To minimize environmental impact and to counteract growing protein requirements, food industries and the scientific community are exploring novel and alternative resources for protein. These alternative proteins can be obtained from plants, insects, or microorganism-based sources, such as single-cell proteins, making it possible to develop novel food products high in protein content.
1. Plant-Based Meat Products
Plant-based meat products are based on protein obtained from plants following processing, such as silking, extrusion, and conditioning
[1]. In the past, plant-based food materials, such as wheat, pea, rice, and peanut, have been used as meat alternatives in food products
[2]. Most plant-based meat alternatives are currently developed from soybean due its higher protein content, nutritional properties, and low price.
The major problem that needs to be solved in developing meat alternatives using plant-based sources is the reconstruction of plant protein’s globular structure into animal muscle protein’s fibrous structure. Meat’s color, taste, and flavor must also be reproduced. Plant-based meat substitutes are generally developed from soy and wheat proteins. Products made from soy proteins with 30% wheat protein substitution have attained the fibrous structure, chewiness, hardness, and texture closest to meat
[1]. Pea proteins have also been used to produce plant-based meat alternatives as they have no beany smell, which leads to greater acceptability, and are not comprised of the allergens primarily associated with proteins from soybean
[3]. Moreover, plant proteins obtained from legumes, such as lupins, chickpeas, and peanut, and grain proteins, such as proteins from corn, have been proven to be potential sources for plant-based meat alternatives
[4].
2. Cultured Meat
One of the most promising meat alternatives is cultured meat, since animal-based proteins can be obtained directly from ex vivo cultivation of stem cells without raising and slaughtering animals
[5][6]. Production of cultured meat products provides a more sustainable and environmentally friendly alternative to traditional meat production with similar flavor, taste, and nutritional profiles, so it is a potentially revolutionary meat production technology
[7][8]. The production process for the development of cultured meat can be divided into three steps: (A) preparation of raw material (e.g., preparation of culture medium and isolation of animal stem cells); (B) formation of tissue cultures, such as the proliferation and growth of stem cells in large bioreactors, for the development of tissues and muscle fibers; (C) processing of end products—developed muscle cells are processed into required meat products.
Many types of stem cells can be used to develop cultured meat, such as endothelial cells, blood cells, and fibroblasts. However, obtaining highly purified muscle stem cells is the major challenge in stem cell acquisition. For this purpose, fluorescence-activated cell sorting technology has been widely used to purify the known population of stem cells
[9]. To attain effective sorting of cells, expensive antibodies are required. In short, a culture system of various cell types is needed to selectively promote the growth of required stem cells and inhibit the growth of other cell types based on the metabolic characteristics of stem cells
[10]. Using induced pluripotent stem cell (iPSC)-based technology, efficient derivation of animal muscle protein from porcine iPSCs in culture has been achieved by Genovese et al. and proved to be helpful for the development of meat substitutes
[11] that have the potential for large-scale production in bioreactors
[12]. The development of induced pluripotent stem cells from adult cells can be used to obtain cultured meat.
3. Single-Cell Proteins
Single-cell proteins, also known as microbial proteins, are also considered as meat substitutes. These proteins are primarily used in animal feed due to their high nutritional value
[13]. This edible microbial protein industry uses wastewater from forestry, animal husbandry, and agriculture for the development of single-cell proteins; therefore, the production of these proteins is economical and cost-effective as it promotes the minimization of waste. Single proteins are currently consumed as meat alternatives after disruption of cell walls, extraction, and purification of proteins.
Single-cell proteins are comprised of eight essential amino acids that include lysine, which is usually absent in plant proteins
[8]. In addition, single-cell proteins have been proved beneficial in terms of having a wide range of producing organisms, reduced growth time, and high production efficiency
[14]. Single-cell proteins can be made suitable for human consumption by degrading the cell wall of microorganisms and removing nucleic acid
[15]. These animal proteins exhibit various advantages, such as water retention, thermal gelation ability, fiber-forming properties, and ease of digestion
[16].
In addition to single-cell proteins, edible fungi are also suitable meat substitutes due to their high nutritional value. They contain high levels of protein and dietary fiber, low levels of fat, and high levels of sulfur-containing amino acids; furthermore, some kinds of edible fungi produce a meaty flavor. These edible proteins can be attained from various species of fungi, such as
Pleurotus eryngii,
Lentinus edodes,
Agaricus bisporus,
Pleurotus ostreatus, and
Flammulina velutipes. Edible fungal protein is cost-effective and economical compared to plant/animal or bacterial proteins. Some edible fungi are easy to cultivate and harvest. Moreover, these proteins have healthy, beneficial biological activities; additionally, they are widely accepted by consumers in terms of their safety and health benefits
[17]. Further studies o disputing the necessity of animal proteins are needed to increase consumer acceptance of these proteins.
4. Insects
Insects are a significant source of protein and are used as animal feed to provide sustainable protein content. Insects are comprised of primary fat content (PUFA), protein, minerals, and vitamins. Moreover, they utilize low levels of land and water resources and produce fewer greenhouse gases
[15][18]. Significantly, they feed on organic waste, garbage, and other waste streams. They can significantly reduce environmental pollution and production costs. Nearly 1900 species of insects have been found to be suitable for consumption as human food. Compared to chicken, cattle, and pigs, the feed conversion efficiency of insects is significantly higher, leading to a reduction in food wastage
[19]. The insect species traditionally consumed are different for different regions of the world, but beetles are consumed commonly in various parts of the world. Crickets and mealworm larvae are the two most common insects used in food and feed industries
[20].
However, various factors limit the use of insects as meat substitutes; most prominently, consumer acceptance and issues regarding food safety. Food safety issues include the aflatoxin content exceeding the limit of 10 microgram/kg in some edible dried insects
[21]. Some insect proteins can contain allergens and pathogenic bacterial strains
[19][22]. Insects have significant potential to be used as meat substitutes if they can achieve higher customer acceptance by being carefully treated, safely farmed, and carefully processed.
Table 1. Protein content and different functional properties of various alternative proteins.
Protein Type *
|
Protein Content (%)
|
Functions
|
References
|
Plant-based proteins
|
Soybean
|
40
|
Gelation, fiber formation, emulsification, coil binding
|
[23]
|
Pea
|
20–25
|
Fiber formation, gelation, emulsification
|
[24]
|
Cowpea
|
40
|
Gel formation, emulsification, foaming, thickening
|
[25][26]
|
Zein (corn)
|
45–50
|
Solubility, foaming, moisture adsorption
|
[27]
|
Faba bean
|
29
|
Improve physical and oxidative stability of oil in water emulsions
|
[28]
|
Wheat
|
14
|
Elasticity, extensibility, fibrous structure
|
[29]
|
Insect-based proteins
|
Telegryllus emma (cricket)
|
54–56
|
Water-holding capacity, oil-holding capacity
|
[30]
|
Protaetia brevitarsis (larvae)
|
43–45
|
Gelation
|
[30]
|
Schistocerca gregaria (locust)
|
76
|
Foaming properties
|
[31]
|
|
Zophobas morio
(larvae)
|
24–26
|
Gel formation, emulsification
|
[32]
|
Single-cell proteins
|
Saccaromyces cerevisiae (sugarbeet bagasse)
|
45–49
|
Foaming, emulsion, bulk density
|
[33]
|
* At the moment, information about cultured meat’s protein content and functional properties is extremely limited.
This entry is adapted from the peer-reviewed paper 10.3390/su142215370