| Zhenjiang Vinegar is one of the most famous and popular vinegars in China for its outstanding flavor.With increasing interest in the potential health effects of vinegar worldwide,Zhenjiang vinegar has attracted much public interest.However,the fresh vinegar is unacceptable due to the harsh taste and pungent smell.The traditional natural aging method is not suitable for the trend of vinegar industry development because of the large number of containers,long production cycle and difficult management.The ultrasound as a kind of technology to urging the aging of vinegar has been supported by the theories.At present,the mechanism of ultrasound aging is limited,and can’t explain its mechanism.Based on the ultrasound condition of previous research,the effects of the ultrasound on free radical,water molecules(Half width of Water),and hydrogen bonding were studied.The results of the research are as follows:(1)Under ultrasonic treatment,the total amount of amino acids in vinegar decreased by 24.2%.The acetic acid was decreased,but the nonvolatile organic acid was increased after ultrasonic treatment.The lactic acid,succinic,focal glutamic acid,citric acid and a-ketoglutaric acid were all higher than the fresh vinegar,which increased by 13.12%,17.6%,25.5%,23.8% and 24.7% respectively.After ultrasonic treatment,the volatile components of vinegar were changed to varying degrees.The esters,aldehydes and heterocyclic increased significantly.The acids and alcohols decreased,but the ketones and phenols were not obvious.The changes of the above indexes of vinegar were consistent with the natural aging vinegar.The ultrasonic treatment vinegar was determined to be equivalent to 2-3 years of natural aged Zhenjiang vinegar.The 17 kinds of ingredients can be better applied to distinguish the age of Zhenjiang vinegar.(2)Ultrasonic chemistry yield is measured by the release of iodine.It proved that the ultrasonic chemical yield were significantly increased in the range of 10-50 W/100 mL,and slowly increased in the range of 50-90 W/100 mL.The determination of dissolved oxygen and electrical conductivity,indicated that the solution had a higher oxidation ability after ultrasonic treatment.Ultrasound resulted in hydrogen peroxide,hydroxyl radical and superoxide anion radical,generally increases with the increasing of ultrasonic power and time.It indicated that ultrasound can accelerate chemical reactions by inducating the generation of free radicals by in vinegar.The 17 O half-peak breadth of water clusters is 57.65 Hz at 30 min.The activity of the water and chemical reaction rate in the vinegar were accelerated by ultrasound.The hydrogen bonding reached maximum in ultrasonic power 50 W/100 mL,and ultrasonic time 75 min.Ultrasound attenuated the pungent odor of vinegar by changing the hydrogen bond.The results showed that the maximum of browning and intermediate product were respectively obtained under the condition of ultrasonic power 50 W/100 mL,ultrasonic time 60 min and 75 min.The furfural was produced in fructose-glycine system,indicating ultrasound could accelerate the Maillard reaction in vinegar.The mechanism of ultrasonic urging esterification and oxidation reaction was verified by ethanol-acetic acid and ethanol-benzyl alcohol system.The results showed that ethyl acetate was not detected in ethanol-acetic acid system.A small amount of phenylacetaldehyde and phenylacetic acid were detected in the phenylethanol-ethanol system,but none phenylacetate,indicating ultrasound could accelerate the oxidation reaction in vinegar.Under the experimental conditions,the results show that ultrasound can’t catalyze the esterification reaction. |
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