2.2. Characteristics of powders
The fat, protein and lactose contents of the powder were carried out by Dairy Technical services Ltd. (5/352 Macaulay Road, Kensington Victoria, Australia 3031) according to Australian Standard
(1988), IDF (1993) and IDF (1974) respectively. The solventextractable fat (free-fat) was determined using GEA Niro analytical method (GEA Niro analytical method No. A10a, 2005) using petroleum ether as the solvent. The petroleum ether/powder mixture was agitated in a flask in the shaking device for 15 min. The petroleum ether was evaporated and the flask with the remaining contents (free-fat) was dried in an oven for an hour at 102 C ± 1 C.Measurements were carried out in triplicate. The content of freefat is expressed as a percentage of the powder.
The insolubility index was carried out according to Australian standard AS 2300.4.4 (1994). Briefly powder (10 g) was reconstituted in 100 mL of deionised water in a mixer at high speed
(3800–4000 rpm) for 90 s at 24 C. De-foaming agent (2–3 drops) was added and the milk was left for 15 min. The mixture was transferred into a graduated 50 mL centrifuge tube with a conically
graduated bottom. The sample was centrifuged (at 800g for 5 min), the sediment-free liquid was removed by vacuum and the tube was filled again with deionised water to the 50 mL mark.
The sediment was gently dispersed into the water phase with a piece of wire. The sample was re-centrifuged (at 800g for 5 min). The volume of the resultant sediment was read and the results
obtained were the average of the two readings.The oxidative stability under accelerated conditions (0.5 MP a oxygen pressure) was determined using an OXIPRES (Mikrolab Aarhus A/S, Denmark) which measures oxygen uptake by the sample. A glass vessel containing the powder (12.5g) was placed in the pressure cell and mounted onto the holding rack and heated to 80 C. The initial oxygen pressure rises when the cell is heated to 80 C from room temperature (22 C). The oxygen uptake was recorded as a function of time in duplicate.