LWT 39 (2006) 947–951 Research note In vitro digestion rate and resistant starch content of tortillas stored at two different temperatures Jose´ Juan Islas-Herna´ndez a , Rodolfo Rendo´n-Villalobos a , Edith Agama-Acevedo a , Felipe Gutie´ rrez-Meraz a , Juscelino Tovar b , Gero´nimo Ara´mbula-Villa c , Luis Arturo Bello-Pe´rez a,Ã a Centro de Desarrollo de Productos Bio´ticos del IPN, Apartado postal 24 C.P., 62731, Yautepec, Morelos, Me´xico b Instituto de Biologı´a Experimental, Facultad de Ciencias, Universidad Central de Venezuela, Apartado Postal 47069, Caracas 1041-A, Venezuela c Centro de Investigacio´n y de Estudios Avanzados del IPN, Unidad Quere´rato. Libramiento Norponiente No. 2000. Fracc. Real de Juriquilla. Quere´taro C. P. 76230, Me´xico Received 24 February 2005; received in revised form 7 June 2005; accepted 14 June 2005 Abstract In vitro indicators of starch bioavailability were evaluated in freshly prepared maize tortillas and compared to those exhibited by 24, 48 or 72 h-stored samples. Storage took place either at room temperature (approx. 25 1C) or under refrigeration (4 1C). Potentially available starch (AS) content decreased from 670 g kg 1 in the control tortilla to 583 g kg 1 in 72 h-stored preparations. Concomitant increases in total resistant starch (RS) and retrograded resistant starch (RRS) were recorded upon storage. RRS content in 72 h-stored samples (35–39 g kg 1 ) doubled that of freshly prepared tortillas. Changes in AS, RS and RRS were not affected by storage temperature. Both initial rate and final point of starch hydrolysis by pancreatic amylase were reduced in samples kept for 48 and 72 h, without influence of storage temperature. Storage length is suggested as a major determinant of the bioavailability of starch in tortillas. r 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. Keywords: Tortilla; Storage; Resistant starch; Digestion rate; Digestibility 1. Introduction The nixtamalization is a traditional Mexican process developed by the Mesoamerican civilizations and is still utilized in the production of ‘‘tortillas’’ and other maize- based food products. Tortillas are the principal staple food in the Mexican diet, representing the main source of carbohydrates and calcium (Campus-Baypoli, Rosas- Burgos, Torres-Cha´ vez, Ramı´rez-Wong, & Serna-Saldı´- var, 1999). Nowadays, table tortillas are highly popular in United States and, to some extent, also in Canada and several European countries (Yau, Waniska, & Rooney, 1994). Many studies have been conducted on nutritional aspects of nixtamalized maize, but only limited research has been carried out on the bioavailability of its carbohydrate constituents (Agama-Acevedo et al., 2004; Rendo´ n-Villalobos, Bello-Pe´ rez, Osorio-Dı´az, Tovar, & Pare´dez-Lo´pez, 2002). Carbohydrates repre- sent the main fraction of cereal grains, accounting for up to 500–700 g kg 1 of the dry matter; of these, starch and nonstarch polysaccharides (dietary fiber) are the major constituents. Starch owes much of its functionality to two major high-molecular-weight carbohydrate compo- nents, amylose and amylopectin, as well as to the physical organization of these macromolecules into the granular structure (French, 1984). When starch is cooked in excess water, the granules swell and, at the same time, part of the components solubilize, giving rise ARTICLE IN PRESS www.elsevier.com/locate/lwt 0023-6438/$30.00 r 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2005.06.010 Ã Corresponding author. Tel.: +54 739 42020; fax: +52 739 41896. E-mail address: labellop@ipn.mx (L.A. Bello-Pe´rez).