| Animal health is highly associated with the quality of protein feed. However, proteins are often exposed to oxidants or oxidizing conditions during feed transportation, processing and storage, which are vulnerable to oxidative modification. At present, little information is available concerning effects of protein oxidation on quality of protein feed, dietary oxidized protein on animal health and associated regulation measurement. Therefore, current study evaluated protein oxidation in soy protein isolate (SPI) as affected by heat treatment and soybean oil inclusion in vitro, and oxidized SPI on growh performance, digestive function and redox status and the alleviation of different types of vitamin E (VE) in broilers. This study was composed of 6 trials as below:Trail 1 was conducted to evaluate protein oxidation in SPI as affected by heat treatment and soybean oil inclusion. The SPI, SPI mixed with 1% soybean oil (SPIOl) or SPI mixed with 2% soybean oil (SPI02) incubated at 100? for 8 h were used to determine the protein oxidation of SPI, respectively. Increase of protein carbonyl content (P<0.05),decrease of protein sulfhydryl groups (P<0.05) and NSI (P<0.05) of SPI were observed as incubation time increased in all treatments. Decreased in vitro digestibility of DM and CP were also observed in SPIO1 and SPI02 (P<0.05). Inclusion of 2% soybean oil increased protein carbonyl content of SPI at 8 h incubation (P<0.05) and accelerated the decline of NSI as compared with other treatments. SDS-PAGE analysis indicated that heat caused fragmentation of polypeptide chain in SPI as evidenced by the decline of intensity of ?, B and ?, ? bands.Trail 2 was conducted to explore growth performance and digestive function of broilers fed oxidized protein diets. A total of 216 one-day-old Arbor Acres broiler chickens were randomly divided into 3 groups with 6 replicates of 12 birds for a 21-d feeding trial.Birds were fed a basal diet (CON), 8 h heat-oxidized SPI diet (HSPI) or 8 h heat-oxidized mixture of SPI and 2% soybean oil diet (HSPIO), respectively. HSPI and HSPIO decreased body weight gain,serum total protein content at 14 and 21 d,relative jejunum weight and pancreatic trypsin activity at 21 d (P<0.05). HSPIO decreased anterior intestinal contents trypsin activity at 14 d and amylase and trypsin activity at 21 d, pancreatic amylase activity at 21 d and apparent digestibility of DM, OM and CP of broilers from 18 to 20 d (P < 0.05).Trail 3 was conducted to determine the redox status of broilers fed oxidized protein diets. Experimental design was the same as that of trial 2. Compared with CON group,serum T-AOC, GSH and liver CAT activity of broilers in HSPI and HSPIO groups was decreased (P<0.05).HSPIO decreased serum, duodenal mucosa and jejunal mucosa GSH-Px activity and liver GSH (P<0.05). Broilers fed HSPIO diet exhibited lower hydroxyl radical scavenging capacity of liver and superoxide anion radical scavenging capacity of jejunal mucosa (P<0.05). Increased serum and jejunal mucosa carbonyl(P<0.05),liver AOPPs (P<0.05) and serum MDA (P<0.05) were observed in broilers fed HSPI and HSPIO diets. HSPIO increased liver carbonyl (P<0.05), serum AOPPs (P<0.05),liver and jejunal mucosa MDA (P<0.05) as compared with that of CON. Same trend was also observed in jejunal mucosa AOPPs (P<0.05) of broilers in HSPIO group compared with others.Trail 4 was conducted to study the protective effects of VE on growth performance,antioxidant capacity and Nrf2 signaling pathway of broilers fed oxidized protein diet. A total of 400 one-day-old Arbor Acres broiler chickens were randomly divided into 5 groups with 8 replicates of 10 birds for a 42-d feeding trial. Birds were fed a basal diet (CON), 8 h heat-oxidized mixture of SPI and 2% soybean oil diet (HSPIO), HSPIO plus 200 mg/kg synthetic VE (dl-a-tocopherol acetate) (SE), HSPIO plus 200 mg/kg natural VE (?-,?-, ?-,8- mixed tocopherol) (NE), HSPIO plus 100 mg/kg synthetic VE (dl-a-tocopherol acetate)and 100 mg/kg natural VE (?-,?-, ?-, ?- mixed tocopherol) (SNE), respectively. HSPIO decreased ADG in finisher and whole phase, pancreas relative weight at 42 d and serum GPT activity at 21 d of broilers. Increased ADG in SE and SNE group, decreased pancreatic relative weight at 42 d and serum GPT activity at 21 d in VE groups were observed as compared with that of HSPIO. Higher content of a-tocopherol and total tocopherol in serum,liver and jejunal mucosa were observed in SE (P<0.05), same trend was also found in ?-+?-tocopherol content in serum of broilers in NE group (P<0.05). Liver and jejunal antioxidant capacity and mRNA expression of antioxidant enzymes of broilers were inhibited by feeding HSPIO, whereas those of which were enhanced by dietary addition of different types of VE. HSPIO decreased Nrf2 protein expression in liver as compared with that of CON (P<0.05),whereas that of which was increased in NE group(P<0.05).Dietary treatment did not alter Keapl protein expression in liver (P>0.05).Trail 5 was conducted to evaluate cell apoptosis in liver and jejunal mucosa of broilers fed oxidized protein diet. Experimental design was the same as that of trial 4. Increased caspase-3 content in liver and jejunal mucosa(P<0.05), decreased Bcl-2 in liver (P<0.05)were observed in broilers fed HSPIO as compared with that of CON at 42 d. Decreased content of liver caspase-3 in SE and SNE groups (P<0.05), jejunal mucosa caspase-3 in VE groups (P<0.05) and jejunal mucosa Bax in SE and SNE groups (P<0.05) were noticed as compared with that of HSPIO. HSPIO increased mRNA expression of liver caspase-3, Bax and p53 (P<0.05) and jejunal mucosa caspase-3 (P<0.05) at 21 d and decreased Bcl-2 mRNA expression (P<0.05) in liver at 42 d as compared with that of the CON. Decreased liver mRNA expression of caspase-3 in NE group (P<0.05), Bax in VE groups (P<0.05),p53 in SE and NE groups (P<0.05) at 21 d and liver caspase-3 in VE groups (P<0.05) at 42 d, increased liver mRNA expression of Bcl-2 in SE and SNE groups (P<0.05) at 21 d and Bcl-2 in SNE group (P<0.05) at 42 d were observed as compared with that of the HSPIO.Same trend was also noticed in mRNA expression of 21 d jejunal mucosa caspase-3 in SE and NE groups (P<0.05) and 42 d jejunal mucosa Bcl-2 in SE and SNE groups (P<0.05).HSPIO increased liver caspase-3 (P<0.05) and cleaved caspase-3 (P<0.05) protein expression and decreased Bcl-2 (P<0.05) protein expression as compared with that of the CON,while those of which were improved in VE groups (P<0.05) and NE group (P<0.05),respectively. Liver Bax protein expression were not differ among dietary treatments(P>0.05).Trail 6 was conducted to study the protective effect of VE on meat chemical composition, meat quality and antioxidant capacity of broilers fed oxidized protein diets.Experimental design was the same as that of trial 4. The yield of breast muscle and thigh muscle of broilers was decreased by feeding HSPIO (P<0.05), whereas breast muscle yield was increased by dietary supplementation of VE (P<0.05). The chemical composition and amino acid content of breast muscle of broilers did not differ among treatments (P<0.05).Decreased pH45min,a*45 min and a*24 h and increased 24-h drip loss of breast muscle were observed in broilers fed HSPIO(P<0.05). Broilers fed VE diets exhibited higher a-tocopherol and total tocopherol in breast muscle as compared with broilers receiving HSPIO diet (P<0.05), while highest ?-+?-tocopherol in breast muscle was observed in broilers fed NE(P<0.05). Increased GSH-Px activity in SE and NE groups (P<0.05), GSH content in SE and SNE groups (P<0.05), decreased protein carbonyl and MDA in SE and SNE groups (P<0.05) in breast muscle were observed as compared with that of the HSPIO.It can be concluded as follows:(1) Exposure of SPI to heat treatment resulted in protein oxidation as evidenced by accumulation of protein carbonyl and diminution of sulfhydryl. The solubility and in vitro digestibility of oxidized SPI were also decreased. Addition of 2% soybean oil accelerated protein oxidation during heating.(2) Growth performance, digestive function and antioxidant capacity of broilers were depressed by receiving oxidized protein diets and this impairment was more pronounced in broilers fed diet containing heat-oxidized mixture of SPI and 2% soybean oil.(3) Growth performance, antioxidant capacity and associated mRNA expression were depressed in broilers given oxidized protein diet, whereas those of which were enhanced by dietary inclusion of different types of VE (especially in mixed VE group) as evidenced by increased tocopherol content, activating Nrf2 signaling pathway, increased antioxidant enzyme activities and associated mRNA expression in serum,liver or jejunal mucosa,resulting in an improvement of the redox status of broilers.(4) Cell apoptosis in tissues of broilers fed oxidized protein diet was induced by increased caspase-3 and Bax content and associated mRNA or protein expression,decreased Bcl-2 content and associated mRNA or protein expression, whereas those of which were improved in broilers fed diets supplemented with different types of VE. Among which, synthetic VE or natural VE were better in regulating contents of cell apoptosis factors or protein expression of cell apoptosis factors, respectively.(5) Broilers fed oxidized protein diet exhibited inferior muscle yield, meat quality and antioxidant capacity. Dietary supplementation of different types of VE especially synthetic VE could increase breast muscle yield and breast muscle tocopherol content, resulting in an improvement of antioxidant capacity and meat quality. |
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