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Study of Calcium Ion Diffusion in Nixtamalized Quality Protein Maize as a Function of Cooking Temperature

¹Posgrado en Ingeniería, Universidad Autónoma de Querétaro, Cerro de las Campanas S/N, Querétaro, México. ²Facultad de Estudios Superiores Cuautitlán, Universidad Nacional Autónoma de México, Campus Cuautitlán, Cuautitlán, México. ³Posgrado en Química, Universidad Nacional Autónoma de México, Campus Cuautitlán, Cuautitlán, México. ⁴Facultad de Ciencias Naturales, Licenciatura en Nutrición, Universidad Autónoma de Querétaro, Querétaro, México. ⁵Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias, Campus Celaya, Celaya, Guanajuato, México. ⁶Instituto de Física, Universidad Nacional Autónoma de México, México, D. F. ⁷Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, C.P. 76230, A.P. 1-1010, C.P. 76000, México. ⁸Corresponding author. Phone: 52-442-2381141. Fax: 52-442-2381165. E-mail: marioga@fata.unam.mx

In this report, the effect of temperature on the calcium content of Quality Protein Maize (QPM H-368C) during the nixtamalization process as a function of the steeping time for three cooking temperatures (72, 82, and 92°C) is presented. Also, for the first time, we report in physico-chemical terms the end of the cooking stage during the nixtamalization process that was established when the moisture content in corn kernels reached a value of 36% (w/w) with a lime concentration of 1% (w/v), independent of the cooking temperature. Atomic absorption spectroscopy was used to determine the calcium concentration in the whole kernel and in its different anatomical components (pericarp, endosperm, and germ) as well as in 10% of the outermost layers, the next 10%, and the remaining 80% of the endosperm as a function of the steeping time. It was found that if the cooking temperature increases, the calcium content increases also. For steeping times in the range of 5–7 hr, a relative maximum was found in the calcium contents of 0.24, 0.21, and 0.18% (w/w) in QPM H-368 flours at 92, 82, and 72°C, respectively. Calcium was found in the most external layers in the endosperm and minimum diffusion occurs in the internal 80%. Phosphorous was measured by using UV spectroscopy and the results showed that it remains constant at 0.24% throughout the process. Scanning electron microscopy analysis was used to explain the calcium ion diffusion in the kernel. The physical changes in the pericarp govern the calcium diffusion process.