Effects of different concentrations of sodium azide and chloramphenicol on the preservation of raw milk samples

Franciele Rampazzo Vancin,Carlos Bondan,Laura Beatriz Rodrigues,Luciane Daroit,Luciana Ruschel Dos Santos,Bruna Webber

doi:10.1590/0103-8478cr20190425

Franciele Rampazzo Vancin, Carlos Bondan + Show 4 more

Open Access

https://doi.org/10.1590/0103-8478cr20190425

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Abstract

ABSTRACT: The preservation of milk samples for microbiological analyses by the Brazilian Network of Milk Quality Control Laboratories requires the addition of preservatives to maintain the microbiota from the time of sample collection to the moment of analysis. The number of microorganisms can change as a result of the active ingredients and concentration of the preservative, as well as due to interactions between the preservatives, incubation time, and packaging temperature. The objective of this research was to evaluate the conservation potential of different concentrations of sodium azide and chloramphenicol on the analytical shelf life of milk samples. Two farms were selected, one with a low bacterial count and one with a high bacterial count. The milk was dispensed into sterile vials and tested after the addition of the usual concentrations of sodium azide and chloramphenicol, doubled concentrations, tripled concentrations, and as a control, without preservatives. The samples were incubated at 3 ± 1 °C, 6 ± 1 °C, and 9 ± 1 °C for 14 days and analyzed daily for their bacterial count by flow cytometry. The tripled preservative concentrations improved conservation, increasing the timespan of the analytical viability of the samples without altering the results.

Highlights

Following the Normative Instructions by the Brazilian Ministry of Agriculture, Livestock, and Food Supply, milk samples destined for processing at federally inspected establishments must undergo monthly analyses at accredited laboratories (BRASIL, 2002) that are a part of the Brazilian Network of Milk Quality Control Laboratories
For Group 1, with a bacterial count according with current regulations, comparing the results from the date of collection (Day 0) with the other days within the same treatment and temperature revealed differences (P
The samples from the two treatments incubated at 6 °C and 9 °C did not significantly differ until after Day 4 (6 °C: usual azidiol dosage (T-1), 4.80 ± 0.07 and double azidiol dosage (T-2), 4.82 ± 0.03, P >0.05; 9 °C: T-1, 4.91 ± 0.09 and T-2, 4.82 ± 0.06, P >0.05)

Summary

Introduction

Following the Normative Instructions by the Brazilian Ministry of Agriculture, Livestock, and Food Supply, milk samples destined for processing at federally inspected establishments must undergo monthly analyses at accredited laboratories (BRASIL, 2002) that are a part of the Brazilian Network of Milk Quality Control Laboratories. The parameters analyzed included the bacterial count, which is typically done by flow cytometry. The bacterial count reflects the hygiene of the storage conditions during sample collection and the period between milking and milk collection on the farm. Milk can be contaminated by microorganisms in the environment, which could be failures in the milking, water, or udder management (SAMPAIO et al, 2015). One main source of contamination is a failure in the milk cooling process during tank storage, which can impair the microbiological quality

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