Scientific Alert Note

Grape fibres as inhibitors of oxidation in fish mince

: Isabel with a cod head, which could be used as raw material for a mince product

As a part of the SEAFOODplus training programme, Isabel Sánchez-Alonso from Instituto del Frío-Spain (CONSUMERPRODUCTS) visited Dr. Ingrid Undeland (LIPIDTEXT) and her research group at Chalmers University, Sweden, to study if white grape dietary fibre (WGDF) stopped oxidation in washed cod mince models fortified with trout haemoglobin (Hb). WGDF prevented oxidation during 10 days ice storage both at 2 and 4 % (w/w). Ethanol extracts of the WGDF were also tested, and the results showed that the extractable polyphenols prevented lipid oxidation as efficient as whole grape dietary fibres. Addition of the ethanol extracted dietary fibre residue to the Hb-fortified cod model showed about 50% of the inhibition relative to the whole WGDF. Grape fibres were also tested in a fatty model (washed cod with 10 % of cold-pressed herring oil added). The grape fibres gave a strong inhibition also here; however, not as efficient as in the lean system.

Author: Isabel Sánchez-Alonso, Instituto del Frío (CSIC), Madrid, Spain

Introduction

Lipid oxidation has a negative effect on flavour, odour, colour, texture, and nutritional value of muscle seafood during storage. The addition of antioxidants during processing of seafood is applied as an effective methodology to minimize such quality deterioration. Nowadays, there is a growing interest in using naturally occurring antioxidants. Along with this, there has been increasing interest within the industry in using plant extracts to minimize or retard lipid oxidation in various food products. The grape dietary fibre concentrates are considered natural products that combine the beneficial effects of dietary fibre and antioxidant properties. It has been shown in the last years that haemoglobin (especially the met-form) appears to be the main pro-oxidant present in post-mortem fish tissue. All natural strategies to inhibit oxidation caused by this catalyst is therefore currently of high interest for the industry.

The study

The aim of this study was to evaluate whether the addition of a white grape dietary fibre concentrate at a level of 2% and 4% (w/w) could prevent haemoglobin-mediated oxidation of the membrane lipids of washed cod mince during storage in ice. It was also to be evaluated how added triacylglycerols in the form of crude herring oil chemically affected the efficiency of the WGDF as antioxidants, and further how the sensory properties were affected.

In addition to testing the effect of whole WGDF, the antioxidant properties of different extracts from WGDF were also tested. An ethanol extract and the remaining ethanol-extracted dietary fibre residues were thus tested as antioxidants in the washed cod mince model system. In all trials, sensory evaluation of rancid odour and red colour estimation supplemented the chemical measurements of peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) as indicators of oxidation.

: Karin Svensson at Chalmers University instructing in the laboratory

Addition of 2% and 4% WGDF to the model system completely inhibited haemoglobin-mediated development of rancid odour during the entire ice storage (ten days). TBARS development and red colour losses correlated well with the sensory data. The addition of 10% herring oil to the washed cod mince did not change the rate of lipid oxidation, but very slightly reduced the effectiveness of 2% WGDF. The ethanol extractable polyphenols (EEP) of the WGDF had the same high antioxidant capacity as whole WGDF, while the ethanol-extracted fibre residue had about 50% of this activity. Thus, this study showed great potential of WGDF to prevent rancidity in fish; mainly due to EPP, but also to the dietary fibre itself.

Conclusion

These results indicate that WGDF is effective in delaying lipid oxidation in the studied model systems and hence could be used as an ingredient to prevent oxidation in minced fish.