The wooden shelf surface and cheese rind mutually exchange microbiota during the traditional ripening process.

The rind acts as a protective barrier for internally-bacterial ripened cheeses. Unlike surface-inoculated smear cheeses, centripetal maturation is not assumed to occur in these cheeses. This research was aimed to evaluate the microbial diversity of the wooden shelves used for the ripening of Protected Denomination of Origin (PDO) Pecorino di Filiano and Protected Geographical Indication (PGI) Canestrato di Moliterno cheeses. The microorganisms associated with the rind of these cheeses were also investigated. Both wooden shelf surfaces and cheese rinds were sampled by brushing method to collect their biofilms. Wooden shelves showed levels of total mesophilic microorganisms (TMM) between 5.6 and 7.2 log CFU/cm2, while cheese rinds between 6.1 and 7.8 log CFU/cm2. The major dairy pathogens (Salmonella spp., Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus) were never detected, while mesophilic and thermophilic bacteria dominated the surfaces of all wooden shelves and cheese rinds. LAB community was represented by Enterococcus spp., Leuconostoc spp., and Marinilactibacillus spp. Among yeasts, Debaryomyces spp., Candida spp., were identified, while Aspergillus spp., and Penicillium spp., dominated the community of filamentous fungi. MiSeq Illumina analysis identified 15 phyla, 13 classes, 28 orders, 54 families, and 56 genera among bacteria. Staphylococcus spp. was identified from all wooden surfaces, with a maximum abundance of 71 %. Brevibacterium, Corynebacterium and halophilic bacteria were detected in almost all samples. Regarding fungi, wooden shelves mainly hosted Aspergillus, Penicillium and Debaryomyces hansenii, while cheese rinds especially Penicillium and D. hansenii. Alpha diversity confirmed a strict correlation between the microbiota of wooden shelves and that of cheese rinds for the majority of factories. This study confirmed that the wooden shelves used for cheese ripening are microbiologically active and represent safe systems. Furthermore, the results of this work clarified the transfer flow between wooden shelves and PDO Pecorino di Filiano and PGI Canestrato di Moliterno cheese surfaces: smear-active microorganisms are mainly transferred from wooden shelves to cheese rind, which potentially contribute to the development of the final organoleptic characteristics; meanwhile, cheeses transfer LAB that are potentially involved in defining the safety aspects of the shelves.

Identification, activity and delivery of new LysFA67 endolysin to target cheese spoilage Clostridium tyrobutyricum.

Bacteriophages and their endolysins are potential biocontrol agents for the anaerobic spoilage organism Clostridium tyrobutyricum, which causes cheese late blowing defect. This study sequenced and compared the genomes of eight bacteriophages from Spanish dairy farms that were active against C. tyrobutyricum, to identify novel species and phage proteins. Phages vB_CtyS-FA67 and vB_CtyS-FA70 shared >94% intergenomic similarity to each other but neither phage had significant similarity to ΦCTP1, the unique C. tyrobutyricum phage sequenced to date. Taxonomic analysis indicated that both phages belong to the class Caudoviricetes and are related to dsDNA viruses with long non-contractile tails. vB_CtyS-FA67 had no other close relatives and encoded a novel endolysin, LysFA67, predicted to belong to the glycoside hydrolase GH24 family. LysFA67 lysed 93% of C. tyrobutyricum cells after 4 min in turbidity reduction assays, retaining lytic activity at pHs 4.2-8.1 and at 30-45 °C. The endolysin remained stable after 30 d storage at 4, 12 and 25 °C, while its activity decreased at -20 °C. LysFA67 lysed several clostridia species, while common dairy bacteria were not affected. Lactococcus lactis INIA 437, used as a cheese starter, was engineered to deliver LysFA67 and red fluorescent LysFA67-mCherry to dairy products. We demonstrated that these engineered strains were able to maintain lytic activity and fluorescence without affecting their technological properties in milk.

Reduction of histamine, putrescine and cadaverine by the bacteria Lacticaseibacillus casei depending on selected factors in the real condition of the dairy product.

One way to effectively reduce the number of biogenic amines (BAs) in food is through enzymatic reduction using bacteria, such as lactic acid bacteria. This study focuses on the ability of the bacterial strain Lacticaseibacillus casei CCDM 198 to reduce the number of three important BAs (histamine, putrescine and cadaverine) over time, depending on different conditions (temperature and pH) in vitro and for the real dairy product - skimmed milk. The obtained results show that the studied strain significantly (P < 0.05) affects the number of individual amines, and the content of all amines has a decreasing character compared to the initial relative content of BAs at time zero. Furthermore, a statistical dependence (P < 0.05) of the rate of amine degradation on the combination of investigated factors was demonstrated. The presence and the activity of multicopper oxidase enzyme was also detected in this bacterial strain. This is the first known publication demonstrating multicopper oxidase activity in Lacticaseibacillus casei CCDM 198. Moreover, the studied strain is able to reduce the tested BAs in skimmed milk and would be a good candidate for degrading these toxic compounds in other dairy products, such as cheese. These findings could significantly enhance the food safety of dairy products.

Isolation and characterization of lactic acid bacteria with probiotic potential from traditional fermented special Kurdish cheese (Zhazhi) in Kurdistan Region, Iraq.

 Zhazhi cheese is a unique farmhouse traditional fermented dairy of the Kurdistan Region in Iraq for its desired aroma and flavor. Undoubtedly, the lactic acid bacteria (LAB) are the critical factors in developing the aroma, flavor, and texture of Zhazhi cheese but it has not been studied or characterised. LAB has many important nutritional benefits, including increasing the nutritional value of food. Therefore, this research was performed to isolate and identify the potential probiotic LAB from traditional homemade Kurdish cheese. Then, the identified strains were tested to determine their probiotics traits, which include acid resistance, bile-salt tolerance, haemolytic, DNase, hydrophobic, autoaggregation, antimicrobial and antibiotic activities. The isolated five LAB strains comprised Lactobacillus casei, Lactobacillus rhamnosus, Enterococcus faecium, Pediococcus pentocaseus and Lactobacillus helvaticum were recognized as promising and the most potential probiotics for further applications. This is the first report on the direct selection of potentially probiotic LAB from Kurdish special cheese (Zhazhi).

Epicoccum sp. as the causative agent of a reddish-brown spot defect on the surface of a hard cheese made of raw ewe milk.

Colour defects can affect the appearance of cheese, its flavour, the safety of its consumption, and the price it can demand. This work reports the identification of five fungal isolates from a dairy plant where the surface of most cheeses was affected by patent, reddish-to-brown stains. One of these isolates was obtained from cheese, two from brine, and two from a bulk tank containing ewe milk. Molecular identification by partial amplification, sequencing, and database comparison of the concatenated sequence of the genes coding for the largest subunit of RNA polymerase II (RPB2), ß-tubulin (ß-TUB), and the large subunit of the rRNA molecule (LSU), plus the internal transcribed sequence (ITS) regions, assigned the isolates to Epicoccum layuense, Epicoccum italicum, and Epicoccum mezzettii. Features of the growth of these different species on different agar-based media, and of the morphology of their conidia following sporulation, are also reported. The strain isolated from cheese, E. layuense IPLA 35011, was able to recreate the reddish-brown stains on slices of Gouda-like cheese, which linked the fungus with the colour defect. In addition, two other strains, E. italicum IPLA 35013 from brine and E. italicum IPLA 35014 from milk, also produced stains on cheese slices. Epicoccum species are widely recognized as plant pathogens but have seldom been reported in the dairy setting, and never as human or animal pathogens.

Impact of sodium chloride and carbon dioxide on conidial germination and radial growth of Penicillium camemberti.

Penicillium camemberti is a domesticated species adapted to the dairy environment, which is used as adjunct cultures to ripen soft cheeses. A recent population genomics analysis on P. camemberti revealed that P. camemberti is a clonal lineage with two varieties almost identical genetically but with contrasting phenotypes in terms of growth, color, mycotoxin production and inhibition of contaminants. P. camemberti variety camemberti is found on Camembert and Brie cheeses, and P. camemberti variety caseifulvum is mainly found on other cheeses like Saint-Marcellin and Rigotte de Condrieu. This study aimed to evaluate the impact of water activity (aw) reduced by sodium chloride (NaCl) and the increase of carbon dioxide (CO2) partial pressure, on conidial germination and growth of two varieties of P. camemberti: var. Camemberti and var. Caseifulvum. Mathematical models were used to describe the responses of P. camemberti strains to both abiotic factors. The results showed that these genetically distant strains had similar responses to increase in NaCl and CO2 partial pressure. The estimated cardinal values were very close between the strains although all estimated cardinal values were significantly different (Likelihood ratio tests, pvalue = 0.05%). These results suggest that intraspecific variability could be more exacerbated during fungal growth compared with conidial germination, especially in terms of macroscopic morphology. Indeed, var. Caseifulvum seemed to be more sensitive to an increase of CO2 partial pressure, as shown by the fungal morphology, with the occurrence of irregular outgrowths, while the morphology of var. Camemberti remains circular. These data could make it possible to improve the control of fungal development as a function of salt and carbon dioxide partial pressure. These abiotic factors could serve as technological barriers to prevent spoilage and increase the shelf life of cheeses. The present data will allow more precise predictions of fungal proliferation as a function of salt and carbon dioxide partial pressure, which are significant technological hurdles in cheese production.

The impact of environmental conditions and milk type on microbial communities of wooden vats and cheeses produced therein.

Wooden vats are used in the production of some traditional cheeses as the biofilms on wooden vat surfaces are known to transfer large quantities of microbes to cheese. Variability in microbial communities on wooden vats could lead to inconsistent cheese production. In the present study, the influences of environmental conditions and milk type (raw or heat-treated) on the microbial composition of vat biofilms and cheeses made in the vats were studied using amplicon sequencing of bacterial 16S rRNA and fungal internal transcribed spacer genes. Results showed that the microbial composition of biofilms was influenced by environmental conditions but not the milk type used in cheese production. The microbial composition of cheeses can be further affected by bacterial contributions from milk and the selective forces of environmental conditions. Results of this study suggest that controlling environmental conditions could maintain a more consistent microbial composition of biofilms on wooden vats and resulting cheeses. The use of wooden vats coupled with heat-treated milk at one or more stages of cheese production might be a viable approach to produce cheese with high microbial diversities and reduce risks of undesirable microbes related to food safety and quality.

Fabrication of carboxymethyl chitosan films for cheese packaging containing gliadin-carboxymethyl chitosan nanoparticles co-encapsulating natamycin and theaflavins.

In this study, gliadin-carboxymethyl chitosan composite nanoparticles (GC NPs) co-encapsulated natamycin (Nata) and theaflavins (TFs) were constructed and added as an antioxidant, antifungal, and structural enhancer to carboxymethyl chitosan (CMCS) films. The stabilized GC NPs with a particle size of 160.7 ± 2.8 nm, a zeta potential of -29.0 ± 0.9 mV, and a protein content in the supernatant of 96 ± 1 % could be fabricated. Tests of pH and salt ions showed that the stability of NPs dispersion was based on electrostatic repulsion. Co-encapsulation of TFs enhanced the photostability of Nata and the antioxidant activity of the NPs dispersion. The interactions between gliadin with Nata and TFs were studied by molecular simulations. As a functional additive, the addition of Nata/TFs-GC NPs could improve the optical properties, mechanical properties, water-blocking capability, and antifungal and antioxidant activities of the CMCS films. The in-vivo test showed that the functional film could be used to inhibit the growth of Aspergillus niger on cheese.

Potential probiotic lactobacilli strains isolated from artisanal Mexican Cocido cheese: evidence-based biosafety and probiotic action-related traits on in vitro tests.

The biosafety of four potentially probiotic lactobacilli strains, isolated from artisanal Mexican Cocido cheese, was assessed through in vitro tests aimed to determine (1) the antibiotic susceptibility profile by broth microdilution, (2) the transferability of antibiotic resistance determinants by filter-mating, and (3) the phenotypic and genotypic stability during serial batch sub-culture (100-day period) by evaluating physiological and probiotic features and RAPD-PCR fingerprinting. Lactobacilli strains exhibited multidrug-resistance; however, resistance determinants were not transferred in the filter-mating assay. Significant (p < 0.05) differences were observed in bacterial morphology and some functional and technological properties when strains were serially sub-cultured over 50 generations (G50), compared to the initial cultures (G0). Conversely, the strains did not show mucinolytic and hemolytic activities either at G0 or after 100 generations (G100). Genetic polymorphism and genomic template instability on selected strains were detected, which suggest possible evolutionary arrangements that may occur when these bacteria are largely cultured. Our findings suggest that the assessed strains did not raise in vitro biosafety concerns; however, complementary studies are still needed to establish the safe potential applications in humans and animals.

Comparison of Two Shiga Toxin-producing Escherichia coli (STEC) Isolation Protocols in Raw Cow's Milk Cheese Enrichment Broths: Direct STEC Isolation Versus Techniques Based on Immuno-concentration.

The presence of Shiga toxin-producing Escherichia coli (STEC) in dairy products made with raw milk is a major concern for food safety authorities and industries. Two approaches have been proposed to isolate STEC from food. In the IC-Protocol (immuno-concentration protocol), specific serogroups are identified in the enrichment broth after the detection of the stx and eae genes. An immuno-concentration of the targeted serogroups is performed before isolating them on specific media. In the DI-Protocol (direct isolation protocol), a direct isolation of all STEC present in the enrichment broth is carried out after the detection of stx genes. We compared the ability of these two methods to isolate STEC O26:H11, O103:H2, O111:H8, O145:H28, and O157:H7 after artificial inoculation in four different raw milk cheeses. Across all serogroups and cheese types, STEC were isolated in 83.3% of samples when using the IC-Protocol but only 53.3% of samples with the DI-Protocol. For two cheese types, the DI-Protocol failed to isolate STEC O157:H7 strains altogether. Our results suggest that IC-Protocol is a robust methodology to effectively isolate STEC across a range of cheese types.

Control of Listeria monocytogenes in a fresh cheese using aromatic and medicinal plants and enterocin: a comparative study.

The aim of this study was to investigate the effectiveness of essential oils (EOs) or crude extracts (CEs) of eight aromatic and medicinal plants (AMPs) and its association with enterocin OS1 on Listeria monocytogenes and food spoilage bacteria in Moroccan fresh cheese. The cheese batches were treated with EO of Rosmarinus officinalis, Thymus vulgaris, Syzygium aromaticum, Laurus nobilis, Allium sativum, Eucalyptus globulus, or CE of Crocus sativus and Carthamus tinctorius, and/or enterocin OS1, and stored for 15 days at 8°C. The data were subjected to correlations analysis, variance analysis, and principal components analysis. Results clearly showed a positive correlation between L. monocytogenes reduction and storage time. Moreover, reduction on Listeria counts induced by Allium-EO and Eucalyptus-EO reached 2.68 and 1.93 Log CFU/g with respect to untreated samples after 15 days, respectively. Similarly, enterocin OS1 alone has significantly reduced the L. monocytogenes population with 1.46 Log CFU/g. The most promising result was the synergy observed between many AMPs and enterocin. Indeed, treatments with Eucalyptus-EO + OS1 and Crocus-CE + OS1 decreased the Listeria population to undetectable after only 2 days and throughout the storage period. These findings suggest a promising application/use of this natural combination, which preserves the safety and long-lasting conservation of fresh cheese.

Antibiotic Resistance/Susceptibility Profiles of Staphylococcus equorum Strains from Cheese, and Genome Analysis for Antibiotic Resistance Genes.

In food, bacteria carrying antibiotic resistance genes could play a prominent role in the spread of resistance. Staphylococcus equorum populations can become large in a number of fermented foods, yet the antibiotic resistance properties of this species have been little studied. In this work, the resistance/susceptibility (R/S) profile of S. equorum strains (n = 30) from cheese to 16 antibiotics was determined by broth microdilution. The minimum inhibitory concentration (MIC) for all antibiotics was low in most strains, although higher MICs compatible with acquired genes were also noted. Genome analysis of 13 strains showed the S. equorum resistome to be composed of intrinsic mechanisms, acquired mutations, and acquired genes. As such, a plasmidic cat gene providing resistance to chloramphenicol was found in one strain; this was able to provide resistance to Staphylococcus aureus after electroporation. An msr(A) polymorphic gene was identified in five strains. The Mrs(A) variants were associated with variable resistance to erythromycin. However, the genetic data did not always correlate with the phenotype. As such, all strains harbored a polymorphic fosB/fosD gene, although only one acquired copy was associated with strong resistance to fosfomycin. Similarly, a plasmid-associated blaR1-blaZI operon encoding a penicillinase system was identified in five ampicillin- and penicillin G-susceptible strains. Identified genes not associated with phenotypic resistance further included mph(C) in two strains and norA in all strains. The antibiotic R/S status and gene content of S. equorum strains intended to be employed in food systems should be carefully determined.

Virulence factors and antimicrobial resistance of Escherichia coli isolated from commercialized fresh cheese in the south of Espírito Santo.

Cheeses are dairy products that can potentially contain a diverse range of harmful bacteria that could be consumed by humans, including the enteric pathogen Escherichia coli. This study aimed to characterize the presence of total coliforms, assess the antimicrobial susceptibility profiles of the main commercial antimicrobial classes and biocides, and evaluate the ability of 50 E. coli isolates obtained from fresh cheese sold in the southern region of Espírito Santo, Brazil, to produce biofilms. The counts of total coliforms + E. coli obtained averages of (A) 7.22 × 106 CFU/g, (B) 9.35 × 107 CFU/g, and (C) 1.16 × 106 CFU/g for different brands. All isolates were capable of forming biofilms, with 8%, 76%, and 16% of these isolates presenting high, moderate, and low adherence in biofilm formation, respectively. Most strains showed inhibition halos for the biocides chlorhexidine digluconate 2% (16 mm ± 4.34), iodopovidone 10% (7.14 mm ± 0.36), and sodium hypochlorite 2% (7.12 mm ± 0.33). Out of the 50 strains, 21 (42%) were resistant to at least one of the antimicrobials. Regarding the multiple resistance index, 3 (6%) strains were resistant to 3 or more antimicrobial classes. Furthermore, 2 (4%) were extended-spectrum beta-lactamases producers. Resistance to ampicillin and amoxicillin was observed in 20% and 40% of the strains, respectively. In contrast, gentamicin was the most effective antimicrobial, with a sensitivity rate of 100%. The findings indicate that E. coli present in fresh cheese may possess unique physiological characteristics that could be associated with their persistence, virulence, and multidrug resistance. These results raise significant public health concerns since contaminated food can pose risks to consumers' health, emphasizing the importance of reinforcing hygienic-sanitary controls at all stages of production.

Microbiological Quality and Safety of Pizza Held Out of Temperature Control in University Dining Halls.

Pizza is a popular food consumed around the world every day. Hot food temperatures were obtained from 19,754 nonpizza samples and 1,336 pizza temperatures were taken from dining facilities operated by Rutgers University between 2001 and 2020. These data showed that pizza was more frequently out of temperature control than many other foods. A total of 57 pizza samples that were out of temperature control were collected for further study. Pizza was tested for total aerobic plate count (TPC), Staphylococcus aureus, Bacillus cereus, Lactic acid bacteria, coliforms, and Escherichia coli. Water activity of pizza and surface pH of each individual pizza component (topping, cheese, bread) were measured. Predictions for the growth of four relevant pathogens were made for select pH and water activity values using ComBase. Rutgers University dining hall data show only about 60% of all foods that are pizza are held at the appropriate temperature. When pizza contained detectable microorganisms (∼70% of samples), average TPC ranged from 2.72 log CFU/g to 3.34 log CFU/g. Two pizza samples contained detectable S. aureus (∼50 CFU/g). Two other samples contained B. cereus (∼50 and 100 CFU/g). Five pizza samples contained coliforms (4-9 MPN/g), and no E. coli were detected. Correlation coefficients (R2 values) for TPC and pickup temperature are quite low (<0.06). Based on the pH and water activity measurements, most (but not all) of the pizza samples would be considered to potentially require time temperature control for safety. The modeling analysis shows that the organism most likely to pose a risk would be S. aureus, and the largest magnitude increase predicted is 0.89 log CFU at 30°C, pH 5.52, and water activity 0.963. The overall conclusion from this study is that while pizza represents a theoretical risk, the actual risk would likely only manifest for pizza samples that are held out of temperature control for time periods of more than eight hours.

High throughput qPCR analyses suggest that Enterobacterales of French sheep and cow cheese rarely carry genes conferring resistances to critically important antibiotics for human medicine.

Bacteria present in raw milk can carry acquired or intrinsic antimicrobial resistance genes (ARGs) and mobile genetic elements (MGEs). However, only a few studies have evaluated raw milk cheese as a potential reservoir of ARGs. This study thus aimed at providing new data regarding resistance markers present in raw milk cheese. Sheep (n = 360) and cow (n = 360) cheese samples produced in France were incubated in buffered peptone water supplemented with acriflavin or novobiocin; as corroborated by 16S metabarcoding, samples were enriched in Gram-negative bacteria since Escherichia coli and Hafnia alvei respectively accounted for 40 % and 20 % of the samples' microbiota. Screening of the samples for the presence of 30 ARGs and 16 MGEs by high throughput qPCR array showed that nine ARGs conferring resistances to 1st-generation beta-lactams, aminoglycosides, trimethoprim/sulfonamides and tetracyclines occurred in >75 % of both sheep and cow samples. This is neither surprising nor alarming since these resistance genes are widely spread across the One Health human, animal and environmental sectors. Conversely, genes conferring resistances to last-generations cephalosporins were rarely identified, while those conferring resistances to carbapenems or amikacin, which are restricted to human use, were never detected. Multiple MGEs were detected, the most frequent ones being IncF plasmids, confirming the potential transmission of ARGs. Our results are in line with the few studies of the resistome of milk or milk cheese showing that genes conferring resistances to 1st-generation beta-lactams, aminoglycosides and tetracyclines families are widespread, while those conferring resistances to critically important antibiotics are rare or absent.

Brazilian artisanal Colonial cheese: characterization, microbiological safety, and survival of Salmonella enterica serovar Enteritidis during ripening.

The artisanal Colonial cheese is typical of the southern region of Brazil and dates back to the colonization by Italian and German immigrants. Produced with raw milk, it is the main cheese produced by more than 15,200 small rural proprieties. The consumer increasingly appraises food with territorial valorization, demanding specific sanitary norms for this type of cheese. This work aimed to know the physical-chemical characteristics of the cheeses produced in the west of Santa Catarina State, to study the ripening time to reach microbiological safety, and to experimentally observe the survival of Salmonella enterica serovar Enteritidis ATCC 13076 during the ripening. The physical-chemical characterization was performed with 129 samples of cheeses. Five dairies were selected for evaluation of the ripening process. Salmonella survival using a challenge test was performed on three batches prepared in a pilot plant. The cheeses were classified as high (15.4%), medium (74.6%), and low moisture (9.2%), and concerning fat content as semi-fat (37.5%) and fat (62.5%). Salmonella challenge test demonstrated their survival for up to 28 days, depending on the initial contamination. The ripening monitoring showed that thermotolerant coliforms could be a good indicator of the process because they are the most persistent microorganisms.

Improved functional properties of the potential probiotic Lacticaseibacillus paracasei ItalPN16 growing in cheese whey.

The production of probiotic bacteria requires specific and expensive culture media for maintain their viability and metabolic response during gastro-intestinal transit and cell adhesion process. The aim of this study was to compare the ability of the potential probiotic Laticaseibacillus paracasei ItalPN16 to grow in plain sweet whey (SW) and acid whey (AW), evaluating changes in some probiotic properties related to the culture media. Pasteurized SW and AW were suitable media for L. paracasei growth, since counts above 9 Log CFU/ml were achieved using <50% of the total sugars in both whey samples after 48 h at 37°C. The L. paracasei cells obtained from AW or SW cultures showed increased resistance to pH 2.5 and 3.5, higher autoaggregation, and lower cell hydrophobicity, as compared with the control of MRS. SW also improved the biofilm formation ability and cell adhesion capability to Caco-2 cells. Our results indicate that the L. paracasei adaptation to the SW conditions, inducing metabolic changes that improved its stability to acid stress, biofilm formation, autoaggregation, and cell adhesion properties, which are important functional probiotic properties. Overall, the SW could be considered as low-cost culture medium for sustainable biomass production of L. paracasei ItalPN16.

Essential oil-loaded starch/cellulose aerogel: Preparation, characterization and application in cheese packaging.

Novel antimicrobial emitting aerogels based on starch/cellulose/Thymus daenensis Celak essential oil (SC-TDEO) were developed and optimized for antimicrobial packaging of Koopeh cheese. An aerogel formulation containing cellulose (1 %; extracted from sunflower stalks) and starch (5 %) in a 1:1 ratio was selected for in vitro antimicrobial assay and subsequent cheese application. The minimum inhibitory dose (MID) of TDEO in the vapor phase against Escherichia coli O157:H7 was determined by loading various concentrations of TDEO onto the aerogel, and an MID of 256 µL/Lheadspace was recorded. Aerogels containing TDEO at 25 × MID and 50 × MID were then developed and used for cheese packaging. During a 21-day storage period, cheeses treated with SC-TDEO50 MID aerogel exhibited a significant 3-log reduction in psychrophile counts and a 1-log reduction in yeast-mold counts. Moreover, significant changes in the population of E. coli O157:H7 were observed in cheese samples. After 7 and 14 days of storage with SC-TDEO25 MID and SC-TDEO50 MID aerogels, the initial bacterial count became undetectable, respectively. Sensory evaluations indicated that the samples treated with SC-TDEO25 MID and SC-TDEO50 aerogels received higher scores compared to the control group. These findings demonstrate the potential of the fabricated aerogel to develop antimicrobial packaging suitable for cheese applications.

Does the high biodiversity of lactococcal bacteriophages allow predictions about their different UV-C susceptibilities?

Fermentation processes can only succeed if intact and active starter cultures are present. Bacteriophages, which can lyse bacteria and thus bring entire fermentation processes to a standstill, therefore pose a major threat. Cheese production, for example, is often affected. The by-product whey can be highly contaminated with bacteriophages (≤109 plaque-forming units/mL) and in this state, further utilization is a quality and processing risk. Therefore, an orthogonal process consisting of membrane filtration followed by UV-C irradiation could be applied to eliminate bacteriophages and to generate "phage-free" whey. In order to define suitable process parameters, 11 lactococcal bacteriophages belonging to different families and genera and differing in their morphology, genome size, heat resistance, and other attributes, were screened for their UV-C resistance in whey. P369 was found to be the most resistant and could thus be well-suited as a biomarker. Starting from a 4 log unit bacteriophage reduction by membrane filtration, another 5 log unit decrease should be realized when applying a UV-C dose of 5 J/cm2. A clear correlation of UV-C sensitivity to the chosen attributes studied such as bacteriophage morphology and genome size was difficult and ambiguous, presumably because other yet unidentified parameters are important. Mutation experiments were performed with the representative bacteriophage P008 by multiple cycles of UV-C irradiation and propagation. A few mutational events were found, but could not be linked to an artificially generated UV-C resistance, indicating that the process used would probably not lose its effectiveness over time.

Probiotic and technological characterization of selected Lactobacillus strains isolated from different egyptian cheeses.

BACKGROUND: Fresh milk and natural environmental conditions are used to produce traditional cheeses. Such cheeses are produced by dozens of different types of microbes. Non-starter lactobacilli are the most responsible genus of lactic acid bacteria exhibiting key technological and health promoting traits. The purpose of this study is to isolate Lactobacillus bacteria from conventional Egyptian cheeses and analyse their probiotic potential and technological properties. RESULTS: Lactobacillus isolates (33 isolates) were isolated from different Egyptian cheeses. Our results revealed that 18.18% of the isolates were fast-acidifying, 30.3% were medium-acidifying and 51.5% were slow-acidifying isolates. The results of autolytic activity showed that 24.3% of the isolates were good autolysis, 33.3% were fair autolysis, while 42.4% were poor autolysis. Fifteen isolates produced exopolysaccharides, while 9 isolates exhibited antimicrobial activities against Lactobacillus bulgaricus 340. All the isolates were resistant to pH 3 for 3 h except isolate No. 15 (MR4). The growth rate of the isolates ranged from 42.25 to 85.25% at 0.3% bile salts after 3 h of incubation. The surviving percentage of the Lactobacillus isolates decreased with increasing incubation time or the percentage of bile salts greater than 0.3%. All the isolates grew after incubation in artificial gastric and intestinal fluids. The auto-aggregation of 15 isolates ranged from 43.13 to 72.77%. Lacticaseibacillus paracasei BD3, Lactiplantibacillus plantarum BR4 and Limosilactobacillus fermentum MR2 were sensitive to the majority of the tested antibiotics and showed good bile salt hydrolase activity. CONCLUSION: L. paracasei BD3, L. plantarum BR4 and L. fermentum MR2 were isolated from Egyptian cheeses and showed probiotic and technological characterization, which are valuable for their practical application as starters, adjunct and protective cultures in cheese making.