**2. Agricultural co-products as a source of bioactive peptides**

Agricultural co-products involve a vast variety of materials with great potential as a substrate for bioactive peptide production due to the low value and high protein content. It is estimated that about 9000 tons in dairy, 3 and 9 million tons in seafood and livestock industries, respectively, are annually discarded [4]. Skins, bones and heads are rich in collagen. Collagen is known as a promising source of peptides with several bioactivities which could exert physiological functions. Collagen comprises of hydrophobic amino acids, particularly proline and hydroxyproline, offering a higher chance of being absorbed through epithelial membrane. These amino acids also make them stable against proteases in gastrointestinal digestion tract and brush border, so that the intact peptides could be absorbed and reach the target organ. Blood is also high-protein co-product obtained in a large volume in a slaughterhouse. It has been reported that about 2.5 billion tons of blood are annually generated only in Europe [5]. Hemoglobin in red corpuscles and albumin, globulins, and fibrinogen in plasma are the major proteins [6]. Whey is a predominant co-product of dairy industry with an annual production of approximately 180–190 million tons [7]. The whey-derived peptides have also lower allergenicity beyond their bioactivities, because β-lactoglobulin (β-lg) as a main whey protein contributing to allergenicity would degrade within hydrolysis process [8].

Production of bioactive peptide from some plan-based materials are restricted due to difficulties in protein recovery from their unique rigid structure of polysaccharides. To meet the challenge, pretreatment of these substrates would improve protein recovery and provide other benefits such as reduction of time and energy consumption, leading to a higher efficacy in bioactive peptide production [9]. Corn gluten meal was immersed in alkali solution, treated with α-amylase and cooked prior to proteolysis [10]. Ultrasound exposure of watermelon seed caused structural changes, leading to production of peptides with higher antioxidant activity than those without any treatment. Ultrasound could degrade interactions in matrix and unfold proteins, so that more hydrophobic residues and reactive sites are exposed, resulting in a higher efficacy in protein hydrolysis [9]. Oat bran polysaccharide was digested by cellulase and viscozyme to ease protein recovery prior to proteolysis and production of antioxidant peptides [11].

**159**

*Bioactive Peptides from Agriculture and Food Industry Co-Products: Peptide Structure…*

with production of about 50–60 and 90 million tons every year, respectively. Albumin, globulin, prolamin and glutelin are the major proteins in bran with a total protein content of 12–20% [12]. Seeds are also another source of bioactive peptides, among them those harvested for oil production generate a large mass of co-product. Soybean, rapeseed and canola meals with the crude protein contents of about 48, 36 and 38%, respectively, are important cases of protein-rich co-products obtained from oil industries [13]. Corn gluten meal is also a major proteinaceous co-product generated in a large quantity from corn wet milling process in which, zein and glutelin are the main proteins (68 and 28%, respectively). Zein composes of mainly hydrophobic amino acids by which, more hydrophobic peptides are likely produced [14]. Hydrophobicity is an important feature of peptides to exert some bioactivities

Bran from rice and wheat, is a main protein-rich co-product in cereal industry

Thus far, peptides with various bioactivities *in vitro* and *in vivo* levels have been recognized from these low value co-products. Conversion of these co-products to more value-added hydrolysates and/or peptides would ultimately lead to develop-

Several bioactivities and physiological functions of peptides derived from both animal- and plant- based agricultural co-products have been reported. These activities include antioxidant, antihypertensive, antidiabetic and antibacterial properties.

Reactive oxygen species (ROS) are formed during normal cellular metabolism of providing energy, respiration and also when cells are exposed to exogenous oxidative stress [15, 16]. Normally, these products are neutralized by endogenous antioxidant defense systems, such as antioxidant enzymes (superoxide dismutase: SOD, glutathione peroxidase: GPx and catalase), glutathione (GSH) and others. But, the excessive level of ROS could result in many health disorders, such as cancer, cardiovascular, respiratory, neurodegenerative and other diseases [16, 17]. Therefore, antioxidant-containing diet could help to overcome ROS and subsequently their corresponding disorders. Nowadays, attempts have been made to find new antioxidant compounds from natural resources due to their benefits over synthetic compounds. To that direction, antioxidant peptides from agricultural co-products are gaining more attractions, because of their nontoxicity and safety besides their nutritional properties. Antioxidant hydrolysates/peptides production from agricultural coproducts including skins, bones, viscera, whey as animal-based and brans, seeds, leaves, gluten as plant-based co-products have been extensively reviewed [17–21]. Lower molecular weight (MW) peptides with hydrophobic and aromatic amino acids (HAAs and AAA, respectively) have been generally reported to exert good antioxidant activities [22]. The HAAs could improve peptides accessibility toward ROS through binding with lipid and reaching to free radicals, so that the peptides could quench them effectively. The AAAs including Trp, Phe and Tyr are also correlated with the strong antioxidant activity via their high electron transferring capacities of their aromatic rings. Besides HAAs and AAAs, some of hydrophilic amino acids, such as His could improve the activity through its imidazole ring which has been indicated as strong electron donator [23]. Presence of charged amino acids in peptide structure could also improve the activity. A higher negatively charged amino acids (NCAA) have been observed in plasma hydrolysates prepared from

*DOI: http://dx.doi.org/10.5772/intechopen.94959*

such as antioxidant and antihypertensive properties.

ment of health promoting food products.

**3. Biological activities**

**3.1 Antioxidant activity**

*Bioactive Peptides from Agriculture and Food Industry Co-Products: Peptide Structure… DOI: http://dx.doi.org/10.5772/intechopen.94959*

Bran from rice and wheat, is a main protein-rich co-product in cereal industry with production of about 50–60 and 90 million tons every year, respectively. Albumin, globulin, prolamin and glutelin are the major proteins in bran with a total protein content of 12–20% [12]. Seeds are also another source of bioactive peptides, among them those harvested for oil production generate a large mass of co-product. Soybean, rapeseed and canola meals with the crude protein contents of about 48, 36 and 38%, respectively, are important cases of protein-rich co-products obtained from oil industries [13]. Corn gluten meal is also a major proteinaceous co-product generated in a large quantity from corn wet milling process in which, zein and glutelin are the main proteins (68 and 28%, respectively). Zein composes of mainly hydrophobic amino acids by which, more hydrophobic peptides are likely produced [14]. Hydrophobicity is an important feature of peptides to exert some bioactivities such as antioxidant and antihypertensive properties.

Thus far, peptides with various bioactivities *in vitro* and *in vivo* levels have been recognized from these low value co-products. Conversion of these co-products to more value-added hydrolysates and/or peptides would ultimately lead to development of health promoting food products.
