Extruded flours: applications and new functionality
Resumen/Abstract Mario Martínez Martínez Extruded flours: Applications and new functionality Resumen El trigo, el arroz y el maíz, y especialmente su parte almidonosa, son una parte importante de la dieta humana. El almidón puede ser degradado a glucosa, la cual es una fuente de energía importante para el cuerpo humano. Además, el almidón de estas harinas interesa por su efecto sobre las propiedades físicas de muchos de nuestros alimentos. Sin embargo, la innovación continua en materiales
... en materiales alimenticios y sus nuevos requisitos de calidad están forzando a adaptar aquellas materias primas a las necesidades emergentes en términos de funcionalidad y nutrición. Ésta modificación llevada a cabo mediante tratamientos hidrotérmicos están ganando protagonismo, debido, entre otras cosas, a la ausencia de ingredientes químicos o artificiales. Entre estos tratamientos, la extrusión es una de las alternativas más versátiles para lograr la gelatinización del almidón industrialmente. Resumen/Abstract Mario Martínez Martínez Extruded flours: Applications and new functionality Resumen/Abstract Mario Martínez Martínez Extruded flours: Applications and new functionality almidón de las harinas de maíz extruidas. El tratamiento enzimático en sí mismo afectó a la formación de estructuras supramoleculares resistentes, incrementando: 1) las cadenas largas de amilosa susceptibles de retrogradar; 2) el nivel de ordenamiento molecular de pequeño orden, típico de un ordenamiento conformacional de las cadenas laterales de amilosa o amilopectina; 3) y los complejos amilo-lipídicos. En concreto, la combinación de B y MA sobre las harinas extruidas incrementó: 1) el número de ramificaciones y la relación cadenas cortas/cadenas largas en la amilopectina, asociadas con almidón lentamente digestible; 2) y la cantidad de panosa y isomaltosa, catalogados como prebióticos. Resumen/Abstract Mario Martínez Martínez Extruded flours: Applications and new functionality Abstract Among cereals, wheat, rice and maize, and especially their starchy fraction, are an important part of the human diet. Starch can be degraded to glucose, which provides the body with an important source of energy. In addition, starch from these flours is important because of its effect on the physical properties of many of our foods. However, continuous innovation in foodstuff and their higher quality requirements force to adapt those commodities to the emerging needs in terms of functionality and nutrition. The modification of the functionality of starchy ingredients by hydrothermal treatments is becoming of great interest, among other things due to absence of artificial ingredients and chemicals. Among those treatments, extrusion is one of the most versatile alternatives to industrially achieved starch gelatinization. The first objective of this doctoral thesis consisted on the study of the influence of the different extrusion conditions (barrel temperature, feed rate and fed moisture content) on the physicochemical and digestive properties of gluten-containing (wheat) and gluten-free (rice) flours. An increase in the extrusion severity caused a higher amount of gelatinized starch. This gelatinised starch had a great water absorption capacity, enhancing significantly the hydration properties of flours (5-fold water binding capacity and 9-fold swelling compared with untreated wheat flour). This hydration ability leads to higher viscosity in cold solution, which might be very interesting for some food applications. Added to that, the susceptibility to enzymatic hydrolysis increased, which could indicate that these flours can be good raw materials for the starch conversion industry for the production of maltose or glucose. Nevertheless, this high susceptibility also affected negatively the starch digestion properties, decreasing the amount of resistant starch (RS) as the extrusion severity increased in both rice and wheat extruded flours. Resumen/Abstract Mario Martínez Martínez Extruded flours: Applications and new functionality with slowly digestible starch; 2) and the amount of panose and isomaltotriose, categorized as prebiotic. Contents Mario Martínez Martínez Extruded flours: Applications and new functionality Contents Acknowledgments Summary Contents Mario Martínez Martínez Extruded flours: Applications and new functionality 184.108.40.206. Application of exo-acting hydrolases in baking products 3.3. Branching enzymes (BEs) 3.3.1. Catalytic action 3.3.2. Applications of branching enzymes (BEs) 2. Objectives 45 3. Structure 47 4. Section 1: Physicochemical characterization and digestive properties of different flours according to the extrusion conditions 51 4. 1. Modification of wheat flour functionality and digestibility through different extrusion conditions 51 4. 2. Effect of different extrusion treatments and particle size distribution on the physicochemical properties of rice flour 68 5. Section 2: Effect of extruded flours on intermediate products during processing: pastes, gels and batters 86 5.1. Influence of marine hydrocolloids on extruded and native wheat flour pastes and gels 86 5.2. Influence of wheat flour subjected to different extrusion conditions on the rheological behaviour and thermal properties of batter systems for coating 119 6. Section 3: Effect of extruded flours on final products: gluten containing and glutenfree breads 135 6.1. Effect of the addition of extruded wheat flours on dough rheology and bread quality 135 6.2. Influence of the addition of extruded flours on rice bread quality 151 6.3. Texture development in gluten-free breads: effect of different enzymes and extruded flour 171 7. Section 4: Taking advantage of the high chemical reactivity of extruded flours towards enzyme catalysis 191 7.1. Physicochemical modification of native and extruded wheat flours by enzymatic amylolysis 191 Contents Mario Martínez Martínez Extruded flours: Applications and new functionality 7.2. Synergistic maltogenic α-amylase and branching treatment to produce enzyme-resistant molecular and supramolecular structures in extruded maize matrices 207 8. Discussion of the results and final remarks 230 9. Conclusions 236 Mario Martínez Martínez Extruded flours: Applications and new functionality Introduction Members of the grass family (Gramineae), in which cereal grains are included, produce dry and one-seeded fruits. This type of fruit is commonly called a "kernel" or "grain." However, strictly speaking, it is a caryopsis. Among cereals, wheat, rice and maize are the most extensively cultivated all over the world (FAOSTAT, 2013) . Wheat is the most versatile cereal due to the capacity of its storage proteins to interact and develop the gluten network, which forms the basic framework of many bakery products. Because there is a deep crease in the kernel, flour is extracted by a sequence of breaking, sieving, and size-reducing processes, known as the milling process. This process makes it possible to contemporaneously separate the bran and germ regions and to break the endosperm cells into a very fine product, suitable for rapid hydration and gluten development. Milling yield and flour refinement are closely related both to the milling conditions and the variety of wheat used. The latter highly influences the technological performance of the flour (measured by several instrument tests) and bread characteristics. As well as refined flours, increasing attention is being given to whole wheat flours that include the bran and germ fractions, which are presently considered to be by-products despite their richness in several bioactive compounds (Zhou, et al., 2014). Rice is one of the most consumed cereals. Even today, rice grains sustain two thirds of the world's population, although their contribution is different in the developing and developed countries. For instance, rice is the staple food for the Chinese and also for 65% of the total population in India. Rice is primarily consumed as milled rice. However, there are also a number of products where rice is added as an ingredient, conferring creaminess, crunchiness, and firmness. Among all the processed rice-based products that are being launched, bakery products have received special attention. Nowadays, more people are attracted to wheat-free foods because of health concerns or to avoid wheat in the diet. Moreover, rice-based products have been the solution for consumers with allergenic problems (Zhou, et al., 2014). Maize, also known as corn, is a major cereal grown throughout the world, and approximately 800 million tons of maize is produced worldwide, accounting for 35% of the total cereal production and 32% of the total area harvested for the year 2010. Maize provides 15% of total calories and protein, and 7% of fat in Africa. More than 50% of total maize is produced in America (Zhou, et al., 2014). In general, wheat, rice and maize grains are formed by the same parts and they are in approximately the same relationship to each other. Their caryopses develop within floral envelopes, which are actually modified leaves. These are called the "chaffy parts" or "glumes." In rice, the floral envelopes cover the caryopsis so closely and completely that they remain attached to the caryopsis when the grain is threshed and constitute the hull of those grains. In wheat and maize, the grain and hull separate readily during threshing, Mario Martínez Martínez Extruded flours: Applications and new functionality and the grains are said to be "naked" (i.e., to have an uncovered caryopsis). The structure of these industrially important cereal grains is important for many aspects of cereal technology, e.g., for milling of common wheat or durum wheat or for processing of maize or rice. However, it is important to highlight the high content of starch, which is around 60 and 75% of the weight of the grain. Cereal grains are an important part of the human diet, as much of the food that humans consume is in the form of starch. Starch is a major constituent of many food products, including bread, breakfast cereals, cooked rice, pasta, sauces, etc. Starch can be degraded to glucose, which provides the body with an important source of energy. In addition, starch is important because of its effect on the physical properties of many of our foods. For example, the gelling of puddings, the thickening of gravies, the structure of bread crumb and its staling, the structure of a crisp continuous, uniform layer over the food substrate, constituting its final outer coating and the setting of cakes are all strongly influenced by the properties of starch. Starch is also converted industrially into starch syrups, which are used as sweeteners in food and soft drinks as well as in several fermentation processes. Therefore, understanding the starch and its modifications will be crucial to elucidate the flour properties from cereal kernels (Delcour and Hoseney, 2010). In this introduction, the molecular, supramolecular and granular starch structures and properties will be described to later understand their modifications when they are subjected to physical and enzymatic treatments. Subsequently, the effect of physical treatments, and in particular extrusion, on starch structure and functionality will be approached. To conclude, due to the higher susceptibility to the enzyme catalysis of extruded flours, different members of the α-amylase family of enzymes will be described considering their catalytic activity towards starch of flours.