Abstract
On the basis of magnetic molecularly imprinted polymer (MMIP) solid-phase extraction coupled with high performance liquid chromatography, we established a new method for the determination of the 4-methylimidazole (4-MEI) in soy sauce. Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) were used to characterize the synthesized MMIPs. To evaluate the polymers, batch rebinding experiments were carried out. The binding strength and capacity were determined from the derived Freundlich isotherm (FI) equation. The selective recognition capability of MMIPs was investigated with a reference compound and a structurally similar compound. As a selective pre-concentration sorbents for 4-methylimidazole in soy sauce, the MMIPs showed a satisfied recoveries rate of spiked samples, ranged from 97% to 105%. As a result, the prepared MMIPs could be applied to selectively pre-concentrate and determine 4-methylimidazole in soy sauce samples.
Highlights
Soy sauce, which is made by soybean and wheat after the pretreatment of starter-making, fermentation, and heating preparation process, is one of the traditional condiments in China, as well as one of the most popular condiments worldwide
The color and luster of fermented soy sauce are mainly produced in the fermentation process; the color and luster of soy sauce partly come from the additive of caramel color
When using the ammonium sulfite as raw material to produce caramel color, nitrogen heterocyclic compounds, such as 4-MEI will be produced as the by-product. 4-MEI is the important factor that affects the safety of caramel color. 4-MEI can cause high risk in the case of large doses
Summary
Soy sauce, which is made by soybean and wheat after the pretreatment of starter-making, fermentation, and heating preparation process, is one of the traditional condiments in China, as well as one of the most popular condiments worldwide. It is the third popular condiment in the USA (after mayonnaise and ketchup), with a market share worth of 725 million dollars in 2014 [1]. Under the condition of heating, these reducing sugar, amino acid or protein may carry out Maillard Reaction and Caramelization Reaction These chemical reactions can produce the flavor substances, and the small molecules of heterocyclic compounds, such as 4-methylimidazole (4-MEI) [2]. When using the ammonium sulfite as raw material to produce caramel color, nitrogen heterocyclic compounds, such as 4-MEI will be produced as the by-product. 4-MEI is the important factor that affects the safety of caramel color. 4-MEI can cause high risk in the case of large doses
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