A Quick and Simple Method for Extracting Unsaponifiables of Vegetable Oil
HUANG Rui1, LI Yu1, HE Wen-xuan1*, LU Xian-yong2, CHEN Wei-jian1, CHEN Ting1, ZHANG Yan-jie1
1. Department of Materials and Engineering, Minjiang University, Fuzhou 350108, China
2. Fujian Institute of Testing and Technology，Fuzhou 350003, China
Abstract：Infrared spectroscopy combined with chemometrics, has become a popular method for the identification of vegetable oil. However, this combination is currently based on the infrared spectra of vegetable oil. Although the infrared spectra information of the saponifiable of vegetable oil is extracted, the information of unsaponifiable is not effectively extracted. The sensitivity of the constructed vegetable oil identification model still needs to be improved. Unsaponifiable is important characteristic components. In order to effectively obtain their infrared spectra, it is necessary to separate and concentrate it in advance. However, the existing separation and enrichment method is cumbersome and time-consuming, and can’t be adopted for the batch samples of vegetable oil. In this paper, under high alkalinity, instead of reflux heating ultrasonic heating, was used to shorten the saponification time. On this basis, through ① the reasonable ratio of n-hexane, ethanol and water to form an easy layering system; ② one extraction replacing multiple extractions; ③ designing and developing a dedicated solid phase extraction small column to rapid remove residual alkaline substance and water in the organic phase at one time, the extraction time of unsaponifiable was shortened greatly. The time of separation and enrichment was shortened from about 2~3 hours with the national standard method to about 20 minutes with the newly established method. The new method has good stability. The same sample was prepared by different people, and their infrared spectra were the same, which could ensure the same infrared spectra for one sample. The establishment of this method not only solves the key technical problems of constructing a model of vegetable oil identification based on infrared spectra of unsaponifiable combined with chemometrics but also creates a prospect for rapid sample preparation of unsaponifiable by chromatography/hyphenated chromatography. Using the rapid separation and enrichment method to unsaponifiable of five different brands of sesame oil and five different brands corn oil were extracted, and their spectra were collected. The experimental result shows that there is a great difference between infrared spectra of unsaponifiable of sesame oil and that of corn oil, although infrared spectra of sesame oil and corn oil are almost the same. It can be predicted that the infrared spectra of vegetable oils can be combined with their unsaponifiable infrared spectra to greatly improve the sensitivity of identification methods for some kinds of vegetable oil such as sesame oil.
Key words：Vegetable oil; Unsaponifiables; Infrared spectra; Separation and enrichment
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