**Abstract**

Increased awareness on the effects of food on human health and the environment has compelled the need to look for alternative food sources. This resulted in the steady increase in demand for plant-based protein foods as opposed to animal food sources on the premises of significant health benefits, environmentfriendly sustainable production systems and moral ethics. This trend has also been reflected in recently reviewed national food guides. Research on plant-based food systems primarily aims to understand the nutritional and functional roles of dietary proteins sourced from crop seeds. Recent scientific advances in this field explore the use innovative technologies in the research and commercial applications of seed proteins. The objective of this paper is to review and summarize key research efforts and recent advances on the utility of seed-sourced proteins in the food product development applications. Important topics covered in the review are: exploration of sources of dietary protein seeds, the status of seed dietary protein research for nutrition and health, and the deployment of new and innovative technologies for developing dietary seed proteins. The topics draw on research and publications on the availability, functionality, quality, genetics, and innovative technologies to develop value-added products from dietary plant-based proteins. The review will fill knowledge gaps in the utilization of emerging plant-based protein food systems in relation to nutritional and health benefits, process technologies and promoting food system sustainability.

**Keywords:** dietary proteins, grain sources, essential amino acids, protein bio-availability, bioactive peptides, protein functionality, plant protein genetics

## **1. Introduction**

Proteins are in the class of biological macromolecules which are necessary for virtually all activities in living organisms as they engage in complex interactions among themselves and other macromolecules like polysaccharides and nucleic acids to drive cellular functions. In this sense, protein intake from food sources plays essential biological roles in the diets of humans and livestock. Among the three macronutrients (carbohydrates, fats, and proteins), protein insufficiency and deficiency in diets has been found to cause more anomalies to human health and wellbeing [1, 2]. Food-derived health issues constitutes the new threat to global food security and human health. The Food and Agriculture Organization (FAO) of

the United Nations estimated that about 15% of the world's population is chronically hungry due to nutritional inadequacy [3]. Gosh et al. [4] estimated that about 1 billion people face nutritional insecurity, suffering from myriads of nutrient deficiencies and poor health because of insufficient protein intake.

Until recently, dietary proteins have been sourced primarily from animal products including meat, eggs, dairy, and blood. However, the production of dietary proteins from animal food sources is raising adverse ecological footprint concerns. In addition, there is a need to double the present global food production by 2050 [5]. Meeting this challenge in environmentally sustainable ways compel the search for alternative protein sources. The body of literature that quantifies sustainability of animal-based versus plant-based agroecosystem models is growing and most of them found better sustainability in plant-based protein food system [6]. For example, Eshel et al. [7] estimated that by replacing meat proteins with plant alternatives, the US could save 35–50% of the Greenhouse Gas (GHG) emission. Besides this, the cultural practices in animal protein production systems are known to depleting non-renewable resources like phosphorous. Continuing the current rate of phosphorous consumption required in animal production operations was estimated to potentially depleting the limited reserves of the world's phosphorus within 50–100 years [8, 9]. Hence, besides health challenges, findings in the environment frontier warrants further research on plant-based protein alternatives.

The plant-based dietary protein supply is being sustained by the grain commodity markets. Grains constitute important ingredients of the diets of livestock and humans. Generally, grains are botanically the seeds of cereals, pseudo-cereals, and legumes commodity crops [10]. Most of the commercially available plant protein foods in the industry are made from ingredients containing crops of each of these classes of grains. A visualized analysis of FAO's [11] food production datasets in the last decade showed steady growth in the value of food ingredients used in the plantbased protein industry using the pseudo-cereals, legume and cereal crops groups (**Figure 1**). This data suggests that the availability of grain commodities in commercial quantities enable the market to meet the raw material demand for production of plant protein products.

The dominance of cereal crop production value does not necessarily interpret to growth over the years. The steady growth in the value of legumes over the last decade indicates value addition of these crops due to the shifts in the

#### **Figure 1.**

*Value of major grain commodities used as ingredients for producing plant-based protein foods over the last decade. Data adapted from FAOSTAT [11].*

**65**

*Advances in Food Development with Plant-Based Proteins from Seed Sources*

consumption of plant dietary protein sources. Over the years, growing concerns over the health implications of gluten diets common in wheat and other cereal crops compels the need to diversify the sources of plant-based proteins. For example, an analysis of the grains production dataset of cereals against pulses over the decade shows that global cereals production trails behind that of leguminous pulses (**Figure 2**), depicting the shift to gluten-free diets and the revolution of consumption of high protein crops. The consumption pattern also depicts the research investment in diversifying the sources of plant-based foods with protein composition that are suitable for the production of gluten-free foods. Moreover, concerted research efforts tend to focus on enhanced health benefits [12, 13]. Along these trends comes the growing knowledge in grain processing for plant-based protein diets, with ripple effects on research-intensive

*Gross production value of cereals and pulses grain crops over the last decade. Data from FAOSTAT [11].*

The aim of this chapter was to review recent studies on food development based on dietary protein from grain sources. The review seeks to consolidate the state of knowledge in the actively growing field of plant-based proteins that has elicited numerous publications, innovations and technologies in the last few years. In this review, we probed PubMed and associated libraries along with other sources of compelling information or datasets like FAO and WHO etc. The keywords for the calls in PubMed contained "plant-based seed proteins", covering 2010 to 2020. We probed four research themes - crop source exploration and diversification, health and functional food development, product improvement through processing for

In this section, we shall explore the scope of crop exploitation for the production of seed dietary proteins *vis-a-vis* the development of value-added products in the food industry. It should be noted that while the authors of this chapter recognize the broad diversity of seed protein sources in the plant kingdom, the main focus of this chapter is plant protein sources from the grains, which invariably constitutes the

*DOI: http://dx.doi.org/10.5772/intechopen.96273*

regulatory policies [14, 15].

**Figure 2.**

functionality, and crop genetics (**Table 4**).

**2. Exploration of dietary protein sources**

dominant input of the plant-based protein food industry.

*Advances in Food Development with Plant-Based Proteins from Seed Sources DOI: http://dx.doi.org/10.5772/intechopen.96273*

#### **Figure 2.**

*Grain and Seed Proteins Functionality*

protein alternatives.

plant protein products.

the United Nations estimated that about 15% of the world's population is chronically hungry due to nutritional inadequacy [3]. Gosh et al. [4] estimated that about 1 billion people face nutritional insecurity, suffering from myriads of nutrient

Until recently, dietary proteins have been sourced primarily from animal products including meat, eggs, dairy, and blood. However, the production of dietary proteins from animal food sources is raising adverse ecological footprint concerns. In addition, there is a need to double the present global food production by 2050 [5]. Meeting this challenge in environmentally sustainable ways compel the search for alternative protein sources. The body of literature that quantifies sustainability of animal-based versus plant-based agroecosystem models is growing and most of them found better sustainability in plant-based protein food system [6]. For example, Eshel et al. [7] estimated that by replacing meat proteins with plant alternatives, the US could save 35–50% of the Greenhouse Gas (GHG) emission. Besides this, the cultural practices in animal protein production systems are known to depleting non-renewable resources like phosphorous. Continuing the current rate of phosphorous consumption required in animal production operations was estimated to potentially depleting the limited reserves of the world's phosphorus within 50–100 years [8, 9]. Hence, besides health challenges, findings in the environment frontier warrants further research on plant-based

The plant-based dietary protein supply is being sustained by the grain commodity markets. Grains constitute important ingredients of the diets of livestock and humans. Generally, grains are botanically the seeds of cereals, pseudo-cereals, and legumes commodity crops [10]. Most of the commercially available plant protein foods in the industry are made from ingredients containing crops of each of these classes of grains. A visualized analysis of FAO's [11] food production datasets in the last decade showed steady growth in the value of food ingredients used in the plantbased protein industry using the pseudo-cereals, legume and cereal crops groups (**Figure 1**). This data suggests that the availability of grain commodities in commercial quantities enable the market to meet the raw material demand for production of

The dominance of cereal crop production value does not necessarily interpret to growth over the years. The steady growth in the value of legumes over the last decade indicates value addition of these crops due to the shifts in the

*Value of major grain commodities used as ingredients for producing plant-based protein foods over the last* 

deficiencies and poor health because of insufficient protein intake.

**64**

**Figure 1.**

*decade. Data adapted from FAOSTAT [11].*

*Gross production value of cereals and pulses grain crops over the last decade. Data from FAOSTAT [11].*

consumption of plant dietary protein sources. Over the years, growing concerns over the health implications of gluten diets common in wheat and other cereal crops compels the need to diversify the sources of plant-based proteins. For example, an analysis of the grains production dataset of cereals against pulses over the decade shows that global cereals production trails behind that of leguminous pulses (**Figure 2**), depicting the shift to gluten-free diets and the revolution of consumption of high protein crops. The consumption pattern also depicts the research investment in diversifying the sources of plant-based foods with protein composition that are suitable for the production of gluten-free foods. Moreover, concerted research efforts tend to focus on enhanced health benefits [12, 13]. Along these trends comes the growing knowledge in grain processing for plant-based protein diets, with ripple effects on research-intensive regulatory policies [14, 15].

The aim of this chapter was to review recent studies on food development based on dietary protein from grain sources. The review seeks to consolidate the state of knowledge in the actively growing field of plant-based proteins that has elicited numerous publications, innovations and technologies in the last few years. In this review, we probed PubMed and associated libraries along with other sources of compelling information or datasets like FAO and WHO etc. The keywords for the calls in PubMed contained "plant-based seed proteins", covering 2010 to 2020. We probed four research themes - crop source exploration and diversification, health and functional food development, product improvement through processing for functionality, and crop genetics (**Table 4**).

#### **2. Exploration of dietary protein sources**

In this section, we shall explore the scope of crop exploitation for the production of seed dietary proteins *vis-a-vis* the development of value-added products in the food industry. It should be noted that while the authors of this chapter recognize the broad diversity of seed protein sources in the plant kingdom, the main focus of this chapter is plant protein sources from the grains, which invariably constitutes the dominant input of the plant-based protein food industry.

#### **2.1 Comparative sources of dietary proteins**

Recently, the evaluation of protein quality shifted from raw weight or caloric estimates of food dietary content to estimates of nutrient value in foods. The emphasis of dietary protein quality now tends to be based on the bioavailability of individual nutrients measured in terms of true digestibility of amino acids, namely, the essential amino acids (EAA) content retained after digestion [16, 17]. EAAs are the amino acids that humans and experimental animal models do not produce in sufficient amounts *de-novo*, and so they must be acquired from food sources. There are nine EAAs namely; leucine, isoleucine, valine, lysine, threonine, tryptophan, methionine, phenylalanine and histidine. Fürst et al. [18] introduced the concept of conditionally indispensable amino acids in terms of adequacy especially in relation to disease conditions, thus extending the list of EAAs to include arginine, cysteine, glutamine, proline, and tyrosine.

Many studies that evaluated animal or vegetal foods for dietary proteins established that plant-based proteins have unbalanced EAA nutritional value when compared with animal-based sources [18, 19]. Growing evidences from research are however showing that the EAA content of some seed-sourced proteins are quite comparable to those of animal sources. **Table 1** shows data from a recent review of studies that compared amino acid profiles of selected high-protein seeds from cereals (wheat), legumes (soybeans), and a pseudo-cereal (quinoa) with animal food products like whey protein, casein, diary, and beef [19]. The EAA content is considerably comparable between both food sources. Though the findings have generated ambiguity in comparing protein dietary sources, some answers to this puzzle are coming from the accuracy of measurements of protein food quality in terms of the metrics of digestibility and bio-availability of their EAAs.

The measurement of protein quality in terms of digestibility and bioavailability of EAAs was revised in the early 1990s to 2012 from Protein Digestibility Corrected Amino Acid Score (PDCAAS) to Digestible Indispensable Amino Acid Score (DIAAS) [21, 22]. PDCAAS was dropped because of concerns in the capacity to


#### **Table 1.**

*Essential amino acid scores (EAA) of selected animal-and plant-based protein sources. (data adapted from Gorissen and Witard [19].*

**67**

**Figure 3.**

*FAO [11].*

*Advances in Food Development with Plant-Based Proteins from Seed Sources*

accurately evaluate protein content in terms of digestibility. Firstly, PDCAAS truncates the scores at 1.00, missing out on proteins with higher digestibility values than 1.00. Secondly, its values likely overestimate protein quality since the method uses fecal analysis to obtain protein digestibility. It misses data on nitrogen disappearance in the large intestine, which is not as a result of protein digestion and absorption, but rather to microbial degradation. On the other hand, DIAAS is considered a superior measure of protein quality because it is calculated using ileal digestibility,

DIAAS is an active area of research in the study of grain-based dietary proteins

**Figure 3** summarizes the amino-acid content of plant food sources of proteins as compiled by FAO. The visualized summary indicates a linear increase in protein and EAA contents from cereal sources to pulses and oilseed crops. The shift to pulses for grain-based proteins was recognized by the 68th United Nations (UN) General Assembly's declaration of 2016 as the "International Year of Pulses" (IYP) [30]. The UN-FAO in their implementation of the declaration recognized 12 types of pulses: dry beans, dry broad beans, dry peas, chickpeas, cowpeas, pigeon peas, lentils,

*Dietary protein and equivalent essential amino acids (EAA) of cereals and legume sources. Data from* 

[24, 25]. However, evidences from previous studies that compare grain-based dietary proteins to animal proteins typically indicate that animal proteins have higher digestibility scores compared to plant proteins in the human gut [26–29]. One of the studies on plant-based dietary proteins compared digestibility values for four animal proteins and four plant proteins in pig guts instead of rats [29]. The researchers found that the DIAAS of most of the indispensable amino acids from animal sources like whey protein isolates, whey protein concentrate, and milk protein concentrate were significantly greater (*P* < 0·05) than for pea protein concentrate, soya protein isolate, soya flour and wheat. DIAAS evaluation open new

*DOI: http://dx.doi.org/10.5772/intechopen.96273*

and the values are not truncated at 1.0 [23].

research vistas on the true quality of seed proteins.

**2.2 Seed sources of dietary proteins**

#### *Advances in Food Development with Plant-Based Proteins from Seed Sources DOI: http://dx.doi.org/10.5772/intechopen.96273*

accurately evaluate protein content in terms of digestibility. Firstly, PDCAAS truncates the scores at 1.00, missing out on proteins with higher digestibility values than 1.00. Secondly, its values likely overestimate protein quality since the method uses fecal analysis to obtain protein digestibility. It misses data on nitrogen disappearance in the large intestine, which is not as a result of protein digestion and absorption, but rather to microbial degradation. On the other hand, DIAAS is considered a superior measure of protein quality because it is calculated using ileal digestibility, and the values are not truncated at 1.0 [23].

DIAAS is an active area of research in the study of grain-based dietary proteins [24, 25]. However, evidences from previous studies that compare grain-based dietary proteins to animal proteins typically indicate that animal proteins have higher digestibility scores compared to plant proteins in the human gut [26–29]. One of the studies on plant-based dietary proteins compared digestibility values for four animal proteins and four plant proteins in pig guts instead of rats [29]. The researchers found that the DIAAS of most of the indispensable amino acids from animal sources like whey protein isolates, whey protein concentrate, and milk protein concentrate were significantly greater (*P* < 0·05) than for pea protein concentrate, soya protein isolate, soya flour and wheat. DIAAS evaluation open new research vistas on the true quality of seed proteins.

#### **2.2 Seed sources of dietary proteins**

*Grain and Seed Proteins Functionality*

glutamine, proline, and tyrosine.

**2.1 Comparative sources of dietary proteins**

Recently, the evaluation of protein quality shifted from raw weight or caloric estimates of food dietary content to estimates of nutrient value in foods. The emphasis of dietary protein quality now tends to be based on the bioavailability of individual nutrients measured in terms of true digestibility of amino acids, namely, the essential amino acids (EAA) content retained after digestion [16, 17]. EAAs are the amino acids that humans and experimental animal models do not produce in sufficient amounts *de-novo*, and so they must be acquired from food sources. There are nine EAAs namely; leucine, isoleucine, valine, lysine, threonine, tryptophan, methionine, phenylalanine and histidine. Fürst et al. [18] introduced the concept of conditionally indispensable amino acids in terms of adequacy especially in relation to disease conditions, thus extending the list of EAAs to include arginine, cysteine,

Many studies that evaluated animal or vegetal foods for dietary proteins established that plant-based proteins have unbalanced EAA nutritional value when compared with animal-based sources [18, 19]. Growing evidences from research are however showing that the EAA content of some seed-sourced proteins are quite comparable to those of animal sources. **Table 1** shows data from a recent review of studies that compared amino acid profiles of selected high-protein seeds from cereals (wheat), legumes (soybeans), and a pseudo-cereal (quinoa) with animal food products like whey protein, casein, diary, and beef [19]. The EAA content is considerably comparable between both food sources. Though the findings have generated ambiguity in comparing protein dietary sources, some answers to this puzzle are coming from the accuracy of measurements of protein food quality in

The measurement of protein quality in terms of digestibility and bioavailability of EAAs was revised in the early 1990s to 2012 from Protein Digestibility Corrected Amino Acid Score (PDCAAS) to Digestible Indispensable Amino Acid Score (DIAAS) [21, 22]. PDCAAS was dropped because of concerns in the capacity to

Histidine 2.1 2.6 3.1 1.9 2.7 2.7 3.6 Isoleucine 4.1 4.7 4.7 6.4 5.0 5.1 5.0 Leucine 6.8 8.0 7.8 9.9 8.9 9.5 8.5 Lysine 1.4 6.6 7.2 9.2 7.6 6.9 9.3

Threonine 2.5 4.0 4.5 6.7 4.3 4.0 4.8 Valine 4.2 4.9 6.1 6.3 6.3 6.2 5.2

*Essential amino acid scores (EAA) of selected animal-and plant-based protein sources. (data adapted from* 

*Scores were calculated based on EAA recommendations for a healthy human adult [20].*

**Plant-Based Proteins Animal-Based Proteins Wheat Soybeans Quinoa Whey Casein Milk Beef Essential amino acid scores (% total protein)\***

1.6 1.3 2.6 2.0 2.6 2.5 2.8

5.1 5.1 5.3 3.8 4.9 4.6 4.4

terms of the metrics of digestibility and bio-availability of their EAAs.

**66**

*\**

**Table 1.**

Methionine + Cysteine

Phenylalanine + Tyrosine

*Gorissen and Witard [19].*

**Figure 3** summarizes the amino-acid content of plant food sources of proteins as compiled by FAO. The visualized summary indicates a linear increase in protein and EAA contents from cereal sources to pulses and oilseed crops. The shift to pulses for grain-based proteins was recognized by the 68th United Nations (UN) General Assembly's declaration of 2016 as the "International Year of Pulses" (IYP) [30]. The UN-FAO in their implementation of the declaration recognized 12 types of pulses: dry beans, dry broad beans, dry peas, chickpeas, cowpeas, pigeon peas, lentils,

Bambara beans, vetches, lupins and pulses nes (not elsewhere specified – minor pulses that do not fall into one of the other categories) [30]. It's known that pulses and oilseed crops like soybeans are leguminous species, which are capable of fixing atmospheric nitrogen in symbiosis with Rhizobium (nitrogen fixing bacteria). The profile of legume proteins is mainly albumin, globulin, prolamins, and glutelin in varying compositions [31]. In grain pulses, legumin and vicilins a predominant and in soybeans there are mainly glycinin and beta-conglycinin, and 2S albumin, all of which generally belongs to the globulin family of seed storage proteins [31].

Data on digestibility and bioavailability of legume proteins in terms of DIAAS is still growing. Much of what is known thus far about DIAAS scores of digestibility of EAAs from plant-based proteins comes from comparison of food proteins in the animal guts [26–29]. There are however a number of studies reported on DIAAS of legume grains in the guts of different ages of experimental animals and humans. A recent article reported a study on the true digestibility values (percentage of the total indispensable AA from ileal extracts) of some Chinese pulses. The results of the experiment in humans older than 3 years to adults shows that DIAAS was 88% for kidney bean, 86% for mung bean, 76% for chickpeas, 68% for peas, 64% for adzuki bean and 60% for broad beans [32]. In another study, Kashyap et al. [33] used the isotopic method to estimate DIAAS for mung bean and reported that the true mean ileal IAA digestibility of mung bean was 70.9 ± 2.1% after dehulling, demonstrating inconsistencies in methodologies of amino acid digestibility and indicating research gaps and need for elaborate datasets for seed dietary protein measurements to meet the quality challenge in the development of grain-based proteins [33].

As knowledge is advancing on protein quality evaluation of plant-based food sources, Herreman et al. [34] recently published a comprehensive review of DIAAS scores for 17 various sources of dietary proteins including some seed sources. The data shows that animal sources of dietary protein have high digestibility of lysine and methionine, comparable only with pea and soybeans, while the cereal sources showed the lowest DIAASS for these EAAs (**Figure 4**). The higher digestibility estimates of lysine and methionine in potatoes and hemp than cereal

#### **Figure 4.**

*Digestibility scores (DIAAS) of limiting EAAs (lysine and methionine+cysteine) and DIAAS of 17 dietary protein sources according to the 0.5-to 3-year-old reference pattern score. Data from Herreman et al. [34].*

**69**

*Advances in Food Development with Plant-Based Proteins from Seed Sources*

seeds and some pulses as shown in in Herreman's dataset, indicates that there are non-conventional sources of plant dietary proteins besides cereals and grain legumes. There are reports on pseudo-cereals (Amaranth, quinoa, hemp, and chia) as sources of plant-based protein ingredients comparable with animal proteins in human diet because of the special functional properties [35–37]. Other workers reported the presence of high levels of limiting EAAs *i.e.* lysine and sulfur containing amino acids (methionine + cystine) in cereal and legume proteins respectively [38–40]. Mattila et al. [41] published the nutritional values for seven plant-based dietary protein sources namely: buckwheat, fava bean, flaxseed, hemp seed, lupin, quinoa, and rapeseed. The sheer volume of plant species waiting to be explored as dietary protein sources provide opportunities for more research and reviews, especially on DIAAS, to consolidate the knowledge for scaling these research outcomes.

**3. Advances in seed protein development for nutritional and health** 

Since dietary protein and it's EAAs provide nitrogen (N), which is required to support basic metabolic processes such as protein synthesis and all other cellular activities, it's crucial to the health of the living systems. Hence advances in this area of research had been very steady in the last decade. We have reviewed a number of reports on health benefits of various grain-based proteins firstly as nutrient sources

**3.1 Functional foods and nutritional benefits from seed dietary proteins**

Krajcovicova-Kudlackova [43] identified the risk of lower protein synthesis for vegans due to reduced lysine and indispensable Sulfur EAAs in many single plant-based proteins diets. That is same risk of falling short of the recommended daily allowance (RDA) for to achieve N-balance (i.e., N-loss = N-intake), which is about the efficient use of dietary proteins depending on Metabolic Demand (MD) [44–46]. This coupled with lower bio-availability of plant-based proteins compared to animal proteins compels the need to augment plant protein foods for limiting EAAs. This is the background for research on producing functional foods

and secondly as revolutionary bio-refinery health products.

Much of the interest in plant-based protein sources are driven by health reasons.

Health Canada defines functional foods as "ordinary food that has components or ingredients added to give it a specific medical or physiological benefit, other than

Because plant-based dietary proteins are not known to provide all the EAAs,

Recent reviews show that research in this area can be rounded up in two main strategies – protein complementation and fortification [47, 48]. It's however noteworthy that both research strategies work with protein/EAA quality evaluation in most of the projects. Protein complementation strategies have been studied in various combinations of blending foods that are deficient in certain EAAs with other ingredients that provides the limiting EAAs. Protein blending strategies can either be plant with plant sources, or plant sources with other protein sources to complement limiting EAAs. Márquez-Mota [49] found that blending low lysine cereal proteins (corn) with low Sulfur amino acids of legume (soybeans) proteins elicited improved metabolism (mTORC1-signaling pathway and hepatic polyribosome profile). Another published research strategy of plant protein complementation involves blending with protein of animals (casein, whey and diary) with plant-sourced ones

*DOI: http://dx.doi.org/10.5772/intechopen.96273*

**benefits**

a purely nutritional effect" [42].

with plant-based proteins.

(soybeans isolates or concentrates) [50–52].

*Advances in Food Development with Plant-Based Proteins from Seed Sources DOI: http://dx.doi.org/10.5772/intechopen.96273*

*Grain and Seed Proteins Functionality*

Bambara beans, vetches, lupins and pulses nes (not elsewhere specified – minor pulses that do not fall into one of the other categories) [30]. It's known that pulses and oilseed crops like soybeans are leguminous species, which are capable of fixing atmospheric nitrogen in symbiosis with Rhizobium (nitrogen fixing bacteria). The profile of legume proteins is mainly albumin, globulin, prolamins, and glutelin in varying compositions [31]. In grain pulses, legumin and vicilins a predominant and in soybeans there are mainly glycinin and beta-conglycinin, and 2S albumin, all of which generally belongs to the globulin family of seed storage proteins [31].

Data on digestibility and bioavailability of legume proteins in terms of DIAAS is still growing. Much of what is known thus far about DIAAS scores of digestibility of EAAs from plant-based proteins comes from comparison of food proteins in the animal guts [26–29]. There are however a number of studies reported on DIAAS of legume grains in the guts of different ages of experimental animals and humans. A recent article reported a study on the true digestibility values (percentage of the total indispensable AA from ileal extracts) of some Chinese pulses. The results of the experiment in humans older than 3 years to adults shows that DIAAS was 88% for kidney bean, 86% for mung bean, 76% for chickpeas, 68% for peas, 64% for adzuki bean and 60% for broad beans [32]. In another study, Kashyap et al. [33] used the isotopic method to estimate DIAAS for mung bean and reported that the true mean ileal IAA digestibility of mung bean was 70.9 ± 2.1% after dehulling, demonstrating inconsistencies in methodologies of amino acid digestibility and indicating research gaps and need for elaborate datasets for seed dietary protein measurements to meet

the quality challenge in the development of grain-based proteins [33].

As knowledge is advancing on protein quality evaluation of plant-based food sources, Herreman et al. [34] recently published a comprehensive review of DIAAS scores for 17 various sources of dietary proteins including some seed sources. The data shows that animal sources of dietary protein have high digestibility of lysine and methionine, comparable only with pea and soybeans, while the cereal sources showed the lowest DIAASS for these EAAs (**Figure 4**). The higher digestibility estimates of lysine and methionine in potatoes and hemp than cereal

*Digestibility scores (DIAAS) of limiting EAAs (lysine and methionine+cysteine) and DIAAS of 17 dietary protein sources according to the 0.5-to 3-year-old reference pattern score. Data from Herreman et al. [34].*

**68**

**Figure 4.**

seeds and some pulses as shown in in Herreman's dataset, indicates that there are non-conventional sources of plant dietary proteins besides cereals and grain legumes. There are reports on pseudo-cereals (Amaranth, quinoa, hemp, and chia) as sources of plant-based protein ingredients comparable with animal proteins in human diet because of the special functional properties [35–37]. Other workers reported the presence of high levels of limiting EAAs *i.e.* lysine and sulfur containing amino acids (methionine + cystine) in cereal and legume proteins respectively [38–40]. Mattila et al. [41] published the nutritional values for seven plant-based dietary protein sources namely: buckwheat, fava bean, flaxseed, hemp seed, lupin, quinoa, and rapeseed. The sheer volume of plant species waiting to be explored as dietary protein sources provide opportunities for more research and reviews, especially on DIAAS, to consolidate the knowledge for scaling these research outcomes.
