188 CEREAL CHEMISTRY In Vitro Starch Digestibility of Tortillas Elaborated by Different Masa Preparation Procedures Luis A. Bello-Pérez, 1,2 J. Rodolfo Rendón-Villalobos, 1 Edith Agama-Acevedo, 1 and José Juan Islas-Hernández 1 ABSTRACT Cereal Chem. 83(2):188–193 Starch digestibility was evaluated in freshly prepared tortillas elaborated from masa obtained from different procedures (laboratory-made masa, commercial masa, and nixtamalized corn flour) and from laboratory- made masa with added commercial hydrocolloid, and stored for 24, 48, and 74 hr. Tortillas prepared with commercial masa had the highest available starch (AS) content and the commercial tortillas had the lowest, showing a decrease in AS content when storage time increased. Tortilla of commercial masa showed the lowest resistant starch (RS) content that agrees with the AS measured. However, tortilla of laboratory-made masa presented the highest AS and RS contents. RS increased with storage time, a pattern that is related to the starch retrogradation phenomenon observed when retrograded resistant starch (RRS) was quantified. Com- mercial tortillas showed predicted glycemic index (pGI) values of 62– 75% using a chewing/dialysis procedure (semi in vitro method). Index values were lower than those determined in vitro. The pGI of tortillas decreased, and the values were different depending on the method used to prepare the masa and tortilla. Commercial tortilla and tortilla of NCF had the lowest pGI. Therefore, the procedure to obtain masa and thereafter obtain tortillas influenced the starch digestibility of the product. The term corn means “what sustains the life”; its fruits or grains meant currency, religion, and food for diverse cultures of the world, and it is believed that domestication decisively influ- enced the development of the American cultures (Reyes 1990). Nixtamalization (corn grain treated with lime) is an ancient process developed by the Aztecs; it is still utilized to produce tortillas (Robles 1986). Tortillas represent an important source of calories, proteins, and calcium for diverse countries of Latin America such as Mexico and Guatemala, and the Mexican people living in the United States (Campas-Baypoli et al 1999; Billeb and Bressani 2001). Due to the expansion of the tortilla market, tortillas today are produced from nixtamalized corn flour (NCF) supplemented with hydrocolloids with the aim to yield products with longer textural shelf-life. In Mexico, the tortilla is part of the diet of all socioeconomic classes, with consumption per capita of 120 kg/year. To date, tortilla production in Mexico is ≈11 million tons, of which 22.8% is from dry corn flour; the rest is from commercial fresh masa nixtamalization or traditional self-prepa- ration in rural areas (Serna-Saldivar et al 1990; Paredes-López et al 2000). Carbohydrates are the main fraction of tortillas (60– 75%, db), where starch is the major constituent. Current knowledge of nutritional features of starch indicates that the bioavailability of polysaccharides in foods may vary widely (Tovar 2001). Hence, a nutritional classification of dietary starch has been proposed that takes into account both the kinetic degradation and the complete- ness of its digestibility, thus comprising rapidly digestible, slowly digestible, and indigestible (or resistant) fractions (Englyst et al 1992). Resistant starch (RS) is defined as the sum of starch plus the products of starch degradation not absorbed in the small intestine of healthy individuals (Asp 1992). RS intake has been associated with health benefits (Champ et al 2003). Therefore, agencies and health organizations recommend the intake of foods that contain significant amounts of RS. Starch is the major component of the tortilla. Its consumption is associated with the liberation of a high amount of glucose toward the blood and an increase in corporal weight. However, the quantity of digestible starch can be low in comparison with other foods from cereals such as bread. Tortillas in Mexico grow stale within hours, an effect associated with starch retrogradation and therefore with a decrease of starch digestibility. The objective of the present study was to evaluate the effect of the type of tortilla processing in determining the effect of storage time on in vitro digestibility of the starch and the glycemic index. MATERIALS AND METHODS Sample Preparation Experimental tortillas were prepared from laboratory-nixtama- lized maize using standardized conditions throughout the process. Batches of 5 kg of maize (commercial grain distributed for Indus- triales de la Masa y Tortilla de México) were cooked in 15 L of lime solution. Lime was added at 1% (grain weight basis). Maize was cooked for 1 hr at boiling temperature and then steeped in the same cooking vessel over 16 hr. The cooking solution (or “nejayote”) was discarded and the resulting nixtamal was washed three or four times with tap water to remove bran and excess lime. Nixtamal was ground into a masa using a commercial stone grinder (Nixtamex, México, D.F.) with stones 6.5 cm wide and 12.5 cm in diameter. Water was added during grinding at the rate of 90 mL/kg. Laboratory-made masa was hand-kneaded with com- mercial hydrocolloids TC-1 (0.5%) (Gum Technology Corpora- tion, Tucson, AZ). On the other hand, masa and tortillas were purchased from one small factory called a tortilleria where the traditional method of nixtamal production was used. NCF was obtained from the largest tortilla company in Mexico (Maseca, León, Guanajuato, México). The NCF was hydrated (100 g of flour/120 g of water) to obtain masa. All masas (from laboratory, laboratory-made with hydrocolloids, tortilleria, and NCF) were molded by pressure and extruded (Tortilladoras González, Naucalpan, Estado de México) into thin circles to obtain tortillas 1 mm thick. Tortillas were baked on a hot griddle (Hotpoint, 6B4411LO, Leisser S.A. de C.V., San Luis Potosí, México) for 1 min per side at an approximate temperature of 250 ± 5°C. After cooling, tortillas (including the commercial tortilla) were packed into polyethylene bags (20 × 30 cm, Plásticos de México, S.A. de C.V., México) and stored for 1, 2, 3, 7, and 14 days at 4°C. Tortillas with hydrocolloids were stored for 7 and 14 days. The fresh (stored 0 hr) and the stored samples were frozen in liquid nitrogen and freeze-dried (25 SL, Virtis Company, Gardiner, NY). Stored tortilla samples were reheated in a home gas-fired oven for 30 sec on each side at an approximate temperature of 250 ± 5°C, cooled to 30°C, frozen in liquid nitrogen, and freeze-dried. Tortillas were ground using a commercial grinder (Mapisa Inter- nacional S.A. de C.V., México, DF) to pass a US No. 50 sieve and stored at room temperature in sealed plastic containers. 1 Centro de Desarrollo de Productos Bióticos del IPN. Km 8.5 Carr. Yautepec-Jojutla, Colonia San Isidro, Apartado Postal 24, 62731 Yautepec, Morelos, México. 2 Corresponding author. Fax: +5273941896. E-mail: labellop@ipn.mx DOI: 10.1094 / CC-83-0188 © 2006 AACC International, Inc.