Why is pasteurization used

In this work, the specific needs of a human milk bank setting were considered to design an HTST equipment for the continuous and adaptable time-temperature combination processing of donor milk. Microbiological quality, activity of indicator enzymes and indices for thermal damage of milk were evaluated before and after HTST treatment of 14 batches of donor milk using different temperature and time combinations and compared to the results obtained after Holder pasteurization.

The HTST system has accurate and simple operation, allows the pasteurization of variable amounts of donor milk and reduces processing time and labor force. Breast milk provides all the nutrients, vitamins, and minerals, required for infant growth. In addition, its content in specific bioactive compounds such as immunoglobulins, enzymes, cytokines, growth factors or hormones, also protects against infections and modulates maturation of the digestive and immune systems and neurodevelopment.

Furthermore, human milk composition is highly variable within feeds, diurnally, over lactation in order to promote both survival and healthy development of the infant Ballard and Morrow, Therefore, mother's own milk MOM is the gold standard for the feeding and nutrition of term and preterm newborn during the first months of life Section on breastfeeding American Academy of Paediatrics, The use of DHM is associated to a reduction in the incidence of necrotizing enterocolitis, protection against late-onset sepsis and improved feeding tolerance compared to formula milk in this high-risk group of infants Quigley and McGuire, ; Sisk et al.

Human Milk Banks HMBs are established to recruit and screen milk donors, collect, treat, store, and distribute donated milk. The microbiological quality of DHM is one of the main concerns in most HMBs as it will be administered mainly to preterm or sick infants, who are especially susceptible to infections. The manipulation involved in DHM extraction and management may be an exogenous source of microbial contamination to DHM.

In fact, contaminated human milk has occasionally been a vehicle for pathogenic microorganism, to preterm and very low birth weight infants causing late onset sepsis Widger et al. To ensure microbiological safety, DHM is pasteurized in most HMBs in order to kill all non-spore forming and potentially pathogenic microorganisms Landers and Updegrove, At present, a Low-Temperature Long-Time heating at High-risk viruses, such as cytomegalovirus, papillomaviruses, and human immunodeficiency, T-lymphotrophic, Ebola, Marburg, and Zika viruses, are also destroyed after HoP of human milk Orloff et al.

On the other hand, some nutritional and biological components, such as immunoglobulins, hormones or enzymes, result negatively affected after HoP Peila et al. Another disadvantage associated with the available commercial units for HoP is that the volume of production in a working day is limited to the number of containers with DHM that can be placed in the equipment.

Different experimental systems, such as laboratory capillary heat exchangers, industrial heat exchangers or benchtop pasteurizers for small volumes, have been used for HTST pasteurization of DHM Goldblum et al.

Alternative treatments to DHM thermal processing, including high pressure processing or UV irradiation, have been proposed. These alternatives seem to better preserve some biological components, such as total immunoglobulin A or lysozyme activity, compared to HoP Christen et al. However, they require further investigation about the influence on other milk components as well as performing exhaustive microbiological analyses before they could be used to treat DHM.

In this context, the objective of this work was to design a continuous HTST system to pasteurize DHM in the HMB operating environment and to evaluate its effect on the microbiological quality of DHM when tested at different temperatures and holding times. The content of these bottles was mixed to achieve a final volume of about 10 L a production batch in the stirred feed vessel of the HTST equipment Figure 1.

The length of the holding tube internal diameter of 9. The validation of the holding tube was done by operating the pasteurizer with water, injecting a saturated salt solution in the holding tube, and measuring the time required for the injection to traverse the tube Food and Drug Administration, 1. All measurements of residence time were performed in triplicate. To avoid microbiological contamination, DHM processing always started using the slowest flow rate, corresponding to the most stringent processing condition 25 s , and increased sequentially in order to obtain samples subjected to shorter processing times.

Therefore, processing of one production batch delivered five DHM samples treated at one fixed temperature and five different processing times 5, 10, 15, 20, and 25 s. After pasteurization, the containers were transferred immediately into another shaking water bath Jeio Tech BS filled with ice-cold water for fast cooling.

A wireless temperature data logger thermometer Mesa Labs, Inc. After bacterial counting, at least one bacterial colony showing a characteristic morphology color, size, shape, halos of each of the types present on every plate was selected for identification. This assay uses p -nitrophenyl phosphate p NPP as the substrate. The activity was determined after a diazo coupling reaction with the released p -nitroaniline by monitoring the increase in absorbance at nm using a microplate spectrophotometer Zenyth RT.

Resmini et al. All analyses were done in duplicate, and the values were expressed as milligrams of furosine per g of protein. Lactulose concentration in raw and heat-treated DHM samples was determined by gas chromatography with flame ionization detector, following the method described by Montilla et al.

The identity of lactulose present in the samples was confirmed by comparison with relative retention times of a standard. Quantitative analysis was carried out by the internal standard method. The significance of differences between means was assessed using one-way ANOVA and Tukey multiple comparison post-hoc tests or paired Student's t -tests.

The HTST system consists of the following major units: holding tanks and pumps, heat exchange and holding sections, temperature and flow controllers, and a recording device Figures 2A, B. Figure 2. The open stirred feed vessel 20 L that provides a constant supply of milk was equipped with an impeller driven by a DC motor, used at low speed 90—95 rpm , to mix the pooled DHM and avoid phase separation during the process.

A tuning fork switch controls the volume of milk present in this vessel and also allows the recirculation of fluid, if required. The flow rate of the solution is regulated by adjusting the rotor disc speed and is measured by an electromagnetic flow meter. The heating and cooling sections are corrugated mono-tube heat exchangers that are installed in series and arranged into two separate sections.

The monotube configuration of the heat exchangers determines that the milk flows through the inner tube while the hot or cold water flows in a counter-current arrangement through the annular space between the inner and the outer tube. The holding tube 0. Sizing of the holding tube was validated by the salt conductivity test.

The average of three measurements was Four temperature transmitters measure the fluid temperature before entering and after leaving the heating section, after leaving the holding tube, and after leaving the cooling section. A pressure transmitter monitors continuously the pressure of heat-treated milk at the exit point.

Two independent secondary circuits provide hot and cold water for the process. A closed isothermal tank 25 L with an impeller driven by a direct current motor and used at low speed 90—95 rpm holds the pasteurized milk Figure 2A.

This tank allows separating milk packaging from heat processing and is located in a laminar flow safety cabinet provided with a filter 0. The tank has a manual valve for dispensing the required volume of pasteurized DHM in sterile containers, according to the demand of the HMB. The equipment also has a control unit composed of a touch screen display to adjust all operating parameters and procedures and a recorder to gather the records of all parameters such as milk flow rate, temperature of the fluid at several points of the process, and temperature of the hot water circuit Figure 2A.

All acquired data were downloaded and analyzed with dedicated software in order to assess the adequacy of the process. A typical profile of fluid temperature and flow during the operation of the HTST unit is shown in Figure 3. Figure 3. Time-temperature and fluid flow profiles of a representative HTST process. The main steps of operation are: 1: Sanitizing; 2: Conditioning; 3: Heat processing and cooling. The inlet temperature in the heating section either hot water in steps 1 and 2, raw DHM in step 3, or water or cleansing solutions in steps 4—8 is shown in yellow; the temperature of the fluid at the exit of the holding tube is shown in red; and, the temperature of the fluid at the exit of the cooling section is shown in blue.

The gray line at the bottom represents the fluid flow. The cleaning procedure comprises four steps after each processing. The effectiveness of the thermal sanitizing step was checked for each processing cycle by microbiological analysis. Identification of the isolates obtained in the different growth media revealed their poor selectivity since some bacterial species could be isolated from up to three different growth media e.

Figure 4. Microbiological counts in raw DHM. The number of different microorganisms in a same raw DHM production batch ranged from 3 to 10, although seven was the most frequent number Supplementary Table 2.

In relation to Gram-positive bacteria, S. Table 1. Microbiological characterization of the 14 batches of raw DHM analyzed in this study. The variety of Gram-negative bacteria identified was wider than that of Gram-positive ones and, globally, included isolates belonging to eight genera Table 1 , Supplementary Table 2. Although the frequency of detection of some species of Pseudomonas and Stenotrophomonas in raw DHM was lower, such bacteria reached the highest levels 5.

Yeasts were scarcely isolated Table 1. Survivors were detected only in five production batches and were identified as B. Table 2. The analysis of PFGE profiles of the enterococci isolated from DHM samples before and after different heat treatments revealed the existence of, at least, four pulsotypes that were closely associated to specific production batches Figure 5.

In fact, as an example, the same pulsotype was shared by E. Isolates from different batches did not share the same PGFE profile, except for two production batches L4 and L9 where the same profile was shared by all nine isolates.

Figure 5. In all of these cases, B. All hot water samples collected at the end of the sanitation step, and prior the processing of a DHM production batch, over the course of this study were seeded on BHI agar for microbiological analysis.

Bacterial growth was not observed in any sample. Figure 6. Figure 7. Furosine was detected in all DHM samples analyzed, both before and after any of the applied heat treatments, and its content is presented in Table 3.

Holder pasteurization of DHM increased significantly the concentration of furosine mean value of 4. Table 3. The heat exchangers were designed and constructed in order to have a self-draining design and a small dead volume about mL , thereby minimizing DHM losses. In addition, the heat treatment is independent of packaging, allowing packing pasteurized DHM in accordance with the needs and preferences of the HMB.

CIP cleaning and sanitation of the whole HTST system before operation without dismantling the equipment and without direct manipulation of chemical products contributes to enhance safety and DHM quality.

There has been some controversy regarding the use of raw or pasteurized DHM. On the other hand, DHM is a vehicle for potentially pathogenic microorganisms and, as a consequence, most HMBs consider that DHM must be processed in order to guarantee its microbiological safety. In spite of undesirable changes related to heat treatment, pasteurized DHM still retains some beneficial and protective effects, and it is preferred to infant formula Quigley and McGuire, ; Sisk et al. Unfortunately, the pasteurizers commercially available at present are very limited regarding the retention of some bioactive components and the amount of milk that can be processed between 4 and 10 L per batch Underwood, Bacteria could be isolated from all the raw human milk batches in the different culture media employed in this study.

The high concentrations of enterobacteria, Pseudomonas spp. Contaminating bacteria, arising from environment or rinsing water Cervia et al. In dairy industry pasteurization is designed to achieve at least a five-log reduction or Spore-forming bacteria, on the other hand, can survive milk pasteurization Sarkar, The purpose of pasteurization is making DHM safe for consumption, and this requires destroying all common pathogens O'Connor et al.

However, the most thermoresistant non-sporulated microorganism has not been defined in DHM. On the other hand, as the microbiological quality of pasteurized DHM depends on the initial microbiota present in raw DHM, the specific processing conditions applied, and the storage conditions, donors should receive a good education on hygienic milk extraction and storage from the HMB staff. In order to reach the pasteurization objective, this process should be implemented to heat the milk homogeneously, at a consistent temperature and for the correct time.

Only two bacterial species B. Holder pasteurization kills commensal and contaminant vegetative bacterial cells found in DHM but spore-forming bacteria, such as B. Subsequently, such bacteria can grow in heat-treated milk even faster than in raw milk because of the heat damage to the milk bacteriostatic systems and the absence of competitors Ford et al.

In agreement with our results, B. Additionally, it has been found in milk of healthy rhesus monkeys Jin et al. Although any milk bottle with a culture-positive result after pasteurization is rejected by most HMBs, a previous study revealed that all B. However, as the level of virulence is highly variable among different strains Decousser et al.

Refrigeration or freezing of pasteurized DHM should be strictly applied to control the growth of any remaining microorganism. Although a relative high number of B. Despite E. Common milkborne illnesses during that time were typhoid fever, scarlet fever, septic sore throat, diptheria, and diarrheal diseases. These illnesses were virtually eliminated with the commercial implementation of pasteurization, in combination with improved management practices on dairy farms. Pasteurization is the process of heating a liquid to below the boiling point to destroy microorganisms.

It was developed by Louis Pasteur in to improve the keeping qualities of wine. Commercial pasteurization of milk began in the late s in Europe and in the early s in the United States. Pasteurization became mandatory for all milk sold within the city of Chicago in , and in Michigan became the first state to require that all milk for sale within the state be pasteurized. In the U. Public Health Service developed the Standard Milk Ordinance to assist states with voluntary pasteurization programs.

Departments of Health and Human Services and Public Health, and the Food and Drug Administration and defines practices relating to milk parlor and processing plant design, milking practices, milk handling, sanitation, and standards for the pasteurization of Grade A milk products.

Each state still regulates milk processing within their own state but dairy products must meet the regulations stated in the PMO for products that will enter interstate commerce.

However, in these conditions were shown to be inadequate for the inactivation of Coxiella burnetii which causes Q fever in humans Enright et al. The product is termed "shelf stable" and does not need refrigeration until opened. All aseptic operations are required to file their processes with the Food and Drug Administration's "Process Authority. About Us. Knowledge Center.