2.3. Preparation of dehydrated pineapple samples
Fresh pineapple (Ananas comosus var. Golden Sweet) purchased
in a local market in Valencia (Spain) was used in the experiments.
A metallic core borer was used to obtain 2 cm diameter cylinders.
The cylinders were sliced obtaining samples with 1 cm of thickness.
The cylinders were submitted to vacuum impregnation (VI),
osmotic dehydration (OD) and air dried (AD) process. The samples
were immersed in a sucrose osmotic solution of 35 Brix and were
submitted to a VI operation in the first step by using a grid to keep
them immersed in the osmotic solution for 30 min, applying
50 mbar of pressure for 10 min and restoring afterwards the atmospheric
pressure for 20 min. As a second step, the samples were
introduced into a sucrose osmotic solution of 65 Brix and stirred
in a bath for 48 h in order to achieve the equilibrium condition.
In both cases, the experiments were carried out at 25 C and the ratio
of the weight of osmotic solution:sample was high enough
(20:1) to avoid any significant change in the osmotic solution
concentration.
In the third step, the samples were submitted to an air drying
(AD) process at 30 C till the same water activity (0.752 ± 0.007)
was reached in all samples. The AD processing was carried out before
or after the application of the coating depending on the
treatments.