Research On The Effect Mechanism Of Ultrasound On Some Substances Related To Flavor And Color Changes In Model Wine System

Recently,ultrasonic treatment,a non-thermal processing technology in food industry,has received considerable attention owning to promising application in accelerating maturation of wine.There is still a lack of investigation regarding changing and reaction mechanism of the components in wines triggered by ultrasound.Flavan-3-ols are extremely crucial components in red wine,which predominantly contribute to wine color,tast,mouth-feel and flavor.Due to the considerable complexity of real red wine condition,a model wine system was usually involved to investigate the complicated reactions in wine,which could diminish the interference of other factors so as to simplify the experiment.Therefore,the investigations included in this dissertation,mainly concentrating on the flavan-3-ols based on model wine system,aim to illustrate the effect of ultrasound on the interaction between ECG and BSA,on the polymerization of catechin to produce xanthylium compounds as well as on the content of sole organic acids which commonly exist in red wine and have great influence on wine quality.These works will illuminate the mechanism of ultrasound in accelerating wine aging to some extents,and provide theoretical support for that.The main results of this dissertation are as follows:1.In the ECG-BSA model wine system,BSA binded ECG assisted by hydrophobic intereaction and hydrogen bond,and the ECG-BSA complex came into existence with fluorescence quenching of BSA by ECG.The increase of ultrasonic frequency resulted in a decrease of binding interaction and the stability of ECG-BSA complex,and could enlarge the distance between the fluorophore of BSA and ECG.However,compared with the control,it should be highlighted that samples exposed to ultrasound of a lower frequency(25kHz)possessed a larger binding constant and shorter critical distance,which might indicate that the binding interaction could be promoted and the increased complex stability.Furthermore,in the light of spectroscopy,the increase of ultrasonic frequency resulted in a regular change in conformation and secondary structure of free BSA and ECG-BSA complex.2.In the catechin-tartaric acid model wine system,the mainly products were xanthylium cation pigments(dimer).It was illustrated that long-term ultrasonic treatment could promote the generation of these compounds,while the effect of short-term ultrasound(only one time)was comparatively limited.Iron ions conld reinforce the ultrasonic effect of accelerating the formation of xanthylium cation pigments,which might be attributed to the activated Fenton reaction together with the iron(Ⅲ)carboxylate complex assisting the oxidation and decomopositon of tartaric acid into glyoxylic acid.Moreover,oxygen also definitely influenced the ultrasonic effect on the generation of xanthylium cations,and insufficient oxygen would limit the ultrasonic effect.With regard to the mechanism,the free radicals triggered by ultrasound predominantly contributed to some of the steps leading to such enhancement.3.In the model wine containing sole organic acid,long-term ultrasonic treatment could result in slight content decrease of tartaric acid and malic acid,while the content changes of succinic acid and lactic acid appeared limited.For the model wine containing tartaric acid,bath-ultrasonic treatment had a 2.08%decrease in tartaric acid concentration,while samples exposed to prob-ultrasonic treatment decreased by 3.98%,which apparently higher than the former.With regard to the model wine invoving malic acid,bath-ultrasound led to a 4.28%drop in concentration,while pro-ultrasound resulted in 4.15%lower concentration of malic acid,which is close to the bath-ultrasound.Consequently,it could be demonstrated that ultrasound could reduce the sourness and harsh-taste derived from tartaric acid and malic acid,and,meanwhile,maintain the mild odors and smooth-taste stemed from succinic acid and lactic acid.