Pepsin-digested bovine lactoferrin prevents Mozzarella cheese blue discoloration caused by Pseudomonas fluorescens

Natural Antimicrobials in Dairy Products: Benefits, Challenges, and Future Trends

This review delves into using natural antimicrobials in the dairy industry and examines various sources of these compounds, including microbial, plant, and animal sources. It discusses the mechanisms by which they inhibit microbial growth, for example, by binding to the cell wall's precursor molecule of the target microorganism, consequently inhibiting its biosynthesis, and interfering in the molecule transport mechanism, leading to cell death. In general, they prove to be effective against the main pathogens and spoilage found in food, such as Escherichia coli, Staphylococcus aureus, Bacillus spp., Salmonella spp., mold, and yeast. Moreover, this review explores encapsulation technology as a promising approach for increasing the viability of natural antimicrobials against unfavorable conditions such as pH, temperature, and oxygen exposure. Finally, this review examines the benefits and challenges of using natural antimicrobials in dairy products. While natural antimicrobials offer several advantages, including improved safety, quality, and sensory properties of dairy products, it is crucial to be aware of the challenges associated with their use, such as potential allergenicity, regulatory requirements, and consumer perception. This review concludes by emphasizing the need for further research to identify and develop effective and safe natural antimicrobials for the dairy industry to ensure the quality and safety of dairy products for consumers.

Innovative Covering Liquids Stabilising Water-Fat Leachate from Fresh Mozzarella Cheese Used as Pizza Topping

This study analyses the possibility of changing the composition of the covering liquid in which mozzarella cheese is stored. The characterisation of mozzarella cheese consumed fresh and during later culinary use as a pizza topping was carried out. Mozzarella cheese from cow's milk and reconstituted sheep's milk were used for this study. The cheese was stored in whey-based covering liquid to which single or double amounts of lactose and/or citric acid (w/w) were added. The results obtained during laboratory analysis showed that the addition of lactose and/or citric acid to the covering liquid significantly impacted the mass of the cheese and the changes that can occur during later culinary use. The observed changes in the cheese during storage in the covering liquid were confirmed by the characteristics of the liquid itself. The smallest mass changes were related to cheeses stored in a covering liquid with double the amount of lactose and a single amount of citric acid. This cheese also displayed positive changes in all assessed descriptors (texture, melt, and colour). The amount of leachate from the cheese was small and occurred relatively late after unpacking and quartering. Based on the results of the study, changes made to the composition of the covering liquids can positively affect the characteristics of mozzarella cheese. Additionally, this data allows for the creation of specialised mozzarella cheeses that can pique the consumer's interest.

Lactoferricin, an antimicrobial motif derived from lactoferrin with food preservation potential

The growth of bacteria and fungi may cause disease inf human or spoilage of food. New antimicrobial substances need to be discovered. Lactoferricin (LFcin) is a group of antimicrobial peptides derived from the N-terminal region of the milk protein lactoferrin (LF). LFcin has antimicrobial ability against a variety of microorganisms, which is significantly better than that of its parent version. Here, we review the sequences, structures, and antimicrobial activities of this family and elucidated the motifs of structural and functional significance, as well as its application in food. Using sequence and structural similarity searches, we identified 43 new LFcins from the mammalian LFs deposited in the protein databases, which are grouped into six families according to their origins (Primates, Rodentia, Artiodactyla, Perissodactyla, Pholidota, and Carnivora). This work expands the LFcin family and will facilitate further characterization of novel peptides with antimicrobial potential. Considering the antimicrobial effect of LFcin on foodborne pathogens, we describe the application of these peptides from the prospective of food preservation.

Application of Commercial Biopreservation Starter in Combination with MAP for Shelf-Life Extension of Burrata Cheese

Burrata is a fresh pasta filata cheese manufactured in Italy. Its demand on the worldwide market is constantly growing, and prolonging its shelf-life is an important challenge for the Italian dairy industry. In the present study, combining a commercial bio-protective starter and modified atmosphere packaging (MAP) was evaluated as a strategy to delay the spoilage of product quality. Three experimental samples of burrata were produced by experimental trials at the industrial level and stored for 28 days under refrigerated conditions. Two samples contained the protective starter but were packaged differently (under MAP and immersed in water), and one did not contain the starter and was packaged under MAP. A sample of burrata without a starter and immersed in water was also prepared and used as a control. The combination of MAP and bio-protective starter delayed the degradation of lactose and citric acid, used as indices of microbial activity. In fact, lower counts of Enterobacteriaceae and Pseudomonas were observed in this sample. In contrast, control burrata had the highest level of total Volatile Organic Compounds (VOC) at the end of the storage period, because of higher microbial activity. Even though all samples were judged to be unacceptable after 28 days from the sensory point of view, the sample with bio-protective starter under MAP had the best score after 21 days, obtaining a shelf-life extension of about 7 days with respect to control. In conclusion, the combination of MAP and protective starter culture could be an easy way to extend the shelf-life of burrata stored under correct refrigerated conditions.

The Complex Role of Lactic Acid Bacteria in Food Detoxification

Toxic ingredients in food can lead to serious food-related diseases. Such compounds are bacterial toxins (Shiga-toxin, listeriolysin, Botulinum toxin), mycotoxins (aflatoxin, ochratoxin, zearalenone, fumonisin), pesticides of different classes (organochlorine, organophosphate, synthetic pyrethroids), heavy metals, and natural antinutrients such as phytates, oxalates, and cyanide-generating glycosides. The generally regarded safe (GRAS) status and long history of lactic acid bacteria (LAB) as essential ingredients of fermented foods and probiotics make them a major biological tool against a great variety of food-related toxins. This state-of-the-art review aims to summarize and discuss the data revealing the involvement of LAB in the detoxification of foods from hazardous agents of microbial and chemical nature. It is focused on the specific properties that allow LAB to counteract toxins and destroy them, as well as on the mechanisms of microbial antagonism toward toxigenic producers. Toxins of microbial origin are either adsorbed or degraded, toxic chemicals are hydrolyzed and then used as a carbon source, while heavy metals are bound and accumulated. Based on these comprehensive data, the prospects for developing new combinations of probiotic starters for food detoxification are considered.

Recent Advances in the Mechanisms and Regulation of QS in Dairy Spoilage by Pseudomonas spp

Food spoilage is a serious issue dramatically impacting the worldwide need to counteract food insecurity. Despite the very expensive application of low temperatures, the proper conservation of fresh dairy products is continuously threatened at different stages of production and commercialization by psychrotrophic populations mainly belonging to the Pseudomonas genus. These bacteria cause discolouration, loss of structure, and off-flavours, with fatal implications on the quality and shelf-life of products. While the effects of pseudomonad decay have been widely reported, the mechanisms responsible for the activation and regulation of spoilage pathways are still poorly explored. Recently, molecule signals and regulators involved in quorum sensing (QS), such as homoserine lactones, the luxR/luxI system, hdtS, and psoR, have been detected in spoiled products and bacterial spoiler species; this evidence suggests the role of bacterial cross talk in dairy spoilage and paves the way towards the search for novel preservation strategies based on QS inhibition. The aim of this review was to investigate the advancements achieved by the application of omic approaches in deciphering the molecular mechanisms controlled by QS systems in pseudomonads, by focusing on the regulators and metabolic pathways responsible for spoilage of fresh dairy products. In addition, due the ability of pseudomonads to quickly spread in the environment as biofilm communities, which may also include pathogenic and multidrug-resistant (MDR) species, the risk derived from the gaps in clearly defined and regulated sanitization actions is underlined.

A Food-Grade Resin with LDH–Salicylate to Extend Mozzarella Cheese Shelf Life

Mozzarella cheese can be considered by far the world’s most popular Italian dairy product. Extending the shelf life of mozzarella cheese is an important issue in the dairy industry due to the high risk of contamination by several bacteria species, including spoilage pseudomonads. In this work, active packaging was prepared by coating traditional polyethylene terephthalate (PET) containers of “ovoline” mozzarella cheese with a food-grade resin mixed with a layered double hydroxide (LDH) in which salicylate anion was intercalatedby ionic exchange.. This antimicrobial molecule is listed in EC-Directive 10/2011/EC of 14 January 2011. Morphological arrangement of the molecule into the LDH layers was evaluated by X-ray diffraction (XRD) and controlled release followed by UV spectroscopy. Then, active trays were used to pack the mozzarella cheeses stored for 20 days at 4 °C and under thermal abuse (15 °C). Samples from both conditions showed coliform reduction (by ca. 2 log CFU/g) throughout the storage period. Depending on temperature, total mesophilic aerobic bacteria, Pseudomonas spp., yeasts, and mold loads were reduced in the first 3 days; at 4 °C. Slower acidification and lower proteolysis were also found in treated samples in comparison to control ones. The fitting of the Gompertz function to coliforms and spoilage pseudomonads highlighted an increase in the shelf life of mozzarella cheese of ca. 2 days at 4 °C. These results suggest that salicylate–LDH-coated PET may be applied to extend the shelf-life of mozzarella cheese and also counteract its spoilage if accidental interruptions to refrigeration occur.

Identification of the Pseudomonas fluorescens group as being responsible for blue pigment on fresh cheese

New cases of blue cheese discoloration has led to recent research to identify the causal agent and factors that favor blue pigment appearing. Nonetheless, very few reports have described the source of contamination and the measurements to eradicate the microbiological source on cheese farms by determining the relation between blue discoloration on fresh cheese and the Pseudomonas fluorescens group. Thus, 60 samples from a cheese farm (cheese, equipment surfaces, tap water, and raw and pasteurized milk) were analyzed by phenotypical, MALDI-TOF, 16S rRNA sequencing and pulsed-field gel electrophoresis tests to determine the causal agent. The results obtained by pulsed-field gel electrophoresis with restriction enzymes XbaI and SpeI confirmed tap water as the initial contaminated source. The above-mentioned result was essential to avoid Pseudomonas contamination due to the most residual microorganisms being inactivated through a new disinfection program.

Interactions between L. monocytogenes and P. fluorescens in Dual-Species Biofilms under Simulated Dairy Processing Conditions

In dairy processing environments, many bacterial species adhere and form biofilms on surfaces and equipment, leading to foodborne illness and food spoilage. Among them, Listeria monocytogenes and Pseudomonas spp. could be present in mixed-species biofilms. This study aimed to evaluate the interactions between L. monocytogenes and P. fluorescens in biofilms simulating dairy processing conditions, as well as the capability of P. fluorescens in co-culture to produce the blue pigment in a Ricotta-based model system. The biofilm-forming capability of single- and mixed-cultures was evaluated on polystyrene (PS) and stainless steel (SS) surfaces at 12 °C for 168 h. The biofilm biomass was measured, the planktonic and sessile cells and the carbohydrates in biofilms were quantified. The biofilms were also observed through Confocal Laser Scanning Microscopy analysis. Results showed that only P. fluorescens was able to form biofilms on PS. Moreover, in dual-species biofilms at the end of the incubation time (168 h at 12 °C), a lower biomass compared to P. fluorescens mono-species was observed on PS. On SS, the biofilm cell population of L. monocytogenes was higher in the dual-species than in mono-species, particularly after 48 h. Carbohydrates quantity in the dual-species system was higher than in mono-species and was revealed also at 168 h. The production of blue pigment by P. fluorescens was revealed both in single- and co-culture after 72 h of incubation (12 °C). This work highlights the interactions between the two species, under the experimental conditions studied in the present research, which can influence biofilm formation (biomass and sessile cells) but not the capability of P. fluorescens to produce blue pigment.

Combining natural antimicrobials and nanotechnology for disinfecting food surfaces and control microbial biofilm formation

The elimination of microbial surface contaminants is one of the most important steps in Good Manufacturing Practices in order to maintain food safety. This is usually achieved by detergents and chemical sanitizers, although an increased demand exists for the use of natural products for disinfection purposes. Several natural substances present antibacterial activity against the main foodborne pathogens, demonstrating great potential for use in the food industry. Some difficulties such as high volatility, residual taste and/or degradation by exposure to harsh processing conditions have been reported. Nanoparticle encapsulation appears as a strategy to protect bioactive compounds, maintaining their antimicrobial activity and providing controlled release as well. This article presents the potential of natural antimicrobials and their combination with nanotechnological strategies as an alternative for food surface disinfection and prevent microbial biofilm formation.

Genomic Analysis of Three Cheese-Borne Pseudomonas lactis with Biofilm and Spoilage-Associated Behavior

Psychrotrophic pseudomonads cause spoilage of cold fresh cheeses and their shelf-life reduction. Three cheese-borne Pseudomonas sp., ITEM 17295, ITEM 17298, and ITEM 17299 strains, previously isolated from mozzarella cheese, revealed distinctive spoilage traits based on molecular determinants requiring further investigations. Genomic indexes (ANI, isDDH), MLST-based phylogeny of four housekeeping genes (16S rRNA, gyrB, rpoB and rpoD) and genome-based phylogeny reclassified them as Pseudomonas lactis. Each strain showed distinctive phenotypic traits at 15 and 30 °C: ITEM 17298 was the highest biofilm producer at both temperatures, whilst ITEM 17295 and ITEM 17299 showed the strongest proteolytic activity at 30 °C. A wider pattern of pigments was found for ITEM 17298, while ITEM 17295 colonies were not pigmented. Although the high genomic similarity, some relevant molecular differences supported this phenotypic diversity: ITEM 17295, producing low biofilm amount, missed the pel operon involved in EPS synthesis and the biofilm-related Toxin-Antitoxin systems (mqsR/mqsA, chpB/chpS); pvdS, required for the pyoverdine synthesis, was a truncated gene in ITEM 17295, harboring, instead, a second aprA involved in milk proteolysis. This work provided new insight into the food spoiler microbiota by identifying these mozzarella cheese spoilers as P. lactis; molecular targets to be exploited in the development of novel preservative strategies were also revealed.

Biofilm and Pathogenesis-Related Proteins in the Foodborne P. fluorescens ITEM 17298 With Distinctive Phenotypes During Cold Storage

In food chain, Pseudomonas spp. cause spoilage by reducing shelf life of fresh products, especially during cold storage, with a high economic burden for industries. However, recent studies have shed new light on health risks occurring when they colonize immunocompromised patient tissues. Likewise to P. aeruginosa, they exhibit antibiotic resistance and biofilm formation, responsible for their spread and persistence in the environment. Biofilm formation might be induced by environmental stresses, such as temperature fluctuations causing physiological and metabolic changes exacerbating food spoilage (by protease and pigment synthesis), and the production of adhesion molecules, chemotactic or underestimated virulence factors. In order to provide a new insight into phenotypic biodiversity of Pseudomonas spoilers isolated from cold stored cheese, in this work 19 Pseudomonas spp. were investigated for biofilm, pigments, exopolysaccharide production and motility at low temperature. Only nine strains showed these phenotypic traits and the blue pigmenting cheese strain P. fluorescens ITEM 17298 was the most distinctive. In addition, this strain decreased the survival probability of infected Galleria mellonella larvae, showing, for the first time, a pathogenic potential. Genomic and proteomic analyses performed on the ITEM 17298 planktonic cells treated or not with lactoferrin derived antibiofilm peptides allowed to reveal specific biofilm related-pathways as well as proteins involved in pathogenesis. Indeed, several genes were found related to signaling system by cGMP-dependent protein kinases, cellulose, rhamnolipid and alginate synthesis, antibiotic resistance, adhesion and virulence factors. The proteome of the untreated ITEM 17298, growing at low temperature, showed that most of the proteins associated with biofilm regulation, pigmentation motility, antibiotic resistance and pathogenecity were repressed, or decreased their levels in comparison to that of the untreated cultures. Thus, the results of this work shed light on the complex pathways network allowing psychrotrophic pseudomonads to adapt themselves to food-refrigerated conditions and enhance their spoilage. In addition, the discovery of virulence factors and antibiotic resistance determinants raises some questions about the need to deeper investigate these underestimated bacteria in order to increase awareness and provide input to update legislation on their detection limits in foods.

The Effect of Lactoferrin and Pepsin-Treated Lactoferrin on IEC-6 Cell Damage Induced by Clostridium Difficile Toxin B

Clostridium difficile infections (CDI) have recently increased worldwide. Some CDI progress to fulminant and recurrent CDI and are associated with high mortality and morbidity. CD produces toxins A and B, which cause intestinal mucosal damage, although toxin B exhibits greater cytotoxicity. Pepsin-treated lactoferrin (PLF) is the decomposed product of lactoferrin (LF), a multifunctional glycoprotein with anti-inflammatory properties. Here, we investigate the effects of LF and PLF in toxin B-stimulated rat intestinal epithelial (IEC-6) cells. Different toxin B concentrations were added to IEC-6 cells with or without LF or PLF. Mitochondrial function and cell cytotoxicity were assessed by measuring WST-1 and LDH levels, respectively. WST-1 levels were higher in IEC-6 cells treated with toxin B and LF or PLF than in the toxin B-only control (P < 0.05). Compared with the toxin B-only control, LDH levels significantly decreased after toxin B and LF or PLF addition (P < 0.05). Wound restitution measurement using microscopy demonstrated significantly greater levels of wound restitution in cells treated with toxin B and LF or PLF than in those treated with toxin B alone after 12 h (P < 0.001). Furthermore, changes in IEC-6 cell tight junctions (TJs) were evaluated by immunofluorescence microscopy and zonula occludens-1 (ZO-1) protein expression. When LF or PLF were added to IEC-6 cells, TJ structures were maintained, and ZO-1 and occludin expression was upregulated. Taken together, these results demonstrate that LF and PLF prevent the cytotoxicity of toxin B and might have the potential to control CDI.

Antibiotic Resistant Pseudomonas Spp. Spoilers in Fresh Dairy Products: An Underestimated Risk and the Control Strategies

Microbial multidrug resistance (MDR) is a growing threat to public health mostly because it makes the fight against microorganisms that cause lethal infections ever less effective. Thus, the surveillance on MDR microorganisms has recently been strengthened, taking into account the control of antibiotic abuse as well as the mechanisms underlying the transfer of antibiotic genes (ARGs) among microbiota naturally occurring in the environment. Indeed, ARGs are not only confined to pathogenic bacteria, whose diffusion in the clinical field has aroused serious concerns, but are widespread in saprophytic bacterial communities such as those dominating the food industry. In particular, fresh dairy products can be considered a reservoir of Pseudomonas spp. resistome, potentially transmittable to consumers. Milk and fresh dairy cheeses products represent one of a few "hubs" where commensal or opportunistic pseudomonads frequently cohabit together with food microbiota and hazard pathogens even across their manufacturing processes. Pseudomonas spp., widely studied for food spoilage effects, are instead underestimated for their possible impact on human health. Recent evidences have highlighted that non-pathogenic pseudomonads strains (P. fluorescens, P. putida) are associated with some human diseases, but are still poorly considered in comparison to the pathogen P. aeruginosa. In addition, the presence of ARGs, that can be acquired and transmitted by horizontal genetic transfer, further increases their risk and the need to be deeper investigated. Therefore, this review, starting from the general aspects related to the physiological traits of these spoilage microorganisms from fresh dairy products, aims to shed light on the resistome of cheese-related pseudomonads and their genomic background, current methods and advances in the prediction tools for MDR detection based on genomic sequences, possible implications for human health, and the affordable strategies to counteract MDR spread.

Spectrophotometric techniques for the characterization of strains involved in the blue pigmentation of food: Preliminary results

Near infrared spectroscopy (NIRs) and ultraviolet visible spectroscopy (UV-vis) have been investigated as rapid techniques to characterize foodborne bacteria through the analysis of the spectra of whole cells or microbial suspensions. The use of spectra collected from broth cultures could be used as a fingerprint for strain classification using a combined polyphasic approach. The aim of this study was to evaluate the feasibility of NIRs and UV-vis for the characterization of blue strains belonging to the Pseudomonas fluorescens group. The bacteria were isolated from different food matrices, including some spoiled samples (blue discoloration). Eightyone strains previously identified at the species level were grown in Minimal Bacterial Medium broth under standard conditions at 22°C. Two biological replicates were centrifuged in order to separate the bacterial cells from the extracellular products. Six aliquots per strain were analyzed on a small ring cup in transflectance mode (680-2500 nm, gap 2 nm). A subset of 39 strains was evaluated by UV-vis to determine changes in the spectral characteristics at 48 and 72 hours. Several chemometric approaches were tested to assess the performance of NIRs and UVvis. According to the variable importance in projection (VIP), the 1892-2020 nm spectral region showed the highest level of discrimination between blue strains and others. Additional information was provided in the 680-886 and 1454-1768 nm regions (aromatic C-H bonds) and in the 2036-2134 nm region (fatty acids). Changes in UV-vis spectral data (at 48 and 72 hours) appear to indicate the presence of phenazine and catecholic compounds in extracellular products.

A review of the design and modification of lactoferricins and their derivatives

Lactoferricin (Lfcin), a multifunction short peptide with a length of 25 residues, is derived from the whey protein lactoferrin by acidic pepsin hydrolysis. It has potent nutritional enhancement, antimicrobial, anticancer, antiviral, antiparasitic, and anti-inflammatory activities. This review describes the research advantages of the above biological functions, with attention to the molecular design and modification of Lfcin. In this examination of design and modification studies, research on the identification of Lfcin active derivatives and crucial amino acid residues is also reviewed. Many strategies for Lfcin optimization have been studied in recent decades, but we mainly introduce chemical modification, cyclization, chimera and polymerization of this peptide. Modifications such as incorporation of D-amino acids, acetylation and/or amidation could effectively improve the activity and stability of these compounds. Due to their wide array of bio-functions and applications, Lfcins have great potential to be developed as biological agents with multiple functions involved with nutritional enhancement, as well as disease preventive and therapeutic effects.

Draft Genome Sequence of Pseudomonas fluorescens Strain ITEM 17298, Associated with Cheese Spoilage

Pseudomonas fluorescens is a genetically and phenotypically heterogeneous species that is often reported as a spoiler of fresh foods, but it has recently been implicated in clinical infection. In this study, we sequenced the genome of P. fluorescens strain ITEM 17298, isolated from mozzarella cheese and able to cause several alterations under cold storage.

Reduction of whey protein concentrate antigenicity by using a combined enzymatic digestion and ultrafiltration approach

The global interest in saving food resources is leading to recycle wasted-food materials to extract useful nutrients. In dairy industry, the recycling of whey proteins determines their utilization in the healthy-addressed foods, which, however, can cause immunological responses in allergic subjects. In this work, a whey protein concentrate (WPC) was alternatively hydrolyzed with pepsin, papain, trypsin and rennin in order to attenuate or abolish the β-lactoglobulin (BLG) antigenicity. The electrophoretic profiles of both pepsin and papain WPC hydrolysates proved the disappearance of the BLG band, even though a slight antigenicity was still found by ELISA. Pepsin hydrolysates, filtered through a 10-kDa cut-off membrane, did not produce immunological response. A deeper investigation carried out on pepsin digested and ultrafiltered samples by LC-MS/MS showed the disappearance of the immunoreactive BLG-fragment IVTQMKGLDIQKVAGTW. The remaining peptides, partially overlapped to major IgE binding epitopes, were not able to give immunoreactivity response. The combined WPC pepsin digestion with ultrafiltration confirmed to be a user-friendly strategy to reduce markedly the WPC antigenicity. The improvement of this two-steps process could be used to produce novel hypoallergenic infant food formulas.

Development of a Synbiotic Beverage Enriched with Bifidobacteria Strains and Fortified with Whey Proteins

The objective of this study was to develop a new synbiotic beverage evaluating the ability of some bifidobacteria strains to grow in this beverage which was fortified with whey proteins up to 20 g L^-1, and enriched with 10 g L^-1 of prebiotic inulin or resistant starch. The ability of Bifidobacterium strains to survive for 30 days at 4°C was evaluated in two synbiotic whey protein fortified beverages formulated with 2% of whey proteins and 1% of inulin or resistant starch. Microbial growth was significantly affected by the whey protein amount as well as by the kind of prebiotic fiber. Resistant starch promoted the growth of the Bifidobacterium pseudocatenulatum strain and its viability under cold storage, also conferring higher sensory scores. The development of this new functional beverage will allow to carry out in vivo trials in order to validate its pre- and probiotic effects.

Influence of Incubation Conditions on Biofilm Formation by Pseudomonas Fluorescens Isolated from Dairy Products and Dairy Manufacturing Plants

In this study, biofilm formation of 64 Pseudomonas fluorescens strains isolated from milk, dairy products and dairy plants was compared. The strains were grown on Tryptic Soy Broth supplemented with 0.2% of glucose, on polystyrene microplates at 10 and 30°C for 48 h. In general, 57/64 P. fluorescens strains formed biofilm, although with great variability at both tested temperatures. Moreover, our results evidenced that the biofilm-forming ability of the strains was temperature- and strain-dependent. Interestingly, the ability of several isolates to form biofilms was associated with the low temperature after 48 h. Our findings evidenced that temperature was more important than incubation time for biofilm formation. Considering the origin of the strains, it is relevant to underline the importance of performing accurate cleaning and disinfection procedures on food processing surfaces.

Strain Diversity of Pseudomonas fluorescens Group with Potential Blue Pigment Phenotype Isolated from Dairy Products

The blue discoloration in Mozzarella cheese comes from bacterial spoilage due to contamination with Pseudomonas. Fourteen Pseudomonas fluorescens strains from international collections and 55 new isolates of dominant bacterial populations from spoiled fresh cheese samples were examined to assess genotypic and phenotypic strain diversity. Isolates were identified by 16S rRNA gene sequencing and tested for the production of the blue pigment at various temperatures on Mascarpone agar and in Mozzarella preserving fluid (the salty water in which the cheese is conserved, which becomes enriched by cheese minerals and peptides during storage). Pulsed-field gel electrophoresis analysis after treatment with the endonuclease SpeI separated the isolates into 42 genotypes at a similarity level of 80%. Based on the pulsotype clustering, 12 representative strains producing the blue discoloration were chosen for the multilocus sequence typing targeting the gyrB, glnS, ileS, nuoD, recA, rpoB, and rpoD genes. Four new sequence typing profiles were discovered, and the concatenated sequences of the investigated loci grouped the tested strains into the so-called ''blue branch'' of the P. fluorescens phylogenetic tree, confirming the linkage between pigment production and a specific genomic cluster. Growth temperature affected pigment production; the blue discoloration appeared at 4 and 14°C but not at 30°C. Similarly, the carbon source influenced the phenomenon; the blue phenotype was generated in the presence of glucose but not in the presence of galactose, sodium succinate, sodium citrate, or sodium lactate.

Modelling and predicting growth of psychrotolerant pseudomonads in milk and cottage cheese

Mathematical models were developed and evaluated for growth of psychrotolerant pseudomonads in chilled milk and in cottage cheese with cultured cream dressing. The mathematical models include the effect of temperature, pH, NaCl, lactic acid and sorbic acid. A simplified cardinal parameter growth rate model was developed based on growth in broth. Subsequently, the reference growth rate parameter μref25°C-broth of 1.031/h was calibrated by fitting the model to a total of 35 growth rates from cottage cheese with cultured cream dressing. This resulted in a μref25°C-cottage cheese value of 0.621/h. Predictions from both growth rate models were evaluated by comparison with literature and experimental data. Growth of psychrotolerant pseudomonads in heat-treated milk (n=33) resulted in a bias factor (Bf) of 1.08 and an accuracy factor (Af) of 1.32 (μref25°C-broth), whereas growth in cottage cheese with cultured cream dressing and in non-heated milk (n=26) resulted in Bf of 1.08 and Af of 1.43 (μref25°C-cottage cheese). Lag phase models were developed by using relative lag times and data from both the present study and from literature. The acceptable simulation zone method showed the developed models to successfully predict growth of psychrotolerant pseudomonads in milk and cottage cheese at both constant and dynamic temperature storage conditions. The developed models can be used to predict growth of psychrotolerant pseudomonads and shelf life of chilled cottage cheese and milk at constant and dynamic storage temperatures. The applied methodology and the developed models seem likely to be applicable for shelf life assessment of other types of products where psychrotolerant pseudomonads are important for spoilage.

Antimicrobial Activity of Lactoferrin-Related Peptides and Applications in Human and Veterinary Medicine

Antimicrobial peptides (AMPs) represent a vast array of molecules produced by virtually all living organisms as natural barriers against infection. Among AMP sources, an interesting class regards the food-derived bioactive agents. The whey protein lactoferrin (Lf) is an iron-binding glycoprotein that plays a significant role in the innate immune system, and is considered as an important host defense molecule. In search for novel antimicrobial agents, Lf offers a new source with potential pharmaceutical applications. The Lf-derived peptides Lf(1-11), lactoferricin (Lfcin) and lactoferrampin exhibit interesting and more potent antimicrobial actions than intact protein. Particularly, Lfcin has demonstrated strong antibacterial, anti-fungal and antiparasitic activity with promising applications both in human and veterinary diseases (from ocular infections to osteo-articular, gastrointestinal and dermatological diseases).

Efficacy of lactoferricin B in controlling ready-to-eat vegetable spoilage caused by Pseudomonas spp

The microbial content of plant tissues has been reported to cause the spoilage of ca. 30% of chlorine-disinfected fresh vegetables during cold storage. The aim of this work was to evaluate the efficacy of antimicrobial peptides in controlling microbial vegetable spoilage under cold storage conditions. A total of 48 bacterial isolates were collected from ready-to-eat (RTE) vegetables and identified as belonging to Acinetobacter calcoaceticus, Aeromonas media, Pseudomonas cichorii, Pseudomonas fluorescens, Pseudomonas jessenii, Pseudomonas koreensis, Pseudomonas putida, Pseudomonas simiae and Pseudomonas viridiflava species. Reddish or brownish pigmentation was found when Pseudomonas strains were inoculated in wounds on leaves of Iceberg and Trocadero lettuce and escarole chicory throughout cold storage. Bovine lactoferrin (BLF) and its hydrolysates (LFHs) produced by pepsin, papain and rennin, were assayed in vitro against four Pseudomonas spp. strains selected for their heavy spoiling ability. As the pepsin-LFH showed the strongest antimicrobial effect, subsequent experiments were carried out using the peptide lactoferricin B (LfcinB), well known to be responsible for its antimicrobial activity. LfcinB significantly reduced (P ≤ 0.05) spoilage by a mean of 36% caused by three out of four inoculated spoiler pseudomonads on RTE lettuce leaves after six days of cold storage. The reduction in the extent of spoilage was unrelated to viable cell density in the inoculated wounds. This is the first paper providing direct evidence regarding the application of an antimicrobial peptide to control microbial spoilage affecting RTE leafy vegetables during cold storage.

Coexistence of Lactic Acid Bacteria and Potential Spoilage Microbiota in a Dairy Processing Environment

Microbial contamination in food processing plants can play a fundamental role in food quality and safety. In this study, the microbiota in a dairy plant was studied by both 16S rRNA- and 26S rRNA-based culture-independent high-throughput amplicon sequencing. Environmental samples from surfaces and tools were studied along with the different types of cheese produced in the same plant. The microbiota of environmental swabs was very complex, including more than 200 operational taxonomic units with extremely variable relative abundances (0.01 to 99%) depending on the species and sample. A core microbiota shared by 70% of the samples indicated a coexistence of lactic acid bacteria with a remarkable level of Streptococcus thermophilus and possible spoilage-associated bacteria, including Pseudomonas, Acinetobacter, and Psychrobacter, with a relative abundance above 50%. The most abundant yeasts were Kluyveromyces marxianus, Yamadazyma triangularis, Trichosporon faecale, and Debaryomyces hansenii. Beta-diversity analyses showed a clear separation of environmental and cheese samples based on both yeast and bacterial community structure. In addition, predicted metagenomes also indicated differential distribution of metabolic pathways between the two categories of samples. Cooccurrence and coexclusion pattern analyses indicated that the occurrence of potential spoilers was excluded by lactic acid bacteria. In addition, their persistence in the environment can be helpful to counter the development of potential spoilers that may contaminate the cheeses, with possible negative effects on their microbiological quality.