Scientific Alert Note

Upgrading white fish by-products in order to increase health benefits

The need for better utilised fishery by-products has been emphasised by recognition of limited resources and environmental problems. One of the main objectives of the SEAFOODplus project PROPEPHEALTH is to recover biologically active, health beneficial molecules from marine by-products using mild technologies. In recent years, it has been reported that enzymatic hydrolysis of proteinaceous fish by-products (e.g. heads, frames, skin, and viscera) can produce hydrolysates rich in bioactive peptides. The work presented here results from a collaboration between two partners of PROPEPHEALTH, UWB (partner 47, field: enzymatic hydrolysis and antioxidant capacity evaluation), and UBS and UN (partners 40; field: membrane separation).

 

Authors:

Aurélie Chabeaud (1), (2), Fabienne Guérard (1), Patrick Bourseau (2), Laurent Vandanjon (2), Pascal Jaouen (3)

1 ANTiOX, U. of West Brittany, Quimper, France

2 LETEE, U. of South Brittany, Lorient, France

3 GEPEA-UMR CNRS 6144, U. of Nantes, Saint-Nazaire, France

 


 

Introduction

How can we upgrade marine by-products obtained from fish fillet processing in a mild and innovative way? Under certain controlled conditions, enzymatic hydrolysis of marine by-products produces peptides with bioactive properties. In addition, the hydrolysate can be fractionated by ultrafiltration to refine the most active fractions, which can enhance the specific activity of the hydrolysate (activity unit gram peptides).

The fractionation process has been developed on a hydrolysate with high antioxidant properties produced from a substrate model, Saithe (Pollachius virens) fillets. It has then been applied to industrial hydrolysates provided by Copalis-CTPP (France, partner 54) and Marinova (Denmark, partner 63), two of the SME partners in the PROPEPHEALTH project. It has been found that some bioactive properties are greatly enhanced by the ultrafiltration fractionation.

Aurélie Chabeaud is currently finishing her Ph.D. thesis regarding the optimisation of the antioxidant capacity of a saithe (Pollachius virens) hydrolysate by enzymatic hydrolysis and membrane separation. Saithe fillet was chosen as a substrate model, on account of (i) saithe processing by-products are abundantly available in Brittany (France); (ii) fillet allows it to be free from the variability of by-products composition.

 

Experimental procedure and results

The first step consists of optimizing the hydrolysis conditions on a laboratory scale with the aim to maximise the antioxidant activity of the hydrolysate. Enzymatic hydrolysis controlled by the pH-stat method was investigated in a 1 L-stirred tank reactor by Alcalase® 2.4 L. Optimal conditions were found to be pH = 8, T = 60°C, E/S = 2.3 %, time = 10.8 min, the activity reached a AC50(*) of 0.8 mg/mL (beta-carotene-linoleate model system assay) for a degree of hydrolysis of 11 %.

The hydrolysis was then scaled up in a 20 L-baffled stirred tank reactor (BSTR), with the equipment of the French network SEAPRO ( www.seapro.fr). The hydrolysate so produced presented a peptide distribution close to the hydrolysate prepared at the laboratory scale. The antioxidant activity reached a AC50 of 0.2 mg/mL.

 

(*) Peptide content allowing to reach 50 % of antioxidant activity..

 

Peptidic profiles of a hydrolysate (in blue), and retentate (in yellow) and permeate (in pink) obtained by ultrafiltration (Size-exclusion chromatography)

The second step is fractionating the hydrolysate by ultrafiltration (UF) aiming to refine the most active population and increase specific activity of the hydrolysate (activity unit per gram peptide). Organic tubular membranes from PCI Membrane Systems, Inc were considered lab-scale and industrial membranes have the same diameter (12.7 mm) which is an interesting characteristic for scaling-up. A polyethersulfone (PES) membrane, nominal molecular weight cut-off 4,000 Da (ref. MTP04) has been selected on the basis of permeation fluxes, selectivity (retention of peptides depending on their size) and cleanability.

Ultrafiltration fractionates a hydrolysate in a retentate and permeate respectively enriched in high and low molecular weight peptides. The volume reduction factor (VRF) appeared to be the main operating parameter in controlling the selectivity of the separation between these two peptide populations. In addition, it was discovered that the transmembrane pressure can be adjusted to settle the MW range of the peptide populations. These results have been directly applied to the refining of peptides lower than 2 kDa, having a potential antioxidant activity.  

The UF fractionating process was then applied to industrial hydrolysates provided by Marinova (DK) and Copalis-CTPP (F). It was shown that the refining effect depends on the peptidic profile of the hydrolysate and therefore on the degree of hydrolysis. The fractionation is more efficient when the nominal MWCO of the membrane is below the size of the highest peptides as shown on the figure.

 

The impact of ultrafiltration on peptide distribution and biological activity depends on the hydrolysate and the intended activity. It has been found that the specific activity was increased in some cases in the retentate or the permate. However, the comprehension of the relationship between the peptidic population of a hydrolysate and its activity remains still an exciting challenge.

 

Aurélie Chabeaud will defend her Ph.D thesis in the spring of 2008. The Ph.D examination committee will include 6 members of SEAFOODplus project PROPEPHEALTH : Patrick Bourseau, Laurent Vandanjon (U. of South Brittany) and Fabienne Guérard (U. of West Brittany) who were the thesis supervisors; Pascal Jaouen (U. of Nantes), Jean-Pascal Bergé (Ifremer Nantes) and Joop Luten (Fiskeriforskning, Norway), coordinator of the RTD Pillar 4  will be members of the Ph.D. examination committee.