Effects Of Ultrasound Treatment On Maturation Of Soy Sauce And The Mechanism Of Accelerated Synthesis Of Pyrazine Compounds

Soy sauce is a traditional condiment in China.Although freshly brewed soy sauce has the general characteristics of soy sauce that can be consumed directly,the taste and flavor of aged soy sauce are more mellow and harmonious to consumers.The traditional aging method has following drawbacks,such as occupying a lot of containers,relatively long period,and easily getting polluted,which is not suitable for modern soy sauce industry.High-intensity ultrasound（HIU）is a potential technology to promote the aging of soy sauce.So far,effect of HIU on aging soy sauce has not been reported.The promoted aging mechanisms of ultrasound has not been revealed.In this study,effects of HIU on the aging of soy sauce were reported,the mechanisms accelerated synthesis of pyrazine were reported.The main findings of the study are as follows:（1）COMSOL multi-physics,including frequency domain pressure acoustics（ACPR）,non-isothermal flow,K-ε（NITF）turbulent flow,and heat transfer model were conjugated and furthermore,simulated the sound pressure,energy density,flow rate,and temperature distribution in the reactor during the HIU-assisted aging.Results show that when the input power of the HIU was 150 W and the cooling water temperature was 54,67,and 87°C,the highest sound pressure and energy field in the reactor appeared under the ultrasonic probe;the peak sound pressure reached 54.7 MPa,the highest energy density was 5.66×10⁶ W/cm³,and the core temperature reached 393,431,and 445℃,respectively.After entering the reaction kettle with the assistance of HIU,the inner liquid was violently disturbed,and the mixing was uniformed.（2）The quality of fresh soy sauce was significantly improved after aging under different HIU conditions:the content of sugars,soluble salt-free solids,total ketones,total acid and total pyrazine,and the relative content of small molecular polypeptides increased significantly,which was significantly higher than that of naturally aged soy sauce（4 years）with the same change pattern.The amino acid content in soy sauce decreased linearly with the increase of HIU aging temperature and the prolongation of aging time.Combined with PCA data analysis and sensory evaluation,the optimal processing conditions were screened out:150 W,90°C,60min.After comparing the heat treatment data,it was found that ultrasound significantly promoted the production of various flavor compounds in soy sauce.The concentration of pyrazine compounds increased with the increase of reaction temperature and time,resulting in the formation of nutty 2,6-dimethylpyridine.2-ethyl-3,5-dimethylpyrazine with cocoa flavor.In addition,the content of total sugar,soluble salt-free solids and total pyrazine in the HIU-aged soy sauce are co-related to the total energy involved in the aging of soy sauce.The results of multi-physics would be futher used to predict the degree of chemical reactions in soy sauce at different HIU conditions.It would be an effective mean of predicting the quality of aged soy sauce.（3）The D-glucose-¹³C₆ in the Maillard reaction（MR）system was labeled through the carbon isotope labeling（CAMOLA）method.The D-glucose-¹³C₆-glycine MR model system was to clarify the carbon skeleton of the MR intermediate and final products,and to reveal the generation pathways of pyrazines in the HIU-assisted MR model system.Results showed that the concentrations of 11 pyrazine compounds in the HIU-MR system were significantly higher than those in the TM-MR system.The results of isotopic distribution in pyrazine show that HIU was significantly improved the aldol-type condensation,i.e.promoting the condensation of carbonyl compounds to the short side chain and extending the length of side chain in the pyrazines.In addition,2,3-dimethyl-quinoxaline,an o-phenylenediamine（OPD）derivative of2,3-butanedione as an intermediate MR product（MRP）,showed an increase in the isotope[M+4]⁺ratio.This phenomenon suggested that the HIU-MR resulted the promoted cleavage of D-glucose-¹³C₆ and subsequently generated a large amount of dicarbonyl compounds as intermediate MRPs.The above studies show that the HIU can be used to promote the MR and furthermore,producing high content and various pyrazines as flavoring MRPs.Results of this study provided a technical support and theoretical basis for the further application of HIU in the field of food flavor synthesis.