Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Food Science and Human Nutrition

Abstract

Corn tortillas are one of the main corn products consumed in Mexico and Latin American countries. Dry corn masa flour has better shelf-life than wet corn masa, and is convenient and easy to use at commercial and home levels. The objectives of the present studies were to determine the extent of lipid oxidation in dry corn masa flours as sold in the retail market, to determine the shelf-life of dry corn masa subjected to different temperatures, and to determine the effects of corn lipids and germ proteins on dough properties and sensory characteristics of corn tortillas;In the first study, a survey of two Mexican and three American flours showed that oil of dry corn masa flour as is it was found in the marketplace was typically quite oxidized, especially during summer. Storage temperature and storage time negatively affected (P < 1%) shelf-life of dry corn masa flour. The shelf-life of dry corn masa flour was 5.8 mo when stored at 25°C, but shelf-life declined to about 2 mo when stored at 45°C. Peroxide value and conjugated dienoic acids contents were not highly correlated with sensory scores. Sensory evaluation of corn tortillas was a much more sensitive measure of rancidity than widely-used chemical indicators of oxidation;In the second study, oil was extracted from lab-made and commercial dry corn masa to determine the effect of oil on physical properties and sensory characteristics of corn tortillas. A laboratory process for preparing dry corn masa was developed and proved to be suitable for studying processing variables. The presence of oil did not affect dough stickiness. Oil had a minor but statistically significant contribution to the typical corn tortilla flavor. The presence of oil significantly improved chewiness and firmness of corn tortillas. The negative effects of oil extraction on flavor, chewiness and firmness of corn tortillas make it unfeasible to extend shelf-life of dry corn masa flour by extracting the oil;In the last study, the effects of degerming the corn during the preparation of dry corn masa flour on physical properties and sensory characteristics of corn tortillas were studied. Degermination did not affect dough stickiness and tortilla rollability. Degermination also did not have a statistically significant effect on the typical corn tortillas flavor, but negatively affected texture and chewiness of corn tortillas. Thus, the corn germ is important to the texture of corn tortillas. The negative effects of degermination on chewiness and texture of corn tortillas made it unfeasible to extend shelf-life of dry corn masa by degerming the nixtamal.

DOI

https://doi.org/10.31274/rtd-180813-12341

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Reyna Luz Vidal-Quintanar

Language

en

Proquest ID

AAI9414030

File Format

application/pdf

File Size

125 pages

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