Effects Of Soy Isoflavones On Growth, Meat Quality And The Mechanism Of Antioxidant Function In Lingnan Yellow Broilers

Five studies were designed to investigate the effects of soy isoflavones on antioxidant property in chick skeletal muscle cells (SMC) and Lingnan yellow male broilers. The first three studies were carried out to investigate the protective effects of a synthetic isoflavone(SI) and genistein(GEN) on antioxidative defense system and membrane fluidity in chick skeletal muscle cells in vitro. The last two studies were conducted to investigate the effects of a synthetic isoflavone on growth performance, meat quality, and antioxidative property in Lingnan yellow male broilers.In study 1, the antioxidant and protective properties of SI were investigated using chick SMC (leg) isolated from 20-day-old Lingnan yellow broiler chick embryo. Chick SMC were cultured in Dulbecco's modified Eagle's medium added with 0,12.5,25,50, 75 and 100μmol/L SI respectively under 80μmol/L H2O2/FeSO4 conditions. After 48h incubation, SI reduced the loss of SMC under oxidative stress by H2O2/FeSO4 The addition of SI significantly promoted SMC proliferation (p<0.01). Supplementation with 25,50,75 and 100μmol/L SI enhanced the activity of total superoxide dismutase (T-SOD) by 17.0%,13.0%,13.3% and 11.9%respectively in the supernatant of media (p<0.05). Compared to the control, the activity of glutathione peroxidase (GSHPx) increased by 90.7% at 25μmol/L concentration of SI (p<0.05). The activity of catalase (CAT) increased by 49.2%and 49.1%respectively at 75 and 100μmol/L SI (p<0.01). The concentration of creatine kinase (CK) in the media decreased by 61.6%and 60.6% respectively at 75 and 100μmol/L SI (p<0.01). Therefore, the SI protected skeletal muscle cells from oxidative damage, attributing to its antioxidant activity.Study 2 was to investigate the protective effect of genistein(GEN) on antioxidative defense system and lipid peroxidation in chick SMC. Chick SMC were treated with 0, 1,4, and 16μmol/L GEN, respectively. The activities of GSHPx, T-SOD and CAT and the concentration of malondialdehyde (MDA) were measured in supernatant of the medium for culture of chick SMC. Meanwhile the expression of GSHPx mRNA was determined by RT-PCR method. Compared to control, treatment with 1,4 or 16μmol/L GEN decreased MDA production yield by 33.85%(p<0.05),33.08%(p<0.05) and 50.77%(p<0.05), respectively. The activity of SOD significantly increased after treated with 1μmol/L or 16μmol/L GEN (p<0.05). The addition of GEN at 4 or 16μmol/L improved the activity of GSHPx (p<0.05). These results indicated that GEN could inhibit lipid peroxidation and improve antioxidative property by inhibiting MDA production and increasing the activities of antioxidant enzymes in chick SMC.Study 3 was conducted to investigate the protective effect of GEN and SI (from 20 to 80μmol/L) on antioxidative defense system and membrane fluidity in chick SMC treated with 50μmol/L H2O2/FeSO4 for 48h. GEN and SI supplementation significantly increased the activities of T-SOD and GSHPx (p<0.05) and decreased the MDA production yield (p<0.05), regardless of H2O2/FeSO4 treatment. GEN at 80μmol/L and SI at 40,80μmol/L decreased the secretion of CK in H2O2/FeSO4 treated cells (p<0.05 or p<0.01). Fluorescence polarization values and micro viscosities observed in H2O2/FeSO4 treated cells were significantly higher than those observed in untreated cells. The addition of 80μmol/L GEN or SI decreased the fluorescence polarization value in H2O2/FeSO4 treated cells (p<0.05). The microviscosity value decreased significantly due to GEN or SI addition (p<0.05). Adding 20μmol/L GEN or SI improved the expression of GSHPx mRNA. These results suggested that GEN or SI has antioxidative effects in SMC.Study 4 was aimed at investigating the effects of SI on growth performance, meat quality, and antioxidation in male broilers. A total of 1500 42-day-old birds were allotted to five treatments with six replicates per treatment (50 birds per replicate). Birds were fed diets supplemented with 0,10,20,40, or 80 mg/kg SI, respectively, for a period of 3 weeks ad libitum. The results showed that dietary supplementations with 10 mg/kg or 20 mg/kg SI increased weight gain by 13.6% and 16.2%(p<0.01), and elevated feed intake by 7.37%(p<0.05) and 11.2%(p<0.01), respectively. Addition of 10mg/kg SI decreased feed:gain by 5.5%(p<0.05). Supplementation with SI in the diet increased water holding capacity (WHC) 24h,72, and 96 postmortem (p<0.01). The addition of 40 mg/kg SI significantly increased the pH value of meat 24h and 96 postmortem (p＜0.01). Adding 40mg/kg SI decreased meat color L value 45min and 96 postmortem (p<0.05). Lactic acid (LD) production yield was significantly decreased in breast muscles of 10,20, or 40mg/kg SI-supplemented chickens 45min postmortem (p<0.01). MDA concentration was reduced in plasma of 10 or 20 mg/kg Si-supplemented chickens (p<0.05), in liver of SI-supplemented chickens (p<0.01), and in breast meat of 20,40, or 80 mg/kg SI-supplemented chickens 45min and 72h postmortem (p<0.05 or p<0.01). The addition of 40 or 80mg/kg SI significantly increased TAOC (p＜0.01) and slightly elevated T-SOD activity (p<0.1) in plasma of chickens. The dose of 80mg/kg SI slightly improved catalase activity in plasma (p<0.1). In breast muscle, dietary SI caused a decrease in T-SOD activity 45min postmortem (p<0.05 or p＜0.01), while increased T-SOD activity 12h,48h and 72h postmortem (p<0.05 or p＜0.01). CAT activity significantly increased 70.61% by the supplemental SI at 40 mg/kg level (p<0.05). The results indicated that dietary SI could improve growth performance and meat quality by decreasing lipid peroxidation and enhancing antioxidative capacity in male broilers.The study 5 was designed as a 2 x 2 factorial arrangement with 2 types of fish oil (oxidized oil and fresh oil) and 2 SI supplementation levels (0 and 20 mg/kg) to determine the effect of dietary SI on performance, meat quality and antioxidative property in male broilers. Six replicates of 45 birds (42 d old) were used for each treatment. The experiment lasted for 3 weeks. The results showed that average daily gain, feed intake, feed conversion and carcass traits were not affected by SI supplementation or fish oil types. The oxidized fish oil treatment significantly increased breast muscle color L value (p<0.01) and decreased a*(p<0.01) and b* values (p＜0.01). The activity of CK and TAOC in plasma decreased by oxidized fish oil treatment (p<0.01). Oxidized fish oil treatment increased MDA concentration and reduced TAOC in breast muscle (p<0.01). The SI supplementation decreased MDA and LD concentrations (p<0.05 or p＜0.01), and improved the activities of T-SOD, GSHPx and TAOC (p<0.05 or p<0.01). The SI supplementation increased the expression of GSHPx mRNA. The interaction effect of fish oil and SI supplementation was significant on the concentrations of MDA and LD and the activities of CAT, GSHPx and TAOC in breast muscle (p<0.05 or p<0.01). The results indicated that oxidized fish oil treatment induced lipid peroxidation and reduced breast muscle color oxidant stability. Dietary SI could improve antioxidative property of meat in male broilers fed oxidized fish oil diet.It was concluded from studies 1,2 and 3 that dietary SI and GEN are effective in protecting SMC from oxidative damage. Studies 4 and 5 suggested that there may be potential for soy isoflavones to inhibit lipid oxidation, improve meat quality by ameliorating the antioxidant status and regulating antioxidant enzyme mRNA expression in vivo.