关键词: 魔芋胶, 黄原胶, 凝胶强度, 流变学特性, 冻融稳定性

Abstract:

【Objective】The effects of xanthan addition amounts on the gel properties and gelation mechanism of konjac glucomannan (KGM) gels were investigated, which was expected to provide a theoretical basis and technique references for developing KGM-related gel foods.【Method】The mixed KGM and xanthan systems were prepared by adding different concentrations of xanthan into 2% KGM solution, and then the mixed polysaccharide systems were subjected to heating at 90℃ for 2 h in the presence of 2% Na₂CO₃. After cooling to room temperature, the composite KGM-xanthan gels were prepared. By determining the gel strength, the effects of deionized water immersion and 2% citric acid immersion as well as freeze-thaw treatment on the composites were investigated. Meanwhile, scanning electron microscope was used to visualize the microstructures of the composite gels, and then the effects of different treatment methods and xanthan addition amounts on the gel structures were also revealed. Moreover, based on rheology, X-ray scattering and thermogravimetric analyses, the gel formation process of the mixed KGM and xanthan systems during heating at hot alkaline condition was explored, and the gelation mechanism was also revealed.【Result】During heating at 90℃ for 2 h, it was found that with the increasing of xanthan addition, the gel strength of the composite gels was decreased, indicating that the presence of xanthan negatively affected the formation of KGM gel network in this process. However, at room temperature, with increasing xanthan content, the gel strength of the composite gels was increased. The higher the xanthan content, the greater the gel strength, indicating that xanthan might strengthen the composite gels during cooling. After dezionized water and 2% citric acid immersion, gel strength decreased, and the gel samples with citric acid immersion showed a more pronounced decreased trend. Besides, after freeze-thaw treatment, KGM gels exhibited significant syneresis effect, with an approximately 50% of syneresis rate. However, after adding xanthan, the syneresis rate of the composite gels was significantly decreased. The higher the xanthan content, the lower the syneresis rate. Rheological test results suggested that during heating at 90℃ for 2 h, with the increasing of xanthan content, the gelling rate of the mixed KGM-xanthan system was decreased, indicating that the addition of xanthan decreased the formation of KGM gel network. Subsequent decreasing temperature sweep results showed that when the temperature decreased from 90℃ to 60℃, the elastic modulus of the composite gels exhibited a decreasing trend. When the temperature was continuously decreased to room temperature, the elastic modulus showed an increasing trend, and the transition temperature was corresponding to 60℃, suggesting that xanthan began to synergistically bind with KGM gel network at this temperature.【Conclusion】The addition of xanthan significantly improved the gel strength of alkali-induced KGM gels at room temperature, and also enhanced the freeze-thaw stability of the gels. This result could provide valuable reference to development of KGM gel-related food.

Key words: konjac glucomannan, xanthan, gel strength, rheological properties, freeze-thaw stability