Understand the stickiness of flour tortillas.

The stickiness found in many tortillas is a highly undesirable characteristic, especially for the food service industry. The difficulty in separating packaged tortillas individually will impact whether they are acceptable to consumers.

Scientists at Rutgers University set out to understand the factors that control stickiness in wheat flour tortilla products. They based their research on understanding the phase-state changes that occur to the product, as well as measuring its surface properties. A fundamental understanding of the phase-state and surface chemistry origins of stickiness will provide the tortilla industry with a tool that will help it formulate, produce and store flour tortillas that are not sticky, ensuring that high-quality products reach consumers.

Commercial wheat tortillas were assigned a wide range of sensory stickiness scores by semi-trained panelists. The tortillas were equilibrated to different water activity (aW) levels--in a range of 0.12 to 0.97--in order to characterize their phase-states at controlled relative humidity and temperature levels.

The researchers developed moisture sorption isotherms. They used differential scanning calorimetry and mechanical spectroscopy to characterize the amorphous phase behavior. They applied wide-angle x-ray scattering technology to characterize crystallinity, and contact angle measurements to determine the product's surface hydrophobicity. An objective instrumental test technique was developed using a texture analyzer to quantify tortilla stickiness.

The researchers linked instrumentally observed stickiness to the surface chemistry of the tortilla samples by calculating the surface energy of tortillas based on contact angles that they had determined using standard test liquids. Instrumental stickiness scores agreed closely to the sensory scores. The state diagram developed by the scientists indicated that both sticky and non-sticky tortillas have similar amorphous phase behavior.

The sticky tortillas had low crystallinity--0.7% to 1.4%--as compared to non-sticky tortillas--3.2% to 5.3%. Water activity had a significant impact on the stickiness of the tortillas. The polar component of surface energy, a marker of surface hydrophillicity, correlated strongly with stickiness.

Further information. Jozef Kokini, Department of Food Science, 65 Dudley Rd., Cook College, Rutgers University, New Brunswick, NJ 08901; phone: [phone]; fax: [phone]; email: [e-mail].