Optimizing the tortilla.

Wheat tortillas are the foundation for burritos, tacos, sandwich wraps and other popular foods. But they are most tasty and functional when they're soft, tender and less than a couple of weeks old. Hoping to give tortillas a longer shelf life to satisfy consumers, USDA-ARS chemists are studying the causes of staling in aging tortillas. With that insight, they'd like to slow the everyday occurrence of staling.

Keeping a wheat-flour tortilla fresh and tender, ready to accept a zesty filling of vegetables or meat, is not easy. It's a race against the clock to beat underlying chemical forces that cause the popular flat breads to become brittle and tasteless. Aiming to please customers and curb losses, the $5 billion tortilla industry is trying to produce tortillas that will stay fresh for up to 25 days.

The perfect tortilla is about 2 millimeters thick and evenly opaque, with an ample diameter and at least a three-week shelf life. Investigators recently developed a test that can determine whether a particular wheat flour will yield this ideal tortilla. The research and the new testing method could eventually help the tortilla industry and breeders develop wheat varieties ideally suited for tortilla production. These varieties would have just the right gluten strength and protein makeup to be grown exclusively for tortilla production. Researchers are currently evaluating more than 300 breeding samples.

The scientists base a tortilla's quality partly on how strips of the flat bread perform when they are stretched across a special plate. The researchers measure the forces involved in this stress test and determine the level at which they cause the tortilla strips to break. Scientists are optimizing the test and are interested in conducting trials in a commercial facility.

A wheat tortilla's tenacity is largely dependent on the types of proteins, or gluten, that are found in its flour. The gluten can impart strength to a tortilla, allowing it to endure the stress of being rolled up without cracking. But when flour from a particular wheat variety has excessively strong gluten, the tortilla made from it will have too much spring, causing it to shrink in and lose valuable surface area when the dough is released from the tortilla press. Finding the right balance of proteins is an important part of the wheat-breeding research.

Meanwhile, the scientists have found that at the heart of the staling process is moisture movement throughout the tortilla via the protein matrix and starch molecules. The researchers also plan to examine the chemistry of the staling process in other grains, like sorghum. Further information. George Lookhart, USDA-ARS Grain Marketing and Production Research Center, 1515 College Ave., Manhattan, KS 66502; phone: [phone]; fax: [phone]; email: [e-mail].