Effects of vacuum impregnation and ohmic heating with citric acid on the behaviour of osmotic dehydration and structural changes of apple fruit

Vacuum impregnation (VI) and ohmic heating (OH) pre-treatments with and without addition of citric acid were used to enhance the mass transfer kinetics during osmotic dehydration (OD) of apple cubes. The VI with citric acid made the following OH treatment more homogeneous and equilibrated the fruit and syrup temperatures. The water loss (WL) and sugar gain (SG) during OD were significantly increased when the apple tissue was pre-treated with addition of citric acid. This was confirmed by calculation of water and sugar diffusivities. The VI and OH pre-treatments led to profound changes in apple fruit structure, evaluated by measurements of fruit firmness and electrical conductivity.