Extraction, purification and characterisation of biofunctional peptides from marine processing co-products

Large quantities of marine processing by-products such as salmon trimmings, or undersized, fouled and cracked mussels as well as mussel byssus are generated annually. Currently these components are discarded or used as fertilizers, animal feed or are sold on for fish oil extraction. However, it is becoming more evident that marine processing by-products are rich reservoirs of structurally diverse biofunctional components such as proteins, peptides and amino acids. These marine processing by-products can contain significant levels of protein (10-23 % (w/w)) and may act as substrates for the generation of bioactive peptides. The potential of by-products of the fish and shellfish industries to generate peptides with angiotensin-converting-enzyme (ACE) and dipeptidyl peptidase IV (DPP-IV) inhibitory and antioxidant activities was assessed. The extraction of protein, gelatin and collagen from the marine by-products, salmon trimmings (ST), mussel meat (MM) and mussel byssus (MB) respectively was optimized and hydrolysates were generated from these extracts. All the hydrolysates generated had ACE and DPP-IV inhibitory and antioxidant activities, although higher in vitro DPP-IV and ACE inhibitory and antioxidant activity levels were seen in ST-derived hydrolysates compared to MM or MB-derived hydrolysates. The most potent multifunctional hydrolysates were the ST proteins hydrolysed with Corolase PP® for 1 h (STP-C1, ACE IC50= 0.96 ± 0.11 mg mL-1; DPP-IV IC50= 0.30 ± 0.01 mg mL-1; ORAC value= 601.47 ± 85.13 μmol TE g-1) and the ST gelatin hydrolysed with Corolase PP® for 1 h (STG-C1, ACE IC50= 0.19 ± 0.05 mg mL-1; DPP-IV IC50= 0.08 ± 0.01 mg mL-1; ORAC value= 540.94 ± 9.57 μmol TE g-1). Furthermore, the STP-C1 and STG-C1 showed no significant change in the bioactivities when subjected to simulated gastrointestinal digestion. The fractionation of these hydrolysates showed that small peptides (mainly dipeptides) rich in proline, tyrosine and phenylalanine, were present in the most potent fractions. The characteristics of these peptides are linked with ACE and DPP-IV inhibition, and antioxidant activities. Based on the in vitro results presented above, marine by-products may have potential as value-added sources of antioxidant, anti-diabetic and cardioprotective functional food ingredients.