K Nn mK - Amecamex.org.mx

Calcium absorption is shown in figure 2. At low temperatures, there is a well defined
tendency to increase as a function of temperature. However, this pattern is lost at 70, 80
and 90°C. At these temperatures the equilibrium was reached up to 0.3% of calcium
content after 6-8 h of nixtamalization. After this concentration, the starch was gelatinized
and the grain structure was collapsed (fig. 1). The calcium is deposited within the external
structure (pericarp).
% Ca (g Ca/100 d.s.)
0.5
0.4
0.3
0.2
0.1
0
25°C I
35°C I
45°C I
70°C
80°C I
90°C I
0 2 4 6 8 10 12
Time (h)
Figure 2. Calcium kinetic absorption during
nixtamalization at several temperatures. 1% of
Ca(OH)2
Water and calcium diffusivity.
These parameters were estimated by the Fick law:
dC 2
dt
= D ⋅∇
The following assumptions were considered:
a) The grain is an infinite slab, then the diffusivity is unidirectional,
b) The diffusivity is not a constant.
By using the next boundary conditions,
t=0 C=Co x=L
t>0 C=C 0< x< L
The analytical solution is expressed as a Fourier series
∑ ∞
2
C − Ce
8 1 ⎡ π ( 2n
−1)
=
exp⎢−
2
2
2
C0
− Ce
π n=
1 ( 2n
−1)
⎣ 4L
Where Ce is the equilibrium concentration, Co is the initial concentration, C is the
concentration at t>0, D is the diffusivity and L is the middle grain thickness.
C
2
Dt ⎤
⎥
⎦