Sorvall Omnimix

Emulsion Capacity and Stability. A 0.5 g sample of the freeze-dried protein fraction was redissolved in a minimum of 0.3 M citrate-phosphate buffer at pH 7.0 and mixed thoroughly with 50 ml of 1 M NaCl for 1 min in a Sorvall Omnimixer at 1000 rpm in a one pint Mason jar set in a water bath (20°C). Crisco oil (50 ml) was added to the jar and an emulsion formed by mixing at 500 rpm with simultaneous addition of oil at the rate of 1 ml/min until the emulsion broke. The endpoint was determined by monitoring electrical resistance with an ohmeter. As the emulsion broke a sharp increase (l KS2 to 35- 0 KSi) was noted. Emulsion capacity was expressed as the total volume of oil required to reach the inversion point per mg protein. This method is similar to that used by Carpenter and Saffle (8) for sausage emulsions. To establish emulsion stability the same procedure was used except that 100 ml of oil was added and a stable emulsion formed by blending at 1000 rpm for 1 min. A 100 ml aliquot was transferred to a graduate cylinder and allowed to stand at room temperature. Observations were made of the volume of the oil, emulsion and water phases at 30, 60, 90 and 180 min. 

Foam Volume. The determination of foamability was carried out using the procedure of Hermansson et al. (9.) with modifications. A 1 g sample of the freeze-dried protein fraction was homogenized with 90 ml of citrate-phosphate buffer in a Sorvall Omnimixer at 3000 rpm. The resultant foam and liquid were transferred to a 250 ml graduated cylinder and the mixer cup washed with 10 ml of buffer. The cup was drained for 2 min and the cylinder allowed to stand for 30 min at which time the foam volume was measured. The influence of pH and ionic strength on foam volume was established using the buffer systems previously described. 

Omnimixer (Sorvall) with adapter for 50-ml centrifuge tubes Centrifuge (with a Sorvall SS-34 rotor or equivalent)... 

As the water uptake ability is partly structural, it is dependent on particle size, and thus the blending process must be standardized. For this purpose, the author has found the Omnimixer (Dupont s Sorvall Division) to be a particularly useful device. It is an upside-down blender that, most importantly, with the appropriate adapter, can be used to blend samples in centrifuge tubes, avoiding the need for quantitative transfer of some very sticky and viscous materials. Again, all the details of the method need to be standardized, even if this is done in an arbitrary fashion. 

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