浆液体系中木薯淀粉乙酰化反应均匀性及基团分布特征

doi:10.11949/j.issn.0438-1157.20190071

摘要/Abstract

摘要：

以木薯淀粉为原料、乙酸酐为酰化剂，在浆液体系中制备乙酰化淀粉，采用4.3 mol·L^-1 CaCl₂溶液对乙酰化淀粉颗粒进行化学表面糊化处理，获得不同表面糊化程度的剩余淀粉颗粒，通过SEM、XRD表征剩余颗粒的形貌及结晶结构，采用皂化法测定剩余颗粒的乙酰基含量，并利用最小二乘法拟合取代基含量在淀粉颗粒径向上的分布曲线，考察乙酰化反应均匀性和乙酰基分布的影响因素。结果发现：乙酰基团在淀粉颗粒中呈现外高内低的非均匀分布，30%以上的乙酰基分布在对比半径0.9~1.0的外部区域，而在0~0.7比较大的范围内仅占28%左右；反应温度升高、反应时间延长和酰化剂用量增大，乙酰基含量在淀粉颗粒内的分布离散程度减小，有利于乙酰化反应和乙酰基团分布更趋均匀；随着表面糊化程度增大，剩余颗粒均能保持木薯淀粉的形貌和“A”型结晶结构特征，但粒径稍有减小，结晶度整体呈现下降趋势，部分稍有突跃。以上结果说明，结晶结构与非晶结构在木薯淀粉颗粒内交替存在，且各区域结晶区和非晶区比例存在一定差异，适当改变反应条件可改善木薯淀粉颗粒内乙酰化反应和乙酰化基团非均匀分布的状况。

关键词: 木薯淀粉, 乙酰化, 浆液体系, 反应均匀性, 基团分布

Abstract:

Using cassava starch as raw material and acetic anhydride as acylating agent, acetylated starch was prepared in the slurry system, and acetylated starch granules were chemically surface-gelatinized with 4.3 mol·L^-1 CaCl₂ solution to obtain different surface gelatinization degree. The morphology and crystalline structure of the remaining granules were characterized by SEM and XRD. The content of acetyl group in the remaining granules was determined by saponification method, the distribution curve of substituent content in the radial direction of starch granules was fitted by least square method, and the factors influencing the homogeneity of acetylation and the distribution of acetyl group were investigated. The results showed that the distribution of acetyl groups in starch granule was inhomogeneous which was external high and internal low, more than 30% of the acetyl groups were distributed in the external region of the contrast radius from 0.9 to 1.0, while only 28% of the acetyl groups were distributed in the larger range from 0 to 0.7; with the increase of reaction temperature, reaction time and the amount of acylating agent, the dispersion degree of group distribution in starch granule decreased, which was favorable for more uniform of acetylation and distribution of acetyl groups. With the degree of surface gelatinization increased, the remaining particles could still maintain the morphology and “A” type crystalline structure of cassava starch, but the particle size decreased slightly, the crystallinity generally showed a downward trend while some of them had a sudden jump. The above results indicate that alternating crystalline and amorphous structures exist in the granule of cassava starch, and the proportion of crystallization and amorphous zones in various regions is different. Appropriate changes in reaction conditions can improve the inhomogeneous status of acetylation and distribution of acetylation groups in the granule of cassava starch.

Key words: cassava starch, acetylation, slurry system, reaction uniformity, distribution of group

中图分类号:

TS 231

沈君利, 谢新玲, 张友全, 刘土松, 朱勇. 浆液体系中木薯淀粉乙酰化反应均匀性及基团分布特征[J]. 化工学报, 2019, 70(6): 2351-2360.

Junli SHEN, Xinling XIE, Youquan ZHANG, Tusong LIU, Yong ZHU. Acetylization uniformity and distribution of acetyl group of cassava starch granule in aqueous slurry systems[J]. CIESC Journal, 2019, 70(6): 2351-2360.

图/表 8

表1 30℃不同CaCl2浓度下木薯淀粉的完全糊化时间

Table 1 Complete gelatinization time of cassava starch at different concentrations of CaCl2 at 30℃

CaCl₂浓度/(mol·L^-1)	完全糊化时间/min
3.8	5
4	15
4.1	25
4.2	35
4.3	45
4.4	105
4.5	180
4.6	210

表2 乙酰化淀粉化学表面糊化结果

Table 2 Results of chemical surface gelatinization of acetylated starch

糊化时间/ min	剩余颗粒的对比质量 (m_i /m ₀)/(g·g^-1)	糊化程度/%	剩余颗粒的平均取代度（ $D S ˉ)$	剩余颗粒的对比半径 (r_i )
0	1	0	0.0924	1
6	0.9246	7.54	0.0866	0.97
12	0.8114	18.86	0.0838	0.93
18	0.6183	38.17	0.0801	0.85
24	0.4034	59.66	0.0748	0.74
30	0.2072	79.28	0.0711	0.59
36	0.0778	92.22	0.0642	0.43

表2 乙酰化淀粉化学表面糊化结果

Table 2 Results of chemical surface gelatinization of acetylated starch

糊化时间/ min	剩余颗粒的对比质量 (m_i /m ₀)/(g·g^-1)	糊化程度/%	剩余颗粒的平均取代度（ $D S ˉ)$	剩余颗粒的对比半径 (r_i )
0	1	0	0.0924	1
6	0.9246	7.54	0.0866	0.97
12	0.8114	18.86	0.0838	0.93
18	0.6183	38.17	0.0801	0.85
24	0.4034	59.66	0.0748	0.74
30	0.2072	79.28	0.0711	0.59
36	0.0778	92.22	0.0642	0.43

图1 样品扫描电镜图

Fig.1 SEM images of some samples

图2 温度对取代基团分布的影响

Fig.2 Effects of temperature on distribution of substituted groups

图3 反应时间对取代基团分布的影响

Fig.3 Effects of reaction time on distribution of substituted groups乙酸酐用量为6%、反应温度为25℃

图4 酸酐用量对取代基团分布的影响

Fig.4 Effects of anhydride amount on distribution of substituted groups

图5 样品XRD图

Fig.5 XRD patterns of samples

表3 样品结晶度

Table 3 Crystallinity of some samples

序号(i=1～6)	糊化时间/ min	剩余颗粒的对比质量(m_i /m ₀)/(g·g^-1)	剩余颗粒的对比半径(r_i )	剩余颗粒的结晶度(θ_i )/%	剥离区域	剥离区域的结晶度(θ_i ′)/%
0	0	1	1	31.85	—	—
1	6	0.9246	0.97	30.42	1~0.97	49.39
2	12	0.8114	0.93	25.70	0.97~0.93	64.25
3	18	0.6183	0.85	20.76	0.93~0.85	41.52
4	24	0.4034	0.74	23.00	0.85~0.74	16.56
5	30	0.2072	0.59	16.84	0.74~0.59	29.51
6	36	0.0778	0.43	17.11	0.59~0.43	16.68

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