Effects of diets containing hemp seeds or hemp cake on fatty acid composition and oxidative stability of sheep milk

Abstract

High levels of polyunsaturated fatty acids (PUFAs) are desirable in milk for its nutritional quality, but make it vulnerable to oxidation. The aim of this trial was to assess the effects of dietary intake of hemp (seeds or cake) on milk production, fatty acid (FA) profile, and oxidative stability when sheep diet included a source rich in PUFAs. The control diet (C), which was composed of hay-based rations and completed with mixed concentrate, was compared with two experimental diets that were designed to provide the same amount of fat via hemp seed (180 g/d) (HS diet) or hempseed cake (480 g/d) (HC diet). The hemp was determined to have significantly increased the yields of milk, energy-corrected milk (ECM), fat corrected milk (FCM) (6.5%), protein corrected milk (PCM) (5.8%) and milk fat. The hemp generated a greater proportion of n-3 FA, notably α-linolenic acid (ALA), which increased by 49–66%. The addition of hemp also led to an increase in C18:1 t11 (vaccenic acid (VA)) and conjugated linoleic acids (CLA), particularly isomer c9, t11 CLA (rumenic acid (RA)). The HC group showed a greater content of milk ALA and VA and tended to show a greater content of c9,t11 CLA than the HS group. The atherogenic index (AI), thrombogenic index (TI), n-6/n-3 FA ratio and hypocholesterolemic/Hypercholesterolemic (h/H) ratio suggest that hemp could be useful in improving milk quality. The results obtained in this study suggest that the inclusion of hempseed cake appears to be more effective in ameliorating these indices than hemp seed. The author determined the concentration of fat-soluble antioxidant (tocopherol and retinol) by high performance liquid chromatography (HPLC), and assessed the total antioxidant capacity (TAC) by measuring the ABTS (2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid) scavenging capacity and degree of oxidative degradation of lipids – using the classical test based on the concentration of malondialdehyde (MDA). The TAC was higher in the milk of the HS and HC groups compared with C, being in direct correlation with the higher concentration of α-tocopherol of milk and lower concentration of MDA, the extent of the change being greatest for the animals fed the HS diet. Therefore, hemp seeds and hempseed cake appear to be ideal supplements for improving the FA profile and health lipid indices and preventing lipid oxidation in raw milk.

Keywords: α-linolenic acid, α-tocopherol, antioxidant activity, atherogenicity index, malondialdehyde