K Nn mK - Amecamex.org.mx

MATERIALS AND METHODS.
A complete factorial design 6X3 (6 temperatures and 3 lime concentrations) with one
replication and three analyses per sample were performed to obtain the experimental data.
Sample preparation. 3 L of water, 500 g of corn and the lime were put in a temperature
controlled cylindrical container. The water and lime experimental concentrations were set
to be in excess such that regardless of calcium absorbed by the grain, the calcium
concentration in solution was the same. Samples were taken until the equilibrium
concentration was reached. The sample was rinsed with unionized distilled water and the
water excess was eliminated.
Water content. The gravimetric method was used to determine water content. Samples
were dried in a vacuum oven at 70 mm Hg and 60°C for 24 h.
Calcium content. This analysis was performed by Atomic Absorption Spectroscopy of
Flame Ionization at 422.7 nm with a 10 mA calcium lamp and a slit of 0.7 nm in dried
samples.
RESULTS AND DISCUSSION.
Water and calcium absorption kinetics. Water absorption at the three lime
concentrations was not significantly different. The 1% lime concentration results are
showed in figure 1 at the studied temperatures. This behavior was expected and confirms
the fact that water and calcium absorption was not limited by lime concentration. The lime
solubility in water is 1.25 mg/L, and then all the concentrations used in this experiment
were oversaturated. This figure shows that at 25, 35, 45 and 70°C, the equilibrium was
reached in 10 h of processing, higher temperatures favored water absorption and the
equilibrium was reached sooner (6-8 h). At these temperatures figure 1 shows an increase
in the final water content of the samples. The equilibrium wasn’t really obtained at these
temperatures because the samples presented gelatinization and the starch was able to
absorb more water in its structure.
HBS (g water/g d.s.)
1.6
1.2
0.8
0.4
0
%H 25°C
%H 35°C
%H 45°C
%H 70°C
%H 80°C
%H 90°C
0 2 4 6 8 10 12 14
Time (h)
Figure 1. Water kinetic absorption during
nixtamalization at several temperatures. 1% of
Ca(OH)2