Host: Japanese Sciety for Food Science and Technology
Name : The 71st Annual Meeting of Japanese Society for Food Science and Technology
Number : 71
Location : [in Japanese]
Date : August 29, 2024 - August 31, 2024
Pages 364-
Purpose: Microwave vacuum drying (MVD) is a technique in which the boiling point of water is lowered under reduced pressure at a kPa level to suppress the temperature increase while supplying the energy necessary for water evaporation of foods by microwaves. We have confirmed that the pre-freezing treatment suppresses sample deformation during the MVD process and produces dry materials with a porous structure. This presentation aims to clarify the relationship between the pore structure and mechanical properties of dried apple MVD products obtained under different conditions.
Methods: Apple pulp was cut into a 10-mm-thick quadrants and used as the samples. The samples pre-frozen in a -20 °C freezer and a -40 °C blast chiller were treated as the slow-frozen and rapid-frozen samples, respectively. In the MVD, samples were dried using a microwave reactor. The microwave power was set at 200 W and the internal pressure was 1 kPa or ambient pressure. The dried samples were evaluated for pore structure using a micro X-ray CT system, mechanical properties using a universal testing machine, and water activity.
Results: The internal porosity and pore size of the dried samples tended to be larger at 1 kPa than at ambient pressure and for the slow-frozen samples than for the rapid-frozen samples. These porous samples showed lower maximum forces and higher number of peaks in mechanical tests. In addition, dried samples with greater sample shrinkage exhibited higher water activity, suggesting that sample shrinkage during drying hinders water evaporation and increases the final water content, which affects the formation of mechanical properties.
