Functional properties of pulse protein largely vary by its chemical composition and isolation methods. Physicochemical and functional properties of pulse protein include solubility, water and fat binding, emulsification, foaming, gelation and viscosity. Some of these properties may be affected by processing such as thermal processing and acid/alkali processing as the processing tends to denature the protein, resulting in altered structure of protein. Water binding capacity of protein are higher when protein is denatured; thus, wet processed protein isolate/concentrate have higher water binding capacity than air classified proteins. Furthermore, different fractions of protein contribute to the difference in water binding capacity. Protein competes with starch for water and absorbs water quicker than starch particles. Film forming capacity of protein contributes to the emulsifying property by coating oil droplets dispersed in an aqueous phase (Boye et al. 2010).
Promising potential of pea protein as an egg replacer is currently being explored. Wet extraction processing by hydrolysis seemingly improves the emulsifying properties in some pulses (Braudo et al. 2001, Obatolu et al. 2007). See chapter 7 for more on the application of pulse protein. Foam capacity and foam stability are important functionalities in food applications such as beverages, cakes and whipping creams. High gelling properties of pulses are attributes of both protein and starch.
Fractionated starch is considered as a byproduct of protein fractionation, as the same processing are used to produce both products. Enabling to achieve up to 98% purity, pea starch isolates are distinctive for their excellent gel strength and bland taste. Such features, along with the ability to contribute to increased volume and expansion in extruded products and puffed snacks, make pea starch perfect for inclusion in cookie and cracker formulations as well as Asian-style noodles. Starch produced with wet fractionation typically contains 75–90% starch, less than 1% protein, and less than 0.5% of fat content. In contrast, dry milled starch is typically less purified with more damaged starch with up to 70% starch, 6–10% protein, and 1–2% fat. Starch from yellow pea is known for its high amylose content and high gelling capacity. Amylose content of yellow peas generally varies depending on varieties and growing conditions ranging from 25% to 50%, which is higher than some of major cereal crops such as wheat, rice and corn in general.
Two major dietary fibers present in pulses are soluble and insoluble dietary fiber. In case of whole pulses, higher insoluble dietary fiber is typical because most of the insoluble fiber is found in the hull. This fiber is often referred to as outer fiber. In contrast, soluble fiber in the cotyledon (inner fiber) makes up more of the fiber composition than in the hull. These fibers vary in its chemical compositions. Cotyledons contain more than 50% of pectic substances, approximately 10% of cellulose and 6–12% of non-starchy non-cellulosic glucans whereas the majority of hulls are cellulose, although the amount varies among varieties and growing conditions (Tiwari and Cummins, 2011).
Commercially available pulse fiber is obtained as a byproduct in split pea production and the removed hull is milled into flour to be used as a fiber, which may contain approximately 80% fiber. However, hulls contribute to the off flavor of pulses and certain antinutrients including polyphenols and tannins. Heat treatments are often used to inactivate enzymes and antinutrients, which reduces negative effects from these compounds. Thermal processing apparently changes both soluble and insoluble fiber contents; yet, there has not been an agreement on how specific processing affect these dietary fiber contents. Pulse fiber fractionation can employ both dry and wet methods; however, the effect on chemical, nutritional and functional properties of fiber has not been sufficiently investigated.
Functionalities of fiber include bulk density, water holding capacities, viscosity, and fat binding capacity. Due to bulky nature of fiber, pulse flour and fiber tend to have higher volume. Water retention capacity increases product yield through increased water addition, it also increases the moisture content of the final product, decrease fat absorption and modifies texture profile. Fat binding capacity of pulses help stabilize high fat products.