Protein demand: review of plant and animal proteins used in alternative protein product development and production

Increased global usage of protein has resulted in demand for protein products to surge over the last few years. Demonstration of equivalent or superior/new functions of novel proteins compared to existing alternatives is essential to protein market success. Additional investigation of nonprotein ingredients and innovation in production technologies for alternative protein products is necessary to continue the expansion of protein offerings in the market. The demand for protein ingredients has surged over the last few years. The global protein ingredient market was valued at USD 38 billion in 2019 and is expected to grow at a rate of 9.1% from 2020 to 2027 (Grandview Research, 2020). Consumption of animal proteins has considerably increased in the recent past, as well as with a growing interest in overall protein, the market for plant protein ingredients is expected to grow significantly. Plant proteins can offset market share from animal proteins (dairy, egg, and meat) because they can be produced at competitive prices. There are multiple factors driving the demand for proteins. The animal protein market will continue to grow because of the associated health benefits of consuming meat. Dairy and other animal proteins also play a major role in demand through diet supplements and food usage. Increases in the vegan, vegetarian, and flexitarian populations have propelled the usage of plant proteins in food products. Additionally, plant proteins are being used in manufacturing a wide range of natural products. Overall, the growing food industry on account of increasing population and consumer awareness is propelling the protein market and the need for alternative protein ingredients. Furthermore, there is a global challenge to address food security and preserve land and water resources due to climate change, population growth, and changing diets. Accordingly, interest in sustainable and biodiverse food systems is on the rise. From a consumer’s perspective, purchasing habits that can improve the environment are gaining prominence. Consumers are seeking transparency and sustainability in their food supply. Accordingly, food industries are interested in commercializing products formulated with ingredients derived from environmentally sustainable crops. Another important reason for seeking novel plant protein ingredients is protein allergenicity. Eggs, dairy, and soy are among the “big eight” major allergens recognized by the Food and Drug Administration. Other opportunistic reasons include utilizing current processing streams to increase the value and revenue (adding value to byproducts), finding a unique and competitive place in the market, and utilizing all possible resources to expand the ingredients supply. Additionally, producers are seeking functional, nonallergenic ingredients that can replace synthetic ingredients (such as synthetic emulsifiers, e.g., monoglycerides and diglycerides) as part of the clean label drive. Given that proteins have multiple functions, including, but not limited to, stabilizing properties, structure building, and flavor enhancement, producers are seeking to replace synthetic ingredients with functional proteins in various applications, including high-value ones, such as encapsulation of bioactive compounds and flavors (e.g., fish oil and orange oil). Therefore, the demonstration of equivalent or superior/new functions of novel plant proteins compared to existing alternatives is essential to their market success. There is limited consumer and producer knowledge of plant proteins other than soy; nevertheless, new plant proteins are gaining traction, including pulse proteins (from pea, lentils, chickpeas, and beans) and proteins from canola, sunflower, oats, potato, rice, corn, and ancient grains among others (Grandview Research, 2016). Food producers are seeking to understand how these plant proteins can partially or wholly replace traditional plant and animal protein ingredients in food or plant-based meat-alternative products to deliver optimal nutrition, flavor, and functionality. Furthermore, advancement in nonprotein ingredient options and functionality are also in demand as these ingredients are combined with plant and meat proteins to fulfill the recipe needs (e.g., color, palatability, and shelf life) in the development of these food products. While there has been some research done to characterize novel plant proteins, the information is far from being comprehensive. Science and technology must catch up with the exponential increase in the demand for novel plant protein. There is a need to explore efficient protein extraction processes to ensure high yields and preservation of the protein quality and functionality, understand structure/function relationship, develop cost-effective protein functionalization strategies, demonstrate ways to overcome flavor and texture challenges, identify unique high-value applications, investigate crop diversity, and secure abundant supply, along with evolving the nonprotein complimentary ingredients used in combination with the plant and animal proteins to satisfy the market demand. Our goal is to provide an overview of protein fundamentals and identify innovation needs and challenges across the protein supply chain to support demand surge in protein products. Protein is a major and versatile constituent of food products (Figure 1). Apart from the nutritive value, the physicochemical and behavioral properties of proteins during processing play a significant role in determining the end quality of food. Due to the structural versatility and amphiphilic nature of proteins, they can interact with other food constituents, such as carbohydrates, fats, water, vitamins, minerals, and other proteins, through a range of interactions and bonds. In food production, animal and plant protein sources offer an array of functionality. Animal- and plant-based protein. Animal- and plant-based protein. Common animal proteins used for processing in the food industry include the following: major milk proteins of casein and whey used for viscosity and stabilization of various food matrices; egg white protein used in forming networks for stability in whipping and heating of food products; and muscle proteins (myofibrillar, sarcoplasmic, and stromal) for applications ranging from gelation to color formation. Soy and pea are two plant proteins used broadly due to excellent functional properties, such as water holding, gelling, fat absorbing, and emulsifying capacities in food products. Gluten, a protein found in cereal grains, has unique cohesive and viscoelastic properties that can form fibrous proteinaceous networks and is commonly used in alternative meat products. Rapeseed and canola oil are oilseed proteins that are gaining attraction as ingredients for plant-based protein products. These proteins provide emulsification and foaming characteristics, as well as can form gels. Lentil, lupine, chickpea, pigeon pea, mung bean, and fava bean are other legume proteins studied on their physicochemical characteristics, including foam stabilization, emulsification, and gel formation. The overview of proteins provided is the surface of available plant and animal protein options and associated functionality for food producers. Plant protein extraction and purification processes commonly begin with oil extraction, as is the case for oilseeds (e.g., soybean; Figure 2). Other initial steps in protein extraction are air classification to separate starch granules and fiber from protein bodies, as is the case for pulses, or steeping as in the corn milling process, which separates the corn into its four components, germ, fiber, starch, and protein. Cleaning and initial concentration steps for protein separation are crop dependent. Following initial separation and concentration, the protein-rich fraction is further processed to produce a protein concentrate (60–80% protein) or isolate (greater than 80% protein). Soybean field in Manitoba, Canada. Soybean field in Manitoba, Canada. The protein from any given source is a heterogeneous mixture of different types of proteins. Therefore, purifying the protein following different methods will result in different protein profile, quality, and functionality. Protein purification can be done by the following methods of membrane filtration, chromatography, salt extraction, or pH solubilization/precipitation. For commercially available plant protein ingredients, namely soy and pea protein, the most common practice is pH solubilization/precipitation. The other purification processes, though may produce a protein ingredient that is more functional, such as chromatography, membrane filtration, or salt extraction, are more involved and costly. Following pH-based extraction, the protein is solubilized at a pH (mostly alkaline, pH >7) where the protein is most soluble, while the starch and/or fiber will precipitate postcentrifugation. To separate the protein from soluble sugars and oligosaccharides, the protein is precipitated at its isoelectric point. The precipitate is washed, neutralized, and spray dried. Sometimes a diafiltration step is introduced prior to drying to reduce the amount of salt. The pH of solubilization may affect functionality, color, flavor, and digestibility. Low pH is often detrimental to the protein, causing denaturation and loss in functionality. Additionally, at alkaline pH, oxidation is favored, which can lead to browning and off-flavors in the presence of high level of polyphenols. Therefore, it is important to optimize protein purification based on the source. Proteins from different sources have different structural characteristics that contribute to differences in their solubility and reactivity under various extraction conditions. Innovation in dry and wet extraction protocols are needed to enhance protein yield and purity while maintaining structural integrity and functionality. The functional properties of the protein are dictated by the structural characteristics, including the amino acid composition and sequence, molecular size, and configuration, as well as physicochemical characteristics, such as surface hydrophobicity, net charge, and presence of reactive groups (e.g., sulfhydryl and hydroxyl groups). These characteristics can be interrelated; for example, the amino acid composition affects hydrophobicity and charge, while the sequence can affect molecular configuration, which, in turn, may affect surface properties. Surface properties affect protein solubility, thermal stability, and emulsifying and foaming properties, as well as gelation ability. For example, whey protein has very low surface hydrophobicity; therefore, it is highly soluble and is the golden standard for protein ready-to-drink beverages. On the other hand, proteins, such as soy protein, with high molecular weight and high surface hydrophobicity, may form polymers under specific conditions and can, thus, be texturized to form products with textural properties similar to meat products. Any change in the protein structure during purification and/or processing will impart a significant change in functionality. Often, protein powders are subjected to several functionalization processes, including agglomeration, lecithin coating, and high-pressure homogenization (Barbosa-Cánovas et These processes affect size, and surface properties. by forming such as starch, or as water can the while lecithin and homogenization with spray drying conditions affects protein functionality. 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