What is Wheat Germ Oil
See Table 1 and Table 2 for the composition comparison between wheat germ oil and several vegetable oils.
|Wheat germ oil
|Rice bran oil
|Sunflower seed oil
|Vitamin E content
|Corn Germ Oil
|Rice Bran Oil
Method for extracting wheat germ oil
Extracting wheat germ oil from wheat germ usually adopts the pressing and organic solvent extraction methods.
- The oil yield rate of the pressing method is 5%；
- The oil yield rate of the solvent method is 8%~10%.
Although the solvent method can improve the oil yield, there are problems such as solvent residue and flammability of the solvent. The wheat germ oil produced by the above two methods has destroyed the value of the germ, the germ residue can only be used as a raw material, and the abundant protein in the germ cannot be fully utilized. At the same time, the wheat germ oil produced by these two methods must be refined through degumming, decolorization, deacidification, deodorization, and other refining steps by chemical and molecular distillation methods to obtain commercial wheat germ oil.
Two CO2 Extraction and Refining Processes of Wheat Germ Oil
CO2 extraction process 1#: Japanese patent
In 1985, Japanese Patent No. 60-58498 introduced the method of extracting wheat germ oil with supercritical CO2 (30~60°C, 7~30MPa) fluid, and proposed to use a separation kettle to separate the extracted wheat germ oil. The ones that come out are collected successively, and wheat germ oil with different components can be obtained.
CO2 extraction process 2#: Chinese patent (CN1066874A)
Wheat germ oil has a higher acid value due to more free fatty acids and has a special odor. In order to improve the separation effect of the extracted product, a Chinese patent (CN1066874A) in 1992 reported a method for supercritical CO2 fluid extraction and refined wheat germ oil, and industrialized production was carried out in 1993. The technological process is wheat germ → pretreatment → supercritical CO2 fluid extraction → two-stage separation → refined wheat germ oil.
The supercritical CO2 extraction method uses two separation kettles to gradually reduce the pressure and change the temperature. The wheat germ oil can be separated from the CO2 step by step according to its properties so that the process of producing wheat germ oil can be reduced due to the use of supercritical CO2 fluid. On the basis of eliminating the decolorization and degumming refining steps by the extraction technology, the refining steps of deacidification and deodorization are further omitted, that is, commercial wheat germ oil can be obtained directly. This method gives full play to the advantages of supercritical CO2 fluid extraction technology, which can be flexibly adjusted according to the target product, and solves the problem of high acid value and the peculiar smell of wheat germ oil because it contains more free fatty acids. At the same time, high-quality defatted germ can also be obtained. The defatted germ is easy to preserve due to the removal of fat and part of the water and can be eaten directly or used as a raw material for the production of high-protein foods to meet the requirements of the low-fat family.
Features of CO2 Wheat Germ Oil
Using supercritical CO2 fluid extraction, one-stage separation and two-stage separation were carried out respectively, the acid value was reduced from 7.89 mg KOH/g oil for two-stage separation to 1.00 ng KOH/g oil for two-stage separation, and the quality of the oil was significantly improved.
Application of Supercritical CO2 Fractionation Technology in the Refining of Wheat Germ Oil
However, the above methods only aim at the standard of refined oil, and there is no higher requirement. In fact, wheat germ oil is a high-nutrition health oil, not a general cooking oil. When choosing extraction conditions, more consideration should be given to the enrichment of physiologically active components in wheat germ oil. However, the system composition of the above “extraction kettle + separation kettle” has great limitations in the purification of substances, which makes it difficult to separate some components although they differ greatly in molecular size, polarity, structure, volatility, etc.
Process for Refining Wheat Germ Oil by Supercritical CO2 Fractional Distillation
Since the solubility of substances such as wheat germ oil decreases with the increase of temperature, the temperature distribution of the rectification column in general supercritical CO2 rectification is the low temperature at the bottom and high temperature at the top, and the pressure remains unchanged. As the CO2 carrying the extract flows from bottom to top, some components will continue to be “eliminated” due to the decrease in solubility, and accumulate to form internal reflux. Only the highly soluble components are recovered in the separation tank through the rectification column.
The technological process for enriching vitamin E in wheat germ oil by supercritical CO2 rectification is wheat germ→pretreatment→extraction kettle→rectification column→separation→product.
Refined wheat germ oil by supercritical CO2 fractionation
The specific operating parameters are: using wheat germ (vitamin E content of 300mg/100g) as raw material, the extraction conditions are 40°C and 35MPa, and the temperature distribution from the bottom to the top of the rectification column is 40°C, 50°C, 67°C, and 70°C respectively. °C, vitamin E in wheat germ oil can be enriched to 550mg/100g.