Abstract

The study investigated the effect of different pretreatments such as citric-acid (CA), potassium-metabisulphite (KMS), and ethylenediamine-tetraacetic acid (EDTA) on the drying kinetics, allicin and colour of garlic slices in a convective hot-air dryer at temperatures of 45, 50 and 55°C. The allicin content of the fresh garlic slices compared with the dried slices increased non-linearly with increase in temperature from 8.6 to 23.5, 13.3 to 22.4, 11.9 to 23.4 and 12.3 to 24.1 µg/ml for the control, CA, KMS, and EDTA samples, respectively. The drying characteristics were evaluated against Page et al. (1949) mathematical models on the basis of the coefficient of determination (R²), reduced chi-square  , and root mean square error (RMSE). The drying characteristics of garlic slices of the control were best described by the Midilli et al. (2002) model whilst the CA, KMS, and EDTA pretreated samples were best described by the Henderson and Pabis (2006) model within the confines of the experiments. The colour of the fresh and dried garlic slices were measured in Hunter parameters. The KMS pretreated samples showed greatest brightness (85.95) and least redness (1.36) in colour at 50°C and 45, respectively compared with the fresh, whereas the EDTA pretreated samples were yellower (17.43) at 45°C.

Key words: Garlic slices, drying models, pre-treatments, allicin content, colour.