Do Milk Samples Stored for 12 Days after Collection Exhibit a Change in Composition Related to the Initial Bacterial Load?

摘要

Total bacterial count (TBC) is a tool used to assess milk quality and is associated with not only the initial sample contamination but also the sample storage time and temperature. Several countries have reported milk samples with a high TBC, and the influence of TBC on milk preservation remains unclear. Thus, the aim of this study was to evaluate the impact of the initial bacterial contamination level on the macrocomponents and somatic cell count (SCC) of raw milk samples preserved with bronopol and maintained at two storage temperatures (7 and 25℃) for up to 12 days. Thus, we collected milk samples from 51 dairy farms, which were divided into two groups according to the initial bacterial load: low TBC (＜100,000 CFU/ml) and high TBC (≥100,000 CFU/ml). We analyzed the sample composition for protein, fat, total solids, lactose, milk urea nitrogen, and the SCC. We did not observe an effect from TBC and storage time and temperature on the concentration of protein, fat, total solids, and lactose. SCC changes were not observed for samples maintained under refrigeration (7℃); however, samples maintained at room temperature (25℃) exhibited a decrease in the SCC beginning on day 6 of storage. For milk urea nitrogen, values increased when the samples were maintained at room temperature, beginning on the ninth storage day. Samples with the preservative bronopol added and maintained under refrigeration may be analyzed up to 12 days after collection, regardless of the milk microbial load.