Significance of Lactose in Dairy Products - Advanced Dairy Chemistry - page 73

increased supersaturation, which would increase the driving force (Hartel and
Shastry, 1991; Hartel, 2001). If -lactose does nucleate, then there exists a
threshold size of detection (crystals of 16-30 mm; Nickerson, 1954; Hartel,
2001; Marshall et al., 2003) beyond which the textural defect of sandiness
becomes increasingly evident. The typical trapezoidal wedge (tomahawk)
shape of the -lactose crystals is readily detected as a very sharp, rough
particle (Figure III.4), which are easily differentiated from ice crystals as the
lactose crystals do not readily melt in the mouth or between fingers. Once
nucleation has occurred, crystallization can proceed quite quickly and once
this level of lactose crystallization has been exceeded in packaged and
flavored ice cream, then disposal is the only recourse. Therefore, it is impera-
tive that formulation, processing and storage conditions are all optimized to
inhibit completely the nucleation of lactose.
The mix formulation is the first consideration for the minimization of
lactose crystallization. The more the lactose present, the greater the degree of
supersaturation and the more prone the ice cream to crystallization. Recom-
mendations regarding maximum levels of total MSNF to avoid lactose
Figure III.4. Lactose crystal protruding through an air bubble in ''sandy'' ice cream as seen by
cryoscanning electron microscopy (width of photograph ¼ 150 mm).