88C-8 |
Thermomechanical properties of corn starch by dynamic mechanic spectrometry and scanning electron microscopy. |
J. F. TORO-VAZQUEZ, Facultad de Ciencias Químicas-CIEP, Univ. Autónoma de San Luis Potosí, Av. Dr. Manuel Nava 6, Zona Universitaria, San Luis Potosí, 78210, Mexico, C. A. Gómez-Aldapa, Facultad de Química-DIPA, Univ. Autónoma de Querétaro, Circuito Universitario, Cerro de las Campanas S/N, Querétaro, Mexico, A. Aragón-Piña, and E. Brito-de la Fuente, Dept. de Biotecnologia y Ciencia de los Alimentos, Univ. Autónoma de México, Facultad de Química, Mexico, 4510, Mexico. The physicochemical properties of starch depend on the interaction of several factors including the amylose to amylopectin ratio, their interchain organization within the granule, and the presence of minor components such as lipids and phosphate groups. On the other hand, starch functionality is based on the physicochemical properties resulting from the starch granules interaction with water under the main effect of the time-temperature variable (i.e., melting, viscoelasticity). The objective of this research was to evaluate the thermo-mechanical properties of corn starch pastes (80% in water) under the effect of lysophosphatidyl choline (LPC) using differential scanning calorimetry (DSC), dynamic mechanic spectrometry (DMS), and scanning electron microscopy (SEM). During the heating stage (25°-95°C, 5°C/min), the onset and peak of melting for starch with and without LPC were detected with both DSC and DMS at around 62°C and 65°C, respectively. However, when compared with starch pastes without LPC, the heat of fusion was lower when LPC was present. This effect was associated with a higher degree of starch granules integrity when LPC was present as observed by SEM. The rheograms of the d-loss angle and the G'and G" modules also showed the lower extent of starch swelling and melting occurring in presence of LPC. On the other hand, during the cooling period (95°C-25°C) the setting of the gel and its retrogradation (25°C during 120 min) were better followed by DMS and SEM than with DSC. In fact, the onset for the tridimensional arrangement of amylose to develop the gel in starch pastes, was very well detected at around 62°C by the d-loss angle obtained by DMS. In contrast, in the presence of LPC the d-loss angle of starch pastes did not show the characteristic profile associated to the tridimensional arrangement of amylose. The behavior of the d-loss angle profile and G'and G" modules for starch pastes with and without LPC were well explained by the structural changes observed by SEM in the starch granules as a function of time and temperature. Then, the use of DMS in combination with SEM provides useful information regarding the effects of additives (i.e., LPC) on the physicochemical properties of corn starch.
Session 88C, Food Engineering: Physical and Chemical Properties
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