In vitro antioxidant properties of chicken skin enzymatic protein hydrolysates and membrane fractions

Highlights

• Chicken skin protein hydrolysates scavenged various free radicals.

• Antioxidant activity of the hydrolysates was dependent on enzyme type.

• Membrane fractionation improved hydrolysate scavenging of superoxide radical.

• Antioxidant activity was inversely related to peptide size.

Abstract

Chicken thigh and breast skin proteins were hydrolysed using alcalase or a combination of pepsin and pancreatin (PP), each at concentrations of 1–4%. The chicken skin protein hydrolysates (CSPHs) were then fractionated by membrane ultrafiltration into different molecular weight peptides (<1, 1–3, 3–5 and 5–10 kDa) and analysed for antioxidant properties. Results showed that the CSPHs had a significantly (p < 0.05) lower scavenging activity against DPPH radicals when compared to reduced glutathione. The chicken breast skin hydrolysates had significantly higher DPPH scavenging activity than the chicken thigh skin hydrolysates. DPPH scavenging and metal ion chelation increased significantly (p < 0.05) from 29–40% to 86–89%, respectively with increasing proteolytic enzyme concentration. In contrast, the antioxidant properties decreased as peptide size increased. We conclude that CSPHs and their peptide fractions may be used as ingredients in the formulation of functional foods and nutraceuticals for the control and management of oxidative stress-related diseases.

Introduction

Erdmann, Cheung, and Schroder (2008) defined biologically active peptides as “food-derived peptides that exert, beyond their nutritional value, a physiological, hormone-like effect in humans”. Bioactive peptides consist of natural amino acid sequences (often 2–20 residues) encrypted in the parent or natural protein molecule, and are usually inactive within the sequence of the protein. They are, however, released during gastrointestinal digestion or in vitro protein hydrolysis with proteases and play important roles in the regulation and modulation of metabolism during digestion of food in the intestine. Thus, bioactive peptides have the potential of being metabolic aid supplements, in the form of nutraceuticals and functional food ingredients for the promotion of health and prevention of diseases (Bernardini et al., 2011).

Bioactive peptides have been isolated from various food sources such as milk and whey (Erdmann, Cheung, & Schroder, 2008), meat and fish (Martinez-Maqueda et al., 2012, Samanarayaka et al., 2010) and quinoa seeds (Aluko & Monu, 2003). The potential metabolic regulatory effects of bioactive peptides relate to nutrient uptake, antihypertensive, antioxidant, anticancer, antithrombotic, opioid or antiproliferative as well as antimicrobial activities (Erdmann et al., 2008, Samanarayaka et al., 2010, Udenigwe and Aluko, 2012). Many of the known bioactive peptides exhibit multifunctional properties, are easily absorbed and could be used to reduce symptoms of oxidative stress, hypertension and dyslipidemia, which are all risk factors of coronary heart disease (Erdmann et al., 2008, Lee et al., 2010, Samanarayaka et al., 2010). Of particular interest to human health is the uncontrolled production of free radicals (superoxide, hydroxyl, singlet oxygen, peroxyl) during cellular metabolism/oxidation, which leads to oxidative stress. Oxidative stress has been implicated in the initiation or progression of many vascular diseases due to extensive damage of critically important biological polymers such as DNA, proteins and lipids (Erdmann et al., 2008). The toxic free radicals can also modify low density lipoprotein (LDL), which may lead to increased atherogenicity of oxidized LDL (Erdmann et al., 2008). This in turn can be a causative factor in many terminal degenerative diseases such as cardiovascular disease, diabetes, cancer, Alzheimer’s disease and a host of other conditions (Bernardini et al., 2011, Erdmann et al., 2008, Naqash and Nazeer, 2011, Ryan et al., 2011).

Antioxidants play an important role in human health and nutrition as they are known to protect the body against reactive oxygen species (ROS) (Martinez-Maqueda et al., 2012, Ryan et al., 2011). The use of bioactive peptides as antioxidative agents is generating interest not only as natural alternatives to synthetic antioxidants, but for their beneficial effects in terms of health implications, non-residual side effects and their functionality in food systems (Bernardini et al., 2011, Erdmann et al., 2008, Girgih et al., 2010, Ryan et al., 2011). The ability of endogenous enzymatic antioxidants (catalase, superoxide dismutase and glutathione peroxidase) to regulate this process is often weakened when excess free radicals are produced beyond cellular antioxidant capacity.

Food-derived bioactive peptides with antioxidant properties have been reported in several foods, such as milk and eggs (Erdmann et al., 2008), fish and a few domestic animal muscles (Bernardini et al., 2011, Ryan et al., 2011). They have also been isolated from poultry viscera protein hydrolysate (Jamdar, Rajalakshmi & Sharma, 2012) and flying fish backbone (Naqash & Nazeer, 2011). However, information on the antioxidant properties of chicken skin protein hydrolysates is scanty. Chicken skin is a by-product derived from chicken meat processing which is highly underutilized, constituting huge cost for waste disposal and danger to the environment as well as the loss of nutritional value (Feddern et al., 2010). Several attempts have previously been made at developing novel chicken skin based products in order to diversify the utilisation of chicken skin as well as reduce waste, such as chicken meat balls (Bhat, Kumar, & Kumar, 2011), collagen (Bonifer and Froning, 1996, Cliche et al., 2003), sausages (Biswas, Chakraborty, Sarkar, Barpuzari, & Barpuzari, 2007) and chicken meat frankfurter (Babji, Chin, Chempaka, & Alina, 1998). However, an area of research that is yet to be explored is the development of chicken skin based products with functional and health promoting values. The high protein content (dry weight basis) could, in addition to contributing to nutrition, also serve as a very active source of value-added products, including bioactive peptide-containing hydrolysates. Therefore, the objective of this study was to determine the effects of muscle source as well as type and level of protease on the in vitro antioxidative properties of chicken skin enzymatic hydrolysates and their ultrafiltration membrane peptide fractions.