| In April 2002, scientists from Sweden reported the presence of acrylamide in a wide range of fried or baked food samples. From then on, acrylamide has attracted worldwide attention because it has been classified as "potential carcinogen". Model system studies have shown that acrylamide is formed during the Maillard reaction of reducing sugars with asparagine, when carbohydrate-rich food is processed at high temperature. Many Chinese herbal medicines are derived from plant roots and fruits with high starch content. Some of them need to be processed at high temperature to make it more fit to be used. Whether or not acrylamide will be produced during the heating process is a question that attracts our research interest. In this work, Radix Asparagi, a kind of traditional Chinese herb which contains relatively high amount of reducing sugars and asparagine, has been chosen as a model to study on the detection method and the influencing factors for the formation as well as the possible ways for the reduction of acrylamide. This thesis consists of four chapters:Chapter one:The development of various analysis methods for the determination of acrylamide in food was reviewed, and the influencing factors for the formation as well as the possible ways for the reduction of acrylamide were summarized.Chapter two:A new precolumn derivatization-HPLC method was established for the determination of acrylamide. Acrylamide could form a stable thioether when reacted with 2-mercaptobenzoic acid. The derivative reaction is based on Michael Addition:the small acrylamide molecule reacted with 2-mercaptobenzoic acid to form a stable thioether. With a benzene ring in its structrue, the acrylamide derivative has stronger UV absorbance at higher wavelength, and consequently the detection sensitivity of acrylamide was improved. As the polarity of the acrylamide derivative was weakened, its retention on RP-HPLC column was enhanced. In this paper, ultrasound was adopted to accelerate the derivative reaction. Factors influencing the derivative reaction were evaluated in detail. The final extracted acrylamide derivative was separated on a C18 column by using a mixture of acetonitrile and acetic acid (1 g/L water solution) (20:80, v/v) as mobile phase. The flow rate was 0.7 ml·min-1 and the detection wavelength was set at 238 nm. The calibration curve of acrylamide showed good linearity in the range of 0.1μg/kg-5.0μg/kg with correlation coefficient of 0.9998. The limit of quantitation was estimated to be 0.2mg/kg based on the signal-to-noise ratio of 3 recorded at 238nm. Relative standard deviation was lower than 5.35%。Chapter three:Acrylamide formation was found to occur during the browning process by Maillard reaction of reducing sugars with asparagine at temperatures above 120℃. In our experiment, it was found that acrylamide was produced in traditional Chinese herb Radix Asparagi during heating process, and the amount of acrylamide varied with heating time and temperature. The influence of heating temperature on the formation of acrylamide was evaluated by using HPLC-UV as detection method. When the heating time was fixed at 20 min, it was found that acrylamide could be detected at 120℃, and the amount of acryalmide reached the maximum value at 170℃. When the temperature was higher than 170℃, the formation of acrylamide decreased with the rise of heating temperature. If the heating temperature was kept at 170℃, the formation of acrylamide increased with the extention of heating time until the amount of acryalmide reached the maximum value when heated for 20 min. Then the formation of acrylamide decreased with the extention of heating time. Similar changes were observed when the herb was heated at 190℃for different period of time. Through our experiment, we found that the aqueous extract of the heating processed herb had different colors at different heating time and temperature, so we used Model 721 spectrophotometer to detect the aqueous extract to demonstrate the difference between samples heated for different period of time at different temperature.Chapter four:Preliminary methods were investigated for the inhibition of acrylamide formation in traditional Chinese herb Radix Asparagi during heating process. The effects of different pretreatment conditions on the formation of acrylamide were mainly discussed. It was found that the formation of acrylamide could be inhibited by immersing the raw material in salt solution. Lower level of acrylamide formation was observed when the raw material was treated with divalent cation rather than monovalent cation. Sodium tartrate exerted stronger inhibition effect on the formation of acrylamide than sodium chloride and sodium sulfate. As for acid salt, neutral and alkaline salt, the inhibition effect on the formation of acrylamide was as follws:acid salt> alkaline salt> neutral salt. |
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