Research On Enzymatic Hydrolysis Of Corn Cob For Xylose Production

To make corn cob which is a common kind of agricultural waste comprehensive utilizated, perchase a low price, moderate, no pollution and highly feasible treatment option, end to make xylose released completely form corn cob xylan.At the first the smashed corn cob was pretreated with various methods: heat pretreated at 120℃for 2 h, steam explosion treatment at 1.01×10⁶ Pa (dry powder, dry powder: H2O=1: 2, dry powder: H2O=1: 4, w/v), at 2.02×10⁶ Pa (dry powder, dry powder: H2O=1: 2, dry powder: H2O=1: 4, w/v), at 2.02×10⁶ Pa (dry powder: 0.1% sulfuric acid =1: 2, w/v). Based on the amount of both soluble total sugar and reducing sugar corn cob released, 4 pretreatment methods as follows were selected as the substrate of enzyme: heat pretreated at 120℃, steam explosion treatment at 1.01×10⁶ Pa (dry powder), at 2.02×10⁶ Pa (dry powder: H2O=1: 2 and dry powder: 0.1% sulfuric acid =1: 2, w/v). All pretreated corn cob were incubated with different xylanase preparations (4 IU/mg substrate, taking xylanase as a standard) at 40℃for 24 h and the xylose released at intervals were dertermined, choose the best xylanase preparation for next experament.The results showed that: the maximum xylose yield was 33%, obtained with the steam explosion pretreated corn cob at 1.01×10⁶ Pa (dry powder) as the substrate and by the xylanase preparation from Penicillium decumbens 6, almost all of the xylose was hydrolysis. As for the heat pretreated corn cob (120℃, 2 h), the xylanase preparation from Aspergillus niger 2107 achieved the highest xylose yield of 19.5% from the start of 0.9%. While the xylanase preparation from A. niger 30197 showed a better hydrolysis result on the explosion pretreated corn cobs than on the heat pretreated one, with the xylose yield of 26.7%, 27.7%, and 29.6% to the steam explosion pretreated corn cob at 1.01×10⁶ Pa (dry power), at 2.02×10⁶ Pa (dry powder: H2O=1: 2, w/v), and at 2.02×10⁶ Pa (dry powder: 0.1% sulfuric acid =1: 2, w/v). The hydrolysates were assayed by thin-layer chromatography and xylose was found to be the major end product. At last determined substrate concentration 150 g/L, temperature at 40℃, the xylanase preparation from A. niger 30197 50 IU/g was the optimum condition which had the highest xylose yield. At the same time , Ca²⁺ and Mg²⁺ were found to be the activation ions for the enzymatic hydrolysis. The main conclusions as follows:1) Heat pretretment at 120℃and steam explosion damaged the structure of corn cob, and then xylanase can analyse the xylan of corn cob. Based on the amount of soluble total sugar, saving energy and environmental protection, 2 moderate pretreatment methods as follows were selected as the substrate of enzyme, heat pretretment at 120℃and steam explosion at 1.01×10⁶ Pa (dry power).2) The maximum xylose yield was obtained with the steam explosion pretreated corn cob at 1.01×10⁶ Pa (dry powder) by the xylanase preparation from Penicillium decumbens 6, higher than acid method which was choosed to produce xylose in China, reported by You xin and Li Mingjie. yet as this xylanase preparation had a low xylanase activity, a large amount of preparation was needed hinting its inefficient application. The xylanase preparation from Aspergillus niger A09,2107,30197 were all had high xylanase activity, and their endo- and exo-type of enzyme components were appropriate, it was feasible for enzymatic hydrolysis of corn cob for xylose production.3) Substrate concentration, enzyme dosage, temperature, and metal ions all had significant effect to the enzymatic hydrolysis. We found the optimal condition: substrate concentration 150 g/L, the xylanase preparation from Aspergillus niger 30197 50 IU/g, Ca²⁺ 4 mmol/L as the activater, hydrolysis at 40℃for 24 h.