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 1H NMR was used to follow the α to β′ 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 α polymorph formed and accelerated the polymorphic transition; however, shear did not affect the final solid fat content (SFC). The α to β′ 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 β′-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 β crystals formed. The study shows that both shear and RO affect the polymorphic behavior of milk fat, and that 1H NMR is able to detect polymorphic transition in blends with up to 30 % w/w RO.
KEYWORDS: Crystal size, Food