不同预处理方法对麦草化学组分及其酶解性能的影响

摘要

以麦草为原料,探讨了高温热水(LHW)、氨水浸渍(SAA)、NaOH和NaOH联合乙醇(NaOH-ET)4种预处理方法对麦草化学组分及其酶水解糖转化率的影响.结果表明:LHW对聚戊糖有较高的去除率,188℃保温40 min处理,木聚糖和阿拉伯聚糖的去除率分别为73.11%和83.10%,但对木质素的去除率较小仅为21.32%.NaOH具有较好的脱木质素和去除灰分作用,麦草经1%NaOH,140℃保温3 h后木质素去除率为72.00%,灰分去除率为75.93%.因木质素在乙醇中有较好的溶解性,相同温度和时间条件下,麦草经1%NaOH与50%乙醇联合预处理,木质素去除率提高至84.11%.XRD检测结果表明,伴随着木质素和半纤维素的溶出,不同方法预处理后物料的结晶度不同程度增加,由原料的28.80%增加至预处理后的31.23%~33.61%.由于木质素和半纤维素的部分脱除,提高了酶对纤维素的可及性,物料经30 FPIU/g(以纤维素质量计,下同)纤维素酶和30 IU/gβ-葡萄糖苷酶酶解72 h后,糖转化率明显提高,其中NaOH-ET预处理物料的酶解总糖转化率(以麦草原料为基准)最高达90.05%,是麦草原料的7.5倍.%Wheat Straw was pretreated by four kinds of pretreatment methods , namely , liquid hot water ( LHW) , soaking aqueous ammonia(SAA),sodium hydroxide (NaOH) and sodium hydroxide combined with ethanol (NaOH-ET).The effects of pretreatments on chemical composition and enzymatic hydrolysis were investigated .The results showed that LHW pretreatment resulted in the highest level of polypentose reduction .The removal rates of xylan and araban were 73.11% and 83.10%respectively at 188 ℃for 40 min, but the delignification rate was only 21.32%.NaOH had a good capability in the removal of lignin and ash.The removal rates of lignin and ash were 72.00% and 75.93% respectively by 1% NaOH at 140 ℃ for 3 h. Because of the good solubility of lignin in the ethanol , the removal rate of the lignin pretreated by the combination of NaOH with 50%ethanol pretreatment was up to 84.11%.XRD results showed that the crystallization index of four pretreated wheat straw were greater than that of the raw material because of the removal of lignin and hemicellulose ; the crystallization index of pretreated samples increased from 28.80% to 31.23%-33.61%. As lignin and hemicellulose were partly removed by pretreatment, the accessibility of cellulose and enzyme inereased .Under the conditions of cellulose enzyme 30 FPIU/g ( of cellulose ) and β-glucose glycosides enzyme 30 IU/g, enzymatic hydrolysis temperature 50 ℃, and reaction time 72 h, conversion ratio of total sugar increased obviously .Especially, total sugar conversion rate of NaOH-ET treated wheat straw reached 90.05%, which improved 7.5 times compared with that of raw material .