Mycofloral succession in pozol from Tabasco, Mexico

Abstract

This paper presents the results of a mycological study of pozol, a food
product of Mayan origin that is prepared br fermentation of maize dough;
the fermented dough is diluted in water am drunk as a basic food by the
Indian and mestizo populations of southeastern Mexico.
The pozol swdied was prepared at Cardenas, Tabasco, Mexico, a tropical
location where pozol is routinely consumed, mainly by the pema nts.
The objecti-.:es of the study were to isolate at the site of manufacture the
mycoflora present at different stages of preparation of pozol: maize kernels,
kernels cooked in lime water, recently made dough, and dough fermented
for 8 hours, and I, Z, 4, and 8 days; and to record pH, moisture content,
relative humidity, and temperature during the whole process.
The acid pH of maize kernels (5.7.1J) was raised to 7.5 due to the treatment
with lime water, which had itself a pH of 11.75. The pH of the dough (6.8)
gradually decreased as fermentation proceeded, reaching 3.93 on the eighth
day. The low moisLUre content of maize kernels (6.24%) increased to 22.7%
after cooking them in lime water, and to 30.5% in the dough. During the
8 days that pozol was being fermented, the moisture content remained
around 30%.
From the maize kernels were isolated FusaTium moniliforme (77%) and
CladospoTium cladosp01·ioides (3%). From the lime treated kernels were
isolated Aspergillus carbonarius (1 %), A. pamsiticus (2%), Monilia sitophila
(10% ), and Trichoderma viride (18%)· Of these molds, only C. cladosporioides
and M. sitophila were isolated from pozol after 2 days of fermentation.
During each of the 8 days of pozol fermentation, the relative humidity of
the ambient air decreased as the temperature increased and vice versa. Pozol
temperaLUre varied less than environmental temperature; the balls o pozol
warmed and cooled slower than the environment.
Six culture media were inoculated with serial dilutions of pozol, ranging
from 1: 10", for recently made pozol, up to 1:1010, for pozol fermented 8 days.
Although many bacteria were found in pozol, they were not studied in detail
but some of them were found to be able to reduce acetylene to ethylene, a
reaction that indicates their capacity to fix nitrogen.
The numbers of yeasts and molds increased as fermentation of pozol proceeded.
Yeasts of the genus Candida as well as Trichosporon cutaneu.m and
Geotrichum candidum were found from the first hours of fermentation and continued
to be present for several days. As the surface of pozol balls progres..
sively dried, and their pH became more acid, molds such as Cladosporium
cladosporioides, Monilia sitophila and Mucor muxianus also invaded pozol to
constitute a complex mixture of bacteria, yeasts, and molds The presence iu the pozol from Tabasco of some yeast and mold species
previously found in pozol samples from other locations indicates a certain
consistency in the pozol microflora since the same or closely related species
oc('ur in the natural proces of pozol fermentation.