**1. Introduction**

Legumes are a cheap and healthy source of nutrition because of their high protein content and complete constituent components, such as fats, essential amino acids, complex carbohydrates, vitamins, and minerals or dietary fibre. This high protein content plays an essential role in producing functional compounds such as bioactive peptides (BPs) that benefit the health and treatment of chronic diseases. For example, BP from legumes is used as an antioxidant compound to prevent degenerative diseases such as atherosclerosis, coronary heart disease, diabetes mellitus, and cancer [1, 2]. The number of deaths due to NCDs (non-communicable diseases), especially cardiovascular disease, cancer, chronic respiratory diseases, and diabetes, increases globally, both in low-income and rich countries. As a result, NCDs are still the cause of most global deaths each year [3]. One way to reduce the risk of NCD is controlling hypertension, regulating diet and obesity.

Protease enzymes have an essential role in producing BP as a result of protein hydrolysis. Food processing, microbial fermentation, germination, or other process involving protease enzymes are examples of proteolytic processes. The involvement of protease enzymes in producing BP is significant because BP is mainly composed of 2–20 amino acids [4]. Some countries have healthy food products from legumes. Examples of fermented foods such as natto [5], douchi [6], tempe [7], and others, have antihypertensive activity. Fermented foods represent, on average, one-third of total food consumption [8]. Fermented food has a delicious taste, easy to digest, nutritious and has beneficial properties. Such as antidiabetic, hypocholesterolemic, and anti-inflammatory activities [8, 9].

Many researchers have proven (both in vitro and in vivo using experimental animals) that BP from legumes has functional properties as a healthy food. However, this functional effect depends on the stability of BP to withstand the action of digestive enzymes while in the digestive tract on its way to reach the target organs [10]. In this target organ, BP will act to provide health effects for the body. One of the determining factors to be bioavailable is the number of amino acids, hydrophobic amino acid content, and resistance to digestive enzyme activity [11]. This chapter aims to describe the quality of various legumes, the BP of legumes and their effects on health. Also, an explanation of the factors that affect the stability, absorption, bioavailability and bio-activity of BP and food technology to develop functional food.

## **2. Legume, as a source of bioactive peptides**

One of the excellent sources of essential amino acids and protein is legumes. As a source of bioactive peptides (BPs), an ingredient must have a high enough protein content. In addition, legumes also contain many components needed for body health, such as antioxidant compounds, resistant starch, dietary fibre and others [12]. However, it is a fact that the nutritional content and phytochemical composition among legumes vary widely, as shown in **Table 1**. The differences in their genetics, varieties, geographical location and climatic conditions may cause the nutritional content variation [18].

In general, the protein content of legumes ranged from 17.0 to 39.8% (w/w). Soybean is the legumes that have the highest protein content. Soybean is also the most studied legume regarding its function on health. According to FAO [22] world soybean production in 2019 was 333,671,692 tonnes (the highest among the types of legumes produced), of which Brazil produced 34.25% as the world's No. 1 producer country. Apart from soybean, some legumes also have a high protein content as a source of BPs, such as jack beans, velvet beans, lima beans, mung beans, and kidney beans (**Table 1**).

In addition to the protein content, it is also necessary to pay attention to the amino acid composition in choosing ingredients. Peptides with hydrophobic amino acids (Tyr, Phe, Trp, Ala, Ile, Val, and Met), positively charged amino acids (Arg and Lys), or contain Pro at the C end will have higher biological activity. For example, inhibition of ACE enzymes [23], Diabetes mellitus type 2 (T2DM) inhibitory activity [24], or other biological functions. Angiotensin-Converting Enzyme Inhibitor (ACEI), is a BP that affects lowering blood pressure. Meanwhile, DPP-IV inhibitors are compounds that can inhibit dipeptidyl peptidase-IV, an enzyme associated with T2DM disease [25]. So the presence of hydrophobic amino acids in short-chain peptides (between 2 and 20 amino acids in length) [4] is related to biological activities beneficial to health. Soybean, jack bean, velvet bean and mung bean are legumes that have high hydrophobic amino acid content (**Table 1**). Enzymatic breakdown through food processing produces short-chain peptides. For example, fermentation (to produce tempeh, soy sauce, natto, miso, douche, or other legume fermented products), germination (mung bean sprouts, soybean sprouts, or other sprouts), or other processes can break the polypeptide chain.


#### *Bioactive Peptides from Legumes and Their Bioavailability DOI: http://dx.doi.org/10.5772/intechopen.99979*

**Table 1.**

*Protein and hydrophobic amino acid content of several legumes.*

Apart from these benefits, legumes contain substances that are considered anti-nutritional compounds [26]. Despite having a high protein content, some toxic anti-nutritional substances limit the use of legumes. Food processing, such as soaking (hydration), cooking, autoclaving, germination, and combination, could reduce or eliminate anti-nutritional compounds [27, 28]; these processes can increase the digestibility value of protein ingredients. **Table 2** shows some of the anti-nutritional compounds present in some legumes. Kalpanadevi and Mohan [26] said that the soaking process and continued germination was less effective in removing antinutrients. However, the process would be effective if the germination process was extended (96 hours) or continued with the heating process (or autoclaving process). With this combination process, the effect of anti-nutritional compounds can be eliminated, such as phenolics, tannins, hydrogen cyanide, phytic acid, trypsin inhibitors, oligosaccharides and Phyto-hemagglutination activity.

Other researchers stated that the fermentation process is also very effective for reducing/removing anti-nutritional compounds because the fermentation process is a combination of several processes, including soaking, heating, and proteolytic hydrolysis by starter microbes [31]. For example, the process of fermenting koro bean tempe (*Canavalia ensiformis*) for 48 hours can eliminate 100% of concanavalin-A (Con-A) and reduce almost 99% of its HCN content [31]. Moreover, the fermentation process causes the percentage of peptides with MW <1 kDa to increase to the highest [33]. Short-chain peptides (between 2 and 20 amino acids) are associated with biological activities beneficial to health [4]. As shown by peptides from *Phaseolus lunatus* and *Mucuna pruriens*, peptides with MW < 1 kDa have higher ACE inhibitory activity [7, 34].


**Table 2.**

*Anti-nutritional compounds in legumes.*

*Legumes Research - Volume 2*
