The effect of soybean-sunflower oil and antioxidant supplementation on feedlot lamb performance and meat quality

Thesis (MScAgric)--Stellenbosch University, 2024.

ENGLISH ABSTRACT: Plant oils in feedlot diets can have several beneficial effects on lamb production. As an alternative energy source, plant oils can increase the lipid density in feedlot lamb diets to substitute a portion of carbohydrates and manipulate the fatty acid profile of the product. However, using plant oils rich in unsaturated fatty acids could adversely affect meat quality with an increased susceptibility to lipid oxidation. To preserve meat quality over the retail display period and during thermal processing, dietary antioxidants could be used to incorporate the antioxidants within the muscle tissue. There is a trend towards using natural antioxidants in food production because synthetic antioxidants are perceived as potentially harmful to animal and human health. This study aimed to investigate the effects of low inclusion levels of plant oils and synthetic or natural antioxidants on the production, product yield and meat quality of feedlot lambs. Substituting a portion of carbohydrates (crushed yellow maize) with a soybean-sunflower oil blend (1.62%) had no effect on the feedlot performance of Dohne Merino lambs fed for 52 days (N = 120). However, the plant oils increased polyunsaturated fatty acids, specifically the conjugated linoleic acid (CLA) within the intramuscular fat (IMF) of the M. longissimus thoracis et lumborum (LTL, N = 40) without increasing IMF. The increased CLA content decreased the oxidative stability of lamb meat during retail display conditions over seven days. The plant oils negatively affected the colour of the LTL, and that both a synthetic and natural antioxidant successfully mitigated this colour deterioration. Using natural antioxidants resulted in lower free carbonyls after seven days under retail display conditions. However, lipid oxidation was unaffected when estimated by TBARS (2-thiobarbituric acid reactive substances), as neither the plant oil nor the antioxidant had any beneficial effect on the TBARS after seven days. A trained descriptive sensory panel did not note any differences between the treatments for the respective sensory attributes and sensory-related physical attributes. Similarly, the cooking loss percentage and WBSF (Warner-Bratzler shear force) values were unaffected, suggesting that neither the soybean-sunflower oil blend nor the use of dietary antioxidants altered the sensory profile of the lamb meat. This study has shown that plant oils can be used at 1.62%, without dietary antioxidants, in feedlot lamb diets, and not adversely affect lamb feedlot performance, TBARS and sensory quality of lamb meat. However, the plant oils would increase the conjugated linoleic acid content of the IMF, and without the addition of dietary antioxidants, it would lead to colour degradation over a seven-day retail display period.

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Masters