Digestion of food proteins: the role of pepsin

“…have determined the milk coagulation properties with different apparatus, which are summarized by Troch et al. (2017) and Lucey (2002), including rheology, microscopy (Everett 2007 Gilbert 2009; Gilbert 2019; Adams et al. 2019; de Kruif 2014; Gilbert 2023; Bayrak et al. 2021; Yang et al. 2025).”

“The major globulins observed in pulse legumes can be subdivided into 11S and 7S globulins, for example, legumin (11S) and vicilin (7S) in pea, and glycinin (11S) and β-conglycinin (7S) in soybean (Han et al. 2022).”

“Native ovotransferrin and lysozyme can be rapidly hydrolyzed by pepsin (Liu et al. 2017; Liu et al. 2018; Yoshino et al. 2004), whereas ovotransferrin is more susceptible to pepsinolysis than ovalbumin and lysozyme (Liu et al. 2017; Fu, Abbott, and Hatzos 2002; Moreno 2007).”

“Based on the solubility differences in various solvents, plant proteins have been distinguished as water-soluble albu-mins, salt-soluble globulins, alcohol-soluble prolamins, and dilute alkali/acid-soluble glutenins, respectively (Osborne 1924; Fallahbaghery et al. 2017).”

“…and pH in the gastric environment (Culioli and Sherman 1978; Kameswaran and Smith 1999; Mohamed A Mehaia and El-Khadragy 1998), heat treatment of proteins (Wilson and Wheelock 1972; Anema, Kim Lee, and Klostermeyer 2007), and the type of mammals from which the milk is obtained (Roy et al. 2020b).”

“As temperature affects pepsin activity (Zhao et al. 2011) and enzyme-induced milk coagulation behavior (Nájera, De Renobales, and Barron 2003; Dalgleish 1983; Horne and Lucey 2014), milk temperature has a profound effect on the structural organization of pepsin-induced curd.”

“Hemoglobin digestive activity was determined at pH 2.0 (Foltmann 1992; nielsen and Foltmann 1995; tang et al. 1959). c assay at pH 6.3 (Foltmann 1992; tang et al. 1959). the value of porcine pepsin B is estimated from a “caseogram” assay (Foltmann, szecsi, and tarasova 1985). the highest value is…”

“…used model relies on the use of a first-order reaction; for example, a two-parameter kinetic model has been applied to simulate the digestion of milk proteins under conditions of moderate enzyme inactivation (Margot, Flaschel, and Renken 1997; Yang et al. 2022; Carlson, Hill, and Olson 1987a).”

“During in vitro gastric digestion, pepsin hydrolyzes the ovomucoid almost completely, producing free amino acids and di-and tri-peptides (Jiménez-Saiz et al. 2011; Matsuda et al. 1985; Kovacs-Nolan et al. 2000; Abeyrathne et al. 2015).”

“Not all four caseins may be required to construct a casein micelle, as human milk and elephant milk do not contain either of the α s -caseins (Lönnerdal 1996, Madende et al. 2015).”

“Physicochemical processes and pretreatments, such as pulsed electric fields, high-pressure processing, and cooking, affect digestive processes, thereby affecting the release and bio-availability of amino acids (Gong et al. 2020; Bhat et al. 2021b).”

“In addition, the structure formed during digestion plays an important role (Ye 2021); for example, the proteins from cow milk will coagulate, whereas oat “milk” does not show substantial changes in structure and physical stability during in vitro gastric digestion with pepsin (Xin Wang et al. 2022).”

“Legumins (11S) are degraded more by pepsin than by trypsin, leading to a small decrease in IgE binding capacity (van Boxtel et al. 2008; Bavaro et al. 2018; Mattison, Grimm, and Wasserman 2014; Orruño and Morgan 2011).”

“The initial step in protein digestion is degradation at the acidic pH in the stomach and hydrolysis by the action of pepsin with varying substrate specificities (Whitecross et al. 1973; Silk, Grimble, and Rees 1985).”

“During in vitro gastric digestion, pepsin hydrolyzes the ovomucoid almost completely, producing free amino acids and di-and tri-peptides (Jiménez-Saiz et al. 2011; Matsuda et al. 1985; Kovacs-Nolan et al. 2000; Abeyrathne et al. 2015).”

“…caseins in the micelle interior and the aqueous environment. κ-casein can be specifically hydrolyzed by pepsin at a relatively high pH (>5) (Plowman and Creamer 1995; Kageyama 2002); therefore, several changes occur for milk proteins in the gastric environment with decreases in pH during…”

“…used model relies on the use of a first-order reaction; for example, a two-parameter kinetic model has been applied to simulate the digestion of milk proteins under conditions of moderate enzyme inactivation (Margot, Flaschel, and Renken 1997; Yang et al. 2022; Carlson, Hill, and Olson 1987a).”

“…amino acids, and preferably aromatic amino acids, such as tryptophan, tyrosine, and phenylalanine (Mohseni-Shahri, Moeinpour, and Nosrati 2018; Inouye and Fruton 1967; Fujimoto et al. 2004), whereas it does not hydrolyze bonds containing valine, alanine or glycine (Monogioudi et al. 2011).”

“The coagulation behavior of proteins depends on several underlying phenomena: the rate of enzymatic action, the critical degree of hydrolysis of κ-casein for curd formation, and the rate of aggregation of destabilized casein micelles (Garnot and Corre 1980).”

“…for hydrolyzing bonds adjacent to aromatic and hydrophobic amino acids, such as phenylalanine, tyrosine, tryptophan, and leucine (Dunn 2002; Inouye and Fruton 1967), with an optimum pH of approximately 2.0 (Kondjoyan, Daudin, and Santé-Lhoutellier 2015; Pletschke, Naudé, and Oelofsen 1995).”

“…used model relies on the use of a first-order reaction; for example, a two-parameter kinetic model has been applied to simulate the digestion of milk proteins under conditions of moderate enzyme inactivation (Margot, Flaschel, and Renken 1997; Yang et al. 2022; Carlson, Hill, and Olson 1987a).”

“…have determined the milk coagulation properties with different apparatus, which are summarized by Troch et al. (2017) and Lucey (2002), including rheology, microscopy (Everett 2007 Gilbert 2009; Gilbert 2019; Adams et al. 2019; de Kruif 2014; Gilbert 2023; Bayrak et al. 2021; Yang et al. 2025).”

“Consequently, milk coagulation time is inversely dependent on enzyme concentration (Figure 3B3) (Dalgleish 1993; Carlson, Hill, and Olson 1987a; López, Lomholt, and Qvist 1998; Foltmann 1959; Hyslop, Richardson, and Ryan 1979).”

“For example, insoluble aggregates form in an ovotransferrin/lysozyme mixture and lysozyme/ovalbumin mixture when heated above 70 °C, at pH 9 (Matsudomi, Takasaki, and Kobayashi 1991; Matsudomi, Yamamura, and Kobayashi 1986).”

“The most commonly found glutelin is that found in wheat (glutenin), although glutelins are also present in barley and rye (Shang et al. 2005).”

“Native ovotransferrin and lysozyme can be rapidly hydrolyzed by pepsin (Liu et al. 2017; Liu et al. 2018; Yoshino et al. 2004), whereas ovotransferrin is more susceptible to pepsinolysis than ovalbumin and lysozyme (Liu et al. 2017; Fu, Abbott, and Hatzos 2002; Moreno 2007).”

“This, in turn, affects the passage of gastric chyme, further degradation of proteins and peptides, and the absorption of free amino acids in the small intestine (Moughan 2009).”

“Human milk β-casein and bovine milk κ-casein are sufficient to produce reassembled casein micelles (Sood, Erickson, and Slattery 2002).”

“However, recent work indicates that structural changes induced by alkali extraction improve the in vivo digestibility of prolamin (Kubota et al. 2010; Kumagai et al. 2006; Kubota et al. 2014).”

“The trypsin inhibitory activity of ovomucoids is reduced by pepsin digestion (Konishi et al. 1985), but the residual activity may help maintain the integrity of ovomucoid peptide fragments (Kovacs-Nolan et al. 2000).”

“For α S2 -casein, except for regions 34–59 and 198–207, which barely provided any proteolytic fragments, peptides were distributed throughout the entire protein sequence (Lisson, Lochnit, and Erhardt 2014).”

“Not all four caseins may be required to construct a casein micelle, as human milk and elephant milk do not contain either of the α s -caseins (Lönnerdal 1996, Madende et al. 2015).”

“However, humans show wide variations in gastric and pancreatic secretions, which vary with the type of food consumed (da Silva Gomes et al. 2003; Armand et al. 1996).”

“…have determined the milk coagulation properties with different apparatus, which are summarized by Troch et al. (2017) and Lucey (2002), including rheology, microscopy (Everett 2007 Gilbert 2009; Gilbert 2019; Adams et al. 2019; de Kruif 2014; Gilbert 2023; Bayrak et al. 2021; Yang et al. 2025).”

“After heat treatment (95 °C for 5 min), the Phe 105 -Met 106 bond of κ-casein was reported to be less accessible to pepsin, leading to inhibition of the hydrolysis of κ-casein (Yang et al. 2023b).”

“Li, Zhao, et al. (2020) observed poor digestibility of myoglobin owing to its low susceptibility to pepsin (from porcine gastric mucosa, CAS No. 9001-75-6) digestion, brought about by the rigid structure of the hydrophilic surface and hydrophobic pocket (Kaur, Banipal, and Banipal 2017).”

“By changing the pH to 2, native ovalbumin could be more extensively hydrolyzed by porcine pepsin (Kitabatake, Indo, and Doi 1988).”

“For example, insoluble aggregates form in an ovotransferrin/lysozyme mixture and lysozyme/ovalbumin mixture when heated above 70 °C, at pH 9 (Matsudomi, Takasaki, and Kobayashi 1991; Matsudomi, Yamamura, and Kobayashi 1986).”

“Ovomucoid comprises three tandem domains, each cross-linked by three intradomain disulfide bonds, which lead to resistance to proteolytic digestion and heat denaturation (Matsuda et al. 1985; Kovacs-Nolan et al. 2000; Kosti et al. 2013; Shin, Han, and Ahn 2013).”

“The hydrolysis rate and extent of a globulin protein fraction by pepsin (from hog stomach mucosa, 3200 units mg −1 ) was at least twice that of the albumin protein fraction (Bhatty 1988).”

“He et al. 2022).”

“…have determined the milk coagulation properties with different apparatus, which are summarized by Troch et al. (2017) and Lucey (2002), including rheology, microscopy (Everett 2007 Gilbert 2009; Gilbert 2019; Adams et al. 2019; de Kruif 2014; Gilbert 2023; Bayrak et al. 2021; Yang et al. 2025).”

“…several factors, such as the pepsin concentration and pH in the gastric environment (Culioli and Sherman 1978; Kameswaran and Smith 1999; Mohamed A Mehaia and El-Khadragy 1998), heat treatment of proteins (Wilson and Wheelock 1972; Anema, Kim Lee, and Klostermeyer 2007), and the type of mammals…”

“Traditional bioinformatics tools, such as PeptideCutter, provide rule-based predictions based on known cleavage preferences for hydrophobic and aromatic residues but lack flexibility for complex substrates (Du and Li 2022; Tamam et al. 2020).”

“…animal-derived proteins provide the essential amino acids in the ratios needed to sustain growth and metabolic processes in the human body (Kaur et al. 2022), whereas plant-based protein sources typically have suboptimal levels and ratios of the essential amino acids (Schimbator et al. 2020).”

“After heat treatment (95 °C for 5 min), the Phe 105 -Met 106 bond of κ-casein was reported to be less accessible to pepsin, leading to inhibition of the hydrolysis of κ-casein (Yang et al. 2023b).”

“At the same pepsin-to-κ-casein ratio, sheep milk has the fastest rate of κ-casein hydrolysis, followed by cow and goat milk (Figure 3A7) (Yang et al. 2024).”

“…have determined the milk coagulation properties with different apparatus, which are summarized by Troch et al. (2017) and Lucey (2002), including rheology, microscopy (Everett 2007 Gilbert 2009; Gilbert 2019; Adams et al. 2019; de Kruif 2014; Gilbert 2023; Bayrak et al. 2021; Yang et al. 2025).”

“According to Zhang et al. (2022), the formation of cross-links between glutelin molecules generated aggregates during storage, and the aggregation restricted access of pepsin and trypsin to their sites of action in glu-telin, which eventually reduced the in vitro digestibility of glutelin.”

“Traditional bioinformatics tools, such as PeptideCutter, provide rule-based predictions based on known cleavage preferences for hydrophobic and aromatic residues but lack flexibility for complex substrates (Du and Li 2022; Tamam et al. 2020).”

“After heat treatment (95 °C for 5 min), the Phe 105 -Met 106 bond of κ-casein was reported to be less accessible to pepsin, leading to inhibition of the hydrolysis of κ-casein (Yang et al. 2023b).”

“Digestive characteristics of protein gels significantly influence the release of nutrients and delivery of bioactive ingredients (M. Yang, Yang, et al. 2025 ).”