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Elin Hallenstvedt defended her thesis on February 11th 2011
Ane Gro Siri SkjelfjordThe influence of dietary fatty acid composition and sex on pork quality
Abstract from the thesis - PhD thesis 2011:04
Norway is an important fish catching and producing country and has traditionally used fish and fish by-products in feed for monogastric animals, the pig is no exception. Fish and fish by-products are excellent sources of essential amino acids, healthy fatty acids, vitamins and serves as a mineral supplier. Extended use has, however, caused negative effects on pork quality in terms of fat firmness, off-flavours and off-odours. During the last years feed recommendations, for most pigs in Norway, have been: no use of fish or fish by-products in feed for slaughter pigs, maximum iodine value product (IVP) 57/feed unit and minimum 200 mg/kg vitamin E. These limitations have challenged the formulation of pig feeds. The overall aim of this thesis was to evaluate the effects of different dietary fat level, fatty acid composition and of sex (entire male and female) on sensory, technological and nutritional pork quality parameters.
Three feeding experiments were conducted using entire males and females of the crossbreed [(Norwegian Landrace x Yorkshire) x (Duroc)]. Pigs were individually and restricted fed. Fat sources used were soybean oil, palm kernel oil and fish oil. Experimental diets varied in IVP: 31 to 118, fish oil inclusion in percent: 0, 0.25, 0.48, 0.52, 0.72 and 3.0 and fat level in percent of dry matter 2.9 up to 9.6. The ribs, pork chops and mince for meat balls were short-term frozen stored at -20 °C for 3 months, and belly and neck were short-term frozen stored for 2 and 4 months, respectively, at 80 °C. All products were tested by sensory profiling after short-term frozen storage. Long-term stored ribs, loins and meat balls were wrapped in plastic bags and frozen stored at -20 °C for additional 6 months and meat balls for additional 7 months. The ribs were long-term stored in darkness while the chops and meat balls were exposed to light simulating normal retail display. Long-term stored bellies were stored for 12 months at -80 °C with additional 6 months at -20 °C. Fatty acid composition was measured in shoulder fat (outer and inner layer), in backfat (outer and inner layer) at P2 location and in neutral lipids and phospholipids of M. longissimus dorsi (LD). Backfat firmness and colour, and meat colour were also evaluated.
The results from the present study showed that the fatty acid composition of backfat, inner and outer layer and neutral lipids of LD changed towards the dietary fatty acid composition. Feeding low fat diets seemed to enhance the de novo fatty acid synthesis, producing SFA and MUFA, especially C18:1. Pigs fed low fat diets had low percentages of the very long chain (VLC) n-3 fatty acids, mostly C22:5n-3 in backfat and in neutral fat of LD. These pigs had also a high C20:4n-6 percentage indicating production from C18:2n-6. Dietary soybean oil, giving a high IVP, led to an increase in the percentage of C18:2n-6 linearly to the dietary contribution. These pigs were also low in VLC n-3 and still the C22:5n-3 was dominating. When introducing fish oil, high in VLC n-3 fatty acids, a substantial increase in the percentages of C20:5n-3, C22:5n-3 and C22:6n-3 in backfat and neutral lipids of LD was found indicating a higher nutritional quality. Increasing the fat level, by use of other added fat in combination with fish oil, seemed to improve the wanted incorporation of VLC n-3 fatty acids into both backfat and neutral fat of LD.
Our results further suggest that fish oil and high PUFA diets can be used for slaughter pigs without detrimental effects on sensory attributes like odour and flavour on short-term frozen stored products. After long-term frozen storage rib, meat balls and belly were not negatively influenced by high dietary PUFA, or dietary fish oil up to 0.7%. Only pork chops from the highest dietary IVP group showed increased odour and flavour rancidity and intensity. Long-term stored belly from pigs fed the second highest fish oil inclusion (0.5%) gave no off-flavour or off-odour. Only tendencies to higher fish oil flavour in the long-term stored belly was found in the highest fish oil group. After reheating, bellies from the highest fish oil group had a slightly increased fish oil flavour and odour together with a significant rancid flavour and odour.
Dietary IVP slightly influenced the backfat firmness. Higher firmness scores were obtained when the dietary IVP declined. Fat colour was less influenced by the dietary fatty acid composition.
Phospholipids had, as expected, high percentages of PUFA but were also influenced by the dietary treatments. Both low fat and soybean oil diets gave higher C20:4n-6 percentages and lower percentage of VLCn-3 fatty acids than fish oil fed pigs. The supply of C18:3n-3 seemed to enhance the desaturation and elongation into C20:5n-5 and C22:5n-3 but a decrease in the percentage of C22:6n-3 when feeding these diets strongly supports the view that the synthesis of this fatty acid is very limited in pigs. Providing dietary VLC n-3 fatty acids by using fish oil, these fatty acids were incorporated into phospholipids, now with the C20:5n-3 and C22:6n-3 as the prominent.
Sex had an impact on fatty acid composition. Males had higher PUFA and lower MUFA percentages in outer and inner layers of back fat and shoulder fat and in neutral fat of LD. The percentage of C18:1 was in particular lower in males, indicating a lower delta-9-desaturase activity as compared to females.
In conclusion, it is possible to change the fatty acid composition of pork towards healthier products for human consumption without detrimental effects on important sensory traits. Care must, however, be taken when long term storage or reheating is intended.
Publisert: 01.06.11
Oppdatert: 10.06.11
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