Characteristics of sow milks at different lactation stages and their frozen storage stabilities

Abstract

Characteristics of sow milk fats at different lactation stages, including colostrum (on day-1 of lactation) and milk (on day-15 of lactation), were systematically investigated from the emulsions, milk fat globules (MFGs) to fats. The viscosities of sow milks were significantly influenced by different lactation stages, in which colostrum showed a higher viscosity than milk. Colostrum fat globules had a lower volume-weighted average diameter (D43) (4.03 ± 0.21 μm), surface-weighted average diameter (D32) (2.05 ± 0.13 μm) and higher absolute zeta-potential (10.09 ± 0.09 mV) than those of milk. The unsaturated ratios of MFGs in sow milk were reduced with the increasing size of the globules, resulting in that colostrum fat had a lower melting temperature of 30.26 ± 0.98 °C with a corresponding lower starting crystallization temperature of 7.38 ± 0.55 °C compared with milk fat. The general stability of sow milk during storage could be reflected from the moisture distributions: bound water showed an overall downward trend; while a downtrend of free water was found during frozen storage at −20 °C for 4 months. These results establish the foundations for the improvement and development of sow milk substitutes, as well as for the feasibility of being a substitute for human milk.