Microbiological quality of milk from farms to milk powder manufacture: an industrial case study

Abstract

The experiments reported in this research paper aimed to track the microbiological load of milk throughout a low-heat skim milk powder (SMP) manufacturing process, from farm bulk tanks to final powder, during mid- and late-lactation (spring and winter, respectively). In the milk powder processing plant studied, low-heat SMP was produced using only the milk supplied by the farms involved in this study. Samples of milk were collected from farm bulk tanks (mid-lactation: 67 farms; late-lactation: 150 farms), collection tankers (CTs), whole milk silo (WMS), skim milk silo (SMS), cream silo (CS) and final SMP. During mid-lactation, the raw milk produced on-farm and transported by the CTs had better microbiological quality than the late-lactation raw milk (e.g., total bacterial count (TBC): 3.60 ± 0.55 and 4.37 ± 0.62 log 10 cfu/ml, respectively). After pasteurisation, reductions in TBC, psychrotrophic (PBC) and proteolytic (PROT) bacterial counts were of lower magnitude in late-lactation than in mid-lactation milk, while thermoduric (LPC—laboratory pasteurisation count) and thermophilic (THERM) bacterial counts were not reduced in both periods. The microbiological quality of the SMP produced was better when using mid-lactation than late-lactation milk (e.g., TBC: 2.36 ± 0.09 and 3.55 ± 0.13 cfu/g, respectively), as mid-lactation raw milk had better quality than late-lactation milk. The bacterial counts of some CTs and of the WMS samples were higher than the upper confidence limit predicted using the bacterial counts measured in the farm milk samples, indicating that the transport conditions or cleaning protocols could have influenced the microbiological load. Therefore, during the different production seasons, appropriate cow management and hygiene practices (on-farm and within the factory) are necessary to control the numbers of different bacterial groups in milk, as those can influence the effectiveness of thermal treatments and consequently affect final product quality.

Tracking the Dairy Microbiota from Farm Bulk Tank to Skimmed Milk Powder

“…However, it should be emphasized that relative abundances are reported throughout this paper, and further analysis would be needed to confirm if there were increases and decreases in absolute abundances. It should be noted that the relative-abundance results obtained largely agree with data from corresponding culture analyses (27).…”

Monitoring residue concentrations in milk from farm and throughout a milk powder manufacturing process

“…The collection of samples and preparation of SMP samples for analysis were performed as described by Paludetti et al . (2019).…”

“…This experiment was performed on one occasion during each of mid-(May; 80 DIM) and latelactation (December; 290 DIM). The farms that supplied milk to the factory (mid-lactation: 67 farms; late-lactation: 150 farms), milk storage conditions on-farm, amount of milk produced, milk collection and the skim milk powder manufacturing process was the same as described by Paludetti et al (2019). A schematic drawing of the SMP manufacturing process is shown in supplementary Figure S1.…”

“…Due to the high number of farms (150) necessary to supply sufficient milk volume to undertake the manufacturing process in late-lactation (December), it was not possible to undertake collection and analysis of all individual BT samples. The collection of samples and preparation of SMP samples for analysis were performed as described by Paludetti et al (2019).…”

“…The concentrations of CHLO, PCHLO, TCM and iodine residues were measured in raw milk produced on the same 67 dairy farms sampled in mid-lactation (May, 80 DIM) and in late-lactation period (November; 260 DIM), to investigate the effect of milk production period on residue levels. Milk samples were collected as described by Paludetti et al (2019).…”