Study On Regulated Technologies Of Ethyl Carbamate In High-salt Diluted Sate Soy Sauce

Soy sauce is a traditional Chinese condiment fermented mainly by soybeans.Due to its excellent taste,flavor and nutrient composition as well as a variety of biological activities,such as antioxidant ability,antihypertensive ability,antimicrobial ability,and anticancer ability,it is not only a necessary seasoning for Asian countries like China,Japan and South Korea,but also is accepted and favored all over the word.However,in the fermentation and storage period,there were many harmful substances such as biogenic amines,ethyl carbamate and mycotoxins that will be produced.This phenomenon is closely related to the metabolic activities of fermentation microorganisms.Among them,ethyl carbamate(EC)is a carcinogen(IARC group 2A)to humans,which existed naturally in many fermented foods and alcoholic beverages,In food industry,it is also a secondary metabolite of microorganisms.Because of its potential carcinogenic risk,the maximum residue limit(MRL)in food and alcoholic drinks have been set up by many countries and organizations around the world.In addition,the consumption of soy sauce is very common in Chinese diets,and the long-term intake of EC may have a cumulative effect on human body.Therefore,it is necessary to take measures to reduce EC contamination in soy sauce.In this study,in order to reduce EC production and to ensure the safety of soy sauce,the factors related to EC synthesis,such as common raw materials,yeasts and temperature,were optimized based on the process techniques to find out appropriate fermentation conditions.Firstly,to better isolate and collect yeast cells,a liquid sauce medium that mimics complete sauce fermentation was developed.And the closed non-mash liquid fermentation system not only benefited to the separation of yeast cells,also effectively prevented the contamination by other microorganisms.Secondly,by tracking the EC content and the changes of the basic physicochemical parameters in the fermentation process,the effects of different fermentation factors on EC synthesis were evaluated,and the EC precursor urea and ethanol were also evaluated to explore the mechanism of EC synthesis.The results were as follows:(1)there was no significant difference on the synthesis of EC between the two raw material combinations;(2)yeast was an important factor leading to the increase of EC content,and the Yeast S was more conducive to the control of EC synthesis than Yeast T;(3)compared with the normal temperature fermentation group(30?),the strategy of low temperature fermentation(18?)can effectively control the synthesis of EC and have a good fermentation performance.Finally,by determining the expression levels of genes related to urea and ethanol metabolism,the changes in the metabolism of EC and its precursors were verified at the molecular level.The results showed that the high expression of PDC1 and ADH1 in yeast S during the fermentation process is responsible for the synthesis of a large amount of ethanol.In addition,the high expression of DUR1,2 has an effect on utilizing the residual urea effectively in the sauce,which was considered to be a positive significance for the control of the EC in the soy sauce fermentation.In summary,in this study,the addition of Yeast S and low-temperature fermentation are effective ways for controlling the synthesis of EC.Low temperature inhibits the rapid proliferation of the yeast and cellular activity(down-regulation of gene expression levels).And it also inhibits the massive synthesis of urea and reduces the synthesis of EC in soy sauce.In addition,low-temperature fermentation also helps to reduce the release of volatile flavors such as ethanol,which benefit not only the improvement of the edible safety,but also the flavors in soy sauce.