MATERIAL AND METHODS 2.1. Milk Supply
Fresh raw whole bovine milk was purchased in a local dairy farm. Milk containers were transported from the farm to the laboratory in less than 1h in refrigerated conditions milk
temperature at arrival 10°C, and were then stored at 4°C for maximum of 24h before HPH. Milk pH ranged between 6.6 and 6.7. The milk was equilibrated at 24°C for 40-50 min before
HPH.
2.2. High Pressure Homogenisation
Homogenisation of whole raw milk was performed with Stansted HPH model FPG7400 H, Stansted Fluid Power Ltd., Essex, UK shown in Fig.1.
Fig. 1. Schematic representation of Stansted high pressure homogenisation: T
in
, milk inlet temperature; T1P1, temperature and pressure probes before the HP valpe; T2P2, temperature and pressure probes
at the HP valve outlet; T3 and T4, temperature probes before and after the spiral heat exchanger
This machine comprises a High Pressure HP valve made of HP resistant ceramics, and is able to support up to 350 MPa of pressure. The HP system consists of a single intensifier
80 mL useful volume, driven by a hydraulic pump. The operating cycle comprises 2 steps. The first one 9s corresponds to the filling of the intensifier. The other 10 s corresponds to
the pressure build-up and to the discharge of the intensifier. The pulsed flow rate depends on the homogenisation pressure and ranges from 16.0 Lh-1 at 100 MPa to 13.6 Lh-1 at 300 MPa.
To avoid a loss of homogenisation performance due to a temperature increase in the first stage valve, the second stage valve is cooled by circulating water at 18°C in an external jacket built
Spiral heat Exchanger
T
4
T
3
T
1
P
1
T
2
P
2
HP Valve 1
er
effect Tin
Intensifier
HP Pump HP Valve 2
nd
effect Feed Tank
aroud the valve. The pressures before the HP valve P1 and after the HP valveP2 were measured using two pressure gauges. The milk inlet temperature Tin measured with a
thermistance Checktemp, Hanna Instruments, Tanneries, France, ± 0.2°C accuracy in the feeding tank were 24.0 ± 0.2°C. The fluid temperatures before the HP valve T
1
, immediately after the HP valve T
2
, as well as the temperature before the cooling device T
3
was measured with T-thermocouples of low inertia 1.5 mm diam.; ± 1°C accuracy. Temperature
and pressure were displayed on digital indicators. The homogenised milk was rapidly cooled to 14.7 ± 1.7°C T
4
by passing through a spiral type heat exchanger located after the HP valve and cooled to 10°C using an external cryostat. Milk samples were stored at 4°C for 18 h
before fat globule size determination. Each HP experiment was repeated three times.
2.3 Determination of fat globule size
