Future Prospects of Plant-based Proteins
By 2050, the world's total population is expected to grow or might exceed 9 billion, and, hence, the demand for food, feed, and fibre around the globe is expected to increase by 70 per cent. To meet this increasing demand, new sources must be explored. Nowadays, food derived from plants plays a vital role in the human diet as an important source of bioactive components, such as vitamins, phenolic compounds, or bioactive peptides. Further, several thermal techniques used during food processing could be optimised to improve the quality of plant proteins. Also, they can be isolated from sustainable and cheap sources such as plant- derived wastes from agriculture and by-products of crop and oil industries, which can also regulate food waste reduction.
Recently, plant-based sources of protein have dominated the supply of proteins throughout the world (57 per cent), with the remaining 43 per cent consisting of dairy products (10 per cent), shellfish and fish (6 per cent), meat (18 per cent), and other products from animals (9 per cent). Generally, the daily intake of protein is provided by animal-based foods. However, changes in the consumers' requirement led to adoption of alternative sources of proteins for human consumption.
It is hard and expensive to extract an adequate amount of animal proteins; therefore, an alternative for improving the nutritional status of humans is mainly received from plant proteins. Hence, attention has been paid to evaluating the nutritional quality of proteins from different plant species. The best way to increase the supply of proteins is to improve the protein expression and efficiency of protein production in natural resources.
The advancement of recombinant technologies of protein production, such as engineering of expression hosts, upstream cultivation optimisation such as nutritional, bioreactor design, and physical parameters, and development of methods of protein extraction, as well as purification, has supported the growth of the market. Also, improving the protein functionality in foods through modification, enhancing the plant proteins proportion in human diets, and improving the bioavailability and digestibility of food proteins in the digestion process could be helpful to increase the overall utilisation of plant- based protein.
Based on sources, proteins from plant origin might lack some essential amino acids. For instance, cereals generally contain less lysine, whereas legumes are deficient in sulphur-containing amino acids like cysteine and methionine. However, a good amount of lysine is present in pseudocereals (for example quinoa and amaranth). Sometimes, the same plants have different nutrients due to differences in soil diversity, climatic conditions, precipitation levels, geographic latitude and altitude, agricultural practices, and different varieties/ cultivars.
Some traditional plants have been utilised by human beings as protein sources, including beans, pea, and soybean. Also, new sources such as proteins from insects and algae and unconventional and alternative protein sources like agro-industry by-products from the extraction of edible oil and those discarded by fruit processing have been discovered. In addition, different meat, milk, and egg analogs from plant-based protein sources have also been identified.
Health issues linked with plant-based proteins
There are many health concerns linked with a large intake of dietary proteins derived from plants. Antinutrients, such as tannins, phenolics, saponins, phytates, glucosinolates, and erucic acid, are naturally produced by plants and further interfere with absorption, digestion, and utilisation of nutrients present in food, with other side effects as well. The adverse effects of anti-nutrients might be maldigestion of proteins (protease and trypsin inhibitors), carbohydrates (alpha-amylase inhibitors), autoimmune and leaky gut (e.g., some saponins and
lectins), malabsorption of minerals (oxalates, phytates, and tannins), inflammation and interfering in thyroid iodine uptake (goitrogens), behavioural effects, and gut dysfunction (when converting cereal gliadins to exorphins).
However, these anti-nutrients also show beneficial health effects. For instance, at a lower level of lectins, phytates, enzyme inhibitors, saponins, and phenolic compounds, there is a reduction in plasma cholesterol, triglycerides, and blood glucose levels. Saponins may play a significant role in liver functioning and decrease platelet agglutination.
To reduce the concentration of anti-nutrients in plant proteins and their adverse effects, various treatment processes, such as fermentation, soaking, gamma irradiation, sprouting (germination), heating, and genomic technologies, have been adopted. Food processing techniques also remove most of the antinutrients like phytates, glucosinolates, erucic acid, and also insoluble fibre from canola proteins that further improve and increase the digestibility and bioavailability.
Plant-based proteins have also been linked with food allergy. Foods commonly causing allergy are tree nuts, soy, wheat, fish, peanuts, milk, shellfish, and egg. Other common food allergens based on the countries are lupines (European Union); sesame seeds (Canada, European Union, and Australia); buckwheat (Japan and Korea), and mustard (European Union and Canada). A higher number of children than adults are sensitive to dietary proteins that mainly cause allergy.
Soya protein is associated with both positive and negative health concerns. The adverse effect on health is due to the presence of isoflavones in soya protein, which are chemically similar to oestrogen and could also be bound to oestrogen receptors. Due to soy isoflavones, the issue of endocrine-disrupting effect is seen on thyroid and reproductive hormones at higher doses in rodent and in vitro cell culture studies.
It has also been reported that intake of soya protein might be linked with reducing breast cancer risk in women. Although plant-based diets are mainly linked with reducing the risk of diabetes, it is not clear that substituting the plant-based proteins for animal proteins helps in reducing the risk of diabetes in the population. Studies have shown that 5 per cent substitution of vegetable protein for animal protein was linked with the 23 per cent reduction of type 2 diabetes risk.
Food products containing plant proteins have also been known as functional foods. Various trials have been conducted to test the health benefits of plant-based proteins by observing the concentrations of insulin, blood glucose, and hormones regulating the appetite.
In addition to the nutritional quality of plant proteins and their bioactive properties, they play a major role in food processing and formulation, i.e., the production of gluten- free (GF) and protein-rich foods. Chemical and physical properties of protein help during the storage, consumption, processing, and preparation of food products.
Future prospects & challenges
Most of the plant-based proteins, like flaxseed, soya, and pea proteins, have the combined nature of various proteins with different fractions, and hence, they have a wide range of isoionic points (pi). Therefore, modulating the properties of plant-based proteins for improving their functions and formulation characteristics is essential.
A deep understanding of the functional and physicochemical properties of proteins derived from plants is necessary for improving their utilisation in food formulation and nutritional value. The presence of some particular plant residues considered as anti-nutrients is another challenge of plant-based proteins.
Furthermore, some plant-based proteins have challenges in food applications due to their bitter taste, which can be masked by various modulation techniques. The methods of modification (physical, chemical or biological) for plant-based proteins should be carefully chosen, especially in pharmaceutical and food applications, because these methods have effects on the organoleptic and functional characteristics and nutritional value of plant proteins.
The bio-efficacy of any active compounds generally depends on various factors, like digestibility, solubility, bioaccessibility, food matrix, transporters, metabolising enzymes, and molecular structures. Therefore, identifying the bioavailability of food constituents is challenging.