O. Hanuš, E. Samková, J. Říha, M. Vyletělová, P. Roubal

Determination and interpretation of free fatty acids (FFAs) in milk
Small portion of fatty acids in milk which are not esterified in triglycerides is freely diffused mostly in fat phase and a little bit in water phase and it is called as free fatty acids (FFAs). Current content of FFAs in milk fat lies between 0.5 and 1.2 mmol.100g-1 and maximal enabled is 13.0 for method by churning and 32.0 for method by extraction and titration according to CSN 57 0529 and CSN 57 0533 (Cvak et al., 1992). Gerber´s acidobutyrometrical method for milk fat determination holds as many as 90% of FFA content into milk fat portion but on the contrary the extraction gravimetric method according to Röse-Gottlieb does not include FFAs into fat portion so reliably and thus 70% of them is lost in this way (Kerkhoff Mogot et al., 1982).
Increase of FFAs means negative impacts as lipolysis usually from reason of metabolic problems of dairy cow (Fig. 1). Increased concentration of FFAs causes an aggravation of milk technological properties (Vyletělová et al., 2000 a, b) but mostly deterioration of sensory milk properties as taste and flavour. After that it has lightly bitter smack as consequence and this can damage quality of dairy products. Fat destruction is phenomenon which is caused by native enzymes as lipases (Antonelli et al., 2002; Deeth, 2006; Ferlay et al., 2006) in milk or by lipases which are supplied by bacterial contamination of milk. Therefore lipolysis is spontaneous or induced (Fig. 1). Of course, lipases can be thermoresistent and thus in this way to influence milk also after its heat treatment by dairy product degradation. Wasteful milk handling as often pumping and ripple at manipulation (Sjaunja, 1984; Thomson et al., 2005; Hanuš et al., 2008 b; Genčurová et al., 2009 and 2011) and its freezing on technology surfaces also induce own lipolysis. Heat and mechanical energy which is added into multicomponent milk system destroys the membranes of fat globules and thus releases fatty acids from esteric linkage of triglycerides. Therefore, milk stream (Peterková, 2002) should not exceed the speed 1 till 1.5 m.s-1. Poor hygiene of dairy cow stabling and milking as well as bad storage and treatment of raw milk can lead to propagation of undesirable psychrotrophic, thermoresistant and sporulating milk microflora (Vyletělová et al., 1999 a, b; Cempírková and Thér, 2000; Cempírková, 2001, 2002, 2007; Dankow et al., (2004); Hanuš et al., 2004; Foltys and Kirchnerová, 2006 and 2010; Hantis–Zacharov and Halpern, 2007; Torkar and Teger, 2008; Cempírková and Mikulová, 2009; Cempírková et al., 2009). The mentioned facts can increase the lipolysis intensity (Fig. 1).
Definition of FFAs and paper goal
FFAs are a mixture of fatty acids released from milk fat by lipolysis or such which overpassed from animal blood and body fat tissues. In terms of proportions this mixture is influenceable by animal nutrition and health state, season and other factors which means that this is very hardly seizable, expressible and interpretable from analytical and molar point of view respectively. Analytically this is result of alkaline titration which is not in constant ratio to molar concentrations of individual fatty acids. However, this way of expression corresponds very good to practical dairy purposes as conventional interpretation. Values of FFAs can serve to control the health of dairy cows or raw milk quality in consideration of quality and shelf-life of resulting milk products.
FFA analytical methods are relatively complicated in terms of reliability and expressin of units in spite of matter definition simplicity. Variable mixture of acids form broken triglycerides is namely instable in composition ratios. Authors of various articles were concerned with FFA analytical methods (Sjaunja, 1984; Koops et al., 1990; Foss, 2001, 2004; Bijgaart, 2006; Hanuš et al., 2008 a, 2009) and above mentioned methodical complications ensued on these papers. Reference and routine FFA analytical methods can be so called extraction-titration method, churning-titration method, BDI and mid infrared spectroscopy (MIR) also in modification with Fourier´s transformations (MIR–FT; CSN 57 0533; Koops et al., 1990; IDF, 1991; Cvak et al., 1992; Foss, 2001, 2004; Thomson et al., 2005; Bijgaart, 2006; Mikulová, 2011).
Therefore, aim of this paper was to verify possibilities of MIR–FT method in terms of its calibration to milk fat free fatty acids (FFA) determination, time stability of MIR–FT FFA calibration and calibration levelling in instrument working nets of dairy laboratories.

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Bentley Czech s.r.o. Českomoravská společnost chovatelů, a.s. Mendelova univerzita v Brně Výzkumný ústav mlékárenský s.r.o. Výzkumný ústav živočišné výroby, v.i.i. Výzkumný ústav veterinárního lékařství, v.v.i.