Lipid oxidation and fishy odour in protein hydrolysate derived from Nile tilapia (Oreochromis niloticus) protein isolate as influenced by haemoglobin.

BACKGROUND

Although protein isolates have been proven as a potent raw material for protein hydrolysate preparation, the fishy odour associated with lipid oxidation is still detected. The remaining haemoglobin (Hb) in protein isolates can effectively induce lipid oxidation, leading to the formation of fishy odour in the resulting hydrolysate. The aim of this study was to elucidate the impact of Hb with different forms, oxyhaemoglobin (oxy-Hb) and methaemoglobin (met-Hb), on lipid oxidation and the development of fishy odour during hydrolysis of protein isolates.

RESULTS

During hydrolysis of protein isolate up to 120 min, non-haem iron content, peroxide value and thiobarbituric acid reactive substances slightly increased (P < 0.05). When oxy-Hb or met-Hb was incorporated, the marked increases in all parameters were observed, especially within the first 60 min of hydrolysis. The higher increases were obtained with the latter, suggesting that met-Hb was more pro-oxidative than oxy-Hb. However, no differences in degree of hydrolysis of all samples were observed (P > 0.05). The marked increases in the b*, ΔE*, ΔC* values, fishy odour/flavour and volatile compounds were also found in the resulting hydrolysate containing either oxy-Hb or met-Hb.

CONCLUSION

Hb, particularly met-Hb, induced lipid oxidation and the development of a fishy odour/flavour in fish protein hydrolysate.