酶法降黏工艺在鲜甘薯直接发酵制备乙醇中的应用

doi:10.3864/j.issn.0578-1752.2016.09.012

摘要/Abstract

摘要： 【目的】建立鲜甘薯料液的酶法降黏工艺，并实现鲜甘薯料液不加水直接发酵制备乙醇。【方法】从中国甘薯主产区选择12个种植范围较广的淀粉型甘薯品种作试验材料。分析甘薯主要成分（干物质、淀粉、蛋白质、可溶性糖、果胶、半纤维素、纤维素和木质素）与鲜甘薯料液黏度的相关性并选择对应的降黏酶。研究料水比（1﹕0、2﹕1、3﹕2、5﹕4和1﹕1）、酶处理时间（1、2、3、4和5 h）、酶添加量（纤维素酶：1.0、1.5、2.0、2.5和3.0 GCU·g^-1；果胶酶：1.0、1.5、2.0、2.5和3.0 U·g^-1）和酶处理温度（30℃、40℃、50℃、60℃和70℃）对酶法降黏效果的影响。通过正交试验确定最佳酶处理条件，并分析其在不同品种鲜甘薯直接发酵制备乙醇中的效果。【结果】对于12个供试淀粉型甘薯品种，在所有组分中，除了半纤维素（r=-0.239）和木质素（r=-0.069）外，其他组分均与黏度呈正相关（干物率，r=0.356；淀粉，r=0.211，可溶性糖，r=0.307；蛋白质，r=0.266；果胶，r=0.526；纤维素，r=0.600）。其中，果胶（P＜0.01）和纤维素（P＜0.05）与料液黏度分别呈极显著和显著正相关性。根据极差分析发现，对酶处理效果影响由大到小的酶处理条件分别为酶用量、料水比、酶处理时间和酶处理温度。基于正交试验结果并考虑到工业应用的实际情况，确定最佳酶处理条件为：料水比1﹕0、纤维素酶1.5 GCU·g^-1、果胶酶1.5 U·g^-1、温度50℃、作用3 h。经过酶处理后，鲜甘薯料液黏度明显下降。除皖苏178号（4 930 cp）外，其余品种的料液黏度在经过酶处理后均低于3 000 cp，降黏幅度95.07%—99.31%。乙醇发酵结束后，11个甘薯品种的乙醇含量均高于12%（v/v），其中有9个品种的发酵效率达到90%以上。【结论】果胶和纤维素是造成甘薯料液黏度高的主要成分。在液化前通过添加纤维素酶和果胶酶可以有效降低鲜甘薯料液黏度，并实现鲜甘薯料液不加水直接发酵制备乙醇。

关键词: 鲜甘薯, 黏度, 酶处理, 乙醇发酵, 纤维素酶, 果胶酶

Abstract: 【Objective】 The objective of this research was to establish a viscosity reduction process for fresh sweet potato (FSP) mash by enzymatic pretreatment before liquification and use it for direct ethanol fermentation from FSP without adding additional water. 【Method】 A total of 12 kinds of starch-type sweet potatoes (SP), widely cultured in China, were selected for this research. The main components of SP, such as dry matter, starch, protein, soluble sugars, pectin, hemicellulose, cellulose, and lignin, were detected and the correlation between these components and viscosity of FSP were analyzed. Based on the results, proper enzymes, cellulase and pectinase, were selected for viscosity reduction. Effects of some key factors of enzymatic pretreatment on viscosity reduction were investigated, including the ratio of substrate to water (1:0, 2:1, 3:2, 5:4, and 1:1), enzymatic pretreatment time (1, 2, 3, 4, and 5 h), enzymes doses (cellulase: 1.0, 1.5, 2.0, 2.5, and 3.0 GCU·g^-1 and pectinase: 1.0, 1.5, 2.0, 2.5, and 3.0 U·g^-1), and enzymatic pretreatment temperatures (30℃, 40℃, 50℃, 60℃, and 70℃). The optimum enzymatic pretreatment conditions were determined by orthogonal experiment design and the effects of enzymatic pretreatment on the following ethanol fermentation performance from FSP were also investigated. 【Result】 For 12 kinds of tested starch-type sweet potato varieties, except for hemicellulose (r=-0.239) and lignin (r=-0.069), all the components were positively correlated to the viscosity (dry matter content, r=0.356; starch, r=0.211, soluble sugar, r=0.307; protein, r=0.266; pectin, r=0.526; cellulose, r=0.600). Wherein the pectin (P＜0.01) and cellulose (P＜0.05) were significantly positively correlated to the viscosity. According to the range analysis, the factors affecting enzymatic treatment effects from high to low were enzyme dosage, the ratio of substrate to water, enzymatic treatment time, and temperature. Based on the experiment results and the consideration on the industrial application, the optimum enzymatic pretreatment conditions were determined as: the ratio of substrate to water 1﹕0, cellulase 1.5 GCU·g^-1, pectinase 1.5 U·g^-1, and 50℃ for 3 h. Besides Wansu 178, mash viscosity from other varieties after enzyme treatment was lower than 3 000 cp, and the viscosity reduction rate was 95.07%-99.31%. At the end of fermentation, the ethanol concentration from 11 kinds of SP varieties was higher than 12% (v/v), and the fermentation efficiency of 9 varieties reached more than 90%. 【Conclusion】 Pectin and cellulose are the main factors affecting the viscosity of SP mash. Fresh SP mash can be directly used for ethanol fermentation after enzymatic pretreatment without adding water.

Key words: fresh sweet potato, viscosity, enzyme treatment, ethanol fermentation, cellulase, pectinase

岳瑞雪，钮福祥，孙健，徐飞，王洪云，朱红，张毅. 酶法降黏工艺在鲜甘薯直接发酵制备乙醇中的应用[J]. 中国农业科学, 2016, 49(9): 1757-1766.

YUE Rui-xue, NIU Fu-xiang, SUN Jian, XU Fei, WANG Hong-yun, ZHU Hong, ZHANG Yi. Establishment of a Viscosity Reduction Process by Enzymatic Pretreatment and Its Application in Ethanol Fermentation from Fresh Sweet Potato Without Adding Water[J]. Scientia Agricultura Sinica, 2016, 49(9): 1757-1766.

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