七参数多项式方程拟合氦等离子体处理面粉的水分吸着等温线

Proposing a Seven-parameter Polynomial Equation to Fit the Moisture Sorption Isotherms of Helium Cold Plasma-treated Wheat Flours

为了解释小麦面粉经过冷等离子体处理后面团吸水率增加的成因,采用120 W低压强射频氦冷等离子体处理面粉0~180 s,随着等离子体处理时间增加,小麦面粉吸水率、电导率、水和蔗糖溶剂保持力(SRC)值及糊化衰减值显著增加,深入探究这些指标变化原因,我们提出一个七参数多项式M=A+B·t+C·t^(2)+D·t^(3)+E·ERH+F·ERH^(2)+G·ERH^(3)(M是平衡水分%,ERH是小数表示的平衡相对湿度,t是温度℃,A~G是参数),能够拟合氦冷等离子体处理面粉的水分吸着等温线,拟合度指标优于修正Chung-Pfost(常用)和四参数多项式(不含温度项)方程。七参数多项式方程能够清晰显示面粉样品水分吸附与解吸等温线之间的滞后环,随着温度增加,滞后环下移,且滞后度随ERH增加呈现抛物线形状,抛物线顶点在ERH 40%~50%。冷等离子体处理将单分子层吸附位点转变为多分子吸附位点的区域提前了,由ERH 50%转变为40%。用Dent模型分析显示,氦冷等离子体处理能够降低面粉单分子层含水量和扩展压强,增加毛细管壁弹性,水分子与化学成分形成氢键的能力加大,促进水分子向面粉颗粒均匀分布和渗透。红外光谱扫描显示面粉中淀粉粒表面短程有序化程度及淀粉与蛋白的作用程度增大。氦冷等离子体技术在改善面粉加工品质具有应用潜力。

For seeking the cause of the increase in dough water absorption rate after cold plasma treatment,this study adopted low-pressure,radiofrequency 120 W helium cold plasma(CP)to treat wheat flours from 0 s to 180 s.Results showed that water absorption rate,conductivity,values of water and sucrose solvent retention capacity(SRC),and paste breakdown value in wheat flours increased significantly with increasing CP treatment time.To further explore the change causes in these physiochemical indexes,we developed a seven-parameter polynomial M=A+B·t+C·t^(2)+D·t^(3)+E·ERH+F·ERH^(2)+G·ERH^(3) M was equilibrium moisture(%),ERH was equilibrium relative humidity(decimal),t was temperature(℃),and A~G were parameters.This polynomial could fit moisture sorption isotherms(20-35℃and ERH 10%-90%)of helium CP treated flours,and the goodness-of-fit indexes were superior to those of modified Chung-Pfost(commonly used)and four-parameter polynomial(without temperature term)equations.The seven-parameter polynomial equation clearly showed the hysteresis loops between moisture adsorption and desorption isotherms of flour samples,which shifted downward with increasing temperature.The hysteresis degree showed a parabolic shape curve with increasing ERH,and the vertex of the parabola was at the range of 40-50%ERH.CP treatment shifted the monolayer adsorption sites to multi-molecular adsorption sites ahead of schedule,from ERH 50%to 40%.Further analysis using Dent model showed that the helium CP treatment was able to reduce the mono-layer moisture content and spreading pressure in wheat flour,and increase the elasticity of a capillary wall.The ability of water molecules was increased to form hydrogen bonds with the chemical components,which promoted the uniform distribution and permeation of water molecules into flour particles.Infrared spectral scanning showed that the degree of short-range order at the surface of starch granules and the interaction between protein and starch tended to increase with increasing CP time.Helium cold plasma technology has potential application in improving flour processing quality.