Preparation effects on tortilla mineral content in Guatemala.

We have previously reported that in Guatemala, the calcium, iron, and zinc contents of tortillas from rural areas are higher that that of tortillas from urban centers. This study examines variation in the calcium, iron, zinc and copper content of tortilla according to the implements used for making tortillas and inquires as to whether preparation effects mediate rural-urban variation in tortilla mineral content. Tortilla samples and information on how the tortillas were prepared were collected from the female heads of a total of 50 households from three rural, two semi-urban and one low income urban community. Samples of lime used for making tortillas were collected from 31 households. To grind masa, a hand mill was found to be used in some rural households whereas a motorized mill predominated in the semi-urban and urban areas. Most women used grinding stones called the "mano y metate" to further refine the texture of the masa. Tortillas prepared with the combined use of the hand mill and "mano y metate" had a significantly (p < 0.05) higher iron content. Use of the "mano y metate" was also associated with a significantly (p < 0.05) higher zinc content. These results suggest that the use of certain grinding implements may mediate rural-urban variation in tortilla iron and zinc content. The cooking surface, pot used for nixtamalization, source of water, and amount of lime used did not significantly account for variation in the content of these minerals.