| Fresh grapes are susceptible to infectious diseases during the period of post-harvest storage and transportation.At present,preservatives sustained SO2-release are one of main preservatives used in grape preservation,but the residue of SO2 on grapes may affect human health.Cinnamon essential oil(CEO)is a kind of cell secondary metabolites extracted from dried cinnamon bark.It is an important natural food flavors,it also has good antimicrobial and antioxidant activity,and most importantly,it has no toxic effect on human body.In recent years,it has become a hot spot in fruit natural preservative development.So it is of great significance to study CEO’s antimicrobial mechanism against post-harvest grape pathogens and fresh-keeping effect on post-harvest grape,which can provide theoretical basis for grape preservative development based on CEO.CEO was extracted from different distillation periods through steam distillation assisted by ultrasonic.The chemical composition and content of CEO in different distillation periods were analyzed by GC-MS.The antimicrobial tests to Aspergillus niger,Rhizopus nigra and Penicillium isolated from Kyoho grapes were carried out to analyze the difference of antibacterial activity of CEO in different distillation periods.Initially,inhibition mechanism of CEO on pathogenic bacteria of Kyoho grapes was studied with content of protein and sugar,activity of SOD,POD and CAT in mycelium as indexes.Kyoho grapes were treated with different concentrations of CEO at different temperatures to study the effect of CEO on the preservation to them,which were indicated by following indexes i.e.,rotting rate,grain drop rate,weight loss rate,color,content of Vc,content of soluble solids,content of titratable acid,ethylene release,activity of PPO,POD,and CAT,content of malondialdehyde.The results are as follows:(1)CEO collected in each of distillation periods had good inhibitory activity against Aspergillus niger,Rhizopus nigra,Botrytis cinerea and Penicillium isolated from Kyoho grapes especially to Penicillium.The antimicrobial activity of CEO was significantly different in different distillation periods,and the CEO collected at 3rd h showed the strongest activity.With analysis by GC-MS,the main component of CEO was identified as trans-cinnamaldehyde.The trans-cinnamaldehyde content of the CEO obtained in the 3rd h was the highest among all distillation periods,reaching 72%.The results of antimicrobial test showed that the content of trans-cinnamaldehyde in the CEO was positively correlated with its inhibitory activity.(2)CEO can cause abnormal shrinkage of cell of Aspergillus niger,Rhizopus nigra and penicillium,change the permeability of cell membrane,destroy cell structure of mycelium and therefore cause protein and soluble sugar outflow.CEO can also reduce the activities of several protective enzymes,such as catalase,superoxide dismutase,and peroxidase in Aspergillus niger.The free radicals can not be eliminated in time and the antimicrobial effect arising therefrom.(3)CEO can reduce the abscission rate,weight loss,and decay index of Kyoho grapes stored in 20℃(p<0.05)compared with the control.And 500μL/L of CEO showed the best effect.Compared with in 20℃ the abscission rate,weight loss,and decay index of Kyoho grapes treated by CEO in 4℃ were significantly lower than the former.In 4℃,100μL/L CEO showed the best effect on reducing the abscission rate,weight loss,and decay index of Kyoho grapes in each treatment group.The treatment of medium and low concentration of CEO(10,50,100 μL/L)effectively delayed the change of the color of the grape,while the 500 μL/L CEO accelerated the fading of the grape color.100 μL/L of CEO showed the best effect on postponing the reducation of titratable acid and soluble solid.Medium and high concentration of CEO(100,500μL/L)accelerated the arrival of ethylene spikes of Kyo grape,while low concentration of CEO(10,50 μL/L)reduced value of ethylene release peak and inhibit the production of ethylene.50 μ/L of CEO showed the best effect on inhibiting POD activity of Kyoho grape fruit;50,100 μL/L of CEO showed the strongest effect on inhibiting the increase of PPO activity of Kyoho grape;50 μL/L of CEO showed the most significant effect on depressing the accumulation of MDA of Kyoho grape. |
