K Nn mK - Amecamex.org.mx

to make it more stable through
reducing its water activity (Aw).
Materials and Methods
Raw materials. Corn (Zea mays),
cocoa (Theobroma cocoa), mamee
sapote seeds (Calocarpum
mammosum), Rosita de Cacao
(Quararibea funebris), corozo, and
lime were bought in the local market
of Oaxaca. These products were well
inspected to avoid insects and
microbial damage.
Tejate preparation. 1kg of white
corn, 100g of cocoa, 20g of Rosita de
cacao, 20g of mamme sapote seeds,
3L of water and 250g of lime were
used for tejate preparation (Cortes,
1999). The corn was cooked with lime
for 2h. Then, it was washed and
mixed with the other ingredients
previously roasted. The mixture was
grounded until an homogeneous
dough was obtained.
Tejate drying. The tejate was dried
in a cabinet drier at 60, 70 and 80 °C
in different layer thicknesses (0.25,
0.5 and 0.75 cm) and 1-1.5 m/s of air
velocity. During drying, samples were
taken to obtain the drying kinetics.
The dried product was grounded and
sieved to obtain particle sizes smaller
than 500 mm (Mendoza, 2004).
Sorption Isotherms. The gravimetric
method, with sulfuric acid solutions,
was used to obtain the sorption
isotherm at 15, 25 and 35°C. The
samples were put in glass containers
with the solutions of known Aw. The
containers were closed and vacuum
was made into the containers to avoid
variations in the inside relative
humidity. The samples remained in
the glasses until equilibrium was
reached. Equations of Chung-Pfost
⎡ C
⎤
(1967): Aw = exp ⎢−
1 exp(
− C2H
) ⎥⎦
⎣ RT
and Henderson (1952):.
C
ln(
1−
Aw ) = −C
TH 2
1
Were used, where Aw is water
activity, T is temperature (K), M is
water content (g H2O/g dm), R is
constant of gases and C1, C2 are
constants.
Water Content. Water content of
samples taken during drying and
sorption isotherms were determined
by the AOAC recommended method
(1991).
Results and Discussion
Preliminary drying experiments
showed that dried tejate was very
unstable. Besides, it developed a
rancid flavor attributed to corozo,
which is rich in polyunsaturated fatty
acids. Drying temperatures catalyzed
oxidation reactions provoking the off
flavors. Instead of using antioxidants
to avoid this problem, corozo was
eliminated from the original
formulation. The new formulation was
tasted by 100 tejate producers and
consumers. No difference was found
between the original and new
formulations.
Drying Kinetics. Kinetics of tejate
drying are shown in Figure 1 at the
three tested temperatures. The effect
of layer thickness is clearly notorious
and it was increased with
temperature. At 60 C, this effect is
more important between 0.25 and
0.50 cm than 0.50 and 0.75 cm
thickness. Nevertheless, when the
temperature increases the
thicknesses effect is less important.