| Straw lignocelluloses as structural carbohydrate are an abundant and renewable resource in the world.However,the unreasonable utilization of crop straw resources seriously causes resources waste and environmental pollution.Now,with the rapid development of animal husbandry,animal feedstuffs will account for 50% of all grain production,so the exploitation of new carbohydrate raw materials to replace traditional raw materials is very important in the face of fierce competition between human food and animal feed.This study based on the physiological and nutritional requirements of monogastric animal was to turn straw lignocellulose into glucose and low molecular-weight carbohydrate as energy feed resources of monogastric animal to solve the shortage of energy feedstuffs.In this study,multiple joint chemical-physical pretreatment and enzymatic hydrolysis was combined in developing the new-type saccharification straw.Study on its nutritional value and effect on production performance of broiler was conducted.The results were as following:(1)The reagents of lime(Ca O),sodium hydroxide(Na OH),ammonia(NH3·H2O)and hydrogen peroxide(H2O2)were chosen based on the security for animals.The concentrations of Ca O and Na OH were chosen according to animal feeding standards.The orthogonal experiment was used to optimize the pretreatment conditions of2%Na OH+Ca O,NH3·H2O and H2O2.The result showed that the pretreatments of 2%Na OH+Ca O and H2O2 had insignificant influence on the reducing sugar yield(P>0.05).The optimum pretreatment conditions were 9%(w/w)Ca O supernatant and 2%(w/w)Na OH with liquid-to-solid ratio of 11:1(m L/g)at 80°C for 6 h,15%(v/w)NH3·H2O with liquid-to-solid ratio of 9:1(m L/g)at 80°C for 12 h,4%(v/v)H2O2with liquid-to-solid ratio of 13:1(m L/g)at 50°C for 6 h.By comparison with the combined and independent pretreatments in these conditions,the results showed the reducing sugar yield in the NH3·H2O pretreated corn straw with enzymatic hydrolysis was higher than the independent pretreatments of 2% Na OH+Ca O and H2O2(P<0.05).The reducing sugar yield in the 2% Na OH+Ca O+H2O2 pretreated corn straw with enzymatic hydrolysis was increased by 55.80%,compared with the 2%Na OH+Ca O pretreated corn straw with enzymatic hydrolysis(P<0.05).Compared with the NH3·H2O and 2% Na OH+Ca O+ H2O2 pretreated corn straw with enzymatic hydrolysis,the reducing sugars yield in the NH3·H2O+H2O2 pretreated corn straw was increased by 31.85% and 38.90%,respectively(P<0.05).The maximal degradation rates of lignin in the 2% Na OH+Ca O+H2O2+NH3·H2O+H2O2 pretreated corn straw was 79.95%(P<0.05),and the reducing sugars yield in pretreated corn straw with enzymatic hydrolysis was 484.61 mg/g.The study also indicated that the combined chemical pretreatment had a strict order during chemical reagent adding.(2)In order to increase corn straw degradation,the response surface design was used to optimize the pretreatment conditions of 2%Na OH+Ca O.The result showed that the straw was kept in the combined solution of 15%(w/w)Ca O supernatant and 2%(w/w)Na OH with liquid-to-solid ratio of 13:1(m L/g)at 83.92°C for 6 h,and then added with3%(v/v)H2O2 for reaction at 50°C for 2 h,finally cellulase(32.3 FPU/g dry matter)and xylanase(550 U/g dry matter)was added to keep at 50°C for 48 h.The maximal reducing sugars yield(348.77 mg/g)was increased by 126.42%(P<0.05),and the degradation rates of cellulose,hemicellulose and lignin in pretreated corn straw with enzymatic hydrolysis were increased by 40.08%,45.71% and 52.01%,compared with the native corn straw with enzymatic hydrolysis(P<0.05).The following study indicated that the combined microbial fermentation and enzymatic hydrolysis could further increase straw degradation and reducing sugar yield(442.85 mg/g,P<0.05).The microstructure was analyzed by SEM,the smooth and tightly complete surface in corn straw was damaged after chemical pretreatment,and fiber bundles with many pores were exposed to surface.After the chemically pretreated corn straw was hydrolyzed with the combination of T.koningii fermentation and enzymatic hydrolysis,the large parts of cellulose were decomposed to fragment by microbes and enzyme.(3)In order to increase the saccharification of cellulose and hemicellulose,extrusion,microwave and ultrasonic wave were used to fracture the hydrogen bond between hemicellulose and cellulose,destroy the crystalline structure of cellulose,and reduce the degree of polymerization.The result showed the combined chemical and physical pretreatments significantly improved the efficiency of enzymatic hydrolysis(P<0.05).The pretreatment of extrusion and ultrasonic wave reduced the degree of crystallinity in cellulose(P<0.05).The microstructure was analyzed by SEM,it indicated that the capacity of extrusion+ultrasonic+chemical pretreatment was higher than the chemical pretreatment for breaking up the straw.Most of lignin and hemicellulose were resolved by extrusion+ultrasonic+chemical pretreatment,fiber bundles were completely erodedand exposed to surface.The reducing sugar,cellulose,hemicellulose and lignin in the corn straw treated with extrusion+ultrasonic wave+chemical methods plus enzymatic hydrolysis were 426.23 mg/g,7.47%,3.59% and 2.55%,respectively.It was indicated that the pretreated corn straw with enzymatic hydrolysis could be used as the feedstuffs for monogastric animal.(4)By analysing cellulase and xylanase characteristics,the optimal p H and temperature of enzymatic hydrolysis for the extrusion+ultrasonic+chemical treated corn straw were 4.3 and 50°C,respectively.The single factor and response surface analysis were used to optimize the enzymatic hydrolysis conditions.The result showed the optimal conditions for saccharification of corn straw were adding cellulase 32.30 FPU/g(10%)(contains xylanase 50 U/g)with liquid-to-solid ratio of 10:1(m L/g)for 82.08 h.The maximal reducing sugars yield was 560.09 mg/g.(5)By comparing the compositions of the different treated corn straw,it was indicated that enzymatic hydrolysis could remove by-products produced in the process of pretreatment.The contents of different amino acids were changed in saccharification of corn straw,compared with the native corn straw.Difference method and gavage method were used to determine the apparent metabolic energy(AME)of saccharification corn straw(SCS)for broilers,respectively.The result showed the AME of SCS was 4.85MJ/Kg measured by gavage method.The AME of SCS with 4%,8% and 12% added to basal diet was predicted by difference method to be 15.9,15.7 and 14.3 MJ/kg,respectively,which were higher than the AME of corn(13.56 MJ/kg).The AME of SCS after Candida utilis fermentation was 8.45 MJ/kg predicted by difference method.It was indicated that the SCS as energy raw material could replace corn in broiler diet.This result provided the theoretical basis for the application of SCS in broiler farming.(6)In order to study the effect of SCS on broiler production,and get the suitable adding proportion in diet,the experiment was divided into two-period feeding programs.In the earlier stage(1-21 d),a total of 250 1-day female AA broilers were assigned to 5groups,50 broilers for each group consisting of 5 replicates,10 broilers for each replicate.In the later stage(22-42 d),there was the same design as above.The control group was fed with the basal diet,Group 1,2 and 3 were added with 4%(15.9 MJ/kg),8%(15.7MJ/kg)and 12%(14.3 MJ/kg)SCS in the basal diet,respectively.Group 4 was added with 8%(4.85 MJ/kg,high oil addition)SCS in the basal diet,and the energy was balanced with the control.The result showed that in the earlier stage,the palatability and feed intake of broilers121were not influenced by adding 4%,8% and 12% SCS in diet.The average daily gain(ADG)was not influenced by adding 4% and 8%(high oil)SCS in diet.The ADG and the feed conversation(FCR)were decreased significantly in groups added with 8% and12% SCS(P<0.05).In the later stage,the feed intake was increased with increasing SCS in diet,especially in the group of 12%SCS.The ADG in group 1,2,3 and 4 were increased by 4.47%,7.97%(P<0.05),6.49%(P<0.05)and 15.49%(P<0.05),respectively,compared to control group.The feed/gain was decreased in 8%(high oil)SCS group(P<0.05).In the earlier stage,the metabolic rates of dry matter,energy,CP,EE,Ca and P were not influenced by adding 4% and 8% SCS in diet(P>0.05).The metabolic rates of energy and CP in 12% SCS group were significantly decreased(P<0.05),and the faeces was watery with adding 12% SCS.In the later stage,adding 4%,8% and 12% SCS in diet had no influence on the metabolic rates of dry matter,energy,CP,EE,Ca,P and NDF,and the activities of amylase and protease in duodenum and duodenum(P>0.05),but decreased the activities of amylase and protease in cecum(P<0.05).The E.coli in cecum of 12% SCS group was significantly decreased(P<0.05).By analysing PCR-DGGE,except for the ileum of 8%(high oil)SCS group in earlier stage and the duodenum of 8%,12% and 8%(high oil)SCS group in later stage,the microbial similarity of other intestinal segment in SCS group was greater than 50%,compared with control group.It was indicated that adding SCS could maintain the balance and diversity of microorganisms in intestine.In the earlier and later stages,the slaughter percentage,PEC,PBM,PLM,the growth of immune organs and the relative length of intestinal segment were not influenced by adding 4%,8% and 12% SCS in diet(P>0.05).The relative proportions of intestines and stomach were not influenced by adding 4%,8% and 12% SCS in diet(P>0.05)in earlier stage.The relative proportions of glandular stomach,glandular stomach,jejunum and heart were decreased in adding SCS group in later stage(P<0.05).The liver and pancreas were decreased in adding 8%(high oil)SCS group in later stage(P<0.05),indicating that adding SCS had influence on relative weights of stomach,glandular stomach,jejunum and heart in later stage.Adding 4%,8% and 12% SCS in diet had no influence on “L” value and “b” value of breast muscle and leg muscle(P>0.05),but significantly decreased “a” value of breast muscle and cooking loss of leg muscle(P<0.05).Adding 12% SCS in diet significantly decreased “a” value of leg muscle and drip loss of breast muscle and leg muscle(P<0.05),but increased the shear force of breast muscle(P<0.05).It was indicated that adding SCS decreased “a” value and drip loss of muscle and the cooking loss of leg muscle,and increased the shear force.The analysis of serology indicated that in the earlier and later stage,lactic dehydrogenase(LDH)was decreased in adding SCS group(P<0.05),and the alkaline phosphatase(ALP)was increased in 12%SCS group(P<0.05).The antioxidant ability of broiler was increased by adding SCS in the later stage(P<0.05).The villus length and crypt depth of jejunum were not influenced by adding 4% SCS in the earlier stage and adding 4% and 8% SCS in the later stage(P>0.05).The villus length were decreased and the crypt depth were increased by adding 12% and 8%(high oil)SCS in the later stage(P<0.05).From the observation of villus morphological structure of jejuna,the villus became wide with adding 4%,8% and 12% SCS.The villus was damaged and in a mess with adding 8%(high oil)SCS.The economic benefit in 4% SCS group in the earlier stage was increased by 0.12 yuan per broiler,and the economic benefit in 4%,8%,12% and 8%(high oil)SCS group in the later stage was increased by 0.69,1.27,0.74 and 1.87 yuan per broiler respectively,compared with control group.It was indicated that adding 4% SCS in the earlier stage and adding 4-12% SCS in the later stage could increase the economic benefit.In conclusion,the saccharification corn straw with higher apparent metabolic energy was obtained by the combined chemical and physical pretreatments plus enzymatic hydrolysis.The feeding experiments of broilers showed that the saccharification corn straw replacing grain in monogastric animal diet was economically feasible,that provided basis for the large-scale application. |
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