Denise Beaulieu

Summary

Previously, the authors say they have shown that pork from pigs fed high flaxseed-containing diets can be subject to rancidity. The objective of this experiment was to determine if added vitamin E could mitigate this problem. A total of 96 growing pigs were fed one of three different diets for 11 weeks prior to slaughter. The diets contained either zero or five per cent flaxseed or five per cent flaxseed plus 200 mg/kg vitamin E.

As expected, feeding flaxseed increased the omega-3 fatty acid content of the pork, especially high-fat pork products. This was accompanied by the detection of off-flavours such as rancidity. The added vitamin E lessened these negative side-effects although this pork still did not score as high as that from animals fed no flaxseed.

Introduction

Successful marketing of pork enriched with omega-3 fatty acids requires that other pork attributes are not reduced. The researchers have conducted a series of experiments and shown that the inclusion of five per cent extruded flaxseed in the diet of finishing pigs for 11 weeks prior to marketing enriched some cuts of pork sufficiently to allow a claim of ‘omega-3 enriched’ (300mg omega-3 per 100 grams). At the high levels of enrichment, there was some indication of off-flavours noted by the taste panels.

Vitamin E (DL-α-tocopherol acetate) is a natural fat-soluble vitamin which has been used in high-fat diets to prevent the oxidation of unsaturated fatty acids which can cause rancidity.

The objective of this experiment was to determine the impact of added dietary vitamin E on the incidence of rancidity or off-flavours in omega-3 enriched pork products.

Materials and Methods

The experiment required 96 pigs and was conducted using a completely randomised block design with a 3×2×2 factorial arrangement of treatments: Treatments were three dietary treatments: a) control, b) five per cent flaxseed and c) five per cent flaxseed plus 200 mg (IU)/kg diet vitamin E by two initial weight groups: a) 30±4kg and b) 44±4kg by two genders.

Diets were based on wheat, barley and soybean meal and fed for three phases of growth. The flaxseed was added as Linpro ®, an extruded 50:50 pea/flaxseed blend using extrusion conditions optimized in a previous experiment (Htoo et al. 2008) and supplied by O&T Farms, Regina, SK. Field peas were added to the diets to compensate for the peas added in the Linpro and thus equalise pea content in all diets.

Diets a) and b) contained 11 mg (IU) per kilo vitamin E, meeting the requirement (NRC 1998) for pigs of this age, but providing no ‘safety margin’. Diets were fed for 11 weeks prior to slaughter.

Flax

Pigs were shipped to the Agriculture and Agri-Food Canada, Lacombe Research Centre, and were slaughtered in a simulated commercial manner. Sensory analysis of fresh, cooked pork and burgers was conducted by a trained taste panel.

Results

As expected, a diet containing 5 per cent flaxseed, fed as a 50:50 co-extruded pea/flaxseed blend increased the omega-3 content of pork fat, and thus of pork commercial cuts containing fat regardless of the content of vitamin E (Table 1). Omega-3 fatty acids are highly unsaturated which results in a decreased fat hardness.

Feeding five per cent flaxseed to pigs for 11 weeks had minimal or no effect on flavour, including rancidity, in low-fat cuts of pork. Ground pork, containing 20 per cent fat, from pigs fed five per cent flaxseed had slightly, but significantly, decreased pork flavour, desirability and palatability. A greater proportion of panelists reported pigs fed flaxseed have a rancid or ‘other flavour’ (Table 2). Supplemental vitamin E mitigated the effect of the flaxseed on rancidity, and the other negative attributes.

Conclusions

Although supplementing the diet of finishing swine with five per cent flaxseed for 11 weeks will have minimal or no effects on off-flavours in low-fat cuts of pork, cuts containing a higher content of fat (e.g. ground pork) will be negatively affected. Supplementing the diet with 200 IU/kg vitamin E will mitigate these negative effects (Figure 1).

Figure 1. Sensory analysis of burgers.
(Rancidity is reported as the percentage of panelists reporting meat with this attribute. Palatability is measured on a nine-point scale where 1=extremely undesirable and 9=extremely desirable (a, b. P < 0.05)

Implications

It is well recognised that the production of pork with enhanced nutritional attributes, such as omega-3 enriched, must not compromise pork quality. The rancidity and off-flavours which may accompany increased levels of omega-3 fatty acids in pork can be mitigated by feeding high levels of vitamin E. Further research is required to determine if there are other, more efficient methods, (e.g. post-harvesting technologies) which could alleviate this problem.

Acknowledgements

Project funding was provided by Flax Canada and the Saskatchewan Agriculture Development Fund. We gratefully acknowledge the donation of the LinPro from O & T Farms, SK. Strategic funding provided by Sask Pork, Alberta Pork, Manitoba Pork Council and the Saskatchewan Agriculture and Food Development Fund.

Further Reading

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You can view other papers from the Prairie Swine Research Centre Annual Report 2009 by clicking here.