A study of the structure of triacylglycerols of bovine milk fat : a thesis presented for the degree of Doctor of Philosophy in Biochemistry at Massey University
Loading...
Date
1973
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
Samples of milk fat obtained at different stages
of the dairying season were investigated to determine
the influence of the observed seasonal changes in the
fatty acid (FA) compositions of New Zealand milk fats
on the structure of milk triacylglycerols (TG1s) . Of
the three milk fats studied the January and March
samples had FA compositions typical of hard summer milk
fat, while the September sample had a FA composition
typical of soft spring milk fat .
Each of the three selected samples of milk fat
was effectively separated into TG fractions of high,
medium and low molecular weight which had distinctly
different FA and TG compositions. Stereo specific
analyses o f these fractions showed that in TG fractions
of similar average molecular weight the arrangement of
FA 's within the TG ' s was similar and that in all TG
fractions the FA 's were arranged within positions 1 , 2
and 3 of the TG1s in a highly selective manner.
The TG fractions were separated into TG classes
of different degrees of unsaturation. Corresponding
TG c lasses of the three samples of milk fat had
generally comparable FA compositions. However an
important distinguishing feature was that each TG
fraction of the September sample contained a higher
proportion of unsaturated TG's than the corresponding
TG fractions of the January and March samples.
Thus in New Zealand milk fats of differing FA
composition, the nature of the TG species is similar
but there exist differences in the relative proportions
of the TG species. The variation in the proportions
of the constituent TG species of New Zealand milk fat
would appear to be the overriding factor whic h
influences the seasonal variation in its physical
characteristics.
The thermal properties of TG fractions of milk fat
were examined with a view to determining the influence
of TG structure on the physical characteristics of
milk fat. It was found that the unsaturated TG's of
low molecular weight , were largely responsible for
the considerable proportion of milk fat which melted
below 0ยบ C and consequently for the wide melting range
which is characteristic of milk fat. The structural
difference between these TG's and the remaining TG' s
of milk fat was found to be sufficiently large to
prevent significant formation of solid solutions.
Consequently the wide melting range of milk fat is due
to both the large number of different TG species and
to the large structural difference between the various
TG species.
Description
Keywords
Milk fat, Butterfat, Triacylglycerols, Composition, Testing, Standards