Chemical composition (moisture, total lipids, protein, and apparent amylose) and some physical features (1,000 kernel weight, hardness, and anatomical composition) were determined in 71 accessions representing races of maize from Latin America. Their microstructural characteristics (size and compaction of endosperm cell bodies, pericarp thickness, horny‐floury endosperm ratio, and morphology and size of starch granules) were also evaluated using environmental scanning electron microscopy (ESEM). Compaction was the most important microstructural feature of the maize kernels, representing kernel hardness. Highly compact kernels tended to be hard, with high protein, pericarp, and hard‐endosperm content and high pericarp thickness, but with low moisture, amylose content, and kernel weight and size. The opposite was observed in the least compact kernels. Highly compact kernels tended to have small, polygonal starch granules (<10 μm), while the least compact kernels contained large, spherical granules (>10 μm). These results suggest that microstructure is responsible for the physical features of maize kernels and that microstructure is related to chemical composition.
Seventy‐one races of maize representing races from Latin America were analyzed for microstructural features such as the degree of compaction of the endosperm cell bodies, starch granule size and morphology, and hard‐soft endosperm relationship. Flours were analyzed using rapid visco analysis and differential scanning calorimetry. Compaction grade was the most important microstructural feature of the maize kernels that related to thermal and rheological properties. Highly compact kernels developed low peak and final viscosities; small, polygonal starch granules; and required more time and higher temperature to gelatinize. The opposite was the case for less compact kernels. This indicates that the characteristic protein matrix of highly compact kernels represents a physical barrier to water migration into the granules, retarding the gelatinization process.
El grano de maíz (Zea mays L.) está compuesto principalmente por almidón, cuyo tamaño varía entre razas. El conocimiento del proceso de gelatinización del almidón provee información importante acerca de la funcionalidad, requerimientos energéticos y uso final de este cereal. El objetivo de este estudio fue investigar las relaciones entre el tamaño del gránulo de almidón y sus propiedades térmicas y de pastificado en 71 razas puras de maíz provenientes México, El Caribe, Centro y Sudamérica. Las imágenes de los gránulos se obtuvieron con un microscopio electrónico de barrido ambiental, de muestras de endospermo duro y endospermo suave. Las temperaturas y entalpía de gelatinización fueron obtenidas por medio del calorímetro de barrido diferencial. Las propiedades de pastificado se midieron con un analizador rápido de viscosidad. Se determinaron los contenidos de humedad, proteína, lípidos y amilosa aparente, así como la dureza del grano. Los gránulos pequeños gelatinizan lentamente y a altas temperaturas y entalpía. Los granos suaves mostraron gránulos más grandes en el endospermo suave y pequeños en el endospermo duro; lo contrario se observó en granos duros. La dureza presentó correlaciones altamente significativas con el tiempo y la temperatura para alcanzar el pico de viscosidad. El tamaño del gránulo de almidón correlacionó positivamente con los contenidos de humedad y amilosa aparente, pero negativamente con el contenido de proteína en el endospermo suave de las muestras.
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