Angiotensin-I-converting enzyme and prolyl endopeptidase inhibitory peptides from natural sources with a focus on marine processing by-products

Abstract

Like many natural resource-based processing industries, the seafood processing sector gives rise to a significant volume of organic waste. Environmental issues, economic concerns and legal restrictions regarding the disposal of processing wastes have led to increased research in the discovery of alternative value-added products, such as bioactive peptides from these waste streams. Bioactive peptides have various physiological functionalities in the human body following consumption and these include antihypertensive, antiamnesiac, mineral-binding, immunodulatory, antioxidative and antithrombotic activities. The search for bioactive peptides from a variety of different sources has become a major area of research with potential for the functional foods sector. The isolation of bioactive peptides typically involves the hydrolysis of the protein of choice with different proteolytic enzymes, alone or in combination with Generally Recognised as Safe (GRAS) micro-organisms.

This review details information on angiotensin I-converting enzyme (ACE) and prolyl endopeptidase (PEP) inhibitors derived from natural, marine and marine processing waste streams and their potential for use as high-value added bioactive peptides.

Introduction

In recent years, over-exploitation of fishery resources has become a major concern worldwide. According to data published by the Food and Agriculture Organisation (FAO), approximately 77% of the 143.6 million tons of fish and shellfish caught in 2006 was used for human consumption. The remaining processing leftovers which, includes trimmings, fins, frames, heads, shells, skin and viscera are normally used for the production of fishmeal, fish oil, fertiliser, fish silage and animal feed. These by-products may be identified as processing leftovers that are not normally saleable but which can be recycled after treatment. Annual discard from marine capture and aquaculture fisheries worldwide is estimated to be approximately 20 million tonnes per year (FAO, 2008). In Ireland, figures from An Bord Iascaigh Mhara (BIM; The Irish Sea Fisheries Board), estimated that 63,786 tonnes of marine processing waste were produced nationally in 2000, 45% of which arose from the northwest region (Pfeiffer, 2003). European legislation, Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste, has set specific targets for the amount of municipal waste allowed for disposal at landfills. Landfill is also a costly waste disposal option for the seafood industry. Generation of substantial quantities of marine processing by-products is therefore both an environmental and economic concern for the seafood processing sector (Kim & Mendis, 2006). As a result, there has been increased interest in exploring the possible uses of fish by-products, or rest raw material, so that they become viewed as a potential resource due to their valuable protein and lipid content and sugars and minerals instead of a waste problem (Akihisa et al., 2004, Bruyere et al., 2004, Kelley, 2001, Larsen et al., 2000, Yokoyama et al., 1992).

Proteins from food are sources of numerous bioactive peptides with anti-hypertensive, opioid, anti-thrombotic and immunomodulating activities. The use of fish processing by-products as substrate provides a novel approach for the potential discovery of high-value bioactive products. In the past twenty years, an emerging area of research is the identification of bioactive compounds that may be present in marine by-products. Bioactive compounds are described as ‘food-derived components’ that, in addition to their nutritional value, exert a physiological effect in the body (Vermeirssen, van Camp, & Verstraete, 2004). This review aims to collate information on ACE-I-inhibitory and PEP inhibitory peptides, the isolation and characterisation strategies used to obtain these inhibitors from natural sources, with a focus on marine substrates. It also details the potential health benefits of these peptides and their potential for use as functional food components.