Smoked salmon industry practices and their association with Listeria monocytogenes

Acetic and citric acids effect the type II secretion system and decrease the metabolic activities of salmon spoilage-related Rahnella aquatilis KM05

Rahnella aquatilis causes seafoods to spoil by metabolizing sulfur-containing amino acids and/or proteins, producing H2S in products. The type II secretion system (T2SS) regulates the transport of proteases from the cytoplasm to the surrounding environment and promotes bacterial growth at low temperatures. To prevent premature fish spoilage, new solutions for inhibiting the T2SS of bacteria should be researched. In this study, global transcriptome sequencing was used to analyze the spoilage properties of R. aquatilis KM05. Two of the mapped genes/coding sequences (CDSs) were matched to the T2SS, namely, qspF and gspE, and four of the genes/CDSs, namely, ftsH, rseP, ptrA and pepN, were matched to metalloproteases or peptidases in R. aquatilis KM05. Subinhibitory concentrations of citric (18 µM) and acetic (41 µM) acids caused downregulation of T2SS-related genes (range from - 1.0 to -4.5) and genes involved in the proteolytic activities of bacteria (range from - 0.5 to -4.0). The proteolytic activities of R. aquatilis KM05 in vitro were reduced by an average of 40%. The in situ experiments showed the antimicrobial properties of citric and acetic acids against R. aquatilis KM05; the addition of an acidulant to salmon fillets limited microbial growth. Citric and acetic acids extend the shelf life of fish-based products and prevent food waste.

Natural alternatives for processed meat: Legislation, markets, consumers, opportunities and challenges

Consumers' interest in food with less and/or free from synthetic additives has increased considerably in recent years. In this context, researchers and industries have concentrated efforts on developing alternatives to these compounds. Replacing synthetic additives in meat products is a challenge, given their importance for sensory characteristics and food safety. Complementary technologies combined with the replacement and/or reduction of synthetic additives (hurdle technologies) has been studied focusing on the protection and extension of the shelf life of meat products. This review reports alternatives for replacing and/or reducing the use of synthetic additives in meat derivatives, aiming at the development of more natural and simpler meat products, familiar to consumers and considered clean labels.

Analysis of the Bioprotective Potential of Different Lactic Acid Bacteria Against Listeria monocytogenes in Cold-Smoked Sea Bass, a New Product Packaged Under Vacuum and Stored at 6 ± 2°C

The aim of the work was to monitor the presence of Listeria monocytogenes in cold-smoked fish products (trout, salmon, and sea bass) marketed in Italy. Cold-smoked sea bass is a new product that has not yet been commercialized and was collected from the production facility. Monitoring data have shown that cold-smoked products can be contaminated by L. monocytogenes, the presence of which has been highlighted mainly by enrichment culture (presence in 25 g). The isolated Listeria were serotyped and belonged mainly to low-virulence serotypes (1/2c), followed by serotypes 1/2a, 1/2b, and 4b. Furthermore, considering the ability of L. monocytogenes to grow in these products due to their chemical-physical characteristics (pH > 6.0, Aw > 0.97) and long shelf life at 4°C, an additional aim was to verify the activity of different bioprotective starters, including Lactilactobacillus sakei (LAK-23, Sacco srl, Via Alessandro Manzoni 29/A, 22071 Cadorago, CO, Italy), Carnobacterium spp., Lacticaseibacillus casei (SAL 106), and Lacticaseibacillus paracasei (SAL 211), in cold-smoked sea bass. All starters were bacteriocin producers. For this experiment, smoked sea bass samples were intentionally inoculated with a mixture of three different strains of L. monocytogenes and of each starter culture. After inoculation, the smoked sea bass were vacuum-packed and stored at 6 ± 2°C for 60 days, simulating the typical abuse storage temperature of markets and home refrigerators. At 0, 15, 30, 45, and 60 days, the sea bass samples were analyzed to evaluate the effectiveness of the starters against L. monocytogenes. Listeria monocytogenes growth was prevented only by the addition of the LAK-23 starter. Indeed, at the end of the shelf life, the amount of L. monocytogenes observed was similar to that in the inoculum. Consequently, the use of this starter can allow the inclusion of cold-smoked sea bass or smoked fish products in category 1.3 of Regolamento CE 2073/2005, which are products that do not support the growth of this microorganism. Finally, the activity of the LAK-23 starter did not produce an off flavor or off odor in the smoked sea bass.

Food Safety in Local Farming of Fruits and Vegetables

The world’s population will be around 9 billion people by 2050. Humans need to feed in order to survive and thus the high demographic growth may impact the sustainability of our food systems. Sustainable food production practices such as local farming have been explored. Consumption of vegetables and fruits has been increasing due to their health benefits, but this increase is also related to a significant number of foodborne outbreaks. Foodborne outbreaks pose a threat to public health and the economy on a local and national scale. Food safety begins on the farm and proceeds over the supply chain. Thus, to provide safe products, food producers must follow specific procedures to avoid food hazards along the supply chain. This work aimed to present the importance of food safety in vegetables and fruits in local farming, as this form of production and consumption has increased in several countries of the northern hemisphere and as these are considered a form of providing more sustainable food products.

Combination of Immunomagnetic Separation and Real-Time Recombinase Polymerase Amplification (IMS-qRPA) for Specific Detection of Listeria monocytogenes in Smoked Salmon Samples

Nowadays, Listeria monocytogenes continues to be a major health issue. Therefore, improvements in the speed and reliability of its detection are still needed. In the present study, the combination of real-time Recombinase Polymerase Amplification (qRPA) with immunomagnetic separation (IMS) is described. The proposed methodology was tested against a real-time PCR method, and was successfully applied to 50 smoked salmon samples spiked at levels ranging from 2 to 9.3 × 10² cfu/25 g. L. monocytogenes was detected after a 24 hr pre-enrichment, which represents a great improvement over other previously published RPA methods. Additionally, the evaluation of the method reported a Limit of dDetection 50 (LoD₅₀ ) of 6.3 cfu/25 g, along with relative sensitivity, specificity and accuracy values higher than 90%. Finally, the index of kappa concordance was calculated to be 0.93 which is interpreted as "almost complete concordance" between the reference and alternative method. Overall, the described methodology proved to be faster, specific, and as sensitive as other methods based on RPA or real-time PCR. PRACTICAL APPLICATION: The methodology described in this study significantly reduces the detection time of L. monocytogenes, when compared with culture-based methods, and it requires fewer steps than other molecular methods, making it a reliable and more convenient method for routine testing. Finally, the evaluation of the methodology in spiked food samples, confirms its reliability.

Processing plant and machinery sanitation and hygiene practices associate with Listeria monocytogenes occurrence in ready-to-eat fish products

Listeria monocytogenes causes the foodborne illness listeriosis, which exhibits high fatality among people in risk groups. The incidence of listeriosis has increased in Europe, which raises concerns about L. monocytogenes occurrence in foodstuffs. Ready-to-eat seafood products are considered particularly risky vehicles. Poor hygiene at processing facilities predisposes them to L. monocytogenes contamination, which can be controlled by stringent self-checking system measures. We examined the association of fish-processing plant operational and hygiene practices with the occurrence of L. monocytogenes in vacuum-packaged gravad (cold-salted) and cold-smoked salmon and rainbow trout products. Product sampling of 21 fish-processing plants was carried out, and operational procedures relating to L. monocytogenes control were surveyed using an in-depth risk assessment questionnaire. L. monocytogenes occurred only in sliced and mainly in gravad products of seven fish-processing plants. Shortages in preventive measures were discovered predominantly among the L. monocytogenes positive fish-processing plants. Using generalized linear modeling, we identified the following features associated with L. monocytogenes product contamination: the number of processing machines, deficiencies in the processing environment and machinery sanitation, and staff movement from areas of low toward high hygiene. Furthermore, performing frequent periodic thorough sanitation alongside everyday sanitation practices associated with a decreased risk of product contamination.

The Impact of Chitosan-Divergicin Film on Growth of Listeria monocytogenes in Cold-Smoked Salmon

The aim of this study was to evaluate the impact of chitosan film, with bacteriocin divergicin 35 incorporate, on growth of Listeria monocytogenes in Cold smoked salmon. The simples of Cold-smoked wild salmon were inoculated with L. monocytogenes and treated with chitosan (100 kDa, 94.7% de-acetylated) and divergicin M35 was stored for 3 weeks at 4-8°C. The compounds were applied to the fish flesh in the form of solution or dried film. The film reduced L. monocytogenes to below the detection limit (<50 cfu/g) and kept total counts below 104 cfu per g compared to 109 cfu per g in control samples while the effectiveness of the solution was very limited. The inhibitory activity of the film lasted for 3 weeks, while the solution had no effect on L. monocytogenes counts measured on day 14. The film provided a better preservation of fish color (redness) and firmness than others treatments, while the solution had little impact on these parameters. It kept the volatile basic nitrogen (17.5 mg N/100 g) below the control value 29.9 mg N/100 g. Divergicin-loaded chitosan film thus may represent an interesting alternative for the bio-preservation of cold-smoked fish.

Strengthening the efficacy of official food control improves Listeria monocytogenes prevention in fish-processing plants

Vacuum-packaged cold-salted and cold-smoked fish products are considered typical vehicles for Listeria monocytogenes, the causative agent of the food-borne disease listeriosis, which is increasingly prevalent in the European Union. Efficacy of both the fish processing plant self-checking system and official food control conducted by authorities are crucial for L. monocytogenes prevention in the processing of these risky products. However, the impact of official control on L. monocytogenes prevention in the processing of fish products has not been extensively studied. We investigated the occurrence, control measures, and correction of non-compliances predisposing to L. monocytogenes in Finnish fish processing plants. The following features were associated with L. monocytogenes occurrence: (a) frequency of non-compliances concerning processing machinery, (b) recurrence of non-compliances, and (c) frequency of non-compliances for which official control measures were requested by inspecting authorities. Official control of fish processing plants had focused on risky areas, but non-compliances were common and their correction exhibited deficiencies. We conclude that L. monocytogenes prevention in fish processing can be enhanced by strengthening official food control measures and processing plant compliance. In particular, timely correction of all food safety violations must be improved.

Listeria monocytogenes in Smoked Salmon and Other Smoked Fish at Retail in Italy: Frequency of Contamination and Strain Characterization in Products from Different Manufacturers

Seven hundred seventy-eight samples of packaged smoked fish (774 smoked salmon and 4 smoked swordfish) on sale in Italy, from 50 different manufacturers located in 12 European Union countries, were purchased from the Italian market between May and December 2011. The surface temperatures of the samples on sale ranged from 0 to 13°C (3.4 ± 1.5°C, mean ± SD). Six hundred eighty (87.4%) of 778 samples were stored at ≤4°C. One hundred fifty-seven samples (20.2%, 95% confidence interval 17.5 to 23.1%) were contaminated by Listeria monocytogenes , with 26 samples (3.3%, 95% confidence interval 2.3 to 4.8%) at levels >100 CFU/g. The maximum level of contamination was 1.3 ×10⁶ CFU/g. The differences in the level of contamination of smoked fish between countries (χ² = 91.54, P < 0.05) and manufacturers (χ² = 193.22, P < 0.05) were significant. The frequency of detection for products from different manufacturing premises ranged from 0 to 76.9%. Serotyping by serological agglutination revealed that the main serotypes detected were 1/2a (65.3%) and 1/2b (22.4%). Pulsed-field gel electrophoresis typing with restriction enzymes AscI and ApaI yielded 36 pulsotypes from 144 isolates, clustering into 17 groups. Eight main pulsotypes accounted for 70.8% of the isolates. Three of the main pulsotypes were exclusively from products of a single manufacturer. In general, products from the same manufacturer showed genetic homogeneity, with one strongly prevalent pulsotype. Different manufacturers usually showed very different levels of contamination of the final product, confirming the importance of the management of process hygiene for controlling L. monocytogenes contamination.

Impact of environmental factors on the culturability and viability of Listeria monocytogenes under conditions encountered in food processing plants

The ability of Listeria monocytogenes to adhere to and persist on surfaces for months or even years may be responsible for its transmission from contaminated surfaces to food products. Hence the necessity to find effective means to prevent the establishment of L. monocytogenes in food processing environments. The aim of this study was to assess, through a fractional experimental design, the environmental factors that could affect the survival of L. monocytogenes cells on surfaces to thereby prevent the persistence of this pathogen in conditions mimicking those encountered in food processing plants: culture with smoked salmon juice or meat exudate, use of two materials with different hygiene status, biofilm of L. monocytogenes in pure-culture or dual-culture with a Pseudomonas fluorescens strain, application of a drying step after cleaning and disinfection (C&D) and comparison of two strains of L. monocytogenes. Bacterial survival was assessed by culture, qPCR to quantify total cells, and propidium monoazide coupled with qPCR to quantify viable cells and highlight viable but non-culturable (VBNC) cells. Our results showed that failure to apply C&D causes cell persistence on surfaces. Moreover, the sanitation procedure leads only to a loss of culturability and appearance of VBNC populations. However, an additional daily drying step after C&D optimises the effectiveness of these procedures to reduce culturable populations. Our results reinforce the importance to use molecular tools to monitor viable pathogens in food processing plants to avoid underestimating the amounts of cells using only methods based on cell culture.

Gelatin-Based Films and Coatings for Food Packaging Applications

This review discusses the latest advances in the composition of gelatin-based edible films and coatings, including nanoparticle addition, and their properties are reviewed along their potential for application in the food packaging industry. Gelatin is an important biopolymer derived from collagen and is extensively used by various industries because of its technological and functional properties. Nowadays, a very wide range of components are available to be included as additives to improve its properties, as well as its applications and future potential. Antimicrobials, antioxidants and other agents are detailed due to the fact that an increasing awareness among consumers regarding healthy lifestyle has promoted research into novel techniques and additives to prolong the shelf life of food products. Thanks to its ability to improve global food quality, gelatin has been particularly considered in food preservation of meat and fish products, among others.

Examination of Listeria monocytogenes in Seafood Processing Facilities and Smoked Salmon in the Republic of Ireland

Listeria monocytogenes is a foodborne pathogen that causes listeriosis, a relatively rare but life-threatening disease primarily affecting immunocompromised individuals. The aim of this study was to determine the prevalence of L. monocytogenes in the seafood processing industry in the Republic of Ireland. The occurrence of L. monocytogenes was determined by regular sampling of both food samples and processing environment swabs at eight seafood processing facilities over two calendar years. All samples were analyzed by the International Organization for Standardization 11290-1 standard method, and the isolates were characterized by PCR, pulsed-field gel electrophoresis, serotyping, and the occurrence of some genes related to survival under stress (SSI-1, Tn6188, and bcrABC). A prevalence of 2.5% in 508 samples (433 environmental swabs and 75 food samples) was found. From the isolates obtained, eight different pulsed-field gel electrophoresis profiles were identified, two occurring in more than one facility and one occurring in food and the environment. Five of the eight pulsotypes identified contained at least one of the three stress survival-related genes tested. The tolerance of the isolates to benzalkonium chloride, a representative quaternary ammonium compound, was also examined and ranged from 5.5 ± 0.5 to 8.5 ± 0.5 ppm of benzalkonium chloride. To evaluate the ability of smoked salmon to support the growth of L. monocytogenes, including the T4 widespread pulsotype that was isolated, a challenge test was performed on cold-smoked salmon obtained from two separate producers. The results showed clearly that both types of smoked salmon supported the growth of L. monocytogenes. Although occurrence of L. monocytogenes on seafood was low, this study showed that the smoked salmon used in this study can support the growth of L. monocytogenes; therefore, vigilance is required in the processing facilities to reduce the associated risk.

L. monocytogenes in a cheese processing facility: Learning from contamination scenarios over three years of sampling

The aim of this study was to analyze the changing patterns of Listeria monocytogenes contamination in a cheese processing facility manufacturing a wide range of ready-to-eat products. Characterization of L. monocytogenes isolates included genotyping by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). Disinfectant-susceptibility tests and the assessment of L. monocytogenes survival in fresh cheese were also conducted. During the sampling period between 2010 and 2013, a total of 1284 environmental samples were investigated. Overall occurrence rates of Listeria spp. and L. monocytogenes were 21.9% and 19.5%, respectively. Identical L. monocytogenes genotypes were found in the food processing environment (FPE), raw materials and in products. Interventions after the sampling events changed contamination scenarios substantially. The high diversity of globally, widely distributed L. monocytogenes genotypes was reduced by identifying the major sources of contamination. Although susceptible to a broad range of disinfectants and cleaners, one dominant L. monocytogenes sequence type (ST) 5 could not be eradicated from drains and floors. Significantly, intense humidity and steam could be observed in all rooms and water residues were visible on floors due to increased cleaning strategies. This could explain the high L. monocytogenes contamination of the FPE (drains, shoes and floors) throughout the study (15.8%). The outcome of a challenge experiment in fresh cheese showed that L. monocytogenes could survive after 14days of storage at insufficient cooling temperatures (8 and 16°C). All efforts to reduce L. monocytogenes environmental contamination eventually led to a transition from dynamic to stable contamination scenarios. Consequently, implementation of systematic environmental monitoring via in-house systems should either aim for total avoidance of FPE colonization, or emphasize a first reduction of L. monocytogenes to sites where contamination of the processed product is unlikely. Drying of surfaces after cleaning is highly recommended to facilitate the L. monocytogenes eradication.