Algal meal supplementation of the cows' diet alters the physical properties of milk fat

A three-week algal meal supplementation of the cows' basal diet resulted in an increase in the firmness of milk fat crystallized isothermally at 5 degreesC for 24 h - the apparent elastic constant increased from 100 to 224 N/mm. This was accompanied by a decrease in solid fat content, from 47(.)7% to 44(.)4%. The crystallization behaviour of milk fat was also modified significantly. The rate constant of crystallization (Avrami constant) of the enriched milk fat at 19 degreesC was similar to20 times higher than that of control milk fat. A shorter induction time of nucleation was also observed in the temperature range [20, 27 degreesC]. These effects were attributed to a higher degree of supersaturation of the enriched milk fat. Enriched milk fat nucleated in a more stable beta' polymorphic form at 5 degreesC, while control milk fat nucleated in the metastable alpha form, as determined by powder X-ray diffraction and differential scanning calorimetry. Changes in the microstructure of the material were observed by polarized light microscopy at 5 degreesC. The enriched milk fat displayed a greater amount of crystal clustering than the control. This effect was reflected in a decrease in the box-counting mass fractal dimension (D-b) of the fat crystal network from 1(.)853 to 1(.)809. The decrease in D-b closely predicted the observed 2(.)2-fold increase in the elastic constant of the fat. These changes in mechanical properties, crystallization behaviour and microstructure were driven by an increase in the 18 : 1 trans and a decrease in the 18 : 1 cis fatty acid content of the enriched milk fat.