Low- and High-Moisture Extrusion of Pulse Proteins as Plant-Based Meat Ingredients: A Review

Abstract

Plant-based meat alternatives have become a major staple in the North American marketplace due to changing consumer demands. The main drivers of this market segment are changing dietary patterns, increasing numbers of consumers pursuing vegetarian and flexitarian lifestyles, rising individual income in developing countries, and an increase in global awareness of environmental concerns. Pulse crops and pulse proteins present an outstanding nutritional value chain, along with superior techno-functionality that can meet the requirements of plant proteins for producing meat analogue ingredients. In addition, pulse crops can assist in reducing carbon footprint by fixing nitrogen during agricultural production rotations. Pulse proteins also offer alternative solutions for addressing gluten-free, low-allergen, and GMO-free meat alternatives in the global marketplace. Alternative pulse-based solutions with similar sensory and texture attributes may be used to substitute for meat ingredients in new product applications. Global awareness of healthy lifestyles, increased protein intake, and rising income in developing countries have shifted eating habits toward following a well-balanced diet that consists of a complete combination of proteins, carbohydrates, lipids, and micronutrients (1). As the world population has been predicted to reach 9.5 billion by 2050, the demand for animal proteins would significantly increase due to changing consumption patterns in Asian and Southeast Asian countries (2). However, increased demand for animal-based products and their higher consumption levels may have negative impacts on the nutritional health of consumers and the environmental health of the planet (2–4). Particularly, increased use of animal-based proteins may increase carbon footprint, water consumption, and contribute to increased greenhouse gas formation. Alternative vegetable-based proteins can be considered to reduce these negative impacts and help food manufacturers develop sustainable solutions (3). Meat production has significantly increased in the United States, with 87,409 million pounds produced by November 2019 (8). The global demand for animal-based proteins has been rising as well and is expected to reach twice its current level by 2050 (2). However, the animal protein production industry may negatively affect a sustainable environment and human health. Additionally, the dietary restrictions of various cultures and high cost of animal-based proteins may limit the consumption of animal-based products (5). Thus, a new generation of North American consumers has recently started following a more sustainable and eco-friendly plant-based protein consumption pattern that 1) consumes low-cholesterol, low-fat, high-protein, and high-dietary fiber foods; 2) contributes to a sustainable food supply; 3) contributes to a reduction in pollution and ecological footprint; and 4) assists in the reduction of water consumption in the food production chain (1,2,5–7). Scientists have been conducting research on alternative protein resources that can provide bio-functionality for enhanced nutritional profile and improved techno-functionality attributes (e.g., protein solubility, gelation, water-binding capacity) compared with animal-based proteins to provide sustainable and low-carbon footprint food solutions for this growing market segment (3,7,9). Over the last two decades, pulse crops such as beans, peas, lentils, and chickpeas have received significant interest due to their sustainability benefits, high nutritional values, and technofunctionalities for producing plant-based proteins (10–13). Pulse crops play a vital role in terms of their environmental and economic contributions by decreasing the use of synthetic fertilizers by fixing nitrogen and, thus, reducing greenhouse gas emissions (14). In addition, pulse crops can provide solutions for the gluten-free industry as vegetable-based ingredients (e.g., flour, protein, starch, and fiber) that can present economic, sustainable, and nutritional benefits compared with animal-based proteins (10,12–14). In this article, we discuss the nutritional attributes and technological capabilities of pulse proteins by focusing on pea, lentil, and faba bean proteins as new alternatives for plant-based meat analogue applications. Role of Pulse Proteins in Plant-Based Foods Plant-based proteins can be produced from plant resources using dry and wet separation technologies (4,9,15). Plant-based proteins are utilized in the food industry for their techno-functionalities (e.g., solubility, gelation). In comparison to other plant-based proteins, soybean and pulse proteins are primarily used to replace and blend with animal muscle proteins for meat formulations (1,16). Soybean ingredients have a significant presence in the plant based-protein industry (3) due to their notable nutritional properties, bioavailability, and techno-functionalities, which enhance the textural characteristics of end products (1,17). Soybean ingredients (e.g., soy grits, soy protein concentrates, and soy protein isolates) have been studied extensively to address the needs of the plant-based foods industry (1,17,18). However, during the last two decades, consumers have shown significant interest in pulse proteins, including pea (Pisum sativum), lentil Lowand High-Moisture Extrusion of Pulse Proteins as Plant-Based Meat Ingredients: A Review Serap Vatansever,1 Mehmet C. Tulbek,2 and Mian N. Riaz3,4 1 Department of Plant Sciences, North Dakota State University, P.O. Box 6050, Fargo, ND 581086050, U.S.A. 2 AGT Foods R&D Centre, Saskatoon, SK S7T 0G3, Canada. 3 Department of Food Science and Technology, Texas A&M University, College Station, TX 77843, U.S.A. 4 Corresponding author. Dr. Mian Nadeem Riaz, Department of Food Science and Technology, Texas A&M University, College Station, TX 77843, U.S.A. E-mail: mnriaz@tamu.edu https://doi.org/10.1094/CFW-65-4-0038 © 2020 Cereals & Grains Association CEREAL FOODS WORLD, JULY-AUGUST 2020, VOL. 65, NO. 4 / DOI: https://doi.org/10.1094/CFW-65-4-0038 (Lens culinaris), and faba bean (Vicia faba). Pulse proteins can provide an alternative to soybean proteins as they are low in allergens, are non-GMO protein sources, and have similar amino acid attributes and digestibility scores compared with soybean proteins (1,3,7,9,11,14,17,19). Furthermore, promising techno-functionality attributes (e.g., solubility, gelling, waterbinding, and texturizing properties) of pulse proteins can provide additional benefits in food formulation systems (1,3,5,9,10,20). Structural Composition and Physicochemical Properties of Pea, Lentil, and Faba Bean Proteins Pulses are versatile crops due to their notable compositions, which consist of high protein contents, complex carbohydrates (starch, nonstarch oligosaccharides, and dietary fiber), minerals, vitamins, and phytochemicals (9,10,13,21,22). The high protein contents of peas (14–31%), lentils (21–31%), and faba beans (19–39%) are regarded as important plant-protein sources and a good fit for value-added ingredients that meet human protein intake needs (10,11,14,23,24). Pulse proteins (Table I) are composed of major storage proteins, including globulins (soluble in salt solutions) and albumins (soluble in water) and minor proteins such as prolamins (soluble in alcohol) and glutelins (soluble at dilute acid or base solution) (10,11,12,14,23,24). Pulse globulins are the primary storage proteins of pulse proteins, accounting for 70–80% of the seed proteins, and act as nutrient reservoirs during seed germinations for plant growth. Pulse globulins dissociate at different pH values with the effect of ionic strength (11,12). Based on the sedimentation coefficients of pulse globulins, globulins are classified into two main fractions: legumin (11S) and vicilin (7S). Legumin and vicilin comprise primary globular proteins in pea, lentil, and faba bean, with a legumin/vicilin ratio of 1–3:1 (11,12,21,24-27), 10.5:1 (14,26), and 2:1, respectively (23,24), and with the ratio a function of amino acid profile, surface charges, size, and extrinsic factors (e.g., processing, cultivar, and growing environment). Structural differences between globular proteins are important for the techno-functionality of pulse proteins, such as the higher gelation ability of pea vicilin compared with pea legumin (11,21, 25). In addition, pea globulins contain a minor fraction, convicilin (7S-8S) (11). Legumin (11S) is a hexamer of 300–410 kDa with six subunits (~60–65 kDa) consisting of acidic, a-chain (~40 kDa), and basic, b-chain (~20 kDa), polypeptides that are covalently linked via disulfide bridges (2,21,25) due to the presence of cysteine residues (21,28). The hydrophilic a-chains are located in the outside of the molecule, while hydrophobic b-chains are located in the interior of the molecule (11). Vicilin (7S) is a trimer of 145–190 kDa consisting of 50–70 kDa subunits. Pea vicilin contains a trimer of 150 kDa (3,11,25), while faba bean vicilin has a trimer of 158–163 kDa (12,23). Pea convicilin (7S-8S) is also a trimeric protein of 180–210 kDa, including a ~70–71 kDa subunit (3,11,25). The linkage of subunits (a, b, and g) of vicilin occurs through noncovalent hydrophobic bonding linkages due to the absence of sulfur-containing amino acids (SCAAs), such as methionine and cysteine (12,21,25). Vicilin contains more heterogeneous polypeptides through the cleavage of major subunits into lower molecular weight fragments (10, 11, 17–20, 25–30, and 30–36 kDa) than legumin (3,12,25). In addition, its carbohydrate residues, through glycosylation of the g-subunit, allow more hydrophilic surface than legumin (11,21); this carbohydrate residue was also found in lentil legumins (26). Furthermore, vicilin is a more flexible globular protein than legumin due to its higher heterogeneity polypeptide content and results in better interfacial activity, which may assist with better gel formation (2). Convic