To evaluate their emulsifying and stabilizing effects, freeze dried (i) whole whey and (ii) whey protein concentrate were added to 40%-fat commercial 'light' butter (without emulsifier) at 5, 10 and 20% and 1.2 and 4.8%, respectively. The powders were incorporated into the butter by homogenization at 25°C for 5 min, using a Politron homogenizer (Kinematica GmbH) at speed 5. The test samples, cooled rapidly to 4°C, were compared with 2 commercial 'light' products, one containing monoglycerides and the other gelatin and caseinates, which had been homogenized under the same conditions as the test samples. The comparison covered product composition (DM, moisture, ash, lipids, proteins), a w, effect of centrifugal force on their stability, total bacterial counts and yeast and mould counts. Increasing amounts of (i) led to a decline in a w, although even at 20% addition the a w values did not guarantee retardation of microbiological changes. Stability generally declined with increasing centrifugal force (4000 and 8000 r.p.m.); (i) had a positive effect on the stability of the test samples at 5%, but less so at 10 and 20%, although their stability was comparable to that of commercial samples containing emulsifiers and stabilizers. Addition of (ii) at 1.2% had a beneficial effect on emulsion stability, particularly at low centrifugal forces (2000 and 4000 r.p.m.), the effect being less pronounced at 4.8%. Aspects to be considered if (i) and (ii) are to be used on a commercial scale are discussed.
