The freezing point of raw and heat treated sheep milk and its variation during lactation

Abstract

The freezing point of milk is an important indicator of the adulteration of the milk with water, but heat treatment may also affect its value. The aim of this study was determine freezing point of raw and heat treated sheep milk and its variation during lactation. The freezing point was determined in 42 bulk tank raw sheep milk samples and 42 pasteurized milk samples collected during lactation of sheep at one ecofarm in Moravian Walachia (Valašsko in the Czech Republic). The freezing point was determined in accordance with the standard ČSN 57 0538 using a thermistor cryoscope. The average freezing point of raw milk was -0.617 ± 0.052 °C, with a range from -0.560 to -0.875 °C. The freezing point was lower in the first months of lactation and increased at the end of lactation. The freezing point correlated (r = 0.8967) with the content of total non-fat solids. The average freezing point of sheep milk pasteurized at 65 °C for 30 min was -0.614 ± 0.053 °C, with a range from -0.564 to -0.702 °C. The median of freezing point differences between raw and pasteurized milk was 0.004 °C. Our study extends data about physico-chemical properties of sheep milk and registers for the first time specific changes in the freezing point value of sheep milk by heating.

Milk hygiene in small ruminants: A review

“…The addition of water affects the freezing point (FP) of milk so it is used in the industry as a criterion for economic sanction. Although sheep and goat FP is influenced by many factors (i.e., total non-fat solids, breed, stage of lactation, season, and pasteurization) (Antunac et al, 2001;Park et al, 2007;Mayer & Fiechter, 2012;Janstová et al, 2013), both analytical methodology and preservation strategies have major effects on inter-and intra-laboratory quality testing, as well as for routine sampling strategy. Indeed, FP obtained by Milkoscan FT 6000 has a high repeatability and reliable accuracy compared to thermistor cryoscope method, which is the reference method according to IDF (2002).…”