Richard J. FitzGerald

Milk protein-derived peptide inhibitors of angiotensin-I-converting enzyme.

Numerous casein and whey protein-derived angiotensin-I-converting enzyme (ACE) inhibitory peptides/hydrolysates have been identified. Clinical trials in hypertensive animals and humans show that these peptides/hydrolysates can bring about a significant reduction in hypertension. These peptides/hydrolysates may be classified as functional food ingredients and nutraceuticals due to their ability to provide health benefits i.e. as functional food ingredients in reducing the risk of developing a disease and as nutraceuticals in the prevention/treatment of disease.

Identification of a novel angiotensin-I-converting enzyme inhibitory peptide corresponding to a tryptic fragment of bovine β-lactoglobulin

The angiotensin‐I‐converting enzyme (ACE) inhibitory activity of a tryptic digest of bovine β‐lactoglobulin (β‐lg) was investigated. Intact β‐lg essentially did not inhibit ACE while the tryptic digest gave an 84.3% inhibition of ACE. Peptide material eluting between 20 and 25% acetonitrile during C18 solid‐phase extraction of the β‐lg tryptic digest inhibited ACE by 93.6%. This solid‐phase extraction fraction was shown by mass spectroscopy to contain β‐lg f(142–148). This peptide had an ACE IC50 value of 42.6 μmol/l. The peptide was resistant to further digestion with pepsin and was hydrolysed to a very low extent with chymotrypsin. The contribution of specific amino acid residues within the peptide to ACE inhibitory activity and the potential application of this peptide as a nutraceutical is discussed.

Angiotensin-I-converting enzyme inhibitory activities of gastric and pancreatic proteinase digests of whey proteins

Enzymatic hydrolysates of bovine β-lactoglobulin (β-Lg), α-lactalbumin (α-La) and whey protein concentrate (WPC) were analysed for their angiotensin-I-converting enzyme (ACE) inhibitory activity. The unhydrolysed substrates gave very low ACE inhibitory indices, i.e. < 10%. Hydrolysis of the whey proteins by pepsin, trypsin, chymotrypsin and the commercially available enzyme preparations, Corolase PP and PTN 3.0S, resulted in high ACE inhibition indices, i.e. 73–90%. Hydrolysates generated with elastase displayed relatively low ACE inhibitory activity. The order of trypsin and pepsin addition during the hydrolysis of α-La and β-Lg did not appear to affect the ACE inhibitory activity of the resulting hydrolysate. Preliminary studies indicated that ultrafiltration through 3 and 1 kDa molecular mass cut-off membranes may be exploited to enrich for ACE inhibitory peptides. The ACE IC50 inhibition values obtained for ultrafiltered tryptic digests of β-Lg and WPC ranged from 130–201 mg L−1. The potential application of whey protein hydrolysates as nutraceuticals in the prevention of hypertension is discussed.

Proteinase and exopeptidase hydrolysis of whey protein: Comparison of the TNBS, OPA and pH stat methods for quantification of degree of hydrolysis

Whey protein hydrolysates were generated with Alcalase 2.4L and Debitrase HYW20 which are proteinase and exopeptidase enriched enzyme preparations, respectively. Degree of hydrolysis (DH) values were quantified with the TNBS, OPA and pH stat methods. Poor correlation was observed between the three methods for DH values in Debitrase HYW20 hydrolysates. For Alcalase 2.4L hydrolysates, the OPA method gave DH values that were approximately 15% lower than the pH stat, whereas TNBS DH values were similar to the pH stat method. As whey proteins are relatively rich in cysteine, a weak and unstable reaction between OPA and cysteine was thought to contribute to the under-estimation of DH in whey protein hydrolysates. Since TNBS reacts strongly with cysteine and TNBS DH values were unaffected by the type of enzyme preparation used to generate the hydrolysate, the TNBS method was deemed most suitable for the quantification of DH in whey protein hydrolysates.

Potential Uses of Caseinophosphopeptides

Abstract Caseinophosphopeptides (CPPs) are phosphorylated casein-derived peptides which possess the ability to bind and solubilise minerals, such as Ca2+. Consumption of high concentrations of Ca2+ in early life contributes to the development of maximal bone density, which in turn can prevent osteoporosis in later life. Furthermore, a recent report has shown a positive correlation between Ca2+ intake and the prevention of hypertension. The high bioavailability of Ca2+ from milk and dairy products has, in part, been attributed to the production of CPPs which have different levels of phosphorylation and are produced in vivo following digestion of α s 1 -, α s 2 - and β-casein by the action of gastrointestinal proteinases. CPPs which appear to be resistant to extensive proteolytic degradation, accumulate in the distal small intestine where they are purported to play a role in enhancing the passive absorption of Ca2+ and other trace elements. CPPs have also been produced in vitro using a range of commercially available proteinases of pancreatic origin. Several CPP enrichment procedures from casein hydrolysates have been reported, generally involving Ca2+ induced aggregation followed by ultrafiltration. These CPP enriched preparations have been used to characterise their interaction with Ca2+ and trace elements and to determine their effect on the bioavailability of dietary Ca2+ during animal and human feeding trials. There are conflicting reports, arising from the results of animal feeding studies, on the effectiveness of CPPs in enhancing Ca2+ bioavailability. However, a recent human feeding trial reported improved Ca2+ and Zn2+ absorption following CPP incorporation into a rice-based infant food. In vitro produced CPPs may also find application in the prevention and treatment of dental calculus. This review summarises the production, characterisation and potential applications of CPPs.

Antioxidative peptides: enzymatic production, in vitro and in vivo antioxidant activity and potential applications of milk-derived antioxidative peptides.

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.

BIOACTIVE PROTEINS, PEPTIDES, AND AMINO ACIDS FROM MACROALGAE1

Macroalgae are a diverse group of marine organisms that have developed complex and unique metabolic pathways to ensure survival in highly competitive marine environments. As a result, these organisms have been targeted for mining of natural biologically active components. The exploration of marine organisms has revealed numerous bioactive compounds that are proteinaceous in nature. These include proteins, linear peptides, cyclic peptides and depsipeptides, peptide derivatives, amino acids, and amino acid–like components. Furthermore, some species of macroalgae have been shown to contain significant levels of protein. While some protein‐derived bioactive peptides have been characterized from macroalgae, macroalgal proteins currently still represent good candidate raw materials for biofunctional peptide mining. This review will provide an overview of the important bioactive amino‐acid‐containing compounds that have been identified in macroalgae. Moreover, the potential of macroalgal proteins as substrates for the generation of biofunctional peptides for utilization as functional foods to provide specific health benefits will be discussed.

Opioid peptides encrypted in intact milk protein sequences.

Opioid agonistic and antagonistic peptides which are inactive within the sequence of the precursor milk proteins can be released and thus activated by enzymatic proteolysis, for example during gastrointestinal digestion or during food processing. Activated opioid peptides are potential modulators of various regulatory processes in the body. Opioid peptides can interact with subepithelial opioid receptors or specific luminal binding sites in the intestinal tract. Furthermore, they may be absorbed and then reach endogenous opioid receptors.

Dipeptidyl peptidase IV inhibitory and antioxidative properties of milk protein-derived dipeptides and hydrolysates

Selected synthetic dipeptides and milk protein hydrolysates were evaluated for their dipeptidyl peptidase IV (DPP-IV) inhibitory properties, and their superoxide (SO) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities. DPP-IV inhibition was seen with eight out of the twelve dipeptides and 5 of the twelve hydrolysates studied. Trp-Val inhibited DPP-IV, however, inhibition was not observed with the reverse peptide Val-Trp. The most potent hydrolysate inhibitors were generated from casein (CasH2) and lactoferrin (LFH1). Two Trp containing dipeptides, Trp-Val and Val-Trp, and three lactoferrin hydrolysates scavenged DPPH. The dipeptides had higher SO EC(50) values compared to the milk protein hydrolysates (arising from three lactoferrin and one whey protein hydrolysates). Higher molecular mass fractions of the milk protein hydrolysates were associated with the SO scavenging activity. Trp-Val and one lactoferrin hydrolysate (LFH1) were multifunctional displaying both DPP-IV inhibitory and antioxidant (SO and DPPH scavenging) activities. These compounds may have potential as dietary ingredients in the management of type 2 diabetes by virtue of their ability to scavenge reactive oxygen species and to extend the half-life of incretin molecules.

Milk Protein Hydrolysates and Bioactive Peptides

Milk proteins and milk protein-derived peptides have been widely studied for their health enhancing properties. This chapter presents the updated scientific knowledge on the bioactive properties of milk protein-derived peptides. The different bioactive properties which have been attributed to milk protein-derived peptides are discussed. These include mineral binding, cardioprotective, antidiabetic, satiating, opioid, antimicrobial, immunomodulatory, anticancer and antioxidant activities. The structure-function relationship is presented for the aforementioned bioactive properties based on current scientific knowledge. For each bioactive property, the data obtained in vitro is discussed, followed by an analysis of the information obtained from animal and human intervention studies. To date, most studies have been conducted in vitro. However, an increasing number of in vivo studies testing the efficacy of milk protein-derived peptides are being conducted. In certain instances, the in vivo studies have confirmed the bioactivity of specific milk protein-derived peptides or milk protein hydrolysates. However, conflicting data still exist in the scientific literature, which demonstrates that the bioactive properties observed in vitro do not always translate in vivo. Detailed knowledge of the peptide sequences responsible for the bioactive properties, together with a better understanding of the bioavailability and stability of these peptides in vivo may help to enhance the development of milk protein hydrolysates with health promoting capabilities in humans. Ultimately, this may lead to the approval of health claims by the relevant regulatory agencies.