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.

La calidad del maíz (Zea mays L.) ha sido el principal criterio de selección utilizado por nuestros ancestros para su mejoramiento. De hecho, gran parte del maíz que consume nuestra población ha estado sujeto durante siglos a la selección por sabor, aroma y textura en diferentes productos. Sin embargo, las clasificaciones y los registros de razas, híbridos y variedades se han hecho desde el punto de vista agronómico, citológico y taxonómico, y existen pocos estudios sobre la evaluación de sus propiedades físicas y de calidad. El presente trabajo de revisión tiene por objetivo analizar los resultados que se han publicado en el contexto de la calidad de los maíces nativos (razas) de México, y compararlos con las clasificaciones agronómicas de las razas. Los datos analizados muestran que las clasificaciones agronómicas de los grupos raciales del maíz en México, aunque importantes para el manejo en programas de mejoramiento, no presentaron relación directa con los aspectos de calidad para tortilla y otros usos. La dureza de grano o el índice de flotación fueron las características más relacionadas con el desempeño de las razas en el procesamiento y calidad de los productos y pudiera ser importante incorporarlas a los sistemas de clasificación.

Las poblaciones y tipos de maíces (Zea mays L.) adaptados a condiciones de temporal o secano poseen atributos que pueden ser útiles en el mejoramiento genético. En el Estado de Coahuila, México, se ha identificado la presencia de siete grupos raciales. El objetivo del presente trabajo fue evaluar agronómicamente y determinar el potencial de rendimiento de grano de 90 poblaciones de maíces criollos recolectadas en el Estado de Coahuila. La evaluación agronómica se hizo en 2008 y 2009, en dos localidades: El Mezquite, Galeana, Nuevo León (1890 m) y General Cepeda, Coahuila (1350 m). La combinación de años y localidades fue considerada como cuatro ambientes (MEZ08, MEZ09, GC08 y GC09). Las poblaciones fueron agrupadas de acuerdo con la altitud de procedencia en: bajas (0 a 1000 m), intermedias (1001 a 1800 m), transición (1801 a 2000 m) y de altura (más de 2000 m). Los resultados mostraron diferencias (P ≤ 0.01) entre grupos y en la interacción grupos x ambientes, para floración masculina y rendimiento de grano; también se encontraron diferencias (P ≤ 0.01) entre poblaciones dentro de grupos y en poblaciones dentro de grupo x ambientes. El análisis de la interacción poblaciones x ambientes permitió identificar tres grupos según su adaptación a las localidades: el primero, con adaptación a El Mezquite (33.3 %), el segundo a General Cepeda (42.2 %), y el tercer grupo (24.4 %) con estabilidad a través de ambientes. Las poblaciones 19, 22, 34 y 61 tuvieron adaptación a El Mezquite; las poblaciones 74,76 y 88 a General Cepeda; y las poblaciones 35, 37, 38, 64, 66 y 81 mostraron estabilidad a través de ambientes. Los grupos raciales con mayor potencial de rendimiento fueron Tuxpeño, Tuxpeño Norteño y Ratón.

The final ADD in the part is affected by a number of factors: the tool elements (materials, surface, roughness, etc.), During powder compaction, frictional forces between slenderness, springback, powder behaviour, geometry of the the compact and the tool elements are developed. This final compact, number of punches, presence of lubricants,1 causes pressure gradients in the compact, which proand, fundamentally, the compaction process sequence duces, at the same time, undesirable density differences.(CPS).2 The effect of almost all of these factors is well This work presents a study about the effect of the known,3 but no references have been found where the CPS compaction process sequence (CPS) and the ejection is a variable of study. process on the axial density distribution during the An important fact that contributes to the generation of uniaxial double ended pressing process of a high the axial density gradient in the compacts is the axial slenderness bushing. Different pressing processes were pressure losses during the pressing compaction, as a conselected and carried out with a hydraulic press at sequence of the friction between the compact that is being laboratory and industrial levels (differences in the pressed and the tool elements. In the last three decades, extraction method). Compacts were presintered and many researches have faced the pressure losses with depth cut into thin discs in order to measure the local densities problem, and the well known formula giving the law of along the part, using the Archimedes' method. The pressure decrease as a result of the wall friction during the obtained results show that the compaction process powder pressing has been obtained.4 sequence has an important effect on the axial density It is worth mentioning that to improve the ADD, lubricants distribution in a green compact, mainly in the case can be blended with the powders, but the theoretical density of compacts of high slenderness (>5). The ejection of the compacts drops when the lubricant content increases. causes in the compact a post-compaction modifi-Furthermore, they have to be removed prior to the sintering cation of the axial density distribution. Therefore, it is process, so that it is always convenient to incorporate the necessary to optimise the pressing process to obtain lower quantity of lubricant, in order to obtain the best an adequate density distribution for each specific part.compaction and sintering process. PM/0941This work deals with the study of the effect of the CPS and the ejection process on the ADD, for a particular bush-Dr Sa ´nchez, Dr Boları ´n, Dr Coren ˜o, and Dr ing compact. A modified equation of pressure losses during Martı ´nez are at the Universidad Auto ´noma del axial compaction is proposed to try to explain the results Estado de Hidalgo (UAEH), Centro de Investigaciones obtained for different uniaxial pressing processes (single de Materiales y Metalurgia (CIMyM), Ciudad ended and sequential double ended).