Ultrasonication of reconstituted whole milk and its effect on acid gelation

•Ultrasonication of whole milk caused substantial homogenization of the fat globules.•Acid gel firmness was dependent on the temperature and duration of ultrasonication.•Acid gels from ultrasonicated milk had similar firmness to those from heated milk.•Separated heat and ultrasonication steps had an additive effect on acid gels properties.•Separated heat and ultrasonication steps produced gels with unique textural properties. Ultrasonication (US) of whole milk at 22.5kHz and 50W homogenized fat globules. Extended US without temperature control (attaining >90°C at longest times), or with control at temperatures ⩾60°C caused denaturation of the whey proteins and aggregation of the fat globules and proteins. Acidification of US milk produced gels with increased firmness and reduced gelation times compared to untreated milk. Below 60°C, US of milk produced acid gels with very high firmness without whey protein denaturation; the firmness was similar to gels from heated whole milk. Extensive US without temperature control or with control at ⩾60°C decreased acid gel firmness compared to shorter times or lower temperatures. Higher acid gel firmness could be achieved by subjecting the milk to separate heat (80°C/30min) and US treatment (at 20°C) before acidification when compared with either heating or US alone. This was independent of the order of heating and US treatment.