Bioactive peptides from livestock milk and casein as alternative functional foods

Functional milk peptides, derived from enzymatic hydrolysis of milk proteins such as casein and whey, exhibit a range of bioactivities. These include antihypertensive, antioxidant, antidiabetic, and antimicrobial effects, which contribute to their potential health benefits. Livestock farming has been adopted since ancient times, where farm animals, including cows, buffaloes, sheep, goats, camels, yaks, and donkeys are raised for human consumption and/or milk production (López-Pedrouso et al., 2023). Milk from the livestock is the oldest form of animal food which is well known for its complete nutrition (Ramírez-Rivera et al., 2019). It is a principal source of several essential macro- and micronutrients including protein, calcium, magnesium, potassium, phosphorus, Vitamin A, Vitamin B12, and riboflavin (Keast et al., 2013). These nutrients play a vital role in the health status of low-income households to combat nutrient deficiencies, especially children, females, pregnant, and lactating mothers (Tricarico et al., 2020). Milk is not only important for diet, but also to strengthen the economy of local industries in South Asia, Africa, and the Middle East countries (FAO, 2011). Many previous research studies were conducted on the characteristics, functional properties and bioactive peptides identification of cow milk but recent advanced research studies were focused on the physicochemical, functional, and bioactive properties of protein as well as peptides from minor dairy species, including camel, goat, sheep, yak, donkey, mare, and buffalo (López-Pedrouso et al., 2023). The gross compositions of milk from minor dairy species are shown in Table 1. The advancement of technology has improved the growth of dairy industry, where many enhanced products are innovated from milk, including whey powder, casein powder, cheese, butter, yogurt, cream, and ice cream (Rivas et al., 2010). The production of these dairy products could cause severe environmental pollution as the wastes contained milk residue (Ahmad et al., 2019). Traditionally, the production of cheese resulted in excessive amount of whey, at which 1 kg of cheese produced will produce approximately 9 L of whey (Sar et al., 2022). Fortunately, dairy wastes contain high amount of organic components, so they can be used as inexpensive alternative substrate for microbial production of bioenergy, organic acids, enzymes, biomass, and biopolymer (Sar et al., 2022). There are several types of bioproducts produced from dairy byproducts, including bioactive compounds, enzymes, hormones, vitamins, biomass, polymers, surfactants, organic acids, solvents, and biofuels (Sar et al., 2022). Milk protein can be studied as a whole milk or its major components such as whey or casein (Guha et al., 2021). Milk casein is a solid precipitate that resulted from isoelectric precipitation at pH 4.6, whereas whey protein is the noncasein protein, remaining as a soluble component (Guha et al., 2021). Milk protein possesses many functional characteristics such as solubility, fat binding, water binding, viscosity, emulsifying and heat stabilization properties (Augustin & Udabage, 2007). Moreover, it has many nutritional benefits and its peptides have a wide range of bioactivities, including antihypertensive (Abdel-Hamid et al., 2017), antioxidative (Abdel-Hamid et al., 2017; D. Kumar et al., 2016) and antidiabetic properties (Gong et al., 2020; Mudgil et al., 2018). The bioactive peptides extracted from different source of milk and its casein were summarized in Table 2. This commentary highlights the distinctive health benefits of livestock milk and casein, comparing them with other food sources, and explores the biological activities of peptides derived from these sources. It focuses on their diverse biological activities, emphasizing clinical applications and animal evidence related to bioactive peptides, including their antioxidant, antihypertensive, antidiabetic, and antiinflammatory properties (Nielsen et al., 2023). Understanding these benefits has the potential to advance nutrition and therapeutic strategies, thereby improving health outcomes and stimulating further research in the food and nutrition industry. Milk and its components, especially casein exhibited good anti-oxidative properties. Papain was claimed to be the most efficient enzyme to produce antioxidative buffalo milk protein hydrolysate, compared to pepsin and trypsin (Abdel-Hamid et al., 2017). On the other hand, three different enzymes, which are chymotrypsin (D. Kumar et al., 2016), combination of neutral and alkaline proteases (Li et al., 2013), and 1% metallo-endopeptidase (Megrous et al., 2020) have produced casein hydrolysate with good anti-oxidative properties. The hydrolysis time plays a notable role on their antioxidative properties (Correa et al., 2011). Five novel antioxidative peptides yielded from goat milk casein protein hydrolysate using a combination of neutral and alkaline proteases (1:1) (Li et al., 2013), whereas six antioxidative peptides yielded from yak milk casein hydrolysate extracted using a combination of alcalase and trypsin enzyme (Liu et al., 2020). The 1% metallo-endopeptidase produced casein hydrolysate with strong antioxidant activities against DPPH radicals (Megrous et al., 2020). In summary, protein hydrolysates extracted from milk and its components serve as an alternative source of antioxidants. These hydrolysates can be consumed either as supplements or incorporated into milk products formulations. Enzymatic hydrolysis of milk and its casein have produced protein hydrolysate with good antihypertensive properties. Papain-extracted protein hydrolysates from buffalo skimmed milk (Abdel-Hamid et al., 2017) and yak milk casein (Jiang et al., 2007) are stronger angiotensin I-converting enzyme (ACE) inhibitors, compared to that of pepsin- and trypsin-extracted hydrolysates. Pepsin could produce camel milk casein hydrolysate with the strongest ACE inhibition with 2 h of hydrolysis (Baba et al., 2021), whereas cow milk casein hydrolysate extracted using chymotrypsin with 6 h of hydrolysis yielded the best ACE inhibitory activities (S. Kumar et al., 2020). On the other hand, ovine milk protein hydrolysate extracted using P7 enzyme is a good antimicrobial agent. It possesses antibacteria activity against Bacillus cereus and Corynebacterium fimi, as well as antifungal activity against Aspergillus fumigatus and Penicillium expansum (Correa et al., 2011), whereas camel milk protein hydrolysate possesses antibacteria activity against Escherichia coli, Listeria monocytogenes, Bacillus cereus, and Staphylococcus aureus (D. Kumar et al., 2016). The protein hydrolysate could be applied as a functional food or ingredient to enhance the food shelf life and food safety. Generally, enzymatic hydrolysis of milk and its components could yield protein hydrolysates with potential antihypertensive and antimicrobial properties that are beneficial to health. The research on antidiabetic properties of milk hydrolysates has emerged recently. Alcalase and papain are effective enzymes in extracting antidiabetic hydrolysates from milk (Du et al., 2022; Mudgil et al., 2018). Goat milk hydrolysate extracted using these enzymes have higher potency against α-amylase, α-glucosidase, and dipeptidyl peptidase IV (DPPIV), compared to those hydrolysed using neutrase, trypsin, bromelain, pepsin, and proteinase K (Du et al., 2022). For camel milk, alcalase- and papain-extracted protein hydrolysates exhibited potent DPPIV inhibitory activity but alcalase- and bromelain-extracted protein hydrolysates showed potent α-amylase inhibitory activity (Mudgil et al., 2018). On the other hand, various enzymes have been used to extract milk casein protein hydrolysate and peptides with antidiabetic activities. For instance, flavourzyme-extracted goat milk casein improved glucose metabolism by increasing glucose consumption rate and insulin resistance in HepG2 cells treated with high glucose (Gong et al., 2020), whereas trypsin-extracted protein hydrolysates (Zhang et al., 2015) and pepsin-extracted whey hydrolysate (Lacroix & Li-Chan, 2013) are strong DPPIV uncompetitive inhibitors. Besides that, chymotrypsin-extracted hydrolysate from sheep (Jan et al., 2016) and cow milk casein (S. Kumar et al., 2020) are good α-amylase inhibitor, whereas Bacillus metallo-endopeptidase-extracted cow milk casein hydrolysate showed inhibition towards both α-glucosidase and α-amylase enzymes significantly (Megrous et al., 2020). For combination enzymes, cow milk casein hydrolysate extracted using papain and flavourzyme (1:1) significantly improved liver antioxidant enzymes in diabetic rats by enhancing Nrf2 transcription (Wang et al., 2020). Furthermore, several novel anti-diabetic peptides were successfully identified from alcalase and Pronase E enzymes-extracted camel and bovine milk casein (Mudgil et al., 2021). Overall, enzymatic hydrolysis is efficient in extracting antidiabetic protein hydrolysates and peptides, which are potential alternative functional foods to reduce blood glucose level. The advanced benefits of livestock milk, apart from being a good source of meat, macro- and micronutrients have been highlighted. Milk and its components, including whey and casein, from livestock such as cows, buffaloes, sheep, goats, camels, yaks, and donkeys possess antioxidant, antihypertensive, antidiabetic and antimicrobial properties. The usage and application of milk could then be widened, and its value could be increased while fulfilling the sustainable development goals to improve nutrition and promote healthy living at all ages. Additionally, bioactive peptides derived from natural food sources can be formulated into products or used as supplements tailored for specific consumer groups. Further extensive animal and clinical studies are imperative to establish effective treatment protocols and consumption patterns for hypertension and diabetic patients, ensuring the safety of peptide consumption. Additionally, comprehensive research into the structure–activity relationships of these peptides is crucial for understanding their biological activities in both animal models and clinical settings, thereby advancing their application in therapeutic contexts. Eng Huan Hau: Conceptualization; data curation; formal analysis; writing - original draft. Ling Li: Validation; writing - review and editing. Siau Hui Mah: Conceptualization; project administration; supervision; validation; writing - review and editing. The authors declare no conflicts of interest. None. Data available on request from the authors.