The Health Benefits of Legumes
Increasingly, food industry professionals are looking for ways to make value-added processed foods more nutritious without compromising the taste. Consumers are looking for foods that are more healthful in order to improve their diets. The addition of food legumes such as dry peas and lentils into mainstream diets in the form of flour fits with this aim and is proving a popular approach for consumers and food developers alike.
It is easy to see why. Dry peas, lentils, and chickpeas and other pulses ground into flour are high in complex carbohydrates, fiber, protein, lysine, and other phytochemicals. Pulse hulls boast a nutrient profile similar to wheat bran and an extremely high fiber content. In addition, being low in fat and sodium and rich in Vitamin B folic acid, legumes play a key role in the prevention of many health issues.
Legumes are also high in protein. An essential food component, proteins are important sources of amino acids, are necessary for physical growth and maintenance, and provide functional properties in the foods in which they are incorporated. Peas, and most notably yellow peas, are especially rich in protein, as well as starch and nutrients such as fiber, vitamins, and minerals.
In addition to the nutritional benefits, there are a range of other reasons legume flours are growing in popularity. For people who are allergic to gluten or to wheat itself, legume flour offers an excellent alternative. Non-wheat flours can also provide new and unique flavors and are especially good at thickening liquid mixtures like sauces or soups.
When it comes to baking, however, legume flours can pose some challenges. Because they produce no gluten when mixed with liquid, they require special treatment when intended to be formed into workable dough or batter that will rise, hold its shape, and deliver a pleasing texture.
Successfully incorporating legume flours as ingredients for foods is contingent on the functional characteristics and sensory qualities that the flour brings to the end-product. Functional properties include foaming, emulsification, texture, gelation, water and oil absorption, and viscosity.
Given the unique nutritional and performance attributes of legumes, the specialty diet food market is taking notice and endeavoring to meet the demands of today’s health conscious consumers. In the process, healthful, gluten and casein free alternatives are booming as a growing list of products using legume flour makes its way to grocery shelves. See Appendix C for a collection of sample formulations.
The Role of Rheological Testing
A great deal of interest has been shown in recent years regarding fortifying wheat flour with high-protein, high-lysine legume flour. Such a combination increases the protein content and bolsters the essential amino acid balance, especially of baked products like bread.
Pea flour fortification does, however, alter dough rheological properties. The aim of current research is to explore the functionality and characteristics of how pea flour interacts with wheat flour in a range of bakery products. Also being evaluated are the rheological properties of pea flour compared with wheat flour at certain ratios, as well as making a physical assessment of the dough. This is done to better understand the performance of pea flour in dough systems.
Rheological testing has become a preferred approach for examining the structure and fundamental properties of various flour doughs. Due to their characteristics and sensitive response to the structure variation of flour doughs and proteins, rheological properties are considered an effective way for predicting the processing behavior and controlling the quality of food products. This testing simultaneously measures the viscous and elastic characters of dough.
The rheological characteristics affect both what is referred to as the “machinability” of the dough and the quality of the final product. Influenced by added ingredients, the rheological profile also depends to a great extent on the crop variety, properties, and milling process used.
Gluten forms when two of the proteins in the starch in wheat flour, glutenin and gliadin, combine with water. The presence of gluten increases the viscosity of the batter due to the efficient water binding capacity of the gluten protein. When the proteins are surrounded by water and stretched, they interact and form new bonds that are strong and very elastic. Because pea flour contains no gluten, increasing the amount of pea flour in wheat flours decreases the viscosity of the batter.
Though stability decreases significantly as pea flour is added, there does not seem to be much difference in terms of protein weakening. Protein content in pea flour with hulls increases water absorption and helps lm formation, which binds large amounts of water and contributes to the viscosity of the batter. This higher water absorption may be due to the higher soluble protein content.
Increasing the amount of precooked pea flour (with or without hulls) leads to progressively darker flours than seen in wheat flour mixed with uncooked pea flour. The reason behind the color change is considered to be the result of protein and carbohydrates in wheat flour undergoing carmelization in what is called the Maillard reaction. A Maillard reaction is a non-enzymatic interaction between lysine in protein and reducing sugar. During cooking, it typically leads to development of a brown color in the pea itself. Carmelization results when carbohydrates or sugar are exposed to high temperature. An increase in the amount of uncooked pea flour in wheat flour gives the product a slightly yellowish color.
Antinutritive factors in pea flour such as polyphenols, phytic acid, and trypsin inhibitors, as well as their color and flavor, can limit the use of pea flour as an ingredient in bakery products, meat products, and snack foods. Legumes can, however, be treated to reduce the content of these antinutritive factors as well as to improve the nutritional value of the protein and remove their bean flavor.
The ability of flours to absorb and retain water and oil may help improve binding of the structure, enhance flavor retention, improve mouthfeel, and reduce moisture and fat losses of certain products.