Study of the composition of the residual microflora of milk after pasteurization

The article presents the results of studies of the composition of the residual microflora of pasteurized milk, depending on the bacterial landscape and the initial contamination of raw milk. The thermal stability of test  cultures of microorganisms that significantly affect the  quality and  storage capacity of fermented dairy products has been  studied. To study  the  composition of the  residual microflora of milk after  pasteurization, sterile milk was infected with  test  cultures of microorganisms at doses  from  10¹ CFU/cm³ to 10⁷ CFU/cm³. After infection, the  milk was pasteurized at temperatures of (72 ± 1) °C and  (80 ± 1) °C with  a holding time  of 10–20  seconds. The detection and  enumeration of microorganisms was carried out  by standardized microbiological methods. Microorganisms were identified by visual assessment of dominant colonies and cell morphology in micropreparations. The thermal stability of microorganisms important for dairy products, in particular cheeses, the source of which  is raw milk, has been  studied. It has been  established that of the  coccal  forms,  the  greatest risks are associated with  enterococci. Escherichia coli at  infection doses  above 10⁶ CFU/cm³ partially retains viability both  at low-temperature and  at high-temperature pasteurization. Pasteurization temperatures do not have  a lethal effect on spore  bacilli, their number in pasteurized milk does not decrease, regardless of the  initial dose of infection. Low-temperature pasteurization activates the process of clostridial spore  germination. The ability to reactivate cells after  thermal shock was observed in Escherichia coli, Staphylococcus aureus, Pseudomonas, and  mold  fungi.  Thus,  the  residual microflora of milk  subjected to  low-temperature pasteurization is represented by enterococci, thermophilic streptococci, micrococci, staphylococci, asporogenous bacilli  and  spore bacteria. The above microorganisms constitute  the  residual microflora of pasteurized milk and are involved in the  maturation of cheeses, determining their quality and  safety,  [as well as] affecting the  storage capacity of the finished product.

1. Stoeckel, M., Lidolt, M., Hinrichs, J. (2016). Modeling milk heating processes for the production of milk shelf-stable without refrigeration. Chemie Ingenieur Technik, 89(3), 310–319. https://doi:org/10.1002/cite.201600067

2. Dumalisile, P., Witthuhn, R. C., Britz, T. J. (2005). Impact of different pasteurization temperatures on the survival of microbial contaminants isolated from pasteurized milk. International Journal of Dairy Technology, 58(2), 74–82. https://doi:org/10.1111/j.1471–0307.2005.00189.x

3. Sviridenko, G. M. (2009). Microbiological risks in the production of milk and dairy products. Moscow: Publishing House of the Russian Agricultural Academy, 2009. (In Russian)

4. Dervisoglu, M., Aydemir, O. (2006). Physicochemical and microbiological characteristics of Kulek cheese made from raw and heat-treated milk. World Journal of Microbiology and Biotechnology, 23, 451–460. https://doi.org/10.1007/s11274–006–9246-x

5. Pearce, L. E., Smythe, B. W., Crawford, R. A., Oakley, E., Hathaway, S. C., Shepherd, J. M. (2012). Pasteurization of milk: The heat inactivation kinetics of milk-borne dairy pathogens under commercial-type conditions of turbulent flow. Journal of Dairy Science, 95(1), 20–35. https://doi:org/10.3168/jds.2011–4556

6. Dash, K. K., Fayaz, U., Dar, А. H., Shams, R., Manzoor, S., Sundarsingh, A. et al. (2022). A comprehensive review on heat treatments and related impact on the quality and microbial safety of milk and milk-based products. Food Chemistry Advances, 1, Article 100041. https://doi.org/10.1016/j.focha.2022.100041

7. Cebrián, G., Condón, S., Mañas, P. (2017). Physiology of the inactivation of vegetative bacteria by thermal treatments: Mode of action, influence of environmental factors and inactivation kinetics. Foods, 6(12), Article 107. https://doi.org/10.3390/foods6120107

8. Deeth, H. C. (2022). Encyclopedia of Dairy Sciences (Third Edition). Chapter in a book: Heat Treatment of Milk: Pasteurization (HTST) and thermization (LTLT). Academic Press, 645–654.

9. Yemelyanov, S. A., Khramtsov, A. G., Suyunchev, O. A., Khvorostina, E. N., Ovcharova, G. P., Belashev, A. T. et al. (2006). The effect of temperature on the development of microorganisms in milk and dairy products. Bulletin of the North Caucasus State Technical University, 2, 54–57 (In Russian)

10. Emelyanov, S. A. (2006). Microbiological aspects of the use of heat treatment of raw milk. Bulletin of Saratov State Agrarian University named after N. I. Vavilov, 6–2, 15–20. (In Russian)

11. Evelyn, Silva, F. V. M. (2018). Differences in the resistance of microbial spores to thermosonication, high pressure thermal processing and thermal treatment alone. Journal of Food Engineering, 222, 292–297. https://doi.org/10.1016/j.jfoodeng.2017.11.037

12. McAuley, C. M., Gobius, K. S., Britz, M. L., Craven, H. M. (2012). Heat resistance of thermoduric enterococci isolated from milk. International Journal of Food Microbiology, 154(3), 162–168. https://doi.org/10.1016/j.ijfoodmicro.2011.12.033

13. Li, R., Shi, Y., Ling, B., Cheng, T., Huang, Z., Wang, S. (2017). Thermotolerance and heat shock protein of Escherichia Coli ATCC25922 under thermal stress using test cell method. Emirates Journal of Food and Agriculture, 29(2), 91–97. https://doi.org/10.9755/ejfa.2016–07–97814

14. Abdalla, M. O. M., Salih, H. M. A. (2020). Effect of heat treatment of milk on the physicochemical, microbiological and sensory characteristics of white cheese (Gibna bayda). GSC Advanced Research and Reviews, 3(3), 20–28. https://doi.org/10.30574/gscarr.2020.3.3.0044

15. Knight, G. C., Nicol, R. C., McMeekin, T. A. (2004). Temperature step changes: A novel approach to control biofilms of Streptococcus thermophilus in a pilot plant-scale cheese-milk pasteurisation plant. International Journal of Food Microbiology, 93(3), 305–318. https://doi.org/10.1016/j.ijfoodmicro.2003.11.013

16. Kim, C., Alrefaei, R., Bushlaibi, M., Ndegwa, E., Kaseloo, P., Wynn, C. (2019). Influence of growth temperature on thermal tolerance of leading foodborne pathogens. Food Science and Nutrition, 7(12), 4027–4036. https://doi:org/10.1002/fsn3.1268

17. Velliou, E. G., Van Derlinden, E., Cappuyns, A. M., Geeraerd, A. H., Devlieghere, F., Van Impe, J. F. (2012). Heat inactivation of Escherichia coli K12 MG1655: Effect of microbial metabolites and acids in spent medium. Journal of Thermal Biology, 37(1), 72–78. https://doi.org/10.1016/j.jtherbio.2011.11.001

18. Cebrian, G., Condon, S., Maras, P. (2009). Heat-adaptation induced thermotolerance in Staphylococcus aureus: Influence of the alternative factor sigmaB. International Journal of Food Microbiology, 135(3), 274–280. https://doi:org/10.1016/j.ijfoodmicro.2009.07.010

19. Yaniarti, M. N., Amarantini, C., Budiarso, T. Y. (2017). The effect of temperature and Pasteurization time on Staphylococcus aureus isolates from dairy products. AIP Conference Proceedings, 1908, Article 050003. https://doi.org/10.1063/1.5012727

20. Sоrqvist, S. (2003). Heat resistance in liquids of Enterococcus spp., Listeria spp., Escherichia coli, Yersinia enterocolitica, Salmonella spp. and Campylobacter spp. Acta Veterinaria Scandinavica, 44(1), Article 1. https://doi.org/10.1186/1751–0147–44–1

21. Bang, J., Choi, M., Jeong, H., Lee, S., Kim, Y., Ryu, J.-H., Kim, H. (2017). Heat tolerances of Salmonella, Cronobacter sakazakii, and Pediococcus acidilactici Inoculated into Galactooligosaccharide. Journal of Food Protection, 80(7), 1123–1127. https://doi.org/10.4315/0362–028x.jfp-16–456

22. Hanson, M. L., Wendorff, W. L., Houck, K. B. (2005). Effect of heat treatment of milk on activation of Bacillus spores. Journal of Food Protection, 68(7), 1484–1486. https://doi.org/10.4315/0362–028x-68.7.1484

23. Stoeckel, M., Lücking, G., Ehling-Schulz, M., Atamer, Z., Hinrichs, J. (2016). Bacterial spores isolated from ingredients, intermediate and final products obtained from dairies: thermal resistance in milk. Dairy Science and Technology, 96, 569–577. https://doi.org/10.1007/s13594–016–0279–0

24. Novak, J. S., Call, J., Tomasula, P., LuchanskY, J. B. (2005). An assessment of pasteurization treatment of water, media, and milk with respect to Bacillus spores. Journal of Food Protection, 68(4), 751–757. https://doi.org/10.4315/0362–028x-68.4.751

25. Stoeckel, M., Abduh, S. B. M., Atamer, Z., Hinrichs, J. (2014). Inactivation of Bacillusspores in batch vs continuous heating systems at sterilisation temperatures. International Journal of Dairy Technology, 67(3), 334–341. https://doi.org/10.1111/1471–0307.12134

26. Fan, L., Hou, F., Muhammad, A. I., Ruiling, L. V., Watharkar, R. B., Guo, M. et al. (2018). Synergistic inactivation and mechanism of thermal and ultrasound treatments against Bacillus subtilis spores. Food Research International, https://doi.org/10.1016/j.foodres.2018.09.052

27. Ortuzar, J., Martinez, B., Bianchini, A., Stratton, J., Rupnow, J., Wang, B. (2018). Quantifying changes in spore-forming bacteria contamination along the milk production chain from farm to packaged pasteurized milk using systematic review and meta-analysis. Food Control, 86, 319–331. https://doi.org/10.1016/j.foodcont.2017.11.038

28. Esteban, M.-D., Huertas, J.-P., Fernández, P. S., Palop, A. (2013). Effect of the medium characteristics and the heating and cooling rates on the nonisothermal heat resistance of Bacillus sporothermodurans IC4 spores. Food Microbiology, 34(1), 158–163. https://doi.org/10.1016/j.fm.2012.11.020

29. Evelyn, Silva, F. V. M. (2019). Heat assisted HPP for the inactivation of bacteria, moulds and yeasts spores in foods: Log reductions and mathematical models. Trends in Food Science and Technology, 88, 143–156. https://doi.org/10.1016/j.tifs.2019.03.016