Abstract

Introduction. This study aimed to evaluate the quality of milk produced by six cattlemen’s associations in small, isolated farming communities of Carchi, Ecuador. It involved a herd of 814 cows and lasted eight consecutive months. Another aim was to propose a suitable methodology for milk quality evaluation.
Study objects and methods. All milk samples were analyzed for total solids, protein, fat, acidity, density, total bacterial count (TBC) and somatic cell count (SCC). Each sample was subjected to an extended qualitative methylene blue reduction test (MBRTe) for which 10 mL of milk, with 0.5 mL of methylene blue, was incubated at 37°C for 24 h.
Results and discussion. As a result, we obtained the following types of clots: MBRTe-I (homogeneous solid/liquid clot), MBRTe-II (lumpy clot), MBRTe-III (gaseous clot) and MBRTe-IV (lumpy + gaseous clot). The study showed significant differences in the quality of milk between different associations, suggesting that some of them did not comply with good practices of milking, handling and storage of fresh milk. The quality of milk was classified as good in one association, as regular in another association, and as low in four associations. The MBRTe classified 37% of the samples as MBRTe-I, 18% as MBRTe-II, 14% as MBRTe-III and 12% as MBRTe-IV. Of the MBRTe-I samples, 95% showed the TBC and SCC values of first quality milk. The MBRTe-II had the TBC values of first quality milk, but exceeded the SCC, while the MBRTe-III had good SCC values, but exceeded the TBC. Finally, the MBRTe-IV samples exceeded the permissible levels of both TBC and SCC.
Conclusion. It was proved that the MBRTe can help milk producers evaluate the quality of milk and alert them to the possible presence of mastitis in the herd. The MBRTe is a reliable and cheap method that is quick and easy to perform.

Keywords

Dairy industry, raw milk, dairy cattle, microorganisms, somatic cells

REFERENCES

1. Juan Pablo Grijalva: Exportar leche, una buena solución [Juan Pablo Grijalva: Export milk, a good solution] [Internet]. [cited 2019 Oct 01]. Available from: https://www.revistalideres.ec/lideres/exportacion-leche-ganaderos-lacteosconsumo.html.
2. Un tercio de la producción láctea se dedica al queso [A third of dairy production is dedicated to cheese] [Internet]. [cited 2019 Oct 01]. Available from: https://www.revistalideres.ec/lideres/ecuador-produccion-lactea-queso.html.
3. Esguerra JC, Cassoli LD, Munera-Bedoya OD, Ceron-Munoz MF, Machado PF. Milk quality: milking personnel associated factors. Revista Mvz Cordoba. 2018;23(1):6461–6473. DOI: https://doi.org/10.21897/rmvz.1241.
4. Rodrigues MX, Lima SF, Canniatti-Brazaca SG, Bicalho RC. The microbiome of bulk tank milk: Characterization and associations with somatic cell count and bacterial count. Journal of Dairy Science. 2017;100(4):2536–2552. DOI: https://doi.org/10.3168/jds.2016-11540.
5. Jamali H, Barkema HW, Jacques M, Lavallee-Bourget EM, Malouin F, Saini V, et al. Invited review: Incidence, risk factors, and effects of clinical mastitis recurrence in dairy cows. Journal of Dairy Science. 2018;101(6):4729–4746. DOI: https://doi.org/10.3168/jds.2017-13730.
6. Dalen G, Rachah A, Norstebo H, Schukken YH, Reksen O. The detection of intramammary infections using online somatic cell counts. Journal of Dairy Science. 2019;102(6):5419–5429. DOI: https://doi.org/10.3168/jds.2018-15295.
7. Thornton HR, Hastings EG. Studies on oxidation-reduction in milk: The methylene blue reduction test. Journal of Dairy Science. 1930;13(3):221–245. DOI: https://doi.org/10.3168/jds.S0022-0302(30)93520-5.
8. De Silva SASD, Kanugala KANP, Weerakkody NS. Microbiological quality of raw milk and effect on quality by implementing good management practices. Procedia Food Science. 2016;6:92–96. DOI: https://doi.org/10.1016/j.profoo.2016.02.019.
9. Boor KJ, Wiedmann M, Murphy S, Alcaine S. A 100-year review: Microbiology and safety of milk handling. Journal of Dairy Science. 2017;100(12):9933–9951. DOI: https://doi.org/10.3168/jds.2017-12969.
10. Official methods of analysis of AOAC International, 21th Edition. Washington DC: The Association of Official Analytical Chemists, 2019.
11. Lilliefors HW. On the Kolmogorov-Smirnov test for normality with mean and variance unknown. Journal of the American Statistical Association. 1967;62(318):399–402. DOI: https://doi.org/10.1080/01621459.1967.10482916.
12. Lilliefors HW. On the Kolmogorov–Smirnov test for the exponential distribution with mean unknown. Journal of the American Statistical Association. 1969;64(325):387–389. DOI: https://doi.org/10.1080/ 01621459.1969.10500983.
13. Dallal GE, Wilkinson L. An analytic approximation to the distribution of lilliefors test statistic for normality. American Statistician. 1986;40(4):294–296. DOI: https://doi.org/10.2307/2684607.
14. Arrieta G, Gomezcaceres L, Albis D, Calderon-Rangel A, Rodriguez V. Quality of raw milk for human consumption at two locations in Sucre (Colombia). Revista Mvz Cordoba. 2019;24(3):7355–7361. DOI: https://doi.org/10.21897/rmvz.1829.
15. Kruskal WH, Wallis WA. Use of ranks in one-criterion variance analysis. Journal of the American Statistical Association. 1952;47(260):583–621. DOI: https://doi.org/10.1080/01621459.1952.10483441.
16. Choi W, Lee JW, Huh MH, Kang SH. An algorithm for computing the exact distribution of the Kruskal-Wallis test. Communications in Statistics-Simulation and Computation. 2003;32(4):1029–1040. DOI: https://doi.org/10.1081/sac-120023876.
17. Wilcoxon F. Individual comparisons by ranking methods. Biometrics Bulletin. 1945;1(6):80–83. DOI: https://doi.org/10.2307/3001968.
18. García-Martínez EM, Fuentes-López A, Fernández-Segovia I. Determinación de la calidad higiénica de la leche mediante la medición indirecta del tiempo de reducción del azul de metileno o prueba de la reductasa microbiana [Determination of the hygienic quality of milk by indirect measurement of the reduction time of methylene blue or microbial reductase test]. València: Universitat Politècnica València; 2014. 7 p. (In Spanish).