【作者】 吕俊峰；

【导师】 郭文川；

【作者基本信息】 西北农林科技大学 ， 农业电气化与自动化， 2009， 硕士

【摘要】 粮油是我国多数人口的主食,其产品质量一直是举国上下关心的话题。随着改革开放、市场经济的深入发展以及人民生活水平的日益提高,人们对食用油的质量和营养提出越来越高的要求。为了探索基于介电特性快速检测食用油品质的新方法,开展食用植物油微波介电特性的研究已经成为一项重要的学术课题。此领域的研究是进行食用油品质快速测评、实现在线检测及发挥油脂微波加工技术的重要基础。本文在综述我国食用油质量安全现状,现有检测方法及油脂微波加工中存在问题的基础上,简述了国际先进的同轴探头技术及其应用进展,表明此项技术在研究农产品和食品微波介电特性方面发展空间相当广阔。对食用油介电特性的研究虽说是一个新兴的领域,相关文献报道较少且不系统,但却具有很大研究潜力。为此,以菜籽油、大豆油、调和油、花生油及玉米油为研究对象。采用同轴探头技术研究了200～4500MHz内5种食用植物油经不同温度处理后的微波介电特性,分析介电特性与品质指标的关系。以期为开发新型食用油品质检测技术提供研究基础,具有一定的现实意义和应用前景。通过以上研究,取得的主要结论有:(1)研究了食用油分别加热至20、30、50、70和90℃时,频率和温度对介电参数和穿透深度的影响。品种对介电参数的影响随频率增大而变化幅度不同,同频率下,菜籽油具有最大的相对介电常数εr ’和最小的损耗因数εr’ ’,而玉米油则相反。εr ’随温度升高线性减小,但εr’ ’线性增大, DP随频率和温度的增大均减小。通过线性回归建立了介电参数与加热温度、脂肪酸含量间的回归方程( R 2≧0.83),用于识别食用油种类、预测和监控食用油在贮藏、运输和加工过程中品质随温度的变化情况。(2)对食用油在不同高温(120、150、180、210和240℃)下,加热不同时间(3、6、9、12和15h)后冷却至室温,测定125组不同品质食用油的介电特性。研究频率、加热温度和时间对介电特性的影响。随着频率的增加,εr ’与DP先迅速递减,后趋于平缓,而εr’ ’分布在0.18上下,且变化很小。随着温度的升高,介电参数的变化幅度大于同温下随时间的变化,同频率下,εr ’随加热条件变化与tanδ趋势相反,但与DP相同。通过乘幂(y = axb)和多项式回归建立了介电参数随频率和温度影响因素变化的回归方程( R 2≧0.84),为研究劣质油的介电特性及其品质检测提供理论依据。(3)对食用油在不同高温(120、150、180、210和240℃)下,加热不同时间(3、9和15h)后冷却至室温,测定75组不同品质食用油的酸价和过氧化值。研究高温加热对食用油品质指标的影响随加热温度和时间的变化。以180℃为临界温度,随温度的升高,过氧化值PV在120<T<180℃之间急剧递减,但酸价AV在180<T<240℃迅速递增,两者在180℃值最小。时间不影响PV和AV的温度特性,且同温下对两者变化影响较小。不同品质食用油的介电频谱存在明显差异,通过多项式回归建立了介电参数和品质指标间的预测方程( R 2≧0.80),对于利用介电特性快速测评食用油品质具有重要实用价值。更多还原

【Abstract】 Grain and oil is staple food of majority population in our country, their product quality is always an eternal topic throughout the nation. During innovation opening, market economy develop deeply and improvement of people life level, people demand higher and higher quality and nutrition of edible vegetable oil. To explore new method of quick quality detection for edible oil based on dielectric properties, Developing the study on microwave dielectric properties of edible vegetable oil has become an important academic project. Study on this field is the important foundation, which can be used to make quick evaluation for edible oil quality, to implement detection online, to exert microwave technology in oil and fat processing.This paper is on the foundation of studying quality and safety situation for edible vegetable oil in our country, present measuring methods and problems in microwave processing in oil and fat to brief the national international advance technology and application of coaxial probe, which indicates the technology will get broad space in the aspect of the study on dielectric properties for agricultural products and food. Study on dielectric properties of vegetable oil is a new field, its relative literatures is less and not systemic, but it has tremendous development potential. For this reason, this paper regarded rape oil、soybean oil、peanut oil、corn oil and well-distributed oil as research objects. With the open-ended coaxial probe technology over the frequency range (200～4500MHz), dielectric properties of the vegetable oil was studied which had been treated with different temperatures, the relation between dielectric properties and quality indexes was also analysed, In order to provide investigative basis for the new quality detection technology development for edible vegetable oil, it will be certain practical significance and application future.Main conclusions draw from above studies are:1) The influence of frequency, temperature on dielectric parameter and penetration depth were studied when edible oil was heated to 20、30、50、70 and 90℃. Variety affects variational range of dielectric parameter with the increace of frequency. Relative dielectric constant of rape oil is maximal, and its dielectric loss factor is minimal at the same frequency, otherwise, this conclusion is contrary to corn oil. With a rise of temperature, Relative dielectric constant decreases linearly, but dielectric loss factor increases linearly, penetration depth decreases with the increace of frequency and temperature. Regression equations were established through linear regression, which showed that change of dielectric parameters according to different heating temperatures and fatty acid contents( R 2≧0.83), Which can be used to distinguish variety of edible oil and forecast the quality change during storing, transportation and processing with temperature change.2) Edible oil was heated in different temperature(120、150、180、210 and 240℃), at various times(3、6、9、12 and 15h) and cooled to room temperature before dielectric properties measurement for 125 groups of different qualities. The influence of frequency, heating temperature and time on dielectric properties were studied. With the increace of frequency, relative dielectric constant and penetration depth decline rapidly at first and then declines slightly, dielectric loss factor is about 0.18 and changes slightly. With a rise of temperature, the variation scope of dielectric parameters is larger than that with the increace of time at the same temperature. At the same frequency, the trend of relative dielectric constant is negatively related with the tangent of dielectric loss angle, but it is the same with that of penetration depth, Regression equations were established through power and multivariate regression, which showed that change of dielectric parameters according to frequency and temperature( R 2≧ 0.84), this can provide theoretic foundation for the study on dielectric properties of inferior oil and its quality inspection. there are distinctive differences in dielectric spectrums of different qualities of edible oil.3) Edible oil was heated in different temperature(120、150、180、210 and 240℃), at various times(3、6and 15h) and cooled to room temperature before acid value and peroxide value measurement for 75 groups of different qualities. The influence of heating temperature and time on quality indexes were studied. Critical temperature is 180℃, with the increace of temperature, peroxide value decreases rapidly(120<T<180℃), but acid value increases acutely(180<T<240℃), both are minimal at 180℃. time has no effect on temperature characteristics of peroxide value and acid value, and time has little effect on the change of the two at the same temperature. Regression equations were established through multivariate regression, which showed predictive equations between dielectric parameters and quality indexe(s R 2≧0 .80),it is of significant practical value to evaluate rapidly the quality of edible oil with dielectric properties.更多还原