Abstract
This study demonstrated that homogenization did not increase the activity of lipoprotein lipase (LPL) in spite of a fast accumulation of free fatty acids (FFA). Two homogenization pressures (100 and 170 bar) and two temperatures (40℃and 50℃) were examined. The activity of LPL was analyzed and the formation of FFA was measured with two different methods, the B.D.I.-method and a nonesterified fatty acids (NEFA) method. A homogenization temperature of 50℃ resulted in a decreased LPL activity compared to 40℃. No effect of homogenization pressure was found. Analyzing FFA concentration with the B.D.I.-method resulted in significant effect of homogenization temperature and no effect of pressure. The largest formation of FFA was found in milk homogenized at 40℃. Using the NEFA method, another result was obtained, indicating no effect of homogenization temperature and a larger FFA accumulation at 100 bar than at 170 bar. Both analytic methods demonstrated significant production of FFA during 60 min incubation at homogenization temperature after treatment. The level of FFA in the milk samples immediately after homogenization was very high, demonstrating that LPL cleaves the triglycerides very rapidly when the native membrane was damaged. The regression between the B.D.I.-method and the NEFA was fair in the interval between 4 and 14 mmol/100 g fat, whereas at higher concentrations, the correlation was poor.
Highlights
The majority of fluid dairy products are homogenized in order to avoid creaming of fat globules or to improve rheological properties
This study demonstrated that homogenization did not increase the activity of lipoprotein lipase (LPL) in spite of a fast accumulation of free fatty acids (FFA)
Summarizing the study, LPL activity was not affected by homogenization pressure
Summary
The majority of fluid dairy products are homogenized in order to avoid creaming of fat globules or to improve rheological properties. Homogenization of milk reduces the average milk fat globule (MFG) diameter to < 1 μm which results in a 5 - 10 fold increase in surface area. The new membrane formed after homogenization is not strong enough to protect the triglycerides in the core of the globules from lipolysis which is undesirable due to development of rancid off-flavours. LPL is primarily associated (~75%) to the casein micelles [3]. Cooling of milk causes the casein micelles, and the LPL, to associate to the MFG [4]. Homogenization results in a severe attraction of casein to the milk fat globules. The products of the hydrolysis of the triglycerides, the free fatty acids (FFA), inhibit the LPL enzyme presumably due to FFA binding to the active
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