Simultaneous application of ultrasounds and firming agents to improve the quality properties of osmotic + freeze-dried foods

Dried foods generally show poor rehydration ability and changes in the product properties. In this work, strawberries, used as a model food, were processed using osmotic dehydration (OD) followed by freeze drying (FD) to investigate the effects on the sample colour, texture, microstructure and rehydration. For the first time, a new approach was implemented by adding firming agents (FA) in the osmotic solution to strengthen the cell walls and applying ultrasounds (US) during the pre-treatment to enhance the process mass transfer. FA and US have been implemented often separately but never combined. The resulting samples were then further dried using FD. This strategy revealed to be successful in improving the properties of dried foods compared to FD solely: rehydration capacity was enhanced; colour was better retained, showing colour coefficients closer to the fresh fruit; texture was largely improved, exhibiting the same mechanical properties of the raw material; microstructure was well preserved.