Study On The Ethyl Carbamate In Guangdong Hakka Rice Wine And Its Control Technology

Ethyl carbamate?EC?is always formed in fermentation products and has now been verified to be a carcinogenicsubstance.Safety problems of fermentation products caused by EC have aroused more and more attention.In the present work,EC contents in Rice Wine?RW?,especially in Guangdong Hakka Rice Wine?GHRW?with unique local characteristics,were investigated and analyzed.In addition,effects of key factors which affect the formation of EC in GHRW on the changes of EC contents were systematically studied.Then the alkali-modified diatomite was used to remove EC in GHRW and effects of alkali-modified diatomite on the quality and flavor of GHRW were also investigated.Results obtained in this paper can provide the theoretical basis and scientific guidance for the control of EC in GHRW.The main conclusions obtained were introduced as follows:?1?A sensitive gas chromatography-select ion monitoring-mass spectrometry?GC-SIM-MS?method,based on the solid phase extraction?SPE?,was developed for the determination of EC in RW.Results showed that the SPE conditions were optimized as follows:18 mL of dichloromethane was used as the elution solvent and the extraction time was 10 min.The average recoveries of the established methodwerein the range of89.7%-98.1%.The method limit of detection was 1.8?g/L.The GC-SIM-MS method and the method of national standard?GB 5009.223 2014?consistency analysis results showed that both the detection results of EC in rice wine have no statistical difference.The GC-SIM-MS method has advantages in terms of high accuracy and sensitivity and low consumption,which is suitable for the detection of EC in RW.?2?The contents of EC inRW in Guangdong area wereinvestigated and analyzed.It was found that the contents of EC were related to the origin,sweetness and storage time.EC contents of 110 RW samples in China were determined and results found that EC contents in 87.3%of RW samples were lower than 200?g/L,indicating that RW in China was generally safe.However,according to the regulation in Japan?EC content in drinks wine of Japancannot exceed 100?g/L?,only 70%of which were lower than 100?g/L,indicating that the EC problem in RW could not be ignored.EC content in RW of high sweetness was significantly higher than that of low sweetness of RW.In addition,EC contents in GHRW were higher than those in RW of Jiangsu and Zhejiang provinces.Moreover,linear relation ofy=35.513x-9.9041,?R²=0.9239?was obtained for RW by analyzing EC content?y?and storage year?x?,demonstrating that there was a strong correlation between EC content and storage year for RW,the longer of the storage year,the higher of EC content in RW.?3?A high performance liquid chromatography?HPLC?method was developed for the determination of citrulline in GHRW.Theo-phthaldialdehyde?OPA?was used as the derivating agent for pre-column derivatization.Separation of citrulline was performed by using a gradient elution program with CH₃COONabuffer solution?0.038 mol/L,pH=5.0?and acetonitrile/methanol/water?5/2/1,V/V/V?as the mobile phases.Detection was implemented with a diode array detector?DAD?at the wavelength of 338 nm.Recoveries of98.4%-100.8%were obtained with favorable accuracy and precision.The established method was adopted for the determination of citrulline,the precusor substance of EC,in the main technological processes in GHRW.?4?The changes of urea,citrulline and EC in the whole brewing process were revealed.The precusor substances of EC in GHRW,urea and citrulline,are mainly from the post-fermentation process.However,EC contents increased through frying wine process,post-fermentation process and ageing process by 40.29%,24.88%and 19.09%,respectively.The formation of the three process steps in the EC accounted for 84.26%of the total amount?in aged 6 months?.?5?The sources and formed rules of EC in the process of frying were revealed.Urea and citrulline are the main precusor substances in the frying wine process of GHRW.The EC contents formed by urea and citrulline are 70.9%-87.5%and 12.5%-29.1%of all EC contents,respectively.Under the 75?,85?and 95?conditions,within the degradation of urea and citrulline,about 0.85%¹.20%and 0.05%⁰.10%respectively of which were formed EC.According to the frying wine conditions in wine factory,EC formation and flavor formation in GHRW,85?/20²5min was regarded as the appropriate frying wine conditions.In addition,the ageing temperature has a great influence on EC content in GHRW,the lower of the ageing temperature,the lower of EC content.Considering the EC formation and flavor formation in GHRW,15?was finally selected as the suitable ageing temperature for ageing of GHRW.?6?The conditions of diatomite modification were optimized,and the adsorption conditions of alkali-modified diatomite were screened.The adsorption capacity of diatomite to EC in GHRW could be increased by the alkali-modification of it.The alkali-modification was optimized as follows:temperature of 50?,sodium hydroxide concentration of 10%and absorption time of 20 min.The alkali-modified diatomite addition and the absorption time have great influences on the removal rate of EC in GHRW.The removal rate of EC in GHRW could be 77.49%with the alkali-modified diatomite addition of 0.8%and the absorption time of 40 min,while the removal rate of which was only 30.48%with the unmodified diatomite.?7?The adsorption mechanism of alkali-modified diatomite to EC was expounded.Theadsorption of the alkali-modified diatomite to EC in GHRW was in accordance with the second order reaction model,indicating that the control step to the adsorption velocity of this process for EC is on the basis of the liquid film diffusion process on the surface of the alkali-modified diatomite and the chemical adsorption process of electron with EC and functional groups on the surface of diatomite.Theadsorption of the alkali-modified diatomite to EC was in accordance with the Freundlichand Langmuiradsorption isotherms.Thermodynamic study indicated that this adsorption process was an endothermic process which belongs to the spontaneous chemical adsorption.?8?Effects of the alkali-modified diatomite on the sensory index,conventional physical and chemical indicators,organic acids,amino acids,oligosaccharides and polyphenols could be ignored.Electronic tongue analysis indicated that the sourness,umami and bitterness of GHRW were slightly increased after treatment by the alkali-modified diatomite,while the sweetness of which was slightly decreased.Electronic noseanalysis indicated that the odour of GHRW before and after the treatment of the alkali-modified diatomite had no significant difference.The main volatile aroma compounds for both of them were acetic acid,ethyl acetate,isobutanol,ethyl lactate,isoamyl alcohol,2-methyl-1-butyl alcohol,phenylethyl alcohol,furfural and succinic acid diethyl ester.In addition,the flavor and aroma of GHRW with and without the treatment of the alkali-modified diatomite also had no significant difference.All these results demonstrated that the alkali-modified diatomite has no significant effect on the flavor and other properties and quality of GHRW.