Effects of dietary n-3 polyunsaturated fatty acids and ... - FINS

1 st WorkshopXIII International Feed Technology SymposiumExperimental aspectsAnimals and dietsThe study was performed with the animals given the same diets (concentrate/straw baseddiet, lipid and antioxidant supplements) and stress breeding conditions than for theanalysis of beef lipids and fatty acids (cf. Part I Effects of n-3 PUFA and antioxidants onbeef FA). Intensity of the animal stress was evaluated by plasma cortisol determined i) atthe end of the finishing period, ii) just after slaughter during the bleeding.Beef technological treatmentsLT and ST muscles were collected just after slaughter, stored under vacuum for 12 d at4°C and finally cut as steaks as on the market and packaged at +4°C in a trayoverwrapped with a film either i) under air for 4 d. (A), ii) under modified atmosphere(70:30, O 2 /CO 2 ) for 7 d. (MA), or in a bag iii) under vacuum for 14 d. (V). Beef sampleswere immediately ground into a powder in liquid N 2 and stored at -80°C until analysis.Methods for lipoperoxidation characterizationThe intensity of lipoperoxidation in plasma (jugular vein) and in beef samples atslaughter was determined by the measurement of malondialdehyde (MDA) production(after its extraction by hexane) by HPLC (fluorescence detection) using atetraethoxipropane calibration curve. Plasma and tissue vitamin E was determined byHPLC (UV detection).The in vitro susceptibility of plasma to lipoperoxidation was evaluated by measuring thekinetic production of conjugated dienes (CD) indicating the degree of resistance tolipoperoxidation (Lag phase), the lipoperoxidation velocity (Tx max) et the maximalamount of produced CD (Q max). The Peroxidizability Index (PI) of beef FA wascalculated from the FA composition of total meat lipids according to the equationreported by Hu et al. (1989) as follows: IP = (% dienoic x1) + (% trienoic x2) + (%tetraenoic x3) + (% pentaenoic x4) + (% hexaenoic x5). This index estimated bis-allylichydrogen atoms in PUFA and therefore their susceptibility to peroxidation. Plasma free4-hydroxy-2-nonenal (HNE) and free 4-hydroxy-2-hexenal (HHE), respective specificmarkers of n-6 and n-3 PUFA oxidation, were evaluated by GC-MS.Effects of dietary n-3 PUFA and antioxidants on plasma and beef lipoperoxidation(Gobert et al., 2008a and b, 2009a to c)Plasma lipoperoxidationDietary n-3 PUFA supplements reduced the resistance capacity of plasma againstlipoperoxidation (-11%) favouring conjugated diene (x 1.75) and MDA (x2) formations(Table 4).Only the combined supply of antioxidants (vit E and PERP) effectively protected plasmalipids against peroxidation (LEP diet) that was favoured by dietary n-3 PUFAsupplements, the plasma MDA and lipoperoxidation velocity Tx being reduced by -80and -33% (P=0.01) respectively in the LEP diet compared to the L diet (Table 4).Such protection by the mixture vitamin E and PERP would act not only during thepropagation phase of the lipoperoxidation reaction (by vitamin E that acts as a chainbreaker), but also during the initiation of the reaction by the uptake of free radicals bythe plant polyphenols (EVRP) as earlier demonstrated in rats and sheep (Gladine et al,2007) and in lactating cows (Gobert et al., 2008c).6