Meat constitutes a very important food in our diet because it contributes to the intake of high-quality proteins containing all necessary essential amino acids as well as important micronutrients such as iron, zinc, selenium, magnesium, as well as vitamins B12 and B6, niacin, choline, riboflavin, among others. Further to the well known nutritional content of meat, a number of bioactive peptides with health benefits have been reported to be generated in meat through the hydrolysis of muscle proteins by endogenous peptidases. Such bioactive peptides consist of short sequences (2–20 amino acid residues) that remain inactive while encrypted within the parent protein but that could be activated when released by peptidases during either postmortem aging or further meat processing, or even during the gastrointestinal digestion (Toldrá et al., 2018). Therefore, the generation of bioactive peptides in meat or processed meat is the result of a cascade of enzymatic reactions, initiated by the action of muscle endopeptidases, majorly calpains and cathepsins, that contribute to break muscle proteins into major protein fragments and polypeptides. Such fragments are then further hydrolyzed by muscle exopeptidases like tripeptidylpeptidases and dipeptidylpeptidases into smaller peptides, and by aminopeptidases and carboxypeptidases into free amino acids (Toldrá et al., 2020a). An example of how the different muscle peptidases may act on a fragment of myofibrillar protein is shown in Figure 1.

Bioactive peptides may exert different physiological regulatory activities that promote consumers’ health, but the effects depend on its molecular size, spatial structure, amino acid composition, and hydrophilic and hydrophobic properties. They must also be resistant to gastrointestinal digestion and be absorbed intact through the intestinal barrier, showing good bioaccesibility and bioavailability to exert their physiological benefit. Most usual bioactivities reported in meat are related to peptides with cardioprotective action like the inhibition of angiotensin I–converting enzyme (ACE) and antioxidant activity (Xing et al., 2019), but other activities like anti-inflammatory and dipeptidyl peptidase IV (DPP IV) inhibition has also been reported in all types of meats (Madhu et al., 2022; Ashaolu et al., 2023).

This review is focused on the generation of bioactive peptides by endogenous peptidases in meat and meat products, their major types of bioactivity, and the reported benefits for consumer health.

Bioactive peptides are usually identified in meat and processed meat products through empirical approaches as schematized in Figure 2. This process involves the extraction of bioactive peptides and their separation through chromatographic techniques by collecting fractions and screening bioactivity in order to select the most active fractions for further purification of peptides. The purified peptides are usually identified using mass spectrometry in tandem, and the most active sequences are selected for synthesizing peptides to be used in confirmatory in vitro and in vivo assays (Sánchez-Rivera et al., 2014; Mora et al., 2018). This procedure is tedious and costly and therefore it may be complemented with predictive strategies based on in silico analysis using bioinformatics tools and peptide databases as shown in Figure 3 (Lafarga et al., 2014; Mora et al., 2018). BIOPEP-UWM is a database used for in silico approach and bioactivity prediction (Minkiewicz et al., 2019). The quantitative structure–activity relationships (QSAR) model and molecular docking simulations are useful for the characterization of structural and physico-chemical properties (Carrasco-Castilla et al., 2012; Agyei et al., 2016). In this way, the combined use of empirical and in silico approaches facilitates the location of peptides and the determination of their potential bioactivities in complex matrices like meat and processed meats (Toldrá and Mora, 2022).

The bioavailability of bioactive peptides is assessed in order to ensure that the specific bioactive peptide keeps its bioactivity during gastrointestinal digestion, crossing through the intestinal membrane and flowing within the bloodstream until reaching the target organ (Segura-Campos et al., 2011). Simulated gastrointestinal digestion is usually performed under standard protocols with specific enzyme conditions. The ability to transport peptides through the intestinal epithelium can be assayed using a Caco2 cell monolayer (Gallego et al, 2016; Wang and Li, 2017). Finally, in vivo assays are necessary to confirm that peptides are not degraded by blood plasma peptidases (Bohn et al., 2018).

Postmortem aging of meat is well known to improve tenderness, but it can also contribute to generate peptide fractions, some of them with bioactivity and therefore with potential positive effects on health (Fu et al., 2017). Once meat is ingested, bioactive peptides must be resistant to the digestive enzymes and environmental conditions during the gastrointestinal digestion, and these peptides must remain intact when crossing the intestinal barrier and when reaching the blood stream in order to be able to exert their physiological action (see Figure 4) and its health benefit (Gallego et al., 2016).

The generation of bioactive peptides under conditions of industrial aging of meat is not abundant although certain bioactivity has been reported. Proteolysis mostly breaks proteins into polypeptides and relatively large peptides, also generating some peptides smaller than 3 kDa, the value of which increases with extended postmortem time (Fu et al., 2017). The contributions of such peptides to 2,2-diphenyl–1-picrylhydrazyl (DPPH) antioxidant activity as well as to ACE inhibitory activity have been reported in beef (Fu et al., 2017), pork (Escudero et al., 2012), poultry (Martini et al., 2019), rabbit (Chen et al., 2022), and chicken (Sangsawad et al., 2017). Several peptides with ACE inhibitory activity reported for fresh meat of different animal species are shown in Table 1. Cooking of meat was reported to slightly increase the bioactivity, whereas the subsequent simulated gastrointestinal digestion resulted in a substantial increase of bioactivity. Myosin, actin, titin, collagen, and elastin were reported to be the main proteins of origin for the identified bioactive peptides (Mora et al., 2017; Wang et al., 2020a). Such positive effect was attributed to changes in the conformation of proteins due to heat denaturation when cooked at 70°C that allowed for better access of the digestive peptidases to the cleavage sites of proteins (Bax et al., 2012). It must be taken into account that 1743 peptides were identified from 71 meat proteins after cooking and in vitro digestion (Sayd et al., 2016).

An interesting study compared the peptides generated from beef, pork, chicken, and turkey meat after their gastrointestinal digestion. More than 200 peptides were released in all 4 types of meat although only 62 peptides matched with sequences associated to a proven biological activity such as 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate (ABTS) antioxidant activity, ACE inhibitory activity, and DPP IV inhibitory activity. Near one third of them were in common for all types of meats (Martini et al., 2019).

Recently, it has been reported that hydrolyzates of meat proteins contain cryptides that are short peptide sequences encrypted within longer peptides that need further processing, like during gastrointestinal digestion, to release their bioactivity (Gathercole et al., 2023).

The number and amount of bioactive peptides has been reported to be very large in meat products that have been fermented or exposed to extended drying periods. In this way, bioactive peptides can be generated from muscle proteins due to the action of endogenous endo- and exopeptidases during dry-curing or combined with microbial peptidases during fermentation/ripening. Furthermore, additional peptides may be either generated or degraded by the action of enzymes of the gastrointestinal tract (Toldrá et al., 2020b).

The activity of peptidases, and therefore the extent of proteolysis, may be affected not only by many variables such as the type of ingredients and processing conditions used but also by the type of enzymes and microorganisms used in the case of fermented meats (Toldrá et al., 1993; Zhou et al., 2019). Proteolysis is quite intense in dry-cured ham due to the large length of time of processing, usually more than 9 months. Muscle endo- and exopeptidases have enough time to hydrolyze muscle proteins, releasing numerous peptides that are progressively reduced in size as the process advances. Final products of proteolysis are tri- and dipeptides and free amino acids that accumulate in large amounts by the final stages of processing (Mora et al., 2013). Therefore, a strong proteolysis is reported in the last stages of Jinhua ham due to the higher temperatures used, and this causes a large generation of dipeptides (i.e., VE, PL, AH, and AR) and tripeptides (LPK, SGL, AAP, SGV, and LHA) with 23.59% and 48.28%, respectively, of total relative peak areas (Zhu et al., 2017). The simulated gastrointestinal digestion of Italian Parma ham was reported to generate 21 dipeptides and 12 tripeptides (Paolella et al., 2015). A good number of dipeptides (i.e., TS, TL, FD, VK, AT, and QT) and tripeptides (i.e., SRE, TVQ, NAS, KIE, and GKM) were reported in Spanish dry-cured ham (Gallego et al., 2019).

A variety of peptides with different sequences and lengths are generated in meat and processed meat products as a consequence of proteolysis by endogenus peptidases. Some of the released peptides are bioactive because they exert activities like inhibition of ACE and DPP IV as well as antioxidant and anti-inflammatory activity. Although bioactivities have been checked with in vitro assays and health benefits demonstrated through in vivo assays with animals, further clinical assays with humans are neccessary to demonstrate the health benefits for consumers.