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Analysis of Quality Protein Changes in Nixtamalized QPM Flours as a Function of the Steeping Time

¹Facultad de Ciencias Naturales, Licenciatura en Nutrición, Universidad Autónoma de Querétaro, Querétaro, México. ²Posgrado en Ciencias Químicas, Universidad Nacional Autónoma de México, Campus Cuautitlán, Cuautitlán, México. ³Departamento de Posgrado e Investigacion, Facultad de Ingeniería, Universidad Autónoma de Querétaro, Cerro de las Campanas S/N, Querétaro, México. ⁴Facultad de Estudios Superiores Cuautitlán, Universidad Nacional Autónoma de México, Campus Cuautitlán, Cuautitlán, México. ⁵Laboratorio de Neurofarmacología Marina, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Campus Juriquilla. ⁶Centro de Ciencia y Tecnología de Alimentos, Universidad del Valle de Guatemala. ⁷Facultad de Química, Departamento de Investigación en Productos Naturales, Universidad Autónoma de Querétaro. Cerro de las Campanas S/N, Querétaro, México. ⁸Unidad de Biotecnología. Campo Experimental Bajío, INIFAP. Celaya Guanajuato, México. ⁹Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, C.P. 76230, A.P. 1-1010, México. ¹⁰Corresponding author. Phone: 52-442-2381141. Fax: 52-442-2381165. E-mail: marioga@fata.unam.mx

This study showed the protein changes in Quality Protein Maize (QPM H-368C) during the traditional nixtamalization process as a function of the steeping time from 0 to 15 hr. Protein content (N × 6.25), pH, protein fractionation, reactive lysine, essential amino acids, and protein digestibility were analyzed to explain the protein quality modifications in nixtamalized corn flours (NQF). The thermoalkaline process increased significantly (P ≤ 0.05) the protein content (5.57 ± 0.86%) in NQF obtained at 3, 5, 7, 9, 11, 13, and 15 hr of steeping time compared with native corn or corn without treatment (NC). The pH values of NQF were not proportional to the steeping time and significantly different (P ≤ 0.05) between them. At 5 hr critical steeping time, the total lysine and reactive lysine content decreased severely (36 and 32%, respectively) with statistical differences (P ≤ 0.05) compared with NC. On the other hand, the tryptophan content decreased significantly (P ≤ 0.05) at steeping times of 5–15 hr (38.70 ± 6.7%) compared with NC. The changes in the lysine and tryptophan content were not proportional to the steeping time. The protein recovery in the albumin and globulin fraction diminished (P ≤ 0.05) with respect to raw corn. The protein recovery for γ-zeins, glutelin-like proteins, glutelins, and residue increased. A significant (P ≤ 0.05) decrease was found in the essential amino acids in NQF with 3–7 hr of steeping time compared with NC. Equally important was the reduction in protein digestibility observed in NQF steeped at long steeping times (11–15 hr) with significant (P ≤ 0.05) differences compared with NC. The protein solubility distribution along the steeping step and the essential amino acids location, specifically lysine in corn kernel, could explain partially the protein quality changes observed in this research. Finally, these results contribute to reconciling discrepancies associated with the protein quality modifications in nixtamalized corn reported previously in literature.