The fat globule size distributions were determined in the whole milks,
the SMFG-fractions and the LMFG-fractions by laser light scattering,
using a Mastersizer 2000 (Malvern Instruments, UK) with two laser sources.
The refractive indices used were 1.458 and 1.460 for milk fat at 633 and 466 nm
respectively, and 1.333 for water
. The samples were diluted in 100 ml of water directly
in the measurement cell of the apparatus in order to reach 10%
obscuration. Standard parameters were calculated by the software:
the volume-weighted average diameter d43, defined as Rnid4
i =Rnid3
i
(where ni is the number of fat globules of diameter di), the volume–
surface average diameter d32, defined as Rnid3
i =Rnid2
i , the modal
diameter, which corresponds to the population of fat globules most
present in the size distribution and the specific surface area
S = 6.u/d32 (where u is the volume fraction of milk fat).