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Dairy bulk tank milk was sampled during 1yr from 2 conventional (C1 and C2) and 1 organic dairy (O1) for studying the seasonal variation as well as the variation between dairies in the composition and properties of milk fat. The composition of fatty acids (FA) as well as triglycerides (TAG) in milk fat was analyzed, and the melting properties of milk fat were analyzed by use of differential scanning calorimetry. The main differences in fat content and composition of FA in milk fat between dairies included a higher fat content, greater proportion of C18:0, and smaller proportion of C16:0 in milk from dairy C2, which could be associated with a higher frequency of Jersey herds supplying milk to this dairy. The organic milk was characterized by a higher proportion of C18:3n-3, C18:2 cis-9,trans-11, C6 to C14, a lower proportion of C18:1 cis-9, and a higher melting point of the low-melting fraction. The TAG composition showed a greater proportion of C24 to C38 TAG in milk fat from dairy O1 and a greater proportion of C52 to C54 TAG in milk fat from dairy C2, which was in accordance with the differences in FA composition. Melting point of the low-melting fraction was higher for milk fat from dairy O1 compared with dairies C1 and C2, whereas no differences between dairies were observed with respect to melting points of the medium- and high-melting fractions. The seasonal variation in FA composition was most pronounced for dairy O1 although similar patterns were observed for all dairies. During the summer, the content of C18:0 and C18:1 cis-9 in milk fat was greater, whereas the content of C14:0 and C16:0 was lower. In addition, the content of C18:2 cis-9,trans-11 and C18:1 trans-11 increased in late summer for dairy O1. The differential scanning calorimetry thermograms of individual milk fat samples could be divided into 3 groups by principal component analysis. For dairy O1, summer samples belonged to group 1, spring and autumn samples to group 2, and winter samples to group 3. For dairy C1 winter samples (group 2), were separated from other samples (group 1), and for dairy C2 all samples were in group 1. Individual melting points were related to FA composition, and the melting point of the low-melting fraction was positively correlated to the content of C14:0 and C16:0 in milk fat and negatively correlated to the content of C18:1 cis-9 and C18:0.

The effect of shear on the crystallization kinetics of anhydrous milk fat (AMF) and blends with 20 and 30 % w/w added rapeseed oil (RO) was studied. Pulse 1 H NMR was used to follow the a to b 0 polymorphic transition. The NMR method was confirmed and supported by SAXS/WAXS experiments. Samples were crystallized at 5°C and shear of 0, 74 or 444 s -1 was applied during early crystallization, in the NMR tube. High shear rates decreased the amount of a polymorph formed and accelerated the polymorphic transition; however, shear did not affect the final solid fat content (SFC). The a to b 0 transition occurred faster in the presence of RO allowing more room for the conformational changes to occur. Final SFC decreased with increasing RO content. Shear applied in 20 and 30 % blends caused the destruction of b 0 -related 3L structure leaving only 2L packing. In AMF and statically crystallized samples, both 3L and 2L packing existed. Shear did not affect the amount of b crystals formed. The study shows that both shear and RO affect the polymorphic behavior of milk fat, and that 1 H NMR is able to detect polymorphic transition in blends with up to 30 % w/w RO.

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