Changes in physical properties and relations with allicin degradation during convective drying of garlic

The objective of this work was to establish the relationship between the physical properties and the ability to retain precursors of allicin into the structural matrix of garlic during convective drying. The study evaluated the retention of allicin and its relation to changes in the structural properties: apparent density (rho(b)), true density (rho(p)), porosity (epsilon) and shrinkage (S-b) during the garlic drying process. Drying kinetics, structural properties (SP) and allicin content (AC) were determined in garlic slices subjected to drying temperatures of 50 and 60 degrees C with airflow of 1.5 m/s. To calculate structural properties, the experimental data volume of the solid was determined using volumetric displacement and gas stereopycnometer methods. The AC was determined by the HPLC method. Data were correlated using Pearson's equation. The results showed a strong relationship between AC and S-b, rho(p) and rho(b), while a weak relation to the epsilon was found for both temperatures. The kinetics showed two stages, the first showed a rapid increase in the rho(p), rho(b) and S-b, according to the loss of allicin. In the second, the increase of rho(p), rho(b) and S-b remained without significant losses of allicin. The results suggest that a denser structure prevents the penetration of oxygen through the solid reducing the degradation of bioactive compounds during the first stage. Both, the temperature and changes in the SP affect the retention of allicin. The drying temperature of 60 degrees C can induce more rapid shrinkage and dense structures and partially inactivate the enzyme alliinase.