Feed and Fishy Flavour in Poultry Meat

Nutrition Update
Volume 12 No.2, November 2001

Oxidation and Fishy Flavour

Fishy taste is generally caused by oxidation of the fat in poultry meat. Consider the factors which increase the chances of oxidation.

a) Feeding unsaturated fat to chickens and turkeys will increase the amount of unsaturated fat in the meat. The more unsaturated the fat in the feed ingredient, the more unsaturated the fat in the meat and greater the chance of oxidation.

• Low Risk: Oils and full-fat oilseeds containing mostly linoleic acid would present a low risk for causing fishy flavours. Examples would be soybean, canola, sunflower and safflower oils and seeds. Few problems have been encountered when using these products. Feeding 20% full fat soybean has been reported to cause a less desirable flavour but not a fishy flavour.
• Medium Risk: Flaxseed and linseed oil contain high levels of linolenic acid and oxidation is more likely. Feeding 10% to 20% flaxseed (or about 4% to 8% linseed oil) may cause an off-flavour or occasionally fishy flavour in eggs. The level that will cause problems in meat has not been determined but is likely similar.
• High Risk: The long chain polyunsaturated fatty acids in fish oil and fish meal are very prone to oxidation. Low levels of fish oil (1% or 2%) can cause a fishy taste. The borderline for an off-flavour with fish meal is 5% of the diet. Adding 10% fish meal would be expected to cause an off-flavour and occasionally a fishy flavour. A fishy taste would be expected from feeding 15% fish meal. The level of fat in the fish meal and quality of the meal will influence how readily a fishy taste develops. To prevent a fishy flavour, it may be necessary to withdraw the fish oil or meal from the feed two to six weeks prior to marketing the birds.

b) Storing meat, especially after it has been cooked, will allow oxidation. Meat frozen raw can take months to develop an off-flavour while in some cases cooked meat will only take days or weeks.

c) Cooking oils and bubbling air through them can greatly increase the oxidation of even relatively low risk oils.

d) Deboning meat will release iron from heme (blood) in the meat and the iron will catalyse the oxidation. Grinding the meat will increase the surface area exposed to air and speed oxidation as well.

e) Anti-oxidants in the meat can slow oxidation. Feeding elevated vitamin E levels to birds will increase vitamin E levels in the meat and slow oxidation. The level of vitamin E supplementation needed to reduce oxidation in turkey meat seems to be particularly high (200 to 500 IU/kg of feed). Vitamin E cannot be relied upon to prevent fishy flavour from occurring, especially in birds fed high risk ingredients like fish oil and fish meal.

Trimethylamine (TMA) and Fishy Flavour

A cause of fishy flavour unique to certain strains of brown egg laying hens is trimethylamine or TMA. Some strains of brown egg layers lack the ability to break down this compound and will deposit it in the egg. Feeding 5% traditional rapeseed or fish meal can cause susceptible hens to produce eggs with a tainted flavour. Traditional rapeseed meal does not cause a fishy flavour in poultry meat but perhaps a slight change in odour when 15% or more is added to the diet. No problems with eggs or meat has been reported when feeding modern canola meal. Up to 20% canola meal in the diet has been tested by researchers and no off-flavours have been reported.

 

Prepared By:	Carlyle Bennett, M.Sc.
	Business Development Specialist - Poultry
	Livestock Knowledge Centre
	Manitoba Agriculture, Food and Rural Initiative