Storage Of Raw Milk Research Articles

Implementation of hazard analysis and critical control point (HACCP) in yogurt production.

This study aimed to review hazard analysis and critical control points (HACCP) in the dairy industry for the production of yogurt. The food safety management system (FSMS) was implemented over the last several decades with several amendments. The need for practical and proactive procedures in the dairy industry was identified so that HACCP implementation could ensure that consumers would always have safe food. The concept of HACCP is a systemic and science-based method that can result in safe dairy products such as yogurt based on the complete analysis of manufacturing processes, recognition of hazards potentially present at all stages of production, and risk prevention. In yogurt production, raw milk receipt, pasteurization, packaging, and storage are the steps most susceptible to contamination and were considered critical control points. Further steps also need to be implemented to achieve other related control measures, and these will be discussed.

One-week storage of refrigerated bovine milk does not affect the size, concentration, or molecular properties of extracellular vesicles

Milk extracellular vesicles (EVs) have gained extensive attention as promising diagnostic and therapeutic tools. Pre-analytical raw milk storage at low temperatures is an ordinary and usually necessary step after sample collection. It is known that direct freezing of unprocessed whole milk contaminates the native pool of milk EVs with other cell structures. However, less evidence is available regarding prolonged cooling at 4°C. The current study assessed whether pre-analytical storage of bovine raw milk for several days affected EV isolation and further analysis. To confirm the independence from the health status of the mammary gland, we analyzed milk samples stored at 4°C for 1, 2, 3, and 7 d past collection, respectively, from 2-quarters of the same cow with different somatic cell counts (SCC). Seven days of refrigeration did not change the milk EVs' size, concentration, or morphology. We neither detected changes in the EV cargo regarding the amount of protein and RNA nor the specific EV markers TSG101, CD9, and CD81 in milk from quarters with high and low somatic cell counts. Overall, we observed fewer CD81 and CD9 markers in quarters with a high SCC. Moreover, there was no reduction in the mastitis-related miRNA bta-miR-223-3p, suggesting that refrigeration for several days up to one week is a possible storage option compatible with further EV analyses. The findings of this study enhance the confidence that milk EVs are highly stable in the raw milk matrix.

Modeling the survival of Campylobacter jejuni in raw milk considering the viable but non‐culturable cells (VBNC)

AbstractCampylobacter spp. cannot grow in raw milk, but it is able to transform into a viable but non‐culturable (VBNC) state enabling the survival in such harsh conditions. In this study, Campylobacter jejuni survival in raw milk was investigated taken into consideration colony‐forming units (CFUs) and VBNC cells. CFU from two different strains of C. jejuni (DSM 4688 and BfR‐CA‐18043) were enumerated at three temperatures (5°C, 8°C, and 12°C). In parallel, a viability real‐time PCR was conducted to quantify intact and putatively infectious units (IPIUs) (comprising CFU and VBNC bacteria). The data generated were used to model the viability of C. jejuni during raw milk storage. Here, a one‐step fitting approach was performed using parameter estimates from an intermediate two‐step fit as starting values to generate tertiary models. Different primary model equations (Trilinear and Weibull) were required to fit the CFU and the IPIU data. Strain‐specific linear secondary models were generated to analyze the effect of storage temperature on the maximum specific inactivation rate of the CFU data. The time of the first decimal reduction parameter of the IPIU models could be modeled by a strain‐independent linear secondary model. The developed tertiary models for CFU and IPIU differ significantly in their predictions, for example, for the time required for a one log10 reduction. Taken into consideration that VBNC could revert to a culturable state during the raw milk storage, our results underline the importance of considering IPIU and not only CFU to avoid underestimation of the survival of C. jejuni in raw milk.

Evaluating the Effectiveness of Low Pressure Carbon Dioxide as a Hurdle in Raw Milk Storage

Aims: To evaluate the effectiveness of low pressure carbon dioxide as a hurdle in raw milk storage.
 Study Design: Milk samples were stored at under low pressure carbon dioxide at 29°C for 6 hours and the microbial quality of milk was compared with control milk.
 Place and Duration of Study: Department of Dairy Microbiology, Verghese Kurien Institute of Dairy and Food Technology (VKIDFT), Kerala Veterinary and Animal Sciences University, Mannuthy between January 2020 and December 2020.
 Methodology: Milk samples were collected from an organized farm. The initial microbial quality of milk was determined and samples were carbonated to a pressure of 20 psi and stored for six hours 29°C, uncarbonated milk sample kept at 29°C acted as the control. The microbial quality of the carbonated milk and uncarbonated milk was determined after storage in terms of total viable count, coliform count and gram negative organism count.
 Results: Significant growth suppression (P=0.05) of bacteria was observed in the carbonated milk. Total Viable count showed a suppression of 1.05 log cfu/ml while coliforms showed a suppression of 1.3 log cfu/ml. The greatest log reduction was observed in gram negative organisms with a difference of 2.2 log cfu/ml and psychrotrophic organisms with 1.54 log cfu/ml.
 Conclusion: Carbon dioxide was found to be an effective bacteriostatic agent which could be used for extending the keeping quality of raw milk. The bacteriostatic action could be due to anaerobic conditions developed by carbon dioxide and also due to the increased acidity of the medium.

Isolation and Diagnoses of Some Microbial and Chemical Pollutants in Raw Milk Samples Which Collected From Some Regions in Salah al-din Province

Samples of raw milk were collected from different regions in salah al-din province which marketing to one of ice houses and appropriation to the collection and cooling of raw milk storage at (5 Co) for 24-48 hours before rew marketing to the dairy plants or dealers, the number of samples which taken were (20) Samples. Swabs were taken from the udder of cows belonging to suppliers to determine the causes and incidence of microbial contamination. It was after that diagnosis types of micoorganisms that can found in such circumstances of storage and study their properties with focus on Listeria monocytogenes.
 It was farther determine the degree of contamination of milk samples with some heavy metals, Which including, cadmium, Lead , Zinc , Copper.
 Many types of bacteria were isolated and dignosed belongs to aerobic bacteria and coli from group of lactose fermented species, E. Coli and Klebsiella sp. And non lactose fermented which is Enterobacter aerogenosa, L. monocytogenes and staphylococcus aureus bacteria isolated, as well as yeast and molds , and the rate of total number reached: 5.78, 5.95, 5.71, 2.53, 2.33 log10 cfu/ml. Isolation function are also given other types of bacteria which belongs to Bacillus sp. , Pseudomonus sp., Staph. Aureus , and Micrococcus sp. In 8 swab samples.
 The results showed that the highest concentration of heavy metals of Cd, Pb, Zn, Cu in raw milk samples was 0.18, 0.25, 2.10, 1.05 mg/lit respectively. A sensitivity test of L. monocytogenes toward a number of antibiotics was found that this bacteria sensitive towards both of Ampicillin, Chloramphinicol, Erythromycin, and Tobbramycin. But it is resistant to antibiotics, Naldixic acid, Novabiocin , and cefotaxime.

ε-Polylysine Derived from Marine Bacteria-A Possible Natural Preservative for Raw Milk Storage

Despite the fact that researchers have been working on the preservation of raw milk at room temperature for several decades, most of the processes are limited to the use of chemical preservatives. One of the major problems of raw milk self-life is its spoilage at ambient temperature during the summer season. Therefore, in the present study, research has been conducted to control raw milk spoilage at 4 °C and 35 °C (considered in different regions’ ambient temperatures). ε-Polylysine, a natural preservative approved for food use, was isolated from the fermentation broth of Bacillus licheniformis PL26 grown in an M3G medium, and its antimicrobial preservation properties for milk applications were tested. The raw milk samples containing 0.02% w/v ε-polylysine could be stored at 4 °C for up to 16 days without spoilage, however, raw milk samples without ε-polylysine as preservative spoiled on the 8th day even at 4 °C refrigeration conditions. Raw milk containing 0.02% ε-polylysine in combination with 0.2% sodium bicarbonate (added to avoid acidification) could be stored at ambient temperature (35 °C) for up to 48 h. The changes in milk composition, especially of the casein, lactose, and fat stability, during storage under different conditions with/without ε-polylysine, were studied as well. The present study proves that ε-polylysine can be successfully used as a new biopreservative. Therefore, for the dairy industry, a natural preservative to store milk at room temperature during the summer season, replacing synthetic preservatives derived from renewable sources, can be proposed. Once again, marine bacteria seem to be one of the promising sustainable and renewable sources of biologically active compounds such as new food biopreservatives

Microbiological assessment of raw milk available in the metropolitan city of Sindh, Karachi - Pakistan

Currently, milk quality is judge on its health and hygienic parameters equally as its composition. Raw milk is a rich medium for the growth and proliferation of different pathogenic microorganisms such food-safety hazard may incorporate into the dairy chain, not only affect its safety and quality but also cause various milk borne diseases. Objective: To evaluate the microbiological assessment of raw milk accessible in Karachi with the intention to develop risk tracking strategies and its mitigation plan in future. Methods: Total 270 raw milk samples were collected from different sites throughout the dairy supply chains in each district of the city. Microbiological assessment of raw milk was carried out by following the bacteriological analytical manual (BAM, FDA) protocol. Results: The raw milk safety and quality at the dairy farms were satisfied, except raw milk storage tanks samples. The bacterial count boosted in almost all the samples collected during its transportation, higher aerobic and pathogenic load was observed in the retail shop’s samples however, maximum counts were noticed in the selling point milk samples. None of the milk samples contained other pathogens like Listeria or Salmonella. Conclusions: The milk quality of the supply chain, retail shops and storage tanks at dairy farms were un-satisfied based on different microbiological parameters.

Effect of biofilm formation by antimicrobial-resistant gram-negative bacteria in cold storage on survival in dairy processing lines

Antimicrobial-resistant gram-negative bacteria in dairy products can transfer antimicrobial resistance to gut microbiota in humans and can adversely impact the product quality. In this study, we aimed to investigate their distribution in dairy processing lines and evaluate biofilm formation and heat tolerance under dairy processing line-like conditions. Additionally, we compared the relative expression of general and heat stress-related genes as well as spoilage-related gene between biofilm and planktonic cells under consecutive stresses, similar to those in dairy processing lines. Most species of gram-negative bacteria isolated from five different dairy processing plants were resistant to one or more antimicrobials. Biofilm formation by the bacteria at 5 °C increased with the increase in exposure time. Moreover, cells in biofilms remained viable under heat treatment, whereas all planktonic cells of the selected strains died. The expression of heat-shock-related genes significantly increased with heat treatment in the biofilms but mostly decreased in the planktonic cells. Thus, biofilm formation under raw milk storage conditions may improve the tolerance of antimicrobial-resistant gram-negative bacteria to pasteurization, thereby increasing their persistence in dairy processing lines and products. Furthermore, the difference in response to heat stress between biofilm and planktonic cells may be attributed to the differential expression of heat stress-related genes. Therefore, this study contributes to the understanding of how gram-negative bacteria persist under consecutive stresses in dairy processing procedures and the potential mechanism underlying heat tolerance in biofilms.

The Impact of Raw Milk Quality, particularly Thermoduric, and Storage Temperatures on the Keeping Quality of Pasteurized Milk

Abstract This study was aimed to investigate the effect of raw milk qualities on their corresponding pasteurized milk stored at different chilled temperatures. Raw milk collected from two different sources, Banhong (BH) milk farm and Mae Tha (MT) collection center, were pasteurized at 78 ± 2ºC for 30 s and kept for 21 days at 4-8ºC. During the storage period, representatives of milk treatments were assessed for their chemical, microbiological and sensorial characteristics. Collected data revealed that there was only minor alteration for the chemical properties of pasteurized milk throughout the studied storage period. The microorganism numbers in the pasteurized milk were significantly increased during storage and higher at higher storage temperatures. Poorer microbial quality of raw milk, including thermoduric bacteria, strongly contributed to higher microbial load of the correspondence pasteurized milk during chilled storage. The coliform number of all the pasteurized milk samples was found to be below 1 cfu/ml during 21 days of storage, while no Escherichia coli, Listeria monocytogenes and Staphylococcus aureus was detected in the pasteurized milk samples. The appraisal of the sensory features of pasteurized milk, including color, flavor, odor, creamy taste, texture and overall acceptance, were gradually decreased with longer storage period. Keywords: Pasteurized milk, Storage temperatures, Raw milk, Microbial quality, Chemical properties

Raw Milk for Provolone Valpadana PDO Cheese: Impact of Modified Cold Storage Conditions on the Composition of the Bacterial Biota

The raw milk for production of long-ripened, spicy type, Provolone Valpadana (PV) PDO cheese must be stored, refrigerated, and processed within 60 h from the first milking, according to European and Consortium regulations. Low-temperature storage conditions preserve the hygienic quality, but also reduce the diversity and content of dairy microbiota, which is important to define the characteristics and quality of raw milk cheeses. Eleven bulk, raw milk samples were stored, at laboratory level, under two different time/temperature conditions (i.e., 10 °C or 12 °C for 15 h, then cooled to 4 °C for 45 h). The count of different bacterial groups and the diversity of bacterial communities were determined before and after storage by culture-dependent and DNA metabarcoding methods, respectively. The two-step cold storage conditions increased the mesophilic, psychrotrophic, lipolytic, and proteolytic bacterial load, without affecting the hygienic quality of milk. Among the 66 dominant and 161 subdominant taxa retrieved by DNA metabarcoding, Acinetobacter, Pseudomonas, and the lactic acid bacteria belonging to the genera Lactococcus and Streptococcus were present in almost all the raw milk samples, and their relative abundance was positively related with the total bacterial count. The storage conditions tested could be considered for eventual application in long-ripened PV cheese production to rationalize storage, transfer, and processing of raw milk.

Sodium reduction in “Requeijão cremoso” processed cheese made from fresh and refrigerated sheep milk

The characteristics of traditional and reduced-sodium “Requeijão cremoso” processed cheese made from fresh sheep milk and refrigerated milk (4°C/5 days) were evaluated. Five days were established as the maximum time of storage of raw milk, reaching counts of 106 and 105 CFU/ml of mesophilic and psychrotrophic populations, respectively. The curds produced from refrigerated milk had lower fat content (~20%) and resulted in processed cheese with higher hardness, cohesiveness, and gumminess. The replacement of common emulsifying salt for reduced-sodium salt led to a 50% sodium reduction in the product, with no changes in color, texture, and pH. The results showed that the storage of raw milk had an impact on the curd composition and the texture of processed cheese. On the other hand, the replacement of emulsifying salt only affected the mineral composition of the final product, being an interesting alternative to ensure low-sodium content in processed cheese. Practical applications Studies on determining the limited period of raw sheep milk storage and the consequences on the final product are important for the sheep dairy chain, mainly because sheep milk is produced by smallholdings in many countries. Many producers need to store raw milk for days to accumulate a sufficient volume of milk for processing. In turn, sodium reduction is a global trend, thus knowledge about the impact of the replacement of emulsifying salt in processed cheese may encourage different dairy manufacturers to reformulate their products aiming to develop healthier products.

A Qualitative Assessment of the Risks of Transmission of Microorganisms to Humans Resulting from the Consumption of Raw Milk and Raw Cream in Norway

Pasteurisation of all consumer milk became mandatory in Norway in 1953, and this has been an important component of the protective measures that have reduced the incidence of milk and food borne diseases. In 2004, a complete recast of the hygiene legislation addressing both food hygiene and veterinary aspects was adopted by the European Union, the so-called “Hygiene package”. According to this legislation, each member state may, on its own initiative, prohibit or restrict the marketing of some foods like raw milk or raw cream, intended for direct human consumption within its territory. In response to this, the Norwegian Food Safety Authority (Mattilsynet) commissioned the Panel on Biological Hazards of the Norwegian Scientific Committee for Food Safety (Vitenskapskomitéen for mattrygghet), to prepare a risk assessment regarding the consumption of raw milk and raw cream. In response, an ad hoc Working Group of experts was appointed with the mandate to draft a risk assessment which should include the following components: identification and characterization of microbiological hazardous agents present in Norwegian raw milk; characterization of the public health consequences of these agents; assessment of the probability of transmission of these agents to humans by distribution of raw milk and cream. Additionally, the risk assessment should identify potential hazards to human health from the importation of raw milk, identify hazards associated with equipment used for production and storage of raw milk, and assess the risks associated with the potential transfer of antimicrobial resistance genes.
 
 Observations concerning infections related to consumption of raw milk and raw cream in Norway, other European countries and North America, show that a number of pathogenic microorganisms, including emerging pathogens, can occur in raw milk and raw cream. These pathogenic microorganisms and their toxins may represent a real threat to human health. The panel concluded that the risks associated with E. coli O157:H7 and other EHEC, C. jejuni and L. monocytogenes in raw milk and cream are high. Furthermore the importation of raw milk to Norway may result in the (re)introduction of microorganisms, which have been eradicated, or never previously have been present, in Norway. This can have serious consequences for both human and animal health.

Occurrence of bisphenol A in the milk chain: A monitoring model for risk assessment at a dairy company

Bisphenol A (BPA) as a chemical hazard may enter the milk chain during primary production at the farm and, successively, during milk processing at a dairy company. To identify the potential pathways that play a role in the occurrence of BPA, a monitoring model for risk assessment based on the identification of the hazards at each stage of milk processing was investigated. Milk samples were analyzed using liquid chromatography with fluorescence detection. Quantifiable levels were detected in samples obtained from the raw milk storage tank, pasteurized milk from the storage tank, and packaged milk. The highest BPA contamination levels were detected in raw milk from the storage tank (mean 0.265 µg/L). Despite the fact that dietary exposure levels were below the temporary daily intake, BPA may have adverse effects, particularly for vulnerable population groups. New monitoring programs involving each stage of milk processing should therefore be applied.

Prevalence of Psychrotrophic Bacteria During Frozen Storage of Raw Milk

The study was aimed to enumerate the load of psychrotrophic bacteria in raw milk stored in freezer. Raw milk was collected from 18 different sized dairy farms located in Gazipur and Mymensingh district. From each location equal number (three of each) of small, medium or large farms were randomly selected. The raw milk samples were stored in freezer (-18 to -22 oC) for 28 days and analyzed for psychrotrophic bacterial load at every 7 days interval. For total viable count, bacteria was grown onto plate count agar at 70C for 10 days. Bacteria grown under such conditions referred as psychrotrophs. However, to determine the type of psychrotrophs selected colonies were grown further onto pseudomonas agar base and gram staining, oxidase, catalase and methyl red test for each isolate were perfomed. The psychrotrophic bacterial load in all the samples were low until 14 days of storage. However, from the third week of storage the bacterial load was observed to increase which reached to as high as 1.1 ± 2.3×107 cfu/mL at the end of the storage period (28 days). The milk samples obtained from large farms were lower (1.3×105 to 6.6×106) than that of medium (1.7×105 to 8.8×106) and small (2.0×105 to 1.1×107) type farms. The bacterial load was significantly (P<0.01) varied among the samples suggesting the heterogeneous management practices in dairy farms. All the morphological and biochemical tests confirmed the isolates as pseudomonas. Based on the present findings, it could be suggested that raw milk can store in the freezer maximum for two weeks in terms of psychrotrophic bacterial load.
 Ann. Bangladesh Agric. (2020) 24(1) : 65-76

Studies on physicochemical changes and volatile organic compounds released during storage of raw cow milk

This study aims to determine the changes in physicochemical properties along with the concentration of volatile organic compounds during storage of raw cow milk were discussed until spoilage. The physicochemical properties taken to study the raw milk quality are temperature, humidity, milk pH, milk acidity and concentration of volatile organic compounds. The raw milk sample was tested simultaneously for both the concentration of volatile organic compounds and other physicochemical parameters such as temperature, relative humidity, milk pH and acidity. The experiment was conducted for 10 hours regularly for 5 days. The result reveals that there is an increase in the concentration of total volatile organic acids from 139.50 ± 1.1180 μg/L to 482.25 ± 1.4790 μg/L. The increase in the concentration of volatile organic acids might be due to the metabolic activity of microorganisms such as Lactic acid bacteria, which is responsible for the decrease and increase of pH and acidity of the raw milk respectively. Hence, the concentration of total volatile organic compounds were correlated with milk pH and acidity. In which, the milk pH shows better correlation with the total volatile organic compounds with.

Lactose oxidase: Enzymatic control of Pseudomonas to delay age gelation in UHT milk

Shelf-stable milk is consumed worldwide, and this market is expected to continue growing. One quality challenge for UHT milk is age gelation during shelf life, which is in part caused by bacterial heat-stable proteases (HSP) synthesized during the raw milk storage period before heat processing. Some Pseudomonas spp. are HSP producers, and their ability to grow well at refrigeration temperature make them important spoilage organisms for UHT processors to control. Previous studies have shown that lactose oxidase (LO), a natural and commercially available enzyme that produces hydrogen peroxide and lactobionic acid from lactose, can control bacterial growth in raw milk. In this research, we investigated the ability of LO to control HSP producer outgrowth, and thus delay age gelation in UHT milk. Six strains of Pseudomonas spp. were selected based on their ability to synthesize HSP and used as a cocktail to inoculate both raw and sterile (UHT) milk at a level of 1 × 105 cfu/mL. Groups were treated with and without LO, stored for 4 d at 6°C, and monitored for cell count and pH. Additionally, a sample from each was tested for HSP activity via particle size analysis (average effective diameter at 90° angle and 658 nm wavelength) and visual inspection on each day of the storage period. The HSP activity results were contrasted using Tukey's HSD test, which showed that in UHT milk, a LO treatment (0.12 g/L) effectively prevented gelation as compared with the control. In raw milk, however, a concentration of 0.24 g/L of LO was needed to obtain a similar effect. This test was scaled up to 19-L pilot plant batches of raw milk where they were challenged with Pseudomonas cocktail, treated with LO for 3 d, and then UHT processed. Resulting UHT milk bottles were monitored for gelation. Significant differences in particle size between the LO-treated samples and the control were observed as early as 1 mo after processing, and gelation was not detected in the LO-treated samples through 6 mo of storage. These results demonstrated that LO can be used to delay age gelation in UHT milk induced by HSP-producing Pseudomonas spp., representing an opportunity to improve quality and reduce postproduction losses in the shelf-stable milk market sector.

Investigation of the Applicability of Raman Spectroscopy as Online Process Control during Consumer Milk Production

Online detection of product defects using fast spectroscopic measurements is beneficial for producers in the dairy industry since it allows readjustment of product characteristics or redirection of product streams during production. Raman spectroscopy has great potential for such application due to the fast and simple measurement. Its suitability as online sensor for process control was investigated at typical control points in consumer milk production being raw milk storage, standardization, and heat treatment. Additionally, the appropriateness of Raman spectroscopy to act as indicator for product application parameters was investigated using the example of barista foam. To assess the suitability of a pure online system, the merit of Raman spectra was evaluated by a principal component analysis (PCA). Thereby, proteolytic spoilage due to the presence of extracellular enzymes of Pseudomonas sp. was detected and samples based on the applied heat treatment (extended shelf life (ESL) and ultra-high temperature (UHT)) could be separated. A correlation of the content of free fatty acids and foam stability with spectra of the respective milk samples was found, allowing a prediction of the technofunctional quality criterion “Barista” suitability of a UHT milk. The results underlined the suitability of Raman spectroscopy for the detection of deviations from a defined product standard of consumer milk.

Reservoirs of antimicrobial resistance genes in retail raw milk

BackgroundIt has been estimated that at least 3% of the USA population consumes unpasteurized (raw) milk from animal sources, and the demand to legalize raw milk sales continues to increase. However, consumption of raw milk can cause foodborne illness and be a source of bacteria containing transferrable antimicrobial resistance genes (ARGs). To obtain a comprehensive understanding of the microbiome and antibiotic resistome in both raw and processed milk, we systematically analyzed 2034 retail milk samples including unpasteurized milk and pasteurized milk via vat pasteurization, high-temperature-short-time pasteurization, and ultra-pasteurization from the United States using complementary culture-based, 16S rRNA gene, and metagenomic sequencing techniques.ResultsRaw milk samples had the highest prevalence of viable bacteria which were measured as all aerobic bacteria, coliform, and Escherichia coli counts, and their microbiota was distinct from other types of milk. 16S rRNA gene sequencing revealed that Pseudomonadaceae dominated raw milk with limited levels of lactic acid bacteria. Among all milk samples, the microbiota remained stable with constant bacterial populations when stored at 4 °C. In contrast, storage at room temperature dramatically enriched the bacterial populations present in raw milk samples and, in parallel, significantly increased the richness and abundance of ARGs. Metagenomic sequencing indicated raw milk possessed dramatically more ARGs than pasteurized milk, and a conjugation assay documented the active transfer of blaCMY-2, one ceftazidime resistance gene present in raw milk-borne E. coli, across bacterial species. The room temperature-enriched resistome differed in raw milk from distinct geographic locations, a difference likely associated with regionally distinct milk microbiota.ConclusionDespite advertised “probiotic” effects, our results indicate that raw milk microbiota has minimal lactic acid bacteria. In addition, retail raw milk serves as a reservoir of ARGs, populations of which are readily amplified by spontaneous fermentation. There is an increased need to understand potential food safety risks from improper transportation and storage of raw milk with regard to ARGs.E4kXQjxU9tgRorkuFR9RTiVideo

Sources of psychrotrophic contamination and proteolysis indices in raw milk

Storage of raw milk under refrigeration makes it possible to reduce operating costs for production and prevents losses of this raw material by the acidifying activity of mesophilic bacteria. Meantime, storage for prolonged periods may result in decreased quality of dairy products, due to the growth and enzymatic activity of psychrotrophic bacteria. Thus, in this study, we evaluated the presence of psychrotrophic microorganisms, Pseudomonas spp. and Pseudomonasaeruginosa tracing sources of microbiological contamination in the milking process as well as the level of proteolysis of the milk in the expansion tank. The highest contamination (P <0.05) occurred with the psychrotrophic count, with maximum values of 5.11 log CFU•mL-1a value that has hydrolytic potential for K-casein. Some dairy farms were found to have a maximum caseinomacropeptide value of 142.93 mg•L-1, representing loss of quality for the industry and a raw material that is not suitable for human consumption. The points of greatest contamination were udder surface, insufflator, milking bucket and colling system. According to principal component analysis, the values obtained for the microbiological counts were not determinants of the release of caseinomacropeptide.

Transmembrane Pressure and Recovery of Serum Proteins During Microfiltration of Skimmed Milk Subjected to Different Storage and Treatment Conditions.

Milk pre-processing steps-storage at 4 °C (with durations of 48, 72 or 96 h) and methods for microbiological stabilization of milk (1.4 μm microfiltration, thermization, thermization + bactofugation, pasteurization) are performed industrially before 0.1 µm-microfiltration (MF) of skimmed milk to ensure the microbiological quality of final fractions. The objective of this study was to better understand the influence of these pre-processing steps and their cumulative effects on MF performances (i.e., transmembrane pressure, and transmission and recovery of serum proteins (SP) in the permeate). Results showed that heat treatment of skimmed milk decreased ceramic MF performances, especially after a long 4 °C storage duration (96 h) of raw milk: when milk was heat treated by pasteurization after 96 h of storage at 4 °C, the transmembrane pressure increased by 25% over a MF run of 330 min with a permeation flux of 75 L·h−1·m−2 and a volume reduction ratio of 3.0. After 48 h of storage at 4 °C, all other operating conditions being similar, the transmembrane pressure increased by only 6%. When milk was 1.4 µm microfiltered, the transmembrane pressure also increased by only 6%, regardless of the duration of 4 °C storage. The choice of microbiological stabilization method also influenced SP transmission and recovery: the higher the initial heat treatment of milk, the lower the transmission of SP and the lower their recovery in permeate. Moreover, the decline of SP transmission was all the higher that 4 °C storage of raw milk was long. These results were explained by MF membrane fouling, which depends on the load of microorganisms in the skimmed milks to be microfiltered as well as the rate of SP denaturation and/or aggregation resulting from pre-processing steps.