| At present,the shortage of grain and feedstuffs limits animal husbandry development in China.In the contrast,crop straw resources are very abundant,but a few of them are used because there are no effective methods to handle them.As a result,a lot of them are burnt and depraved to cause pollution and resources waste.If the crop straw can be transferred to feedstuffs for animals,feedstuff shortage will be relieved.This study focuses on physicochemical pretreatment and enzymatic hydrolysis cooperation for transferring corn straw to a new feedstuff for animals.The main results are as following:(1)The single-factor experiments were first conducted to determine three levels of sodium hydroxide concentrations(2.0%,2.5%,3.0%,w/v),solid-liquid ratios(1:6.0,1:7.5,1:9.0)and pretreatment time(15,30,45 min).The orthogonal experiment with three factors and three levels was used to optimize the experiment condition for removing lignin.The result indicated that the optimal condition for lignin degradation was that corn straw added with 3.0% sodium hydroxide at a solid-to-liquid ratio of 1:9 was autoclaved at 121? for 15 min.Under this condition,91.62% lignin(P<0.05),72.70% hemicellulose(P<0.05)and 6.40% cellulose(P<0.05)in corn straw were degraded.This condition is able to break the lignin-hemicellulose protective barrier outside cellulose for increasing cellulose degradation effectively in the future.Therefore,this optimal condition will be used for the following experiments.(2)Sodium hydroxide-dry steam explosion(straw: water=1: 0)and sodium hydroxide-wet steam explosion(straw: water=1: 2)added with different amount of sodium hydroxide(0%,2%,4%,6%,8%,w/w)were carried out to study their effects on degradations of crude fiber in corn straw.The results showed that sodium hydroxide-dry steam explosion had significant effect on cellulose degradation(P<0.05),but it had no significant effect on lignin and hemicellulose degradations(P>0.05).Cellulose degradation was increased with the amount of sodium hydroxide addition increasing(P<0.05).However,sodium hydroxide-wet steam explosion had significant effect on lignin degradation(P<0.05),while it had no significant effect on cellulose and hemicellulose degradations(P>0.05).Lignin degradation was also increased with the amount of sodium hydroxide addition increasing(P<0.05).(3)The corn straw pretreated with sodium hydroxide-high pressure steam was used as the substrate(50 g/L)under the condition of 200 r/min,the four-factor and four-level orthogonal experiment was used to optimize the enzymatic hydrolysis conditions(enzyme dosage,p H,temperature,time).The results showed that the optimal condition for enzymatic hydrolysis was 25.80 FPU/g straw,p H 4.8,40? and 96 h reaction.Under this condition,reducing sugar yield was maximal(P<0.05).Enzymatic hydrolyses of native corn straw,sodium hydroxide-high pressure steam straw,sodium hydroxide-dry steam explosion straw(0%,4%,8%,w/w),sodium hydroxide-wet steam explosion straw(0%,4%,8%,w/w)were carried out under the above optimal conditions.The results showed that the largest reducing sugar yield(575.51 mg/g)was gained from sodium hydroxide-high pressure steam-enzymatic hydrolysis treatment(P<0.05),followed by sodium hydroxide(8%)-wet steam explosion-enzymatic hydrolysis treatment(508.17 mg/g)(P<0.05).Microstructures of the different treated corn straws were analyzed by scanning electron microscope(SEM).It was found that the surface of native corn straw was smooth and tightly integrated,while the surfaces of the treated corn straws were broken.Among the different treated corn straws,sodium hydroxide-high pressure steam-enzymatic hydrolysis treatment was the best method to destroy corn straw completely,named as biological corn straw feedstuff ?(BCSF?),followed by sodium hydroxide(8%)-wet steam explosion-enzymatic hydrolysis treatment,named as BCSF?.(4)Force-feeding method and substitution method were used to determine the apparent metabolic energy(AME)of BCSF respectively.For force-feeding method,a total of 15 YUFEN?cocks were assigned to 3 groups,5 birds for each group,1 bird for each repeat.The birds were fasted for 48 h before the experiment.Group 1 was fed with 30 g native corn straw;group 2 was fed with 30 g BCSF?;group 3 was fed with 30 g BCSF?.The results showed that AME was 1.69,9.35,8.62 MJ/Kg respectively.For substitution method,a total of 20 YUFEN? cocks were assigned to 4 groups,5 birds for each group,1 bird for each repeat.Group 1 was fed with 50 g basal diet;group 2 was fed with 50 g test diet with 30% basal diet replaced by BCSF?;group 3 was fed with 50 g test diet with 30% basal diet replaced by BCSF?;group 4 was fed with 50 g test diet with 50% basal diet replaced by BCSF?.The results showed AME was 13.92,12.44,12.39,11.58 MJ/Kg,respectively.After it was calculated with the formula,AME was 9.01 MJ/Kg for BCSF?,8.66 and 8.91 MJ/Kg for BCSF?,respectively.The AMEs had no significant difference between force-feeding method and substitution method(P>0.05).The AME of BCSF was 5.3 folds more than the native corn straw,1.3 fold more than wheat bran,which was almost the same as soybean meal and about 67% corn AME.It indicated that the nutritional value of BCSF was improved by the above treatments,and it can be applied in animal production as an unconventional feedstuff to relieve feed shortage. |
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