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..