Microflora of Maize Prepared as Tortillas

Very little is known of the microflora in tortillas, the major component in the diet of many Guatemalans and other Central Americans. Based in a Guatemalan highland Indian village, this study examined the types and amounts of bacteria, yeasts, and molds in tortillas and in their maize precursors. Coliforms, Bacillus cereus, two species of Staphylococcus, and many types of yeast were the main contaminants, but low concentrations of alpha-hemolytic Streptococcus, facultative Clostridium, and other bacterial types were also found. When tortillas were first cooked, the bacterial counts dropped to 1,000 or fewer organisms per g, a safe level for consumption. Under village conditions, bacterial counts regained precooking levels (about 10(8) organisms/g) within 24 h and rose even higher after 48 h. Reheating caused very little change; hence, bacterial levels remained very high in old tortillas kept for later consumption. A search for the sources of contamination showed that most came from water used in preparation and from the soiled hands of women preparing the tortillas. As an attempt to correct certain nutritional needs of the population, the Institute of Nutrition for Central America and Panama initiated a tortilla fortification project in the Guatemalan village. The bacterial counts in fortified tortillas did not differ significantly from those in oridinary tortillas. Furthermore, the level of contamination was constant among tortillas of different sizes and among tortillas made from different types of maize.