The effect of grain polyphenols and the addition of vitamin E to diets enriched with α-linolenic acid on the antioxidant status of pigs

Abstract

The aim of this study was to determine the antioxidant status and blood lipid profile of pigs fed diets enriched with α-linolenic acid (ALA) and containing two sets of antioxidants: phenolic compounds of diet components (barley, triticale, naked oat and buckwheat by-products) only, or phenolic compounds and vitamin E supplementation. A three-factorial experiment was performed on growing-finishing barrows (6-7 pigs per group) fed individually diets supplemented with 3% linseed oil, formulated as isoenergetic, isofibre and isofat. The influence of the type of diet (barleytriticale-based control diets vs 40%-oat-based diets), the share of buckwheat by-products (0 vs 10/12% of grower/finisher diets), and vitamin E supplementation (0 vs 100 1U.kg -1) was evaluated. The analysed feed materials could be classified according to their total phenolic compound (TPC) content and in vitro antioxidant capacity (TAC) in the following decreasing order: buckwheat hulls and bran ≫ barley ≫ naked oat triticale. Diets with higher levels of TPC and TAC, i.e. barleytriticale-based control diets and diets containing buckwheat by-products, increased erythrocyte superoxide dismutase and glutathione peroxidase activity, similarly as 100 IU·kg-1 vitamin E supplementation, thus suggesting an improvement in the antioxidant status of pigs. Only vitamin E supplementation significantly (over four-fold) increased vitamin E concentrations in the blood serum and M longissimus dorsi (LD) of pigs, and decreased the rate of lipid oxidation in LD. The obtained results suggest that the phenolics present in cereal grains and in buckwheat, occurring as effects of oat. Since control diets and diets with a 40% share of naked oat contained similar levels of crude fibre, the obtained results could have been affected by a different content of soluble dietary fiber, including soluble -glucan. According to Delaney et al. (2003), not only oat 3-glucan, but also barley-glucan is antiatherogenic. However, assuming a β-glucan content of 3.6% in barley and oat grains, and of 1% in triticale grains (Bach Knudsen, 1997), the administered oat diets had an approximately 45% higher β-glucan content than control diets (21.7 vs 14.8 g kg-1 on average). The different solubility and molecular weight of oat and barley β-glucan could have also influenced the obtained results. Owing to their high TPC content and high antioxidant capacity, buckwheat by-products (hulls, bran) may be valuable components of pig diets. Many feed materials with a high fibre content are recommended not only for gestating sows but also for piglets. Buckwheat hulls and bran, obtained from the hydrothermal treatment of whole grain, may be a rich source of both insoluble fibre and antioxidant compounds.