| Soybean meal is the most widely used raw protein material in livestock production,and its quality directly affects the health status and product quality of livestock.The quality of soybean meal is easily influenced by many factors during the transportation,processing,and storage,where the protein oxidation of soybean meal and its quality degradation easily occour.At present,little information is available regarding the effects of processing and storage conditions on the quality of soybean meal,and researches focusing effects of protein oxidation of soybean meal on laying hens are also scare.This study firstly explored the quality changes of soybean meal under different processing and storage conditions.Moreover,this work also investigated the effects of protein oxidation of soybean meal on laying performance,egg quality,antioxidant function,and antioxidant-related genes expressin levels of Hy-Line Brown laying hens,and the protective effects of dietary curcumin on laying hens fed protein-oxidized soybean meal.This study was composed of three trials as below:Trial 1 was conducted to investigate the effects of manufacture technology on the quality of soybean meal.Soybean,soybean flakes,extruded soybean,dehulled soybean meal(DSBM),and soybean meal(SBM)were collected from soybean meal production line,and the proximate components,protein oxidation-related indicators,amino acids contents and urease activity of each sample were determined.The results were shown as follows:(1)Compared with the soybean,the moisture,crude fat,and crude protein contents in soybean flakes and extruded soybean were decreased,whereas their crude ash content was increased;crude fat content in DSBM and SBM was decreased,while their crude protein content was increased,with DSBM having the highest crude protein content.(2)Compared with the fresh soybean meal,protein carbonyl content in both extruded soybean and soybean flakes were increased significantly(P<0.05);free amine content in soybean flakes,extruded soybean and DSBM was decreased significantly(P<0.05),and total sulfhydryl content in extruded soybean,DSBM and SBM was reduced significantly(P<0.05).(3)Compared with soybean,the content of amino acids in soybean flakes,extruded soybean,DSBM,and SBM was increased gradually.(4)The urease activity in extruded soybean,DSBM and SBM was gradually decreased after extrusion expansion and desolvation of wet meal during the manufacture of soybean meal.Trial 2 studied the effects of storage environment and time on the quality of soybean meal.Fresh soybean meal was stored for 0(CON),10,20,and 30 days at 20℃,0(CON),15 and 30 days in spring(15-30℃),and 0(CON),3,6,9,12,18 and 30 days in summer(30-40℃),respectively.The proximate components,protein quality,in vitro digestibility and amino acid content of soybean meal were determined.(1)There was no significant change in proximate components after soybean meal storage under three conditions(P>0.05).(2)Compared with the fresh soybean meal,the protein carbonyl content of soybean meal storaged at 20℃,spring and summer temperature was increased linearly,respectively(P<0.05),while the total sulfhydryl and free sulfhydryl content were decreased linearlywith the prolongation of storage time(P<0.05).Compared with the CON group,the carbonyl content of soybean meal increased significantly(P<0.05),whereas the total sulfhydryl and free sulfhydryl content decreased significantly at 20 ℃,spring and summer storage,respectively(P<0.05).Summer storage exerted more significant effects on oxidation of soybean meal than the other storage conditions(20℃ and spring storage).(3)Compared with the CON group,the protein solubility and crude protein digestibility of soybean meal decreased significantly during the spring and summer storage periods(P<0.05),and the dry matter digestibility of soybean meal decreased significantly during the summer storage time(P<0.05).With the prolongation of storage time,the protein solubility,crude protein digestibility,and dry matter digestibility decreased linearly(P<0.05).(4)Threonine,lysine and histidine contents in the soybean meal decreased linearly with the prolongation of summer storage time(P<0.05).Trial 3 was aimed to explore the effects of protein-oxidized soybean meal on laying performance,serum biochemical parameter,egg quality,and antioxidant function of laying hens,and the alleviation effect of dietary curcumin.A total of 384 280-day-old Hy-Line Brown laying hens were randomly allocated to 4 dietary treatments with 8 replicates of 12 birds each.The pre-feeding period was 9 days and the experimental period was 42 days.The treatments were shown as follows:(1)Control group(CON),hens fed a basal diet with storaged soybean meal at-20℃ for 30 days;(2)Heated soybean meal group(HSBM),hens fed the experimental diet by using heated soybean meal at 100℃ for 8 hours to replace fresh soybean meal;(3)Storaged soybean meal group(SSBM),hens fed the experimental diet by using storaged soybean meal at spring temperature for 30 days to replace fresh soybean meal;(4)Curcumin group(CUR),hen fed the diet with SSBM and supplemented with 150 mg/kg curcumin.The results were presented as follows:(1)Compared with the CON group,the laying rate in the HSBM group was significantly decreased(P<0.05),while there was a numerical reduction of laying rate in the SSBM group(P>0.05),with more negative effect on egg laying rate being observed when soybean was heated.Compared with SSBM group,the laying rate in the CUR group was significantly increased(P<0.05),while the feed/egg ratio in the CUR group was significantly reduced(P<0.05).(2)Compared with the CON group,hens in the SSBM and HSBM groups exhibited a decrease in total protein(TP)content whereas an increase in urea nitrogen(UN)concentration of serum(P<0.05),with the values of these parameters being similar between the HSBM and SSBM groups(P>0.05).Compared with the SSBM group,dietary curcumin supplementation increased TP concentration whereas decreased UN content in the serum of hens(P<0.05).(3)Compared with the CON group,SSBM decreased haugh units at 20 days,HSBM and SSBM decreased huigh units and egg protein height at 40 days(P<0.05),with similar values of these indexes being observed between the two treatment groups(P>0.05).The haugh units and egg protein height at both 20 and 40 days in the CUR group were significantly higher than those in the SSBM group(P<0.05).Moreover,the yolk color and yellowness value in the CUR group were significantly higher compared with the other three groups(P<0.05).(4)Compared with the CON group,serum total superoxide dismutase(T-SOD)and glutathione peroxidase(GSH-Px)activities and total sulfhydryl content,hepatic GSH-Px activity,and 20-day yolk T-SOD activity were significantly decreased in the HSBM and SSBM groups(P<0.05),and carbonyl content in serum and liver and yolk malondialdehyde content at both 20 and 40 days in the HSBM and SSBM groups were significantly increased(P＜0.05),with no differences on these parameters being observed between the HSBM and SSBM groups(P>0.05).What’s worse,hepatic catalase(CAT)activity in the HSBM group was significantly lower than that in the CON group(P<0.05).Compared with the SSBM group,dietary curcumin significantly decreased serum GSH-Px activity and 20-and 40-day yolk malondialdehyde(MDA)content(P<0.05),significantly increased T-SOD,GSH-Px activity and total sulfhydryl content in serum and liver(P<0.05),whereas significantly decreased carbonyl content in serum and liver,malondialdehyde content in yolk on day 20(P<0.05).(5)Compared with the CON group,the hepatic mRNA expression level of NQO1 of laying hens in the HSBM and SSBM groups was decreased significantly(P<0.05),with the values of these two parameters being similar between the HSBM and SSBM groups(P>0.05).Dietary curcumin inclusion upregulated hepatic Nrf2 and NQO1 mRNA abundances in hens fed SSBM compared with the CUR group(P<0.05).(6)The negative effects of protein-oxidized soybean meal both treated with storage and heat on laying hens were similar.It can be concluded as follows:(1)The indexes related to protein oxidation were changed during processing of soybean meal.The processing can passivate some soybean meal anti-nutritional factors and improve its quality.(2)The quality of soybean meal changed under the storage conditions of 20℃,spring and summer.Summer storage had the most significant impact on the quality of soybean meal among three storage environments,followed by spring storage and 20℃ storage,respectively.(3)Protein-oxidized soybean meal caused by storage and heat had significant negative effects on laying performance,serum biochemical,egg quality,antioxidant capacity and antioxidant-related genes expression levels of laying hens,with the two treatments induced similar adverse effects on laying hens.Dietary curcumin supplementation at a level of 150 mg/kg could ameriolate the above methioned negative effects on laying hens fed the storaged soybean meal and heated soybean meal. |
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