Extend the shelf life of tortillas using fungal amylases.

Tortilla producers represent about 20% of the food market in Mexico, with annual sales of about $4 billion. Annual production totals more than 10 million tons, of which a little more than 20% is produced from maize flour. A variety of additives are used in tortilla manufacturing, including polycarboxylic acids, sorbate and propionate to retard staling or inhibit microbial growth. Gums are used to improve texture.

There has been a lot of research undertaken to extend the shelf life of bread. On standing, especially at refrigerated temperatures, the swollen gelatinized starch granules become rigid by the association of amylopectin. A limited hydrolysis of amylopectin can inhibit retrogradation and extend the product's shelf life. Although amylases are used in commercial bakeries, there are few applications of amylases in tortilla-making.

Scientists at UNAM (Department of Biotechnology, Faculty of Chemistry, Apdo Postal 510-3, Cuernavaca, Morelos 62271, Mexico) investigated the development of an enzymatic process to retard staling in tortillas. It requires no change in process conditions and increases stored product quality. It involves adding fungal amylases at low levels to dry maize flour or in water for making masa. This approach may be a valuable tool with which to reduce starch retrogradation and retard accelerated staling in tortillas.

Corn, the main source of starch and calories in the Mexican diet, is consumed mainly as tortillas, which have a short shelf life. A fungal amylase blend was added during hydration of maize flour to produce masa. The starch was modified during tortilla cooking up to the denaturating temperature. Control and treated tortillas, fresh and staled by storage at -12 C and by freeze-thaw cycles, were compared for amounts of retrograded starch, flexibility, rheological properties and by preference ranking by a panel of 75 judges. Results showed significant improvements in delayed staling, which in turn extended shelf life.

Reaction conditions in masa during cooking produce the required changes in amylose and amylopectin. The enzymes are deactivated as the surface cooking temperature of 90 C is reached. The masa pH is optimal for amylases, as the lime-treated maize is usually washed before milling. Using amylases at low doses to improve shelf life does not produce an increase in costs and results in a tortilla of higher quality. The enzymes also replace gums.

Still, some companies may have a problem substituting enzymes for the gums. The enzymes give better tortillas and are a less expensive and more natural additive, but the gums avoid water loss and increase dough resistance. This is important for machines that produce hundreds of tortillas a minute.

Further information. Agustin Lopez-Munguia; phone: [phone]; fax: [phone]; email: [e-mail].