Efficacy of a stabilized liquid potassium sorbate preservative to prevent bacterial proliferation in bovine colostrum and milk

This study aimed to describe the effect of a potassium sorbate preservative on bacterial proliferation in bovine colostrum and milk, and on colostrum pH and IgG concentrations, when stored at refrigeration (RF) or room temperature (RT) for 96 h. Fifteen batches of previously frozen raw colostrum and bulk tank milk (BTM) were inoculated with Escherichia coli, Salmonella enteritidis, and Staphylococcus aureus. Each batch was divided into 2 aliquots, with one kept as an untreated control (CON) and the other treated with a liquid potassium sorbate preservative (PSP) to achieve a 0.3% and 0.15% solution for colostrum and milk, respectively. The PSP and CON aliquots were subdivided into 2 portions, which were stored at RF (4°C) or RT (20°C) for 96 h. Subsamples were collected from each aliquot (PSP/RF, PSP/RT, CON/RF, CON/RT) at 0, 24, 48 and 96 h. Subsamples were cultured to quantify the concentration (cfu/mL) of naturally occurring bacteria (total plate count [TPC], total coliform count [TCC], streptococci and streptococci-like organisms [SSLO], and Staphylococcus spp.), as well as additional inoculated bacteria; E. coli, Salmonella, and Staphylococcus aureus. Colostrum was also tested for pH using an electronic pH meter and IgG using radial immunodiffusion assay. Milk and colostrum results were analyzed separately. Linear regression was used to determine the effect of PSP on the difference in bacteria counts, colostrum pH, and colostrum IgG occurring between 0 to 24 h, 0 to 48 h, and 0 to 96 h of storage. Because an interaction was present between treatment and storage temperature, and between treatment and storage period (24, 48 or 96 h), results were analyzed separately for samples stored by RF or RT, and by storage period. For RF BTM, results showed little difference in bacteria concentrations in either PSP or CON samples over 96 h, with the exception of a smaller decrease in Salmonella in CON samples between 0 to 24 h. In BTM stored at RT, PSP reduced growth of E. coli, Salmonella, and TCC over 96 h, and TPC at 24 and 48 h. In RF colostrum, PSP resulted in reduced growth for TPC, TCC and SSLO at 24, 48, and 96 h; Salmonella at 24 h; and E. coli at 48 h. In RT colostrum, PSP reduced the difference in TPC, TCC, E. coli, and SSLO at 24, 48 and 96 h; Salmonella and Staph. aureus at 24 h; and Staphylococcus spp. at 24 and 96 h. Also for RT colostrum, PSP resulted in a smaller pH reduction over 96 h. Colostrum IgG concentration was stable for both PSP and CON stored by RF and RT. To conclude, although there was no benefit of preservative in RF BTM, the stabilized liquid 38% potassium sorbate preservative evaluated can be a useful tool to reduce bacterial proliferation in BTM stored for up to 96 h at RT, and it was also effective in reducing bacterial proliferation in raw colostrum stored for up to 96 h by RF or RT, without reducing colostrum IgG concentrations.