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The equilibrium water and calcium concentrations obtained in this study permitted to
C − Ce
allowed the equation (3) because if p 0.
7 the solution of the Fick equation is
C0
− Ce
reduced to
C − C
C
0
e
− C
e
2
8 ⎡ π Dt ⎤
= exp⎢−
2
2 ⎥
π ⎣ 4L
⎦
This equation was linearized and the diffusivity was calculated as the slope obtained by
linear regression.
The D values are shown in Figure 3. The order of magnitude of values is that reported for
food diffusion coefficients. Both D values, for water and calcium, follow the same pattern.
It seems that the diffusivity increases as a function of temperature. Calcium is minimally
soluble in water but results suggest that water and calcium diffuse together into the corn
grain. However, if the diffusivity values are compared against water or calcium content,
(Figure 4), no temperature effect is observed. At low temperatures (25, 35 and 45°C), the
diffusion is independent of temperature, but at 70, 80 and 90°C this is not valid for water
content lower than 0.5 g of water/g dried solid (Figure 5).
D (m2/s)
2.5E-10
2E-10
1.5E-10
1E-10
5E-11
0
Dwa (m/s)
Dca (m/s)
0 20 40 60 80 100
Temperature (ºC)
Figure 3. Water and calcium diffusivities in corn
nixtamalization at 1%. Of lime content