The effects of ultrasound application on skim milk (10% w/w total solids at natural pH 6.7 or alkali-adjusted to pH 8.0) prior to the renneting of milk at pH 6.7 were examined. Skim milk, made by reconstituting skim milk powder, was sonicated at 20kHz and 30°C (dissipated power density 286kJkg(-1)) in an ultrasonic reactor. The rennet gelation time, curd firming rate, curd firmness, and the connectivity of the rennet gel network were improved significantly in rennet gels made from milk ultrasonicated at pH 8.0 and re-adjusted back to pH 6.7 compared to those made from milk sonicated at pH 6.7. These renneting properties were also improved in milk sonicated at pH 6.7 compared to those of the non-sonicated control milk. The improvements in renneting behavior were related to ultrasound-induced changes to the proteins in the milk. This study showed that ultrasonication has potential to be used as an intervention to manipulate the renneting properties of milk for more efficient manufacturing of cheese.
Keywords: Cheese; Coagulation; Gelation; Milk; Rennet; Ultrasound.
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