• The effect of different precooling rates and cold storage on milk microbiological quality and composition

      Paludetti, L.F.; Kelly, Alan L.; O'Brien, Bernadette; Jordan, Kieran; Gleeson, David E (Elsevier, 2018-01-10)
      The objective of this study was to measure the effect of different milk cooling rates, before entering the bulk tank, on the microbiological load and composition of the milk, as well as on energy usage. Three milk precooling treatments were applied before milk entered 3 identical bulk milk tanks: no plate cooler (NP), single-stage plate cooler (SP), and double-stage plate cooler (DP). These precooling treatments cooled the milk to 32.0 ± 1.4°C, 17.0 ± 2.8°C, and 6.0 ± 1.1°C, respectively. Milk was added to the bulk tank twice daily for 72 h, and the tank refrigeration temperature was set at 3°C. The blend temperature within each bulk tank was reduced after each milking event as the volume of milk at 3°C increased simultaneously. The bacterial counts of the milk volumes precooled at different rates did not differ significantly at 0 h of storage or at 24-h intervals thereafter. After 72 h of storage, the total bacterial count of the NP milk was 3.90 ± 0.09 log10 cfu/mL, whereas that of the precooled milk volumes were 3.77 ± 0.09 (SP) and 3.71 ± 0.09 (DP) log10 cfu/mL. The constant storage temperature (3°C) over 72 h helped to reduce bacterial growth rates in milk; consequently, milk composition was not affected and minimal, if any, proteolysis occurred. The DP treatment had the highest energy consumption (17.6 ± 0.5 Wh/L), followed by the NP (16.8 ± 2.7 Wh/L) and SP (10.6 ± 1.3 Wh/L) treatments. This study suggests that bacterial count and composition of milk are minimally affected when milk is stored at 3°C for 72 h, regardless of whether the milk is precooled; however, milk entering the tank should have good initial microbiological quality. Considering the numerical differences between bacterial counts, however, the use of the SP or DP precooling systems is recommended to maintain low levels of bacterial counts and reduce energy consumption.
    • Evaluating the effect of storage conditions on milk microbiological quality and composition

      Paludetti, L.F.; Jordan, Kieran; Kelly, Alan L.; Gleeson, David E (Teagasc (Agriculture and Food Development Authority), Ireland, 2018-07-19)
      In this study, the effect of storage temperature (2 or 4°C) on the composition of milk and microbiological load was investigated over 96 h. Milk samples were collected from farm bulk milk tanks after one complete milking and stored at 2 or 4°C over 96 h. Total bacterial count (TBC), psychrotrophic bacterial count (PBC) and proteolytic bacterial count (PROT) were affected by storage time and temperature and varied significantly between farms (P < 0.05). The levels of TBC, PBC and PROT bacterial count increased from 4.37 to 6.15 log cfu/mL, 4.34 to 6.44 log cfu/mL and 3.72 to 4.81 log cfu/mL, respectively, when the milk was stored for 96 h at 2°C. The milk samples stored at 4°C had higher increases in these bacterial counts after 72 h in comparison to milk samples stored at 2°C. The casein fraction content was lower in milk samples stored at 4°C, which could be due to high levels of PROT bacteria or enzyme activity in these samples. Milk stored for 96 h at 2°C has less impact on composition or processability parameters compared to milk stored at 4°C.
    • Iodine concentrations in milk

      O'Brien, Bernadette; Gleeson, David E; Jordan, Kieran; Irish Dairy Levy Research Trust (Teagasc (Agriculture and Food Development Authority), Ireland, 2013)
      Iodine tends to be supplemented at farm level in the expectation of increasing cow health and fertility. There is concern that such practices may result in high milk iodine, which could affect ingredients for infant formula and, thus, dairy export markets. The objective of this study was to quantify the effect of iodine fortified feed and teat disinfection practices of dairy cows on milk iodine concentration. Thirty lactating cows were fed 7 kg, 3 kg (10 mg iodine/kg) and 0 kg of concentrate feed during 3 periods of 35 days each. During the first 14 days of each period, cows were on dietary iodine treatments only; during days 15–21, one of three teat disinfection treatments (n = 10) was applied (in addition to the dietary iodine treatments): non-iodine (chlorhexidine) post-milking spray; 0.5% iodine spray post-milking; 0.5% iodine spray pre- and post-milking. Cow milk yield was 21.3 kg/day. Individual cow milk samples were analysed for iodine concentration on 2 days at the end of each treatment period. Dietary supplementation of iodine at both 30 mg and 70 mg/day, when compared to the diet with no supplement, increased milk iodine concentrations significantly (P < 0.001) from 449 to 1034 and 915 μg/kg, respectively. Teat disinfection both pre- and post-milking increased milk iodine concentration at each of the dietary supplementation levels of 0, 30 and 70 mg/day compared with a non-iodine teat disinfectant (P < 0.001). In conclusion, both dietary iodine supplementation and teat disinfection iodine increased milk iodine concentrations in an additive manner, exceeding common target values of 250 μg/kg. As both iodine treatments can occur simultaneously on farm, supplementation strategies should be monitored.
    • Review of potential sources and control of thermoduric bacteria in bulk-tank milk

      Gleeson, David E; O'Connell, Aine; Jordan, Kieran; Irish Dairy Levy Research Trust (Teagasc (Agriculture and Food Development Authority), Ireland, 2013)
      Bacteria that contaminate milk include thermoduric bacteria that can survive pasteurisation and subsequently grow in the pasteurised milk or contaminate product. Elimination of thermodurics at milking is not feasible. Therefore, knowledge of their source and strategies for their reduction are important. The major sources of thermodurics in milk are contamination of the teat skin from soil and bedding, and subsequent contamination from deposits that can build up on milking equipment surfaces. Hygiene at milking can reduce the number of bacteria contaminating milk. Teat preparation at milking and a recommended plant cleaning procedure are critical to the prevention of the contamination of milk with thermoduric bacteria.