foods

Article Physicochemical Properties and Resistant Starch Content of Corn Flours Refrigerated at Different Storage Times

Isela Rojas-Molina 1, Monsserrat Mendoza-Avila 1,2, María de los Ángeles Cornejo-Villegas 3 , Alicia Del Real-López 4 , Eric Rivera-Muñoz 4 , Mario Rodríguez-García 4 and Elsa Gutiérrez-Cortez 3,*

1 Laboratorio de Química Medicinal, Facultad de Química Universidad Autónoma de Querétaro, Cerro de las Campanas S/N, Centro Universitario, Querétaro C.P. 76010, ; [email protected] (I.R.-M.); [email protected] (M.M.-A.) 2 Doctorado en Ciencias Químico-Biológicas, Facultad de Química, Universidad Autónoma de Querétaro, Cerro de las Campanas s/n, Las Campanas, Santiago de Querétaro C.P. 76010, Mexico 3 Departamento de Ingeniería y Tecnología, FES-Cuautitlán, Laboratorio de Procesos de Transformación y Tecnologías Emergentes de Alimentos, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, Estado de México C.P. 54714, Mexico; [email protected] 4 Departamento de Ingeniería Molecular de Materiales y Departamento de Nanotecnología, Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, Blvd. Juriquilla 3001, Juriquilla, Querétaro C.P. 76230, Mexico; [email protected] (A.D.R.-L.); [email protected] (E.R.-M.); [email protected] (M.R.-G.) * Correspondence: [email protected]; Tel.: +52-56231919 (ext. 39602)

 Received: 3 March 2020; Accepted: 3 April 2020; Published: 9 April 2020 

Abstract: The tortilla is a foodstuff that has a short shelf-life, causing great losses to the industry. The objective of this work was to evaluate, for the first time, the physicochemical properties and resistant starch (RS) content of flours. These were obtained from nixtamalized corn made with traditional and industrial (commercial) methods, stored at 4 ◦C for 7, 15, and 30 days. The flours were characterized by measuring particle size distribution, color, water absorption index (WAI), water solubility index (WSI), viscosity, , and RS content. Additionally, chemical proximate analysis, scanning electron microscopy (SEM), and thermal analysis were conducted. Storage at 4 ◦C increased the friability of tortillas and shifted the particle size distribution toward a greater content of coarse particles in flours. The commercial corn tortilla flours showed higher WAI and WSI values than the traditional corn tortilla flours. On the other hand, the traditional corn tortilla flours exhibited higher RS content values than commercial corn tortilla flours as well as peak viscosity. X-ray diffractograms revealed the presence of amylose-lipid complexes (RS5) in experimental samples. The thermograms evidenced three endotherms corresponding to gelatinization and melting of type I and type II amylose–lipid complexes.

Keywords: ; corn tortilla flours; friability; resistant starch; refrigeration storage; amylose–lipids complexes

1. Introduction The dietary change as well as a sedentary lifestyle practiced by the population of countries in development implies the intake of hypercaloric diets, rich in calories and low in vitamins and minerals. These have led to an increase in the prevalence of chronic diseases such as diabetes mellitus and cardiovascular diseases. These conditions are important problems for the health sector [1–3]. The food

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