Journal Paper of the Day

On the occasion of arriving in Paris for the summer, a special edition of Journal Paper of the Day.

G. Vázquez, F. Chenlo, R. Moreira, A. Costoyas, “The Dehydration of Garlic. I. Desorption Isotherms and Modelling of Drying Kinetics” and “The Dehydration of Garlic. II. The Effects of Pretreatments on Drying Kinetics”, in Drying Technology, Vol. 17, No. 6, 1999, pp. 1095–1108 and pp. 1109–1120.

Key words and phrases
Drying of sliced garlic (Allium sativum. L.); desorption isotherms; diffusional kinetic model; variation in volume; rehydration ratio; blanching; solutions of potassium carbonate; potassium carbonate and olive oil; sodium hydroxide or sodium metabisulfile.

Key quotes

“There is very little published work on the drying of garlic” (p. 1096).

“Fresh heads of garlic (Allium sativum. L.) were purchased from a local market” (ibid).

Key equation
The solution obtained for diffusion within a planar slab under the assumption that moisture transfer is unidirectional, that the initial moisture is uniformly distributed in the substrate, that external resistance to heat and mass transfer is negligible, and that the volume of the substrate and the effective diffusion coefficient of moisture in it are constant throughout the drying process1: $$X^{*} = \dfrac{X-X_e}{X_0-X_e} = \dfrac{8}{\pi^2} \sum^{\infty}_{n=0} \dfrac{1}{(2n+1)^2} e^{\Biggl[\displaystyle -(2n+1)^2 \dfrac{\pi^2D_{\text{eff}}t}{L^2}\Biggr]}$$ Where $X^{*}$ is the dimensionless moisture content, $X_t$, $X_0$ and $X_e$ are the moisture contents in kg of water per kg dry mass at time t (in s), at $t = 0$ (initial value) and at equilibrium, respectively; $D_{\text{eff}}$ the effective diffusion coefficient (in $m^{2}s^{-1}$); and L is the half-thickness of the slab (in m). Planar slab geometry is justified by geometrical considerations and by structural properties of garlic because the slices were obtained with the natural external wall (less permeable to water) as the cylindrical wall allowing, practically, to remove the water though both planar faces. In the same issue of the journal can be found a technical note on the drying of chopped spring onion.

1. John Crank, The Mathematics of Diffusion, Oxford University Press Oxford, 2nd Edition, 1975.