大孔树脂纯化香蕉皮缩合单宁的吸附特性分析与工艺优化

    Optimizing the adsorption and purification of banana peel condensed tannins by macroporous resin

    • 摘要: 为提高香蕉皮缩合单宁提取物纯度,提升其后续研究与利用价值,该研究采用大孔树脂吸附法纯化香蕉皮缩合单宁,通过比较6种大孔树脂的吸附与解吸性能,筛选出最适宜的树脂型号,并从动力学和热力学的角度分析该树脂对香蕉皮缩合单宁的吸附特性,探究其纯化工艺条件。结果表明:HP-20型大孔树脂是纯化香蕉皮缩合单宁的适宜树脂;静态吸附-解吸动力学试验表明HP-20树脂分别在8、5 h内能够完成对香蕉皮缩合单宁的吸附、解吸过程,该吸附过程符合伪二阶动力学方程(R2=0.997 2);Freundlich热力学模型适用于解释树脂与缩合单宁间的相互作用,这是一种发生在多分子层表面的吸附,模型常数KF与温度成正相关,表明升温利于吸附的进行;热力学参数计算结果为ΔG<0,ΔH=5.13 kJ/mol,ΔS=47.28 J/mol·K,进一步证明了该过程是自发的、吸热的过程,且物理吸附占据主导作用,无序性有所增加。较佳的纯化参数是上样浓度为6 mg/mL、上样流速为1.5 mL/min、上样量为200 mL、洗脱液乙醇浓度为70%、洗脱流速为1.5 mL/min、洗脱液用量为120 mL。经该条件纯化后,香蕉皮缩合单宁纯度由5.79%提高到68.44%。说明HP-20树脂和优化参数对香蕉皮缩合单宁的纯化效果良好。

       

      Abstract: Tannins are the most abundant phenolic compounds after cellulose, hemicellulose, and lignin. Condensed tannins are one class of tannins with diverse functional activities, such as hemostatic and wound healing, anti-inflammatory and anti-allergic behavior. There is a key research topic in the field of plant polyphenols. Banana peel is one of the main by-products of the banana processing industry, which is usually used as animal feed or directly landfilled with a low utilization rate of the functional components. In fact, banana peel can contain many active ingredients, such as condensed tannins. Previous research has been widely used to optimize the extraction parameters for condensed tannins of banana peel. The structural analysis has been conducted to demonstrate their antioxidant, inhibition of Escherichia coli, and anti-hyperglycemic effects. However, the extracted condensed tannins of banana peel are required for purification. Few purification studies have been carried out at present. In this study, macroporous resins were used to purify the condensed tannins of banana peel. A comparison was made on the static adsorption and desorption performance of six macroporous resins. The most suitable resin was selected in this case. Kinetic models, adsorption isotherm, and thermodynamic parameters were then used to analyze the adsorption properties of macroporous resins. A systematic investigation was implemented to clarify the effects of loading concentration, loading flow rate, and volume on adsorption efficiency, as well as the effects of ethanol concentration, elution flow rate, and volume on desorption efficiency. The results showed that the HP-20 macroporous resin shared a high adsorption rate (87.47%) and desorption rate (84.12%), indicating the best purification for the condensed tannins of banana peel. The adsorption kinetics curve demonstrated that the adsorption capacity of tannin on HP-20 resin sharply increased within the first 4 h, thus reaching the maximum adsorption capacity in 8 h, and then maintaining the stability. The desorption kinetics proved that the desorption was essentially realized within 5 h, with a desorption rate of 92.87%. The adsorption curve was fitted to the pseudo-second-order kinetics (R2=0.997 2). Additionally, the adsorption isotherm experiment confirmed that the adsorption of banana peel condensed tannins by HP-20 resin increased, as the temperature raised. Therefore, the higher temperature was favored to the adsorption. The adsorption isotherms curves were fitted using thermodynamic equations. Freundlich thermodynamic model was suitable for the adsorption behavior of banana peel condensed tannins on HP-20, indicating multilayer sorption on a heterogeneous surface. The KF of the Freundlich model increased with the increasing temperature, indicating that the higher temperature was favorable for the adsorption. In both the Langmuir and Temkin models, the parameters RL and KT were used to predict the adsorption from different perspectives. The computed value of RL was less than 1, indicating the favorable adsorption of banana peel condensed tannins onto HP-20 resins. Additionally, KT increased with temperature rising. Consequently, there was a stronger binding energy between condensed tannins and the resin, resulting in a tighter association between them, as temperature increased. Moreover, the thermodynamic parameter was ΔG<0, ΔH=5.13 kJ/mol, ΔS=47.28 J/mol·K. Therefore, the adsorption process was spontaneous and endothermic, with an increased randomness and dominant physisorption. The optimal conditions for purification were determined as the sample concentration of 6 mg/mL, ethanol concentration of 70%, and loading flow rate of 1.5 mL/min, for loading and elution, using volumes of 200 and 120 mL. The purity of banana peel condensed tannins increased from 5.79% to 68.44%. The HP-20 resin and purification conditions were effectively improved for the purity of banana peel condensed tannins.

       

    /

    返回文章
    返回