Seasonal changes in the heat stability of milk from creamery silos in south-west Scotland

Abstract

SummaryThe heat stability of the milk supply to manufacturing creameries in south-west Scotland was examined over 15 months from Nov. 1975 to Jan. 1977. For all but 2 months of this period the heat stability of the milk was very highly significantly correlated with the naturally occurring level of urea. Between 72 and 90% of the variation of coagulation time (CT), measured at the natural milk pH, was accounted for by changes in milk urea alone. For a short period, in May and June, the CT of the milk at natural pH fell within the minimum of the CT–pH profile, but insufficient data were available to allow the occurrence of this phenomenon to be related to changes in milk composition.

Investigation of the effects of season, milking region, sterilisation process and storage conditions on milk and UHT milk physico-chemical characteristics: a multidimensional statistical approach

“…In addition, O'Connell and Fox [26] showed that large casein micelles negatively affected milk in the heat stability test. Changes in casein micelle size [18], fat [29] and heat stability [19] as a function of season have also been reported earlier. All these seasonal variations may be linked to lactation stage, changes in feeding or environmental conditions such as hot temperature [1,3,20,36].…”

Heat stability of concentrated skim milk as a function of heating time and temperature on a laboratory scale – Improved methodology and kinetic relationship

“…Differences in overall heat stability of the individual milk samples were small and an increase in total solids content was seen to be the dominating effect. An increase in soluble calcium and magnesium, a decrease in pH, an increase in ionic strength proportional to volume reduction and an increase in total protein are supposed to be the major variables limiting heat stability of concentrated milks with increasing total solids content (Anema, 2009;Augustin & Clarke, 1990;Dalgleish, Pouliot, & Paquin, 1987;Faka, Lewis, Grandison, & Deeth, 2009;Holm, Webb, & Deysher, 1932;Holt, Muir, & Sweetsur, 1978;Le Ray et al, 1998;Morrissey & O'Mahony, 1976;Sweetsur & Muir, 1982;On-Nom, Grandison, & Lewis, 2012;Pouliot & Boulet, 1991).…”

Effect of selected amides on heat-induced changes in milk

“…A significant positive correlation between the heat stability at 120 °C of bulk milk at its natural pH and the level of non-protein nitrogen (NPN) was shown by Robertson & Dixon (1969) and addition of small amounts of urea, the predominant component of the NPN fraction, to milk was shown to increase its heat stability. Subsequent work (Muir & Sweetsur, 1976, 1977Muir, Abbot & Sweetsur, 1978;Holt, Muir & Sweetsur, 19786) confirmed the stabilizing influence of urea on unconcentrated milks particularly at pH values around the heat coagulation time (HCT)-pH maximum and has shown that natural variations in urea concentration are responsible for most of the variation in the heat stability of bulk milks. However, the heat stability of concentrated milk was not influenced by addition of small amounts of urea .…”