Milk free fatty acids (FFA) and tubular milk pre-cooling

2009-08-24 15:17
charriau
Sales manager

Free fatty acids (FFA) content has been introduced thanks to an increase in the efficiency of modern analytical methods as a milk quality indicator and as an indicator for its price as well.

FFA reduce the quality of milk and dairy products by generating a rancid and soapy taste. Their origin is the spontaneous or induced enzymatic hydrolysis of milk-fat. This results in a financial penalty and poorer end product which producers/processors pride themselves on.

Cooling the milk to 4-5 °C stabilises the milk fat globule membrane upon mechanical treatment, resulting in lower formation of FFA.
Effect of agitation (stirring or pumping) is dependent on other factors such as temperature, the presence of air, and the fat content. The stability of the globules decreases with the presence of air bubbles, causing disruption of them. In addition, at temperatures below 40°C, fat begins to crystallize and the crystals can cause local structural changes to the membrane. Therefore, mechanical treatments can bring the enzymes into contact with the fat globule core fat.
CHARRIAU tubular milk pre-coolers work in counterflow. So milk fat globule membrane crystallize gently.

http://upload.wikimedia.org/wikipedia/commons/7/75/Plate_frame_1.png http://www.real-world-physics-problems.com/images/counter_flow_heat_exch.png

Higher flow velocities during pumping result in greater friction in the liquid itself and between the liquid and the pipe/plate wall. These relative differences in flow velocity perpendicular to the flow direction are called shear rates.
CHARRIAU tubular milk pre-coolers have a lower shear rate than milk plate coolers.

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According to "GIE lait viande" test (average of 30% efficiency without), plate coolers must have a milk pump speed control system in order to achieve the maximum cooling the plate cooler is capable of delivering. Usual systems use the standard "on-off" milk pump control, while milk pump speed control system tries to deliver a steady, gentle, constant flow of milk to your plate cooler. This is what we call churning !
CHARRIAU tubular milk pre-coolers are designed so that they don't use/need milk pump speed control system.

http://www.ilri.cgiar.org/InfoServ/Webpub/fulldocs/SSAoptions/images/above%20right%20%20p21.gif

Dernière modification par charriau (2013-02-13 18:01)

2013-02-13 11:33
charriau
Sales manager

Changes induced to milk fat globules during different treatments and influence of mechanical treatment on milk fat globule stability.
It has been suggested that of the final FFA level in pasteurised milk around 60-70% is due to lipolysis occurring during milking and milk transfer to the bulk tank (Anderson, 1983). Mechanical treatments of the milk such as pumping and stirring subject milk fat globule to physical stress.

Higher flow velocities during pumping in pipes result in greater friction in the liquid itself and between the liquid and the pipe/plate wall. These relative differences in flow velocity perpendicular to the flow direction are called shear rates. The shear rate depends on the diameter of the pipe and the flow velocity. The presence of air, the temperature of the milk and fat content affect the stability of the milk fat globule during mechanical treatments of milk.

In milking systems, the milk is mixed with air, especially when air is used as a transport medium for the milk. The stability of the MFG (milk fat globule) is lowered by mixing with air or any other gas during pumping or agitation of the milk. The contact between a MFG and an air bubble results in rupturing of the MFG, since membrane material and part of the core fat will spread over the air/milk plasma interface and will be released into the milk plasma when air bubbles collapse or coalesce (Evers, 2004). Needs, Anderson & Morant (1986) reported that using a claw piece requiring high air bleed instead of a conventional claw increased FFA level by 21 %. Similar results were  found by O´Brien, O´Callaghan & Dillon (1998) and Rasmussen et al. (unpublished results, 2005).

Pumping of cream is usually conducted at lower flow rates compared with pumping of milk. Studies have suggested that the stability of the MFG decreases linearly with increasing fat content in milk/cream (Hinrichs & Kessler, 1997; Hinrichs, 1998). This is ascribed to the increased friction between fat globules. 

The milk temperature is also a very important factor when milk is exposed to mechanical treatments. Several studies have reported that the maximum accumulation of FFA upon agitation is at a temperature of ~15 °C and again after ~30°C, with low formation of FFA between 20-30 °C (Fitz-Gerald, 1974; Deeth & Fitz-Gerald, 1977; Bhavadasan, Abraham & Ganguli, 1981; Hisserich & Reuter, 1984). At low temperatures the milk fat is more resistant to mechanical stress.
Homogenisation of milk can only be successful at temperatures above 40°C. The effect of temperature on MFG stability is due to crystallization of lipids. One minor factor is that the temperature affects the activity of Lipoprotein lipase (LPL).

Results clearly suggest that cooling the milk to 4-5 °C stabilised the MFG upon mechanical treatment, resulting in lower formation of FFA and lower risk of coalescence of MFGs. By transferring the obtained knowledge to milking systems, it suggested that the milk cooling should be placed as close to the udder as possible. Thereby the transportation of warm milk would be reduced, leading to lower levels of FFA.

Results also clearly demonstrate that increased milking frequency is a factor contributing to the elevated levels of FFA in automatic milking systems. It is also a factor difficult to avoid since more frequent milking increases the milk yield which affects the economic performance of the milk producer.

Extracts from : Milk fat globule stability

Dernière modification par charriau (2013-02-13 17:55)

2013-02-13 13:23
charriau
Sales manager
Density of milk at low temperature Journal of Dairy Science

Some physical properties of milk density Journal of Dairy Science

Relationship among milk density composition and temperature  Master of Science Thesis 1999

Calibrated measuring vessels change their capacity with temperature but the calculation of corrections is straightforward and easy to apply. Measurement by weighbridge is dependent on density but if the temperature and composition of the liquid are known, density can be deduced to within 0.05 per cent from the data given. The arbitrary use of different standard temperatures complicates the picture. Meters are available for any of the liquid dairy products and the best way to achieve accuracy is to calibrate with the right liquid at the right flowrate and the right temperature. Above all, with meters it is important for the installation to be right.