Raw Milk Soft Cheese Research Articles

Multipathogen quantitative risk assessment in raw milk soft cheese

We propose a multipathogen Quantitative Microbiological Risk Assessment (QMRA) model to estimate the risk of foodborne illness from bacterial pathogens in raw milk soft cheese. Our work extends an existing QMRA model for pathogenic Shiga toxin-producing Escherichia coli (STEC) (Basak et al.,under review; Perrin et al., 2014) by incorporating the effects of Salmonella and Listeria monocytogenes. This multipathogen model integrates microbial contamination of raw milk at the farm level, as well as the growth and survival of these bacteria during cheese fabrication, ripening, and storage. The public health impact of multipathogen risk associated with raw milk cheese consumption is assessed using Disability-Adjusted Life Years (DALYs). The model evaluates intervention strategies at both pre- and post-harvest stages to estimate intervention costs. Furthermore, it tests various scenarios of these strategies and optimizes intervention parameters to minimize multipathogen risk and associated costs. This article discusses challenges in QMRA model validation, emphasizes model limitations, and explores future perspectives for improvement.

Quantitative risk assessment of Haemolytic and Uremic Syndrome (HUS) from consumption of raw milk soft cheese

Quantitative risk assessment of Haemolytic and Uremic Syndrome (HUS) from consumption of raw milk soft cheese

Dynamic Modelling to Describe the Effect of Plant Extracts and Customised Starter Culture on Staphylococcus aureus Survival in Goat's Raw Milk Soft Cheese.

This study characterises the effect of a customised starter culture (CSC) and plant extracts (lemon balm, sage, and spearmint) on Staphylococcus aureus (SA) and lactic acid bacteria (LAB) kinetics in goat's raw milk soft cheeses. Raw milk cheeses were produced with and without the CSC and plant extracts, and analysed for pH, SA, and LAB counts throughout ripening. The pH change over maturation was described by an empirical decay function. To assess the effect of each bio-preservative on SA, dynamic Bigelow-type models were adjusted, while their effect on LAB was evaluated by classical Huang models and dynamic Huang-Cardinal models. The models showed that the bio-preservatives decreased the time necessary for a one-log reduction but generally affected the cheese pH drop and SA decay rates (logDref = 0.621-1.190 days; controls: 0.796-0.996 days). Spearmint and sage extracts affected the LAB specific growth rate (0.503 and 1.749 ln CFU/g day-1; corresponding controls: 1.421 and 0.806 ln CFU/g day-1), while lemon balm showed no impact (p > 0.05). The Huang-Cardinal models uncovered different optimum specific growth rates of indigenous LAB (1.560-1.705 ln CFU/g day-1) and LAB of cheeses with CSC (0.979-1.198 ln CFU/g day-1). The models produced validate the potential of the tested bio-preservatives to reduce SA, while identifying the impact of such strategies on the fermentation process.

Inhibitory activity of some functional cultures toward common microbial contaminants in soft cheese manufactured from raw milk

The inhibitory activity of Lb. plantarum NRC AM10, Lb. curvatus NBIMCC 3452, Lb. paracasei NRRL B-4560 and Lb. gasseri NRRL B-14168 were investigated against the microbial contaminants in raw milk soft cheese. Cultures were added at the level of 5 % in T1, T2, T3 and T4 respectively, and the control treatment made without starters. Microbial counts in raw milk sample showed 10.25, 6.85, 5.89, 4.76, 4.42, 4.44, 3.77, 3.64 and 3.46 log cfu/ml for total viable count, total coliforms, Staphylococci, moulds and yeasts, Enterococci, fecal coliforms, spore forming bacteria, psychrotrophic and Salmonella respectively. Some of microbial groups in control cheese were increased in the first 5 days of storage and others were increased until 10 days then all microbial groups were gradually decreased with extending storage period. Staphylococci reached to the lowest counts 3.11 log cfu/ml after 20 days, on contrast moulds and yeasts reached to the highest count 5.22 log cfu/ml at the end of storage period. The inhibition rate % (IR) were influenced by the variety of strain added in cheese treatments and the highest IR 32.58 and 33.96 % against total coliforms and Enterococci were recorded in the treatment containing Lb. plantarum NRC AM10 while the highest IR 25.84 % against fecal coliforms was recorded in the treatment containing Lb. curvatus NBIMCC 3452. Meanwhile, the IR 35.19 and 15.84 % were recorded against Salmonella and spore forming bacteria with strain Lb. gasseri NRRL B-14168. The strain Lb. paracasei NRRL B-4560 showed IR 42.23 and 44.4 % against Staphylococci and psychrotrophic respectively. Moulds and yeasts talked a revers trend of IR because of increasing the counts by acidity development. In conclusion, the only addition of functional cultures to control the growth and survival of pathogens in raw milk products is not enough to produce safe product. Use of pasteurized milk, good hygienic and good manufacturing practices are essential to reduce the risk of microbial contamination and health hazards in dairy products.

An approach to select Lactobacillus isolates as protective cultures for food fermentations

AbstractFood waste reduction can be achieved by applying protective cultures to avoid spoilage of fermented food products. In this study, we present an approach to screen large numbers of strains for potential use as protective cultures in food. A phenotypic screening of 504 Lactobacillus strains for 27 food‐relevant growth conditions revealed variations and physiological limits for the genus. Previously, the strains were tested for their antibacterial activity in a high‐throughput assay. Here, the activity of 22 positive strains from that screening was assessed in more detail, mainly against Listeria, Enterococcus, Rhodotorula, and Candida species. The proteinaceous nature of the inhibiting substances was confirmed by protease digestion. Twenty‐two antibacterial and 42 antifungal strains were detected. In a co‐culture competition‐assay, 1–2 cfu/ml of Lactobacillus plantarum RI‐162 were able to inhibit the outgrowth of Rhodotorula mucilaginosa LME and reduce the cell number below the detection limit of 50 cfu/ml within 48 hr.Practical applicationsTo translate the result to industrial application, the potential protective culture Lactobacillus sakei RI‐409 reduced the initial Listeria ivanovii DSM 12491T concentration in an industrial‐scale salami fermentation by 1.4 log within 5 days. In a small‐scale salami fermentation, one L. sakei strain and five Lactobacillus plantarum strains were tested as protective cultures. Four strains reduced the spiked counts of L ivanovii DSM 12491T from an initial concentration of 105 cfu/g at the start of fermentation to below the detection limit of 100 cfu/g within two days. In a 1,000‐L small‐scale raw milk soft cheese fermentation, the potential protective culture L. plantarum RI‐271 reduced the endogenous enterococci concentration with 1.5 log compared to untreated raw milk. In conclusion, we have developed an approach to select tailor‐made antimicrobial protective cultures for biopreservation in fermented food products.

Impact of Probiotic Strains on Growth of Some Food Poisoning Bacteria from Milk and Soft Cheese

One hundred and twenty samples, 40 each of raw milk, Kareish cheese (raw skim milk soft cheese) and Damietta cheese (white raw milk soft cheese) were collected from supermarkets, dairy shops and street vendors in El- Gharbia governorate, Egypt for microbiological investigation. The obtained results revealed that S. aureus, E. coli and B. cereus could be detected in 60, 52.5 & 20%; 25, 37.5 & 15% and 12.5, 15 & 7.5% of examined samples, respectively. Serological typing of fourteen strains of isolated E. coli proved to belong to ten serotypes; O159, O142, O18, O15, O125, O111, O55, O119, O26 and O128. Salmonella typhimurium could be isolated from one Kareish cheese sample (2.5%) with serological typing proved that the strain has antigenic structure of O: 1, 4, 5, 12, H: i: 1, 2. Concerning the antimicrobial activities of some probiotic bacteria; Lactobacillus planterum (p 1 ), Lactobacillus acidophilus (p 7 ), Lactobacillus brevii (p 102 ) and Lactobacillus casii (l.c) using an agar well diffusion assay against selected isolates of E. coli, B. cereus, S. aureus and Salmonella typhimurium indicated that the used probiotic bacteria appeared to have antimicrobial effect against E. coli and B. cereus, while induce no antimicrobial effect against S. aureus and Salmonella typhimurium. The same probiotic strains were injected with E.coli in sterilized skim milk as in vitro experiment and the results showed a significant reduction in the count of E. coli during the periods of incubation.

Proteolysis and texture changes of a Spanish soft cheese (‘Torta del Casar’) manufactured with raw ewe milk and vegetable rennet during ripening

SummaryProteolysis and textural changes of the Spanish ewe raw milk soft cheese of the Protected Designation of Origin Torta del Casar were studied in four different stages of ripening, with 1, 30, 60 and 90 days. In general, proteolysis in Torta del Casar cheese was weak at 1 and 30 days and it was more intense between the 30–60 days of ripening. Soluble nitrogen non‐protein nitrogen, polypeptide N and free amino acids values significantly increased during cheese ripening. Protein and casein nitrogen decreased significantly after 60 days of ripening resulting in the increase of the other nitrogen fractions measured. Caseins changes determined by capillary zone electrophoresis showed that proteolysis of β‐casein occurred faster than αs1‐casein but the latter suffered higher proteolytic degradation at the end of ripening (day 90). This pattern of degradation of caseins is reversed in other cheeses made with animal rennet. Texture analysis showed that firmness and consistency decreased along ripening while adhesiveness increased. Highly significant correlations were found between textural parameters, residual caseins levels and nitrogen fractions during maturation, which shows the importance of proteolytic changes for an optimal texture formation.

Foodborne Pathogens and Microbiological Characteristics of Raw Milk Soft Cheese Produced and on Retail Sale in Brazil

The consumption of raw milk soft cheeses (RMSC), which are typically manufactured in small dairy farms under unsatisfactory hygiene conditions, is common in Brazil. Due to these production characteristics, this type of cheese is a potential carrier of pathogenic microorganisms, such as Listeria monocytogenes, Salmonella, and enterotoxin-producing Staphylococcus spp. Considering these characteristics, in this work, we aimed to detect the presence of these pathogenic microorganisms in RMC and to evaluate their microbiological quality. Fifty-five samples of this product were collected from different noninspected commercial establishments and submitted to the enumeration of mesophilic aerobes (MA), total coliforms (TC), Escherichia coli, and coagulase-positive staphylococci (CPS), and detection of L. monocytogenes and Salmonella spp. All analyzed samples were negative for Salmonella spp. and L. monocytogenes. All samples presented counts of MA higher than 10(6) colony forming units/g (CFU/g; range, 3.0x10(6) to 4.0x10(9)). TC were present at levels between 1.0x10(3) and 1.8x10(8) CFU/g, and E. coli between 1.0x10(2) and 3.5x10(6) CFU/g. CPS were detected in 17 (30.9%) samples at levels higher than 10(4) CFU/g. These results confirm the poor microbiological quality of raw milk used in the manufacturing of RMC samples, and also the inadequate production conditions. Therefore, the evaluation of microbiological safety and quality of these products must be constantly reported to alert the official agencies about the significance of proper inspection.

A case of sporadic ovine mastitis caused by Listeria monocytogenes and its effect on contamination of raw milk and raw-milk cheeses produced in the on-farm dairy.

We describe a case of listerial mastitis in a flock of 130 sheep. The animals were housed at a farm where the bulk raw ewe milk was processed to produce raw milk soft cheese. List. monocytogenes was shed from the right mammary complex. Shedding was observed over a period of 99 d. A mean level of 4-56 x 10(4) cfu (colony forming units) Listeria monocytogenes/ml was recovered from the raw milk originating from the infected udder. The numbers ranged from 9 x10(1) to 2.95 x 10(5). The bulk milk was contaminated by approx. 5.7 x 10(3) cfu/ml. In the cheese product, 2.0 x 10(2) cfu List. monocytogenes/g were constantly detectable for a period of 7 d post manufacture. The starter culture used for coagulation had a pivotal influence on the behaviour of List. monocytogenes during cheesemaking. Using the same mesophilic buttermilk culture as used by the farmer allowed numbers of Listeria to increase 60-fold within 12 h owing to a delayed acidification of the bulk milk. Addition of a thermophilic yogurt culture reduced the numbers of Listeria within 8 h of incubation.

Estimation of low bacterial concentration: Listeria monocytogenes in raw milk

A time-series bacteriological analysis has been carried out on milk collected on farms from 1997 to 2001 by a plant producing raw milk soft cheese, with the purpose of assessing the time course of the presence/absence of Listeria monocytogenes. A standard data collection procedure was used, in which farms were tested on a monthly or biweekly basis and 2–3 days after the detection of milk tanker contamination. This procedure yielded low figures for contamination frequencies. The average value and the median of the monthly prevalence of farms detected positive for L. monocytogenes were 2.4 and 0%, respectively. A seasonal effect (with peaks in winter) was observed. Between 1997 and 2001, there was no significant decrease of contamination rates, in spite of the efforts on the contaminated farms. Over the last year of the study (from March 2000 to February 2001), a new data collection procedure was implemented that allowed much better detection of sporadic occurrences. Milk samples were collected from the bulk tank of each participating farm just before pick-up, then stored and subsequently analysed whenever the milk tanker was found contaminated. The average value and the median of the monthly prevalence of positive farms were found equal to 7.7 and 0%, respectively (for a mean prevalence of L. monocytogenes in the milk tanker of 3.2%). These results confirm that farm milk contamination is, most often, a sporadic event. In addition to this prevalence study, contamination levels were quantified by enumerating L. monocytogenes using direct plating of small volumes of farm milk previously tested positive. Most often, these levels were extremely low. A simple simulation model shows that, when milk tankers were found positive, contamination levels in the corresponding bulk-tank milk are themselves very low (typically, below 3 L. monocytogenes per millilitre with most probable concentration 0.1 Colony Forming Unit (CFU)/ml and median ranging from 5.10 −2 to 0.1 CFU/ml). Such low levels are very likely to be due to environmental contamination.

A community--wide outbreak of Salmonella enterica serotype Typhimurium infection associated with eating a raw milk soft cheese in France.

In 1997, a community-wide outbreak of Salmonella enterica serotype Typhimurium (S. typhimurium) infection occurred in France. The investigation included case searching and a case-control study. A case was defined as a resident of the Jura district with fever or diarrhoea between 12 May and 8 July 1997, from whom S. typhimurium was isolated in stool or blood. One hundred and thirteen cases were identified. Thirty-three (83 %) of 40 cases but only 23 (55 %) of 42 community controls, matched for age and area of residence, reported eating Morbier cheese (Odds ratio: 6.5; 95 % Confidence Interval: 1.4-28.8). Morbier cheese samples taken from the refrigerators of two case-patients and one symptom-free neighbour cultured positive for S. typhimurium of the same phage type as the human isolates. The analysis of distribution channels incriminated one batch from a single processing plant. These findings show that an unpasteurized soft cheese is an effective vehicle of S. typhimurium transmission.

Acquired antibiotic resistance in lactic acid bacteria from food.

Acquired antibiotic resistance, i.e. resistance genes located on conjugative or mobilizable plasmids and transposons can be found in species living in habitats (e.g. human and animal intestines) which are regularly challenged with antibiotics. Most data are available for enterococci and enteric lactobacilli. Raw material from animals (milk and meat) which are inadvertantly contaminated with fecal matters during production will carry antibiotic resistant lactic acid bacteria into the final fermented products such as raw milk cheeses and raw sausages. The discovered conjugative genetic elements of LAB isolated from animals and food are very similar to elements studied previously in pathogenic streptococci and enterococci, e.g. theta-type replicating plasmids of the pAMbeta1, pIP501-family, and transposons of the Tn916-type. Observed resistance genes include known genes like tetM, ermAM, cat, sat and vanA. A composite 29,871 bp resistance plasmid detected in Lactococcus lactis subsp. lactis isolated from a raw milk soft cheese contains tetS previously described in Listeria monocytogenes, cat and str from Staphylococcus aureus. Three out of five IS elements on the plasmid are almost or completely identical to IS1216 present in the vanA resistance transposon Tn1546. These data support the view that in antibiotic challenged habitats lactic acid bacteria like other bacteria participate in the communication systems which transfer resistance traits over species and genus borders. The prevalence of such bacteria with acquired resistances like enterococci is high in animals (and humans) which are regularly treated with antibiotics. The transfer of antibiotic resistant bacteria from animals into fermented and other food can be avoided if the raw substrate milk or meat is pasteurized or heat treated. Antibiotic resistance traits as selectable markers in genetic modification of lactic acid bacteria for different purposes are presently being replaced, e.g. by metabolic traits to generate food-grade vectors.