of European Sea Bass Fillets

High pressure is an industrially established food preservation process applied for the minimal processing or cold pasteurization of chilled, fresh, or ready-to-eat products. This study aimed to quantify the effectiveness of high pressure on the inactivation of spoilage microflora and the shelf life extension of European sea bass (Dicentrarchus labrax) fillets. Fish fillets were subjected to mild, high pressure conditions (100–400 MPa; 3–25 °C; 5–10 min) and then stored at 0.0 ± 0.2 °C. Their shelf life was evaluated in terms of their microbiological, physicochemical, and sensorial quality. The results indicated that a shelf life extension of 1–5 d at 0 °C was achieved when pressures of 100 MPa were applied, whereas higher pressures resulted in an up to 5-fold increase in the shelf life of the fillets, depending on the applied pressure and temperature. A high pressure treatment combined with vacuum packaging showed an additional effect on the shelf life extension of the fillets, increasing the shelf life by 4–12 d when compared to aerobically stored products. Moreover, the high pressure treatment prevented lipid oxidation throughout the storage period, indicating no formation of secondary lipid oxidation products. The estimated shelf life of the fish fillets based on their sensorial quality was in accordance with the estimation based on the microbiological data.

Insect lipid in fish nutrition: Recent knowledge and future application in aquaculture

AbstractInsect lipid/oil is a by‐product of insect meal production. The quantity and nutritional quality of insect lipid varies with species, life stages, the kind of substrate used to raise the insects, as well as the extraction process. Insect lipid products have been successfully used in animal feeds as source of nutrients, notably energy and indispensable fatty acids. Further some insect lipid products are potential functional ingredients in feed formulations because of the existence of some functional compounds, for example, lauric acid and monolaurin in black solder fly larvae oil (BSFLO). To date, research on the effects of insect product inclusion in aquafeed mainly focused on insect meal as protein source rather than insect oil/lipid as a lipid source. Research to date indicates that insect lipids can replace traditional energy sources in fish nutrition without negatively affecting fish growth and feed utilization performance. By raising the amount of long‐chain polyunsaturated fatty acids in fish fillets, insect lipids can improve fillet quality. Insect lipids may also positively influence general health of fish by stimulating the immune system and manipulating the gut microbiota. As there is a crucial need for searching alternate lipid sources in aquafeed to extend limited global supplies of fish oil and due to the insect lipids content and its fatty acid quality, there is a pressing need to expand experimentation concerning their application in aquafeed to support sustainable growth of the aquaculture industry.

Histological and transcriptomic analysis of muscular atrophy associated with depleted flesh pigmentation in Atlantic salmon (Salmo salar) exposed to elevated seawater temperatures

Tasmania is experiencing increasing seawater temperatures during the summer period which often leads to thermal stress-induced starvation events in farmed Atlantic salmon, with consequent flesh pigment depletion. Our previous transcriptomic studies found a link between flesh pigmentation and the expression of genes regulating lipid metabolism accompanied by feeding behavior in the hindgut. However, the impact of prolonged exposure to elevated water temperature on muscle structural integrity and molecular mechanisms in muscle underlying pigment variation has not been elucidated to date. In this study, we investigated the effect of prolonged exposure to elevated water temperature on the farmed salmon flesh pigmentation and structural integrity, using muscle histological and transcriptomic analysis. On April 2019, after the end of the summer, two muscle regions of the fish fillet, front dorsal and back central (usually the most and least affected by depletion, respectively), were sampled from fifteen fish (weighing approximately 2 kg and belonging to the same commercial population split in two cages). The fish represented three flesh color intensity groups (n = 5 fish per group) categorized according to general level of pigmentation and presence of banding (i.e. difference in color between the two regions of interest) as follows: high red color-no banding (HN), high red color-banded (HB) and Pale fish. Histological analysis showed a distinction between the flesh color intensity phenotypes in both muscle regions. Muscle fibers in the HB fish were partly degraded, while they were atrophied and smaller in size in Pale fish compared to HN fish. In the Pale fish, interstitial spaces between muscle fibers were also enlarged. Transcriptomic analysis showed that in the front dorsal region of the HN fish, genes encoding collagens, calcium ion binding and metabolic processes were upregulated while genes related to lipid and fatty acid metabolism were downregulated when compared to HB fish. When comparing the back central region of the three phenotypes, actin alpha skeletal muscle and myosin genes were upregulated in the HN and HB fish, while tropomyosin genes were upregulated in the Pale fish. Also, genes encoding heat shock proteins were upregulated in the HN fish, while genes involving lipid metabolism and proteolysis were upregulated in the Pale fish. Starvation, likely caused by thermal stress during prolonged periods of elevated summer water temperatures, negatively affects energy metabolism to different extents, leading to localized or almost complete flesh color depletion in farmed Atlantic salmon. Based on our results, we conclude that thermal stress is responsible not only for flesh discoloration but also for loss of muscle integrity, which likely plays a key role in pigment depletion.

Characterization of fillets of Amazon and real hybrid sorubins

Background: There are few studies on the evaluation of meat from hybrid sorubins. Objective: Thus, the aim of this work was to evaluate the physical, chemical, microbiological and sensorial characteristics of fillets of Amazon and real hybrid sorubins. Method: Proximate composition, instrumental colour, water holding capacity, cooking losses and shear force were measured. Microbiological analyses of the fillets were carried out for Salmonella sp. and Staphylococcus aureus to ensure food safety of the judges during sensory analysis. Results: Hybrid sorubim fillets presented an excellent quality, being classified in category A (lipids below 5% and proteins between 15% and 20%). There was no significant difference (p&gt;0.05) between the evaluated fillets for several parameter: the average water holding capacities were 33.72 and 34.67%, the cooking losses were 14.93 and 13.41%, the shear forces were 2.21 and 1.74 kgf, and the luminosities were 49.61 and 45.04 for the fillets of Amazonian hybrid sorubim and real hybrid sorubim, respectively. Discussion: There was an evident relation between water holding capacities and shear forces. Amazonian hybrid sorubim fillets were more accepted due to their lower intensity of red. However, there was no sensorial difference between the hybrids, and both had an acceptance rate above 80%. Conclusion: It was concluded that the hybridization does not alter the sensory characteristics of the fish fillets.

The impact of marine and terrestrial based extracts on the freshness quality of modified atmosphere packed sea bass fillets

The extracts of Padina pavonica (a macroalgae, ME), Rubus fruticosus (blackberry) leaves (BE), Juniperus oxycedrus waste (JWE) and Juniperus communis needles (JE) were used to evaluate their potential effects on chemical, microbial and organoleptic qualities of sea bass (Dicentrarchus labrax). The sensory assessment showed that fish fillets treated with BE, JE and ME were preferred more by the panellists, and rejected at 18 days of storage compared to the control (12 days). All extracts (except JWE) together with modified atmospheric packaging (MAP) decreased the values of biochemical parameters of sea bass fillets. TVB-N, PV, FFA, TBA values remained lower in treatment groups. Microbiological results were consistent with sensory results. Although microbial growth showed a rapid increase in the control and JWE groups during storage, BE, ME and JE groups significantly inhibited the bacterial growth in fish meat (p < 0.05). Lactic acid bacteria in sea bass fillets under MAP condition increased slightly during storage and reached the highest levels in the control and JWE groups, respectively, with the value of 5.60 and 5.52 log cfu/g at the end of storage. This study showed that all extracts except JWE together with MAP application extended the shelf life of sea bass fillets up to 18 days compared to the control (12 days), exhibiting potential antioxidant and antimicrobial agents in seafood industry.

Plasma-activated water for disinfection and quality retention of sea bream fillets: Kinetic evaluation and process optimization

The efficacy of plasma-activated water (PAW) in the decontamination of sea bream fillets at various processing conditions including fish/immersion agent ratio (1/1–1/5) and immersion times (0–20 min), was evaluated. Deionized water (as control samples) and artificially produced water (artificial) with equal reactive species (H2O2, NO2−, and NO3−) concentrations to PAW were also used as immersion agents for comparison purposes. All the fillets were assessed in terms of their microbiological (total aerobic bacteria – TAB, yeasts/molds, hydrogen sulfide (H2S)-producing microorganisms, lactic acid bacteria – LAB, Pseudomonas spp., Brochotrix thermosphacta, and Enterobacteriaceae) and physicochemical (color, texture, lipid oxidation) characteristics. PAW-treated samples exhibited the highest microbial reduction; the loads of TAB, Pseudomonas spp., yeasts/molds, Enterobacteriaceae, H2S-producing bacteria and Brochotrix thermosphacta were reduced by approximately 1.58, 2.25, 3.95, 2.14, 1.96 and 1.48 logCFU/g, respectively compared to the fish initial natural microbiota (6.81, 6.25, 3.95, 5.14, 4.96 and 4.81 logCFU/g, respectively) at the most intense process conditions (fish/immersion agent ratio of 1/5 and immersion time of 20 min) (p < 0.05). Shelf-life study of all treated fillets was conducted to validate the efficiency of PAW. During 10-d storage at 4 °C, the PAW-processed sea bream fillets had lower microbial growth rates (i.e. for TAB growth, the rate was 0.440 d−1 for PAW-treated compared to 0.640 d−1 for untreated fillets) and retained their color and hardness, while total volatile basic nitrogen (TVB-N) remained at low levels (14.90 mg N/100 g) compared to the untreated ones (21.84 mg N/100 g). Their shelf-life was extended by approximately 60% and 30% for PAW- and artificially processed samples, respectively, (2.8- and 1.4-day shelf-life extension compared to control samples, respectively). These aforementioned data show that PAW can be efficiently used as a disinfectant agent to control microbial degradation, while retaining the quality of fish fillets. Industrial relevanceFish fillets are perishable food products, while none of the conventional or novel processing technologies or techniques may be applied for initial microbial population decrease. Storage and transportation at refrigeration temperatures below 1 °C (within Styrofoam insulated boxes full of ice flakes) is the target of the relevant companies for extending the shelf-life as much as possible.An alternative approach for reducing the initial microbial load and the microbial growth rate of fish fillets during storage and transportation is proposed, by immersing the fillets into Plasma activated water with antimicrobial properties. The microbial load is significantly reduced, resulting in a shelf-life extension by at least 60%. This allows for more distant transportation of the fillets and for less food waste since there is more time for consumption before spoilage.

Fish consumption and quality by peri-urban households among fish farmers and public servants in Ethiopia

The goal of this study was to analyse peri-urban households' fish consumption and fish quality along the value chain of the fish-livestock production system. Data on fish consumption per capita and socio-economic characteristics of the household of 366 households were collected along the fish value chain, covering two rural districts (Omonada and Kersa) and one town (Jimma). Effect of socio-economic characteristics on fish consumption of the interviewed households was analysed using Ordinary Least Square Regression. A total of 36 Nile Tilapia fish were collected from eight locations along the fish value chain. Then, the samples were analysed for microbial, physiochemical, and sensorial attributes. The influence of sample location on physiochemical, qualitative characteristics, and microbiological loads of fish fillets was investigated using one-way ANOVA and orthogonal contrast to separate the means. The mean fish consumption per capta in the study area was 0.541 kg/person/year. Fish consumption of the household was significantly influenced by location and household head sex. Fish consumption was positively influenced by education, family size, and wealth, but negatively influenced by age. The fish value chain in the study area extended from the production site (adjacent to Gilgel Gibe I reservoir) and district retailer shops, Jimma town mobile trader and retailing shops. Except the production site, fish quality across the value chain were lower than the standard. Furthermore, fish samples from marketing sites (Jimma town mobile traders, Jimma town retailer shops, and district retailer shops) had lower ash, fat, crude protein levels, higher TVB-N, higher pH and higher aerobic and coliform loads compared to samples from production sites. Fish samples from district shops and Jimma town traders had significantly lower off-flavour scores compared to the production sites (0.94 points and 1.53 points, respectively). Fish obtained from Jimma retailers had significantly less odour compared to those obtained from Jimma mobile traders by 0.87 points. In conclusion, Ethiopian households' consumption of fish in the integrated livestock-fish farming system is generally low. Yet, it could be improved by reducing fish production cost and shortening the fish value chain. Improving cold chain facilities and implementing household to household extension services about fish consumption would be inevitable to enhance fish consumption in the study area.

Effects of different storage conditions on microbial community and quality changes of greater amberjack (Seriola dumerili) fillets

To improve the safety and extend the shelf life of fish fillets, four different temperatures were used to preserve the greater amberjack. The microbial diversity and quality changes were determined. The freezing point of greater amberjack fillets was determined by analyzing the freezing curve, and four storage temperatures were applied, room temperature (20 °C), refrigeration (4 °C), ice temperature (-1 °C) and partial freezing temperature (-3 °C). The shelf life of greater amberjack fillets stored at 20 °C, 4 °C, -1 °C and -3 °C was 30 h, 7 d, 21 d and 36 d, respectively based on TVC and TVB-N results. The microbial community indicated the bacterial richness and diversity were higher at the end of the storage time under -1 °C and -3 °C. Pseudomonas was the specific spoilage bacteria of greater amberjack stored at low temperature. The growth of spoilage bacteria was effectively inhibited when the sample was stored at -1 °C and -3 °C, which were more conducive to maintaining the initial bacterial phase, delaying the spoilage, and prolonging the shelf life. This study showed promising storage temperatures of -1 °C and -3 °C for fish fillets, which would prolong the shelf life and improve the safety of preserved samples.

Isolation and characterization of Aeromonas hydrophila lytic phage, and evaluation of a phage cocktail against A. hydrophila contamination in fish fillet

Besides being a finfish pathogen, Aeromonas hydrophila is also considered an important human enteropathogen. Phage biocontrol is increasingly being accepted as a natural and green technology for the control of bacterial pathogens as well as for minimizing the emergence/spread of antimicrobial resistance. In the present study, an A. hydrophila lytic phage (named D6) was isolated, characterized and subjected to whole-genome sequencing. During host range analysis, phage D6 belonging to order Caudovirales and family Myoviridae was able to lyse 95% of A. hydrophila isolates. The adsorption rate, latent period and burst size of phage D6 were estimated to be ∼95%, ∼60 min and 695 ± 44 plaque-forming unit (PFU)/host cell, respectively. The complete, circularly permuted 259,831 bp long phage genome consisted of 267 open reading frames (ORFs) and 3 tRNA genes. The genome of D6 also contained several genes essential for the phage life cycle. During in vitro host cell lysis test, phage D6 significantly inhibited the bacterial growth until 10 h at all the tested multiplicity of infection (MOI) values. A two-phage cocktail of D6 and previously isolated phage CF7 reduced the A. hydrophila counts by >95% in fish fillets at room temperature (25 °C) as well as at 4 °C. The comparison of phage counts at the start and end of the experiments also confirmed that both phage D6 and CF7 were able to propagate within the A. hydrophila host on the fillet matrix. Besides, phage counts on host-free fillets were stable throughout the experiments. The broad range phage cocktail from the present study could be used to ensure the safety of fishery products against A. hydrophila contamination.

Defatted black soldier fly (Hermetia illucens) in pikeperch (Sander lucioperca) diets: Effects on growth performance, nutrient digestibility, fillet quality, economic and environmental sustainability.

The use of insect meal in aquafeed formulations has recently gained attention. Detailed knowledge about the inclusion levels for pikeperch (Sander lucioperca), a promising candidate for intensive aquaculture in Europe remains, however, fragmented. In the present study, 4 isoproteic (45% dry matter) and isoenergetic (21MJ/kg) diets were formulated, including a control diet (H0) containing 30% fishmeal (FM) on an as-fed basis and the other 3 diets in which FM protein was replaced by defatted black soldier fly (Hemetia illucens) meal (HIM) at 25%, 50%, and 100% (diet abbreviation H9, H18 and H36, corresponding to an inclusion level of 9%, 18% and 36%, respectively). The feeding trial was performed in triplicate groups of 50 juvenile pikeperch (mean weight, 68.7g) fed with experimental diets for 84d during which the growth performance, nutrient digestibility, fillet quality and economic and environmental sustainability of rearing pikeperch were evaluated. Our findings indicated that pikeperch in H0, H9, and H18 groups displayed better results regarding growth performance indices, except for survival rate where no significant difference among groups was recorded (P= 0.642). A significantly lower organ-somatic index, including hepatosomatic, viscerosomatic and perivisceral fat index, was found in fish in H18 groups than other groups (P<0.05). Inclusion of HIM affected the digestibility of the nutrients and resulted in an almost linear reduction in the apparent digestibility coefficient of dry matter and protein. Concerning the fillet quality, dietary HIM negatively affected the protein and ash contents of the fish fillets, while the crude fat remained unchanged. Dietary HIM did not significantly modify total saturated, monounsaturated and polyunsaturated fatty acids in the fillets of fed pikeperch (P>0.05) but did reduce total n-3 fatty acids (P=0.001) and increased total n-6 (P<0.001). Increasing inclusion levels of HIM reduced the environmental impacts associated with fish in-to-fish out ratio but entailed heavy burdens on energy use and eutrophication. Low and moderate inclusion levels of HIM did not negatively affect land use and water use compared to an HIM-free diet (P>0.05). The addition of HIM at a level as low as 9% elicited a similar carbon footprint to that of the control diet. The economic conversion ratio and economic profit index were negatively affected at increased insect meal inclusion levels. This study has shown that the incorporation of HIM in feed formulations for pikeperch is feasible at inclusion levels of 18% without adverse effects on growth performance parameters. The feasibility also highlighted the environmental benefits associated with land use and marine resources required to produce farmed fish.

INFLUENCE OF ELECTROCHEMICALLY ACTIVATED SOLUTIONS ON THE FATTY ACID PROFILE OF FOOD SYSTEMS

The emergence of new types and methods of food processing requires studying the impact on the compo-nents of food systems. Fish products are an important part of the human diet, but as a result of storage, their quality and safety indicators are reduced. An effective way to ensure the biological safety of fish raw materials is the use of electrochemically activated solutions (ECAS) obtained by high-voltage diaphragm electrolysis. The aim of the study was to study the effect of various concentrations of ECAS on the fatty acid profile of food systems using the example of fish oil from Atlantic salmon (Salmo salar) fillet during the shelf life. In the experiments, a ready-made ECAS with an active chlorine concentration (hereinafter Cach) of 500 mg/l (0.05%) was used, from which working ECAS were prepared with a dilution of 50% and 15%, which corresponds to Cach – 250 mg/l (0.025%) and Cach – 75 mg / l (0.0075%). The concentration of ECAS was selected experimentally in order to determine the optimal concentration at which the de-struction of fatty acids (hereinafter FA) of the studied samples did not occur. The determination was car-ried out by gas chromatography using a Crystal-2000M chromatograph. Comparison was made with con-trol samples. Identification of the peaks of FA methyl esters of the tested samples made it possible to de-termine the recommended working concentration of active chlorine ECAS equal to 75 mg/l, at which the content of polyunsaturated fatty acids does not statistically decrease. The research results can be used to ensure the quality and biological safety of fish fillets, taking into account the specific effects of ECAS on individual components of food systems.