【作者】 余君；

【导师】 喻子牛； 张吉斌；

【作者基本信息】 华中农业大学 ， 微生物学， 2008， 博士

【摘要】 本文对纤维素酶酶解稻壳的预处理工艺进行了研究,广泛研究了温和条件下多种化学预处理方法,物理预处理方法,白腐菌的生物预处理方法以及多因子联合预处理方法对稻壳的纤维素酶酶解的效果的影响,结果如下:1.选用了稀酸,稀NaOH,Ca（OH）₂,氨水,H₂O₂等几个化学试剂在常温常压下对稻壳进行了酶解前的预处理,并对这几种试剂的预处理条件进行了优化。结果表明,这几种处理均能提高稻壳的酶解效率,其预处理的效果次序为NaOH＞稀硫酸＞稀盐酸＞Ca（OH）₂＞氨水＞H₂O₂,最好的效果为稀NaOH,1.5%NaOH处理6h后,稻壳的酶解总糖得率可达29.6%。的虽然稀酸的预处理效果也较好,但其会带来大量的半纤维素组分损失。还进行了H₂O₂/NaOH联合碱氧化处理和酸碱联合处理（氨水/H₂SO₄）两种多化学因子的联合处理实验。结果表明,这种多因子的联合处理效果明显好于单因子处理。其中碱氧化预处理效果最好,在1.5%的NaOH与0.6%的H₂O₂碱氧化溶液配比,固液比为1/10,在30℃处理48h,处理后酶解总糖得率可达45.5%。并且进行了碱氧化处理的处理液循环利用实验,结果表明,经过3次滤液回用,可以节省大约28%的NaOH的用量。2.进行了超声波和微波两种物理方法对稻壳的酶解前预处理实验,结果表明,超声波和微波在不改变稻壳组分含量的情况下,能提高稻壳的酶解效率。其中微波的处理效率要高于超声波处理。700W的超声功率时,处理30min,处理后酶解可以获得28.3%的总糖得率。还进行了超声波和微波分别结合稀酸和稀碱的物理与化学因子联合预处理实验。从处理后酶解得糖率分析,这几种预处理的效果依次为微波稀酸＞微波稀碱＞超声波稀碱＞超声波稀酸＞微波处理＞超声波处理。虽然微波稀酸处理后稻壳酶解总糖得率略高于微波稀碱处理,但由于其会降解较多的纤维素和半纤维素,因而总体比较,微波稀碱处理效果要好于微波稀酸处理。1%的NaOH结合700W功率的微波处理20min,处理后稻壳的酶解得糖率为38.7%。3.选取了糙皮侧耳AM-035和草菇AM-066两株白腐菌对进行稻壳的酶解预处理实验,结合处理过程中稻壳组分的变化,菌的木质素降解酶类的产酶情况和处理后稻壳的酶解情况,对预处理条件进行了优化。结果表明两株菌均能有效的提高稻壳的酶解效果,糙皮侧耳的处理效果要好于草菇。用糙皮侧耳处理30d,稻壳酶解得糖率可以达到29.8%,但也会引起20%的纤维素组分和52%的半纤维素组分的损失。处理周期过长和纤维素和半纤维素组分的损失是制约白腐菌预处理进行广泛应用的主要瓶颈。还进行了双菌株联合处理实验,结果表明,这两株菌的联合处理效果要低于二者单独进行处理时的效果。4.选取了H₂O₂和超声波两种方法分别与糙皮侧耳进行了两步的联合预处理实验。这种联合预处理工艺可以有效地缩短糙皮侧耳的预处理时间,进而也可以减少稻壳纤维素与半纤维素组分的损失。常温常压下,2%的H₂O₂处理稻壳48h,再进行18d的糙皮侧耳处理,处理后酶解总糖得率可达39.8%,高于糙皮侧耳单独处理60d后稻壳的酶解得糖率（36.7%）,纤维素与半纤维素的损失却比后者低（纤维素的降解率分别为15.7%和28.1%,半纤维素的降解率分别为44.2%和77.3%）。对联合处理过程中菌的木质素降解酶的产酶情况进行了考察,并对稻壳的结构变化进行了SEM观察。结果表明,联合处理对白腐菌的处理效果的提高的主要原因是第一步处理时对稻壳的结构产生的破坏,提高了木质素降解酶类对木质素的可及度,进而提高了木质素的降解效果。更多还原

【Abstract】 In this study, we investigated some pretreatment methods of rice hull for enzymatic hydrolysis. Results were followed as:1. Some chemical pretreatment methods were investigated, dilute acid, dilute NaOH, Ca（OH）₂, ammonia liquor and H₂O₂ were used to pretreated rice hull in the normal temperature and pressure. Results shown that effects of these methods were as follow: NaOH > dilute acid > Ca（OH）₂ > ammonia liquor > H₂O₂. Pretreatment of NaOH （1.5%, 6 h） led to 29.6% of net yields of total sugar （TS） when enzymatic hydrolysis of the rice hull. Although dilute acid pretreatment led to high net yields of sugar, it could also bring greater losses of the holocellulose （cellulose and hemicellulose）. Two combined pretreatment methods （H₂O₂/ NaOH and H₂SO₄/ NaOH） were investigated. These combined pretreatment were better than each of the single factor pretreatment .The highest net yields of TS （45.2%） when enzymatic hydrolysis of the rice hull was obtained after pretreated by H₂O₂/ NaOH （1.5% NaOH. 0.6% H₂O₂, 30°C, 48 h）. We also studied the reuse of the H₂O₂/ NaOH, results shown that after 3 times reuse of the solution, consume of the NaOH could reduce 28%.2. Two physical factors （ultrasound and microwave） were used to pretreat the rice hull. These factors couldn’t change the compositions of the rice hull, but it could propose the enzymatic hydrolysis of the rice hull. This probably could attribute to the structure change during the pretreatment. Microwave method was better than ultrasound method. And it could lead to 28.3% net yields of TS （microwave, 700 W, 30 min）. The effects of some physico-chemical methods were studied, and the results were shown as follow: microwave/dilute acid > microwave/dilute NaOH > ultrasound/dilute NaOH > ultrasound/dilute acid > microwave > ultrasound. Although the net yields of TS was obtained after microwave/dilute acid pretreatment was slighely higher than that of microwave/dilute NaOH, it could bring greater losses of the holocellulose. There are 38.7% net yields of TS when enzymatic hydrolysis of the rice hull after pretreatment of microwave/dilute NaOH （1% NaOH, microwave 700 W. 20 min）. 3. Pleurotus ostreatus AM-035 and Voluariella voluacea AM-066 were used for biological pretreatment of rice hull. The processes of the pretreatment were optimized. All these fungus could pomote the enzymatic hydrolysis of the rice hull. Effects of the Pleurotus ostreatus were better than that of Voluariella voluacea. Pleurotus ostreatus pretreatment for 60 d led to 29.8% of net yields of TS when enzymatic hydrolysis of rice hull, but 20% of cellulose and 52% of hemicellulose were lost during the pretreatment. Long pretreatment time and loss of the holocellulose were the two fible side of the fungal pretreatment. Effects of combined pretreatment of these two fungi were not as good as each single fungi pretreatment.4. Two novel two-step pretreatments for enzymatic hydrolysis of rice hull （RH） were proposed to lower the severity requirement of fungal pretreatment time. They consisted of a mild physical or chemical step （ultrasonic or H₂O₂） and a subsequent fungal treatment （Pleurotus ostreatus）. The combined pretreatments led to significant increases of the lignin degradation than those of one step pretreatments. After enzymatic hydrolysis of the pretreated RH, the net yields of TS and G increased greatly. The combined pretreatment of H₂O₂ （2%, 48 h） and P. ostreatus （18 d） was more effective than sole pretreatment of P. ostreatus for 60 d. It could remarkably shorten the residence time and reduce the losses of carbohydrates. Ligninase analyses and SEM observations indicated that the enhancing of the efficiency could possibly attribute to the structure disruption of the RH during the first pretreatment step. So, the combined pretreatment could be recommended to different lignocellulosic materials for enzyme based conversions.更多还原