The objectives of this study were to investigate the generation of beta-lactoglobulin fragment (142-148) (beta-LG f(142-148) during the hydrolysis of whey proteins, and the in vitro stability of this fragment upon incubation with gastrointestinal and serum proteinases and peptidases. An enzyme immunoassay (EIA) protocol was developed for the quantification of beta-LG f(142-148) in whey protein hydrolysates and in human blood serum. The minimum detection limit was 3 ng/mL. The level of the peptide in whey protein hydrolysates was influenced by the degree of hydrolysis (DH). As expected, highest levels of this peptide were found in hydrolysates generated with trypsin. Sequential incubation of hydrolysates at different DH values with pepsin and Corolase PP, to simulate gastrointestinal digestion, generally resulted in the degradation of beta-LG f(142-148) as determined by EIA. Reversed-phase HPLC and angiotensin-I-converting enzyme (ACE) activity assays demonstrated that synthetic beta-LG f(142-148) was rapidly degraded upon incubation with human serum. Furthermore, beta-LG f(142-148) could not be detected by EIA in the sera of 2 human volunteers following its oral ingestion or in sera from these volunteers subsequently spiked with beta-LG f(142-148). These in vitro results indicate that beta-LG f(142-148) is probably not sufficiently stable to gastrointestinal and serum proteinases and peptidases to act as an hypotensive agent in humans following oral ingestion. The in vitro methodology described herein has general application in evaluating the hypotensive potential of food protein-derived ACE inhibitory peptides.
"Human blood contains a large number of serum peptidases, which can further hydrolyse the bioactive peptide and reduce activity. For example, the b-lactoglobulin-derived ACE-inhibitory peptide (f142–148; Ala–Leu–Pro–Met– His–Ile–Arg) was shown to be degraded in vitro by gastrointestinal and serum proteinases destroying its potential bioactive properties (Walsh et al. 2004). "
[Show abstract][Hide abstract] ABSTRACT: The beneficial effects of food-derived antioxidants in health promotion and disease prevention are being increasingly recognized. Recently, there has been a particular focus on milk-derived peptides; as a source of antioxidants, these peptides are inactive within the sequence of the parent protein but can be released during enzyme hydrolysis. Once released, the peptides have been shown to possess radical scavenging, metal ion chelation properties and the ability to inhibit lipid peroxidation. A variety of methods have been used to evaluate in vitro antioxidant activity, however, there is no standardised methodology, which hinders comparison of data. This review provides an overview on the generation of antioxidative peptides from milk proteins, the proposed mechanisms of protein/peptide induced antioxidant activity, in vitro measurement of antioxidant activity, in vivo evaluation of plasma antioxidant capacity and the bioavailability of antioxidative peptides. The understanding gained from other food proteins is referred to where specific data on milk-derived peptides are limited. The potential applications and health benefits of antioxidant peptides are discussed with a particular focus on the aging population. The regulatory requirements for peptide-based antioxidant functional foods are also considered.
"There are several examples of peptides, which showed potent ACE-inhibitory activity, but did not exert an antihypertensive effect in vivo. For instance, peptide a S1 -casein f(23–27) showed potent ACE-inhibitory activity, but no hypotensive effect in SHR (Maruyama et al., 1987), and peptide b-lactoglobulin f(142–148) with in vitro ACE-inhibitory activity but no effect in human volunteers (Walsh et al., 2004). "
[Show abstract][Hide abstract] ABSTRACT: In this study, we report novel casein-derived peptide sequences with angiotensin converting enzyme (ACE)-inhibitory activity and antihypertensive activity demonstrated in spontaneously hypertensive rats (SHR). The peptides were obtained by enzymatic hydrolysis of total isoelectric casein with pepsin. To identify ACE-inhibitory peptides, the casein hydrolysate was fractionated by semi-preparative high performance liquid chromatography, and 44 (CN) peptides contained in the active fractions were sequenced by using an ion trap mass spectrometer. Among the identified peptides, three sequences, that corresponded to αs1-CN f(90–94) (RYLGY), αs1-CN f(143–149) (AYFYPEL), and αS2-CN f(89–95) (YQKFPQY), showed IC50 values as low as 0.71 μm, 6.58 μm, and 20.08 μm, respectively. These three peptides also exerted antihypertensive activity when they were orally administered to SHR at a dose of 5 mg kg−1 of body weight. The activity of peptides RYLGY and AYFYPEL in SHR was similar to that found for tripeptide VPP when orally administered at the same dose.
[Show abstract][Hide abstract] ABSTRACT: The high nutritive value and diverse functional properties of milk proteins are well known. In recent years, intense scientific research has been focused on the identification of factors within bovine milk that may be relevant to improving human health. The best characterized wheybased bioactive proteins include α-lactalbumin, β-lactoglobulin, immunoglobulins, lactoferrin, lactoperoxidase and growth factors. These proteins exhibit a wide range of biological activities that may influence the digestive function, metabolic responses to absorbed nutrients, growth and development of organs and disease resistance. Some whey proteins may reduce the risks of chronic human diseases reflected by the metabolic syndrome. Whey proteins are a good source of various bioactive peptides which are encrypted within the proteins and can be released during gastric digestion or food processing by enzymes or microbes. Whey proteinderived peptides have been shown to exert a wide range of bioactivities affecting the cardiovascular, immune and nervous systems. The efficacy of a few peptides has been established in animal and human studies. A number of commercial whey-based protein products with potentital health benefits are on the market and this is envisaged to increase on a global scale.
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