The effects of nisin on Staphylococcus aureus count and the physicochemical properties of Traditional Minas Serro cheese

Evaluation of Extraction Methods to Detect Noroviruses in Ready-to-Eat Raw Milk Minas Artisanal Cheese

This study aimed to assess two homogenization methods to recover norovirus from Minas artisanal cheese (MAC) made with raw bovine milk obtained from four microregions of the Minas Gerais state, Brazil, with different ripening times and geographical and abiotic characteristics. For this purpose, 33 fiscal samples were artificially contaminated with norovirus GI and GII, and Mengovirus (MgV), used as an internal process control (IPC). TRIzol® reagent and Proteinase K homogenization methods were evaluated for all samples were then subjected to RNA extraction using viral magnetic beads and RT-qPCR Taqman® for viral detection/quantification. Proteinase K method showed better efficiency results for both norovirus GI and GII, with means recovery efficiency of 45.7% (95% CI 34.3-57.2%) and 41.4% (95% CI 29.1-53.6%), respectively, when compared to TRIzol method (16.6% GI, 95% CI 8.4-24.9%, and 12.3% GII, 95% CI 7.0-17.6%). The limits of detection for norovirus GI and GII for this method were 101GC/g and 103GC/g, respectively, independent of cheese origin. MgV was detected and revealed in 100% success rate in all types of cheese, with mean recovery efficiency of 25.6% for Proteinase K, and 3.8% for the TRIzol method. According to cheese origin, Triangulo Mineiro MAC had the highest mean recovery rates for the three viral targets surveyed (89% GI, 87% GII, and 51% MgV), while Serro MAC showed the lowest rates (p < 0.001). Those results indicate that the proteinase K adapted method is suitable for norovirus GI and GII detection in MAC and corroborated MgV as an applicable IPC to be used during the process.

Unveiling Safety Concerns in Brazilian Artisanal Cheeses: A Call for Enhanced Ripening Protocols and Microbiological Assessments

Brazilian artisanal cheeses have recently gained significant commercial prominence and consumer favor, primarily due to their distinctive sensory attributes and cultural and historical appeal. Many of these cheeses are made with raw milk and undergo a relatively short ripening period, sometimes ranging from 4 to 8 days, though it is usually shorter than the period stated by law. Moreover, there is insufficient evidence regarding the efficacy of a short ripening period in reducing certain zoonotic foodborne pathogens, such as Brucella spp., Coxiella burnetiid, and Mycobacterium bovis (as part of the Mycobacterium tuberculosis complex). Additionally, a literature analysis revealed that the usual ripening conditions of Brazilian artisanal cheeses made with raw milk may be inefficient in reducing the levels of some hazardous bacterial, including Brucella spp., Listeria monocytogenes, coagulase-positive Staphylococcus, Salmonella, and Coxiella burnetti, to the acceptable limits established by law, thus failing to ensure product safety for all cheese types. Moreover, the assessment of the microbiological safety for this type of cheese should be broader and should also consider zoonotic pathogens commonly found in bovine herds. Finally, a standardized protocol for evaluating the effectiveness of cheese ripening must be established by considering its peculiarities.

Caciocavallo Podolico Cheese, a Traditional Agri-Food Product of the Region of Basilicata, Italy: Comparison of the Cheese's Nutritional, Health and Organoleptic Properties at 6 and 12 Months of Ripening, and Its Digital Communication

Traditional agri-food products (TAPs) are closely linked to the peculiarities of the territory of origin and are strategic tools for preserving culture and traditions; nutritional and organoleptic peculiarities also differentiate these products on the market. One such product is Caciocavallo Podolico Lucano (CPL), a stretched curd cheese made exclusively from raw milk from Podolian cows, reared under extensive conditions. The objective of this study was to characterise CPL and evaluate the effects of ripening (6 vs. 12 months) on the quality and organoleptic properties, using the technological "artificial senses" platform, of CPL produced and sold in the region of Basilicata, Italy. Additionally, this study represents the first analysis of cheese-related digital communication and trends online. The study found no significant differences between 6-month- and 12-month-ripened cheese, except for a slight increase in cholesterol levels in the latter. CPL aged for 6 and 12 months is naturally lactose-free, rich in bioactive components, and high in vitamin A and antioxidants and has a low PUFA-n6/n3 ratio. The "artificial sensory profile" was able to discriminate the organoleptic fingerprints of 6-month- and 12-month-ripened cheese. The application of a socio-semiotic methodology enabled us to identify the best drivers to create effective communication for this product. The researchers recommend focusing on creating a certification mark linked to the territory for future protection.

Impact of the calcium concentration on the efficacy of phage phiIPLA-RODI, LysRODIΔAmi and nisin for the elimination of Staphylococcus aureus during lab-scale cheese production

Staphylococcus aureus is a Gram-positive human opportunistic pathogen that may also cause food poisoning because of the ability of some strains to produce heat stable enterotoxins that can persist in food even after the pathogen is successfully eliminated. In this context, biopreservation may be a forward-looking strategy to help eliminate staphylococcal contamination in dairy products by using natural compounds. However, these antimicrobials exhibit individual limitations that may be overcome by combining them. This work investigates the combination of a virulent bacteriophage, phiIPLA-RODI, a phage-derived engineered lytic protein, LysRODIΔAmi, and the bacteriocin nisin for the elimination of S. aureus during lab-scale cheese production at two CaCl₂ concentrations (0.2 % and 0.02 %), and subsequent storage at two different temperatures (4 °C and 12 °C). In most of the assayed conditions, our results demonstrate that the combined action of the antimicrobials led to a greater reduction of the pathogen population than the compounds individually, albeit this effect was additive and not synergistic. However, our results did show synergy between the three antimicrobials for reducing the bacterial load after 14 days of storage at 12 °C, temperature at which there is growth of the S. aureus population. Additionally, we tested the impact of the calcium concentration on the activity of the combination treatment and observed that higher CaCl₂ levels led to a notable increase in endolysin activity that allowed the utilization of approximately 10-times less protein to attain the same efficacy. Overall, our data show that the combination of LysRODIΔAmi with nisin and/or phage phiIPLA-RODI, and an increase in the calcium concentration are successful strategies to decrease the amount of protein required for the control of S. aureus contamination in the dairy sector with a low potential for resistance selection, thereby reducing costs.

Potentials of Natural Preservatives to Enhance Food Safety and Shelf Life: A Review

Food-borne illnesses are a significant concern for consumers, the food industry, and food safety authorities. Natural preservatives are very crucial for enhancing food safety and shelf life. Therefore, this review aimed to assess the literature regarding the potential of natural preservatives to enhance food safety and extend the shelf life of food products. The review paper indicated that natural antimicrobial agents that inhibit bacterial and fungal growth for better quality and shelf life have been of considerable interest in recent years. Natural antimicrobials are mainly extracted and isolated as secondary metabolites of plants, animals, and microorganisms. Plants, especially herbs and spices, are given more attention as a source of natural antimicrobials. Microorganisms used in food fermentation also produce different antimicrobial metabolites, including organic acids, hydrogen peroxide, and diacetyl, in addition to bacteriocins. Products of animal origin, such as tissues and milk, contain different antimicrobial agents. Natural antimicrobials are primarily extracted and purified before utilization for food product development. The extraction condition and purification of natural preservatives may change their structure and affect their functionality. Selecting the best extraction method coupled with minimal processing such as direct mechanical extraction seems to preserve active ingredients. The activity of natural antimicrobials could also be influenced by the source, time of harvesting, and stage of development. The effectiveness of natural antimicrobial compounds in food applications is affected by different factors, including food composition, processing method, and storage conditions. Natural antimicrobials are safe because they can limit microbial resistance and meet consumers’ demands for healthier foods.

Combination Treatment for Inhibition of the Growth of Staphylococcus aureus with Recombinant SAP8 Endolysin and Nisin

Staphylococcus aureus, a pathogenic species of genus Staphylococcus involved in foodborne illness always remain among the top priorities of the world major concerns. In the present study, we have used recombinant SAP8 endolysin from the bacteriophage SAP8 and commercial nisin to inhibit the viability of pathogenic S. aureus KCTC 3881 cells; however, the approach was not identified as cost-effective. A gradual decrease in the viable S. aureus KCTC 3881 cell counts was observed with an increase in the concentrations of recombinant SAP8 endolysin and nisin. However, combined treatment with recombinant SAP8 endolysin and nisin decreased the viable S. aureus KCTC 3881 cell counts in a significant manner. The combination of 0.01 µM of recombinant SAP8 endolysin with 9 IU/mL and 18 IU/mL of nisin demonstrated a promising decrease in the viable cell counts of the strain. Under the scanning electron microscope, the combination treatment with 0.01 µM of recombinant SAP8 endolysin and 18 IU/mL of nisin showed complete cellular destruction of S. aureus KCTC 3881. We propose that a combination of recombinant SAP8 endolysin and nisin could be a strong alternative to antibiotics to control the growth of S. aureus including MRSA.

Artisanal Brazilian Cheeses-History, Marketing, Technological and Microbiological Aspects

This review focused on the historical, marketing, technological, and microbiological characteristics of artisanal Brazilian cheese. Brazilian cheese production was introduced and developed from the influence of immigrants considering the combination of climate, races of the animals, quality and specificity of milk, technological cheese-making processes and environmental microbiology, among other factors. It resulted in cheese products with specific physicochemical, microbiological, and sensory quality, which represent the heritage and identities of the different Brazilian regions. The production of artisanal cheese increased in many Brazilian regions, mainly in the southeast, especially due to the traditional production and innovative development of new varieties of cheese. The microbiological quality and safety of raw-milk artisanal cheese continues to be a concern and many studies have been focusing on this matter. Special attention needs to be given to the cheeses produced by raw milk, since numerous reports raised concerns related to their microbiological safety. This fact requires attention and the implementation of strict hygiene practices on the production and commercialization, besides appropriate governmental regulations and control. However, more studies on the relationship between technological processes and microbiological properties, which results in a superior culinary quality and safety of artisanal Brazilian cheeses, are needed.

Application of Furcellaran Nanocomposite Film as Packaging of Cheese

There is a serious need to develop and test new biodegradable packaging which could at least partially replace petroleum-based materials. Therefore, the objective of this work was to examine the influence of the recently developed furcellaran nanocomposite film with silver nanoparticles (obtained by an in situ method) on the quality properties of two cheese varieties: a rennet-curd (gouda) and an acid-curd (quark) cheese. The water content, physicochemical properties, microbiological and organoleptic quality of cheese, and migration of silver nanoparticles were examined. Both the number of Lactococcus and total bacteria count did not differ during storage of gouda regardless of the packaging applied. The number of Lactococcus decreased in analogous quark samples. The use of the film slowed down and inhibited the growth of yeast in gouda and quark, respectively. An inhibitory effect of this film on mold count was also observed; however, only regarding gouda. The level of silver migration was found to be lower in quark than in gouda. The film improved the microbiological quality of cheeses during storage. Consequently, it is worth continuing research for the improvement of this film in order to enable its use in everyday life.

Cyclic peptide production from lactic acid bacteria (LAB) and their diverse applications

In recent years, cyclic peptides gave gained increasing attention owing to their pH tolerance, heat stability and resistance to enzymatic actions. The increasing outbreaks of antibiotic resistant pathogens and food spoilage have prompted researchers to search for new approaches to combat them. The increasing number of reports on novel cyclic peptides from lactic acid bacteria (LAB) is considered as a breakthrough due to their potential applications. Although an extensive investigation is required to understand the mechanism of action and range of applications, LAB cyclic peptides can be considered as potential substitutes for commercially available antibiotics and bio preservatives. This review summarizes the current updates of LAB cyclic peptides with emphasis on their structure, mode of action and applications. Recent trends in cyclic peptide applications are also discussed.

Conditions of nisin production by Lactococcus lactis subsp. lactis and its main uses as a food preservative

Nisin is a small peptide produced by Lactococcus lactis ssp lactis that is currently industrially produced. This preservative is often used for growth prevention of pathogenic bacteria contaminating the food products. However, the use of nisin as a food preservative is limited by its low production during fermentation. This low production is mainly attributed to the multitude of parameters influencing the fermentation progress such as bacterial cells activity, growth medium composition (namely carbon and nitrogen sources), pH, ionic strength, temperature, and aeration. This review article focuses on the main parameters that affect nisin production by Lactococcus lactis bacteria. Moreover, nisin applications as a food preservative and the main strategies generally used are also discussed.

Study of the effectiveness of staphylococcins in biopreservation of Minas fresh (Frescal) cheese with a reduced sodium content

Reducing salt content in foods such as cheeses, while limiting the growth of spoilage microorganisms and foodborne pathogens, is a difficult challenge. One method that may prove useful is use of staphylococcins, which are bacteriocins produced by staphylococci. Therefore, staphylococcin antimicrobial activity against six strains of S. aureus isolated from cheese was tested aiming at their industrial application in biopreservation of Minas fresh (Frescal) cheese with reduced sodium content. Three staphylococcins were selected for these tests: Pep 5, aureocin A53 and lysostaphin. All three staphylococcins proved to be bacteriolytic against all six strains of S. aureus. The antimicrobial activity of the partially purified staphylococcins was subsequently investigated against strains S. aureus Q1 and QJ3 in cheese matrices (6.0 log CFU/g) with different NaCl contents (control, a 25% reduction, and a 50% reduction), kept under refrigeration at 4 °C, for 21 days. Both strains were shown to be of concern for food industry as they carry the SEA, SEB and SEH enterotoxin genes, and are resistant to β-lactam drugs and moderate biofilm formers when grown in TSB. When used singly, Pep5, aureocin A53 and lysostaphin reduced approximately 95%, 99% and 99.99% of the viable cell counts, respectively, irrespective of the sodium content of the cheese matrix. The combined action of aureocin A53 and Pep5 resulted in an additional and significant reduction (p < 0.05) of ~1.0 log CFU/g when compared with the reduction caused by the use of either one singly. The combined action of lysostaphin and aureocin A53 or lysostaphin and Pep5 resulted in a reduction similar to or slightly smaller (p > 0.05) than that observed when lysostaphin was employed singly. Lysostaphin also proved to reduce the number of the staphylococcal viable cells to a level (~ 2.0 log CFU/g) at which enterotoxin production should not reach a sufficient quantity to cause food poisoning. Therefore, lysostaphin may have a practical application in the food industry to control staphylococcal contamination of Minas fresh cheese with a sodium content reduced up to 50%, providing consumers with more safe options to reduce their intake of sodium.

Anti-staphylococcal activity of bacteriocins of food isolates Enterococcus hirae LD3 and Lactobacillus plantarum LD4 in pasteurized milk

Bacteriocins of Enterococcus hirae LD3 and Lactobacillus plantarum LD4 have been applied in milk for growth inhibition of Staphylococcus aureus. The enumeration of S. aureus cells in nutrient broth and milk was found log₁₀ 9.7 and 10.2 CFU/mL, respectively, whereas it was reduced with increasing concentration of bacteriocins suggesting loss of cell viability. The lethal concentration (LC₅₀) of enterocin LD3 and plantaricin LD4 against S. aureus was 160 and 220 µg/mL, respectively. Bacteriocin-treated cells were stained red with propidium iodide (PI) indicating dead cells further confirms bactericidal nature. The enterocin LD3-treated cells showed higher infrared absorbance at 1451.82 cm^- 1 corresponding to phospholipids suggesting membrane-acting nature of the bacteriocin. However, plantaricin LD4-treated cells did not show such alterations suggesting different mode of action. Both bacteriocins caused disruption and shrinkage of target cells, and leakage of intracellular contents as observed in transmission electron microscope (TEM). The present study suggests killing of S. aureus in milk, therefore, enterocin LD3 and plantaricin LD4 may be applied in biopreservation of milk and related food products.

Microbiota indigenous milk, mesophilic lipolytic and proteolytic colonial cheese matured, produced at different times of the year

SUMMARY Cheese is the oldest form of preserving milk nutrients having nutritional, economic and cultural importance. The objective of this study was to identify the best time of the year for production, and period, in months, for maturation of traditional colonial cheese, through analysis of water activity, weight loss and counts of lactic acid, mesophilic microorganisms—proteolytic and lipolytic. Records of temperature and relative humidity (RH) were maintained. A completely randomized experimental design was used in a double factorial scheme, considering production periods and maturation times. For all production periods evaluated, there was a significant reduction in the periods for water activity values. The counts of lactic acid bacteria ranged from 104 to 109 CFU/g. There was also stability in the number of colonies for lipolytic mesophilic microorganisms, until the third month of maturation. Low counts of proteolytic mesophiles were observed for the samples produced in May and June (5.70 and 5.53 log), respectively. The production period for the months of May and June corresponding to RH of 80% and average temperatures of 15°C were the most effective for production. Due to the presence of Listeria, it is recommended to respect the minimum time of 60 days of maturation for commercialization.

Long-term antimicrobial effect of nisin released from electrospun triaxial fiber membranes

Electrospun membranes encapsulating nisin in the core of multi-layer coaxial fibers, with a hydrophobic PCL intermediate layer and a hygroscopic cellulose acetate sheath, have been demonstrated to provide long-term antimicrobial activity combined with a hygroscopic outer layer. Antimicrobial performance has been evaluated using modified versions of the antimicrobial textile test AATCC 100 and AATCC 147 against Staphylococcus aureus. The AATCC 147 tests indicate that antimicrobial activity persists up to 7days. The quantitative analysis from the AATCC 100 test indicates that tri-layer coaxial ("triaxial") electrospun fiber membranes provide >99.99% bacteria kill (4logkill) for up to five days. This indicates that the nisin-incorporated triaxial fibers have excellent biocidal activities for up to 5days and then provide biostatic activity for 2 or more days. Compared with other types of electrospun membranes, such as core-sheath coaxial ("coaxial") and single homogenous fibers, triaxial fiber membranes provided more robust and more sustained antimicrobial activity. Single fibers with nisin showed relatively weak activity and only for one day. Coaxial fiber membranes exhibited antimicrobial activity for a long period, but their biocidal activity was much weaker than that of triaxial fiber membranes, and only exhibited >99% bacteria kill (2logkill) after 1day of exposure.

STATEMENT OF SIGNIFICANCE

The increase in drug resistant pathogens has driven the need for alternative treatments that are effective against resistant bacteria and do not contribute to drug resistance. Nisin is an excellent model bacteriocin for antimicrobials because of its size and mode of action, and has been extensively used as FDA-approved food preservatives without any problematic resistance growth in bacteria during past decades. Nisin-containing fibers have been previously reported using conventional electrospinning but sustained antimicrobial effect has not been obtained. Here, we report the encapsulation of nisin into a multi-layered nanofiber construct using triaxial electrospinning in order to obtain a long-term antimicrobial activity. This will be highly beneficial in many applications, such as protective textiles, food packaging and cancer therapy.

Nisin as a Food Preservative: Part 1: Physicochemical Properties, Antimicrobial Activity, and Main Uses

Nisin is a natural preservative for many food products. This bacteriocin is mainly used in dairy and meat products. Nisin inhibits pathogenic food borne bacteria such as Listeria monocytogenes and many other Gram-positive food spoilage microorganisms. Nisin can be used alone or in combination with other preservatives or also with several physical treatments. This paper reviews physicochemical and biological properties of nisin, the main factors affecting its antimicrobial effectiveness, and its food applications as an additive directly incorporated into food matrices.

A Bioengineered Nisin Derivative, M21A, in Combination with Food Grade Additives Eradicates Biofilms of Listeria monocytogenes

The burden of foodborne disease has large economic and social consequences worldwide. Despite strict regulations, a number of pathogens persist within the food environment, which is greatly contributed to by a build-up of resistance mechanisms and also through the formation of biofilms. Biofilms have been shown to be highly resistant to a number of antimicrobials and can be extremely difficult to remove once they are established. In parallel, the growing concern of consumers regarding the use of chemically derived antimicrobials within food has led to a drive toward more natural products. As a consequence, the use of naturally derived antimicrobials has become of particular interest. In this study we investigated the efficacy of nisin A and its bioengineered derivative M21A in combination with food grade additives to treat biofilms of a representative foodborne disease isolate of Listeria monocytogenes. Investigations revealed the enhanced antimicrobial effects, in liquid culture, of M21A in combination with citric acid or cinnamaldehyde over its wild type nisin A counterpart. Subsequently, an investigation was conducted into the effects of these combinations on an established biofilm of the same strain. Nisin M21A (0.1 μg/ml) alone or in combination with cinnamaldehyde (35 μg/ml) or citric acid (175 μg/ml) performed significantly better than combinations involving nisin A. All combinations of M21A with either citric acid or cinnamaldehyde eradicated the L. monocytogenes biofilm (in relation to a non-biofilm control). We conclude that M21A in combination with available food additives could further enhance the antimicrobial treatment of biofilms within the food industry, simply by substituting nisin A with M21A in current commercial products such as Nisaplin® (Danisco, DuPont).

Antimicrobial activity and partial characterization of bacteriocin-like inhibitory substances produced by Lactobacillus spp. isolated from artisanal Mexican cheese

Lactobacillus spp. from Mexican Cocido cheese were shown to produce bacteriocin-like substances (BLS) active against Staphylococcus aureus,Listeria innocua,Escherichia coli, andSalmonella typhimurium by using the disk diffusion method. Crude extracts of Lactobacillus fermentum showed strong inhibitory activity against Staph. aureus, L. innocua, E. coli, and Salmonella cholerae. Complete inactivation of antimicrobial activity was observed after treatment of crude extracts with proteinase K, pronase, papain, trypsin, and lysozyme, confirming their proteinaceous nature. However, antimicrobial activity was partly lost for some of the crude extracts when treated with α-amylase, indicating that carbohydrate moieties were involved. The antimicrobial activity of the crude extracts was stable at 65°C for 30min over a wide pH range (2-8), and addition of potassium chloride, sodium citrate, ethanol, and butanol did not affect antibacterial activity. However, antimicrobial activity was lost after heating at 121°C for 15min, addition of methanol or Tween 80. Fourteen out of 18 Lactobacillus spp. showed antimicrobial activity against different test microorganisms, and 12 presented bacteriocin-like substances. Generation time and growth rate parameters indicated that the antimicrobial activity of crude extracts from 3 different strains was effective against the 4 indicator microorganisms. One of the crude extracts showed inhibition not only against gram-positive but also against gram-negative bacteria. Bacteriocin-like substances produced by this specific Lactobacillus strain showed potential for application as a food biopreservative.

Compositional and biochemical changes in Genestoso cheese, a Spanish raw cow's milk variety, during ripening

BACKGROUND

Physicochemical characteristics, proteolysis and lipolysis were studied throughout the ripening of eight batches of a traditional Spanish variety made from raw cow's milk, in order to establish a basis for its industrial production.

RESULTS

The main compositional characteristics of this cheese after 60 days of ripening were its high proportion of total solids (TS; 752 g kg⁻¹ of cheese), an average content of protein (452.8 g kg⁻¹ TS) and fat (475.1 g kg⁻¹ TS) and the presence of residual lactose (12.5 g kg⁻¹ TS). Its pH value (4.04) was extremely low. Phosphorus (5.13 g kg⁻¹ TS) and sodium (8.29 g kg⁻¹ TS) were the most abundant mineral elements in cheese, whereas calcium levels (1.92 g kg⁻¹ TS) were very low. Proteolysis extension and depth were very low, which resulted in almost zero degradation of αs1- and β-casein. Fat acidity increased during ripening, reaching final values of 50.1 mg KOH kg⁻¹ of fat. The main free fatty acid was C16:0, followed by C18:1 and C14:0.

CONCLUSION

These results suggest that this variety undergoes a limited proteolysis and moderate lipolysis during ripening. The low pH, low calcium content and limited proteolysis led to a crumbly texture in this cheese variety.

Differences in the antibacterial activity of nisin and bovicin HC5 against Salmonella Typhimurium under different temperature and pH conditions

AIMS

To compare the action of nisin and bovicin HC5 in combination with EDTA on Salmonella Typhimurium under different environmental conditions.

METHODS AND RESULTS

Salmonella Typhimurium was treated in BHI broth containing EDTA (1·5 mmol l(-1)) and nisin or bovicin HC5 (200 AU ml(-1)) under different pH and temperature conditions, and according to a central composite design with two factors (temperature and pH). Cell viability was evaluated on plate count agar for 48 h. The combination of nisin or bovicin HC5 with EDTA was able to inhibit the growth of Salmonella, but the temperature and pH conditions promoting inhibition were distinct for each bacteriocin. Nisin was bactericidal over a broad range of temperature and pH, while bovicin HC5 was bacteriostatic in most conditions and bactericidal only in specific conditions (pH >6·0 and temperature >30°C). Salmonella Typhimurium did not show tolerance to bovicin HC5 or cross-tolerance between these lantibiotics.

CONCLUSIONS

Nisin and bovicin HC5 both inhibited the growth of Salmonella, but the activity of each bacteriocin was differently influenced by environmental conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Nisin and bovicin HC5 have the potential to inhibit the growth of Salmonella, but environmental conditions should be considered to establish optimal conditions for its application.

Occurrence of Methicillin Resistant and Enterotoxigenic Staphylococcus aureus in Traditional Cheeses in the North West of Iran

Traditional dairy products are potential sources of a variety of microorganisms which participate in food poisoning. Staphylococcus aureus is a conspicuous example of toxigenic bacteria causative for food-borne diseases. Moreover, resistance to methicillin is a prominent index in food hygiene studies. In the present study, we have aimed at characterization and identification of enterotoxigenic methicillin resistant S. aureus (MRSA) isolated from traditional cheeses in Azerbaijan region in the northwest of Iran during 2012. A number of phenotypical and molecular assays were utilized for screening of S. aureus. Subsequently, the prevalence of the genes responsible for the five staphylococcal enterotoxins (SEA-SEE) and also methicillin resistance gene was assessed. The outcomes of phenotypical methods were in conformity with those of the molecular procedures. The results indicated that 16% of cheese samples were contaminated by S. aureus. 110 isolates were authenticated by both phenotypical and molecular methods. All of the mentioned isolates were positive for coa, nuc, and 16S rDNA primers. 21% of these isolates were mecA positive and 60.8% of these MRSA were positive for SEs. Regarding the frequent outbreaks of enterotoxigenic MRSA, new hygiene policies and management practices should be considered to increase food safety and avoid extra treatment costs.

Effect of starters and ripening time on the physicochemical, nitrogen fraction and texture profile of goat's cheese coagulated with a vegetable coagulant (Cynara cardunculus)

BACKGROUND

The increase in the demand for goat's cheese throughout the world has encouraged research into the development of new related products with different textural characteristics. The aim of this work was to study the effect of three commercial starter cultures through the assessment of physicochemical and textural characteristics of goat's milk cheeses made with vegetable coagulant (Cynara cardunculus) during ripening.

RESULTS

Use of the different starter cultures produced a significant effect (P < 0.05) on moisture, proteins, pH, nitrogen fractions and hardness of the cheeses. Results show that the addition of mesophilic starters ensures the correct acidification rate and produced cheeses with lower pH values and greater hardness. Use of thermophilic starter cultures produces cheeses with less instrumental hardness and the use of mixed cultures produced less proteolysis.

CONCLUSION

These results are found useful for selecting the most suitable starter for the development of new goat's cheeses.

Effects of Nisin and Lysozyme on Growth Inhibition and Biofilm Formation Capacity of Staphylococcus aureus Strains Isolated from Raw Milk and Cheese Samples

Effects of nisin and lysozyme on growth inhibition and biofilm formation capacity of 25 Staphylococcus aureus strains isolated from raw milk (13 strains) and cheese (12 strains) were studied. Nisin was tested at concentrations between 0.5 and 25 μg/ml; the growth of all strains was inhibited at 25 μg/ml, but the resistances of strains showed a great variation at lower nisin concentrations. In contrast, lysozyme tested at concentrations up to 5.0 mg/ml showed no inhibition on the growth of strains. Nisin used at the growth inhibitory concentration prevented the biofilm formation of strains, but strains continued biofilm formation at subinhibitory nisin concentrations. Lysozyme did not affect the biofilm formation of 19 of the strains, but it caused a considerable activation in the biofilm formation capacity of six strains. Twelve of the strains contained both biofilm-related protease genes (sspA, sspB, and aur) and active proteases; eight of these strains were nisin resistant. These results suggest a potential risk of S. aureus growth and biofilm formation when lysozyme is used in the biopreservation of dairy products. Nisin can be used to control growth and biofilm formation of foodborne S. aureus, unless resistance against this biopreservative develops.