热碱致魔芋胶与黄原胶共混凝胶的显微结构与流变规律

doi:10.3864/j.issn.0578-1752.2020.18.014

摘要/Abstract

摘要：

【目的】探究魔芋胶与黄原胶混合溶胶体系在碱性条件下的凝胶形成机理与凝胶特性,为魔芋胶与黄原胶相关凝胶食品的开发提供理论依据。【方法】在总多糖浓度约为2.0%的条件下,配制不同黄原胶与魔芋胶比例的混合溶胶体系,添加2.0%的Na₂CO₃,并于90℃条件下恒温处理各溶胶体系2 h,冷却至室温后制得不同黄原胶与魔芋胶配比的复合凝胶。通过测定复合凝胶添加碳酸钠前后的凝胶破裂强度,揭示热碱处理对混合凝胶破裂强度的影响。分别测定去离子水浸泡、2.0%柠檬酸溶液浸泡以及冻融处理后凝胶破裂强度的变化情况,并结合扫描电镜观测凝胶的微观形貌,探究复合凝胶的凝胶特性。此外,通过流变学手段进一步研究黄原胶与魔芋胶复合凝胶网络的形成机制。【结果】在室温（20℃）条件下,非热碱处理的魔芋胶与黄原胶最佳协同比为5﹕5,热碱处理后的魔芋胶与黄原胶最佳协同比增加至7﹕3,原因可能是魔芋胶碱化后分子链上脱去部分乙酰基,形成分子间三维网络结构,但在随后的冷却过程中,与黄原胶协同结合位点减少,因此在达到最大协同比时,需要更多数目的魔芋胶分子参与。此外,经去离子水和2.0%柠檬酸溶液浸泡后,所有凝胶体系的破裂强度都有所降低,其中经过2.0%柠檬酸溶液浸泡后的凝胶破裂强度下降更为明显。冻融处理后,复合凝胶均出现明显的析水现象,魔芋胶比例越高,析水现象越明显。进一步探究魔芋胶与黄原胶共混体系在2.0% Na₂CO₃浓度、90℃条件下的凝胶化过程,发现随黄原胶添加量增加,凝胶化速率呈减小趋势。此外,凝胶弹性模量在90—60℃呈降低趋势,60℃以下逐渐上升。【结论】在90℃条件下碱处理魔芋胶与黄原胶共混体系时,诱导体系形成热不可逆凝胶。当降低该体系的温度时,黄原胶分子在60℃时开始与魔芋胶网络结合,增加了凝胶的弹性模量。当魔芋胶与黄原胶比例为7﹕3时,室温下混合凝胶的破裂强度最大。经去离子水和2.0%柠檬酸溶液浸泡后,凝胶强度均有所降低。魔芋胶与黄原胶形成的复合凝胶在一定条件下可以改善单纯碱法诱导的魔芋胶凝胶析水多、强度差等缺点。

关键词: 魔芋胶, 黄原胶, 凝胶破裂强度, 流变学特性

Abstract:

【Objective】This study intended to investigate the gelation mechanism and gel properties of the alkaline-induced gelation of mixed konjac glucomannan and xanthan sol systems under heating treatment, in order to provide a theoretical basis for konjac glucomannan and xanthan-related gel food design. 【Method】At a fixed total polysaccharide concentration of about 2.0%, the mixed sol systems with different konjac glucomannan to xanthan ratios were prepared by altering the mixing volume ratio of konjac glucomannan to xanthan. Then, the composite gels were prepared by heating the sol systems at 90℃ for 2 h with Na₂CO₃ as alkaline regulator, followed by cooling to room temperature. The effect of alkaline treatment on the rupture strength of the composite gel was investigated by determining the gel rupture strength with and without alkali addition and at room temperature (20℃). In order to investigate the properties of the composite gel, the gel rupture strength was tested, and microstructure was observed by scanning electron microscope (SEM) after deionized water immersion, 2.0% citric acid solution immersion and freeze-thaw treatment, respectively. Furthermore, rheological analysis was adopted to study the formation mechanism of the composite gel. 【Result】At room temperature, the optimum synergistic ratio of konjac glucomannan to xanthan was 5:5 for without hot alkali treated composite gels. However, the optimum synergistic ratio shift towards 7:3 after hot alkali treatment, because part of the acetyl group was removed from the molecular chain of konjac glucomannan after alkalization, forming a three-dimensional network structure between the molecules. In the subsequent cooling process, the synergistic binding sites of konjac glucomannan and xanthan were reduced. Therefore, more konjac glucomannan molecules were needed to participate in the maximum synergistic ratio. Furthermore, after immersing the gels in deionized water and 2.0% citric acid solution, a slightly decrease in gel rupture strength was observed, and 2.0% citric acid solution immersion caused a more pronounced decrease in gel rupture strength compared with deionized water immersion. Syneresis phenomenon of all composite gels was also observed after freeze-thaw treatment. The higher the ratio of konjac glucomannan to xanthan, the more significant the syneresis phenomenon was. The gelation process of the composite sol system was further revealed under the condition of 2.0% alkali concentration and at 90℃. The results showed that the gelation rate was decreased with increasing xanthan addition. G' of the gels was decreased when the temperature decreased from 90℃ to 60℃, but the G' showed a continuously upward trend as the temperature further decreased. 【Conclusion】 Konjac glucomannan and xanthan could form a thermal irreversible gel under alkaline treatment at 90℃ followed by cooling to room temperature. When the temperature of the system was lowered, xanthan began to combine with konjac glucomannan network at 60℃ and increased the elastic modulus of the whole gel. When the ratio of konjac glucomannan to xanthan was 7:3, the alkaline-treated composite gel showed the highest gel strength. After immersion in deionized water and 2.0% citric acid solution, the gel strength decreased. Compared with alkaline-induced konjac glucomannan gels, the composite gel presented higher gel strength, better freeze-thaw stability and lower syneresis ratio.

Key words: konjac glucomannan, xanthan, gel rupture strength, rheological properties

李培源,李晓飞,李安琪,余文艳,郭绰,杨曦,郭玉蓉. 热碱致魔芋胶与黄原胶共混凝胶的显微结构与流变规律[J]. 中国农业科学, 2020, 53(18): 3792-3804.

LI PeiYuan,LI XiaoFei,LI AnQi,YU WenYan,GUO Chuo,YANG Xi,GUO YuRong. Microstructure and Rheological Behavior of Mixed Konjac Glucomannan and Xanthan Induced by Thermo-Alkali Treatment[J]. Scientia Agricultura Sinica, 2020, 53(18): 3792-3804.

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链接本文: https://www.chinaagrisci.com/CN/10.3864/j.issn.0578-1752.2020.18.014

https://www.chinaagrisci.com/CN/Y2020/V53/I18/3792

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魔芋胶﹕黄原胶 Konjac glucomannan:Xanthan	G'_sat	k	R²
对照（2.0%魔芋胶） Control (2.0% konjac glucomannan)	5944.73	3.58×10^-4	0.9800
9﹕1	3827.16	2.51×10^-4	0.9815
7﹕3	1560.97	1.27×10^-4	0.9939
5﹕5	455.16	0.64×10^-4	0.9829