The Correlation Research On The Quality Of Edible Oil And The Dielectric Property During Frying

In recent years, the fried food has become more and more favorite by consumers because of its unique taste and flavor. The frying process is also widely used in the food industry. However, there will be a series of complex physical and chemical changes during high-temperature frying. These changes not only declined the nutritional value of food, but also produced some toxic substances which is harmful to health. Currently, most scholars have done a lot of research on the traditional method for quality evaluation of frying oil. But, these conventional methods require tedious manual operation and a large number of chemicals. They are negative to the environment and the operator. In recent years, there is the gradual emergence of some new detection methods, such as high performance liquid chromatography, nuclear magnetic resonance, infrared spectroscopy, image analysis, optical methods, electronic nose, etc. These methods require expensive equipment analysis, high testing costs, complicated operation, rigorous pretreatment for samples. It is not conducive to universal. Therefore, this experiment is based on the dielectric properties, working on a method to detect the oil quality during frying. At last, we can find a new real fast detection technology.Dielectric property is the corresponding reaction of the charge of biology molecular to the external electric field. Studying the dielectric property of food is in favor of analyze and control its quality as well as to supply it to processing food, this technology is widely used. Inspection by using the electric physical property provides a major method to the automation and precision control of food processing.In order to knew the dielectric properties of edible vegetable oil in the microwave frequency(100-10000MHz). In this study, several common edible vegetable oils are selected, such as soybean oil, canola oil, peanut oil, olive oil, corn oil, blend oil, sunflower oil and sesame oil. The dielectric property of different oils under different frequency and temperature were measured by coaxial probe technique. The results show that: the dielectric constant of vegetable oil is small and there are some regularity. At low frequencies(100-300MHz), the dielectric constant increases with the frequencies, and then decreases; at high frequency(300-10000MHz), the dielectric constant of vegetable oils decreases with the increasing frequency. There is no significant variation of the dielectric loss during frying among the frequency band. Temperature has a certain effect on the dielectric properties of vegetable oils, certain frequency, the dielectric constant decreases with increasing temperature.In order to explore the root causes affecting the dielectric properties of vegetable oil, the fatty acid of common eight kinds of vegetable oil were measured. And we also explored the relevance for the dielectric constant with fatty acid. The results indicated that at lower frequencies, the positive relationship was between dielectric constant and unsaturated fatty acid except for peanut oil; at higher frequencies, dielectric constant of soybean oil was increasing with the content of linoleic acid.Finally, also the most important part in this paper, we have the relevance research for the quality of edible oil and the dielectric property during frying. Meanwhile, we chose the more common soybean oil as the main object to reduce the unnecessary factors. We use the national standard method for the determination of soybean oil acid value, peroxide value and polarity component. At the same time, detecting the dielectric property of soybean oil, and exploring the relevance of traditional soybean oil quality indicators with dielectric properties. The results show that acid value and polar component content of soybean oil increases during frying, and the peroxide value increases at first, and then decreases. The relevance between the dielectric property and the internal qualities index of edible vegetable oil was significant, take soybean oil as an example. The internal qualities of edible oil can be deduced from dielectric property by those equations and the internal qualities can be measured quickly It offered a scientific and practical procedure for further developing the rapid testing machine for food.