Denise Beaulieu

Summary

Carcasses from growing swine (n=96) fed diets containing either 0, 5 or 10 per cent flaxseed for 76 days were graded and the pork was subjected to a sensory evaluation by a trained taste panel. Feeding flaxseed enriched the omega-3 content of the high fat pork (for example, ground pork with 20 per cent added fat) sufficiently to allow a labelling claim in Canada, however, panellists detected evidence of off-flavours and rancidity in these products. Increasing dietary flaxseed resulted in higher lean yield and reduced belly firmness and fat hardness.

Introduction

It has been shown that the consumption of omega-3 fatty acids, such as a-linolenic (C18:3) is beneficial to human health. Pork fat is representative of the fatty acids consumed by the pig, and the consumption of flaxseed, or flaxseed oil, by finishing pigs will result in a carcass enriched with omega-3 fatty acids.

Several recent experiments conducted at Prairie Swine Research Centre (PSCI) have examined dietary regimes required to increase omega-3 fatty acid concentration of pork effectively. The flaxseed used has been co-extruded with peas giving a product (Linpro®) with improved handling properties and amino acid balance (i.e. PSCI Annual Report 2008). However, primarily because unsaturated fatty acids are susceptible to rancidity and are ‘oilier’ in nature, this experiment was designed to investigate whether increasing the omega-3 fatty acid content of the pork fat had any effect on carcass quality or sensory properties of pork chops and ground pork prepared from these carcasses.

Materials and Methods

A total of 96 animals with an initial body weight of 48±2kg (mean ± SD) were used with 12 pens of barrows and 12 pens of gilts (four animals per pen). Dietary treatments included three levels of flaxseed (0, 5 and 10 per cent) co-extruded 50:50 with field peas (Linpro®, supplied by O&T Farms, Regina, Saskatchewan, Canada). All diets had equal amounts of field peas and diets were formulated and adjusted every four weeks to meet the nutrient requirement of the pigs as they grew (NRC, 1998). After 76 days on test, animals were shipped to Lacombe Research Centre (Lacombe, AB, Canada) and slaughtered in a simulated commercial manner. A trained eight-member panel tasted fresh, frozen loin chops and hamburger and scored each for various attributes using a nine point scale.

Results

Performance

Similar to what we have observed in previous studies, feeding 10 per cent flaxseed for 11 weeks had no effect on performance of growing pigs (data not shown).

Carcass quality

Raw pork chops

Dietary flaxseed did not affect carcass temperature or pH measured 45 minutes post-slaughter. However, there was a slight increase in pH at 48 hours post-slaughter (data not shown). Increasing dietary flaxseed also resulted in higher lean yield and reduced belly firmness and fat hardness (Table 1, P<0.05).

Pork from pigs fed flaxseed was slightly darker as indicated by decreased iodine values (P< 0.01). No effects of diet (P >0.05) were observed on tenderness of pork chops (shear force), cooking loss or cooking time (data not shown).

Sensory attributes

Panellists detected slight decreases in pork flavour and off-flavour intensity in the fresh frozen and reheated loin chops (P<0.05; Table 1). Conversely in ground pork, except for juiciness, all the sensory attributes measured, including tenderness, pork flavour intensity and off-flavour intensity were negatively affected by feeding co-extruded flaxseed (P<0.01). Furthermore, the percentage of panellists detecting a rancid flavour in ground pork was increased. This may be a result of increased opportunity for oxidation with processing.

Fatty acid composition

The fatty acid composition was determined in intramuscular fat and ground pork. The trends were similar, and thus only the results for the ground pork are presented (Table 2). Dietary flaxseed increased the polyunsaturated fatty acid content of the ground pork, primarily due to a dramatic increase in C18:3 (omega-3) (P<0.001). Although the content of C18:2 (n-6) was increased by feeding flaxseed, the omega-6/omega-3 ratio was decreased (P<0.001), which is also beneficial to human health. The increased C18:3 levels in the ground pork (20 per cent added fat) seen following 10 per cent dietary flaxseed supplementation would be sufficient to obtain a source claim of 300mg per 100 gram serving in Canada. However, in pure muscle, with lower fat levels, the C18:3 levels would not meet this requirement.

Conclusions

Feeding co-extruded flaxseed to increase the alpha-linoleic acid content in loin muscle did not result in levels sufficient to meet label requirements in Canada for a source claim if the cuts were trimmed of fat. Moreover, co-extrusion of flax not provide sufficient antioxidant capacity to alleviate texture and flavour problems in high fat products, i.e. ground pork, with elevated polyunsaturated fatty acid content. Although high-fat products are required to allow labelling for an omega-3 enriched product, the added fat may result in some negative effects on palatability.

Implications

Although high fat products are required to allow labelling for an omega-3 enriched product, the added fat may result in some negative effects on palatability. Strategies must be investigated to mitigate these effects.

Acknowledgements

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

Further Reading

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