Studies On Antifungal Mechanism Of Cinnamon Essential Oil In Two Pathogens Isolated From ‘Hongyang' Kiwifruit And Its Application

‘Hongyang' kiwifruit(Actinidia chinensis cv.Hongyang)was the first red flesh variety cultivated from Actinidia chinensis var.rufopulpa in Sichuan province.Kiwifruit was highly susceptible to rot and deterioration after being harvested by pathogenic microorganisms.Moreover,the fruits would produce respiratory metabolism metabolites and gradually enter the senescence stage in physiological and biochemical processes.Therefore,the antiseptic and preservation measures of kiwifruits were necessary factors to improve quality of fruits after postharvest.In this study,Botryosphaeria parva and Colletotrichum acutatum were isolated from the decaying‘Hongyang' kiwifruit,and the biological characteristics of them were systematically explored.In addition,the antifungal activity of cinnamon essential oil and its main components against the two pathogens were explored.Furthermore,the antifungal mechanism of cinnamon essential oil would be preliminary studied.Finally,the preservation of cinnamon oil on ‘Hongyang' kiwifruit was analyzed.1.Study on the biological characteristics of the two pathogensThe mycelium of Botryosphaeria parva contained a diaphragm,branched,growing in sections,and with a complete structure.It was a eukaryotic organism with no conidia.The optimal growth conditions for mycelium were 30 ?,pH = 6.0,glucose and beef extract,and it is insensitive to light.The growth of Botryosphaeria parva included lag phase,log phase,and stable phase.The lethal temperature was treated at 42 ? for 10 min or at 43? for 5 min,resepectively.The mycelium of Colletotrichum acutatum contained a diaphragm,branched,growing in segments,with a complete structure.It was a eukaryotic organism with conidia.The optimal growth conditions for Colletotrichum acutatum were 25 ?,pH = 6.0,maltose,peptone and beef extract,and it was insensitive to light.The growth of Colletotrichum acutatum included lag phase,log phase,and stable phase.The co-lethal temperature of mycelium and conidia for Colletotrichum acutatum was at 50 ? for 20 min or at 51 ? for 15 min,resepectively.The lethal temperature of conidia was treated at 49 ? for 15 min or at 50 ? for 5 min,resepectively.The main sugar on the cell wall was the chitin.Both strains were broad-spectrum phytopathogenic fungi.2.Antifungal activity of cinnamon essential oil and its main componentsTrans-cinnamaldehyde,trans-cinnamic acid and benzaldehyde were the main components in cinnamon essential oil.Both of cinnamon essential oil andcinnamaldehyde had good antifungal activity against Botryosphaeria parva.The minimum fungal concentration of cinnamon essential oil was 0.0225%.The minimum fungal concentration of cinnamaldehyde was 0.0200%.Therefore,cinnamaldehyde was the main antifungal substance in cinnamon essential oil.Cinnamon essential oil and cinnamaldehyde had good inhibitory effect on spore germination and mycelium growth of Colletotrichum acutatum.The minimum antifungal concentration of cinnamon oil was 0.0200%,and the cinnamaldehyde was 0.0200%.Therefore,cinnamaldehyde was the main antifungal substance in cinnamon essential oil.3.The antifungal mechanism of cinnamon essential oil on cell structureAfter the pathogens were treated by cinnamon oil and cinnamaldehyde,resepectively,the cell morphology was changed significantly.The mycelia were unevenly distributed,and the thickness of cell was disordered,as well as the cells were trapped.Therefore,the conidia were arranged in disorder,and the shape was irregular.There was a dose-dependent manner between the antifungal activity and the concentration of antifungal substance.The destruction of cinnamaldehyde was stronger than that of cinnamon essential oil.Cinnamon essential oil damaged the cell wall by inhibiting the synthesis of ?-1,3-glucan,phosphomannan and chitin through cinnamaldehyde.The chitin played a leading role in the cell wall system.The cinnamaldehyde being used,the activity of chitinase was activated,chitin was hydrolyzed,the content of chitin was reduced,and the cell wall was destroyed.Cinnamon essential oil could inhibit the synthesis of ergosterol by cinnamaldehyde,which made the cell membrane structure incomplete.The hydrophobicity and permeability of the cell membranes for two pathogens were improved,which could cause a large amount of cell contents to release.Therefore,the cells could not be normally metabolized.The longer the action time was,the more serious the damage was.The mitochondrial structure of the two pathogens was destroyed by means of cinnamaldehyde.The mitochondrial structure changes from uniform,complete and clear state to cohesive,rough and fuzzy.4.The antifungal mechanism of cinnamon essential oil on cellular respiratory metabolismAfter treatment with antifungal agers,the respiration of the pathogens was inhibited.The antifungal agents mainly destroyed the tricarboxylic acid cycle pathway in the cellular respiratory metabolism through cinnamaldehyde,thereby making the ATP and ATPase activity inhibited.During the whole treatment period,the content ofmetabolites(glucose,pyruvic acid,citric acid)in cellular respiratory metabolism was higher than that of the control group.It was proved again that cinnamon essential oil mainly affected the tricarboxylic acid cycle through cinnamaldehyde.During the whole stage,the activity of important enzymes(isocitrate dehydrogenase,succinate dehydrogenase,malate dehydrogenase)in the tricarboxylic acid cycle was inhibited,indicating that cinnamaldehyde mainly destroyed the above three enzyme sites.5.Preservative effects of cinnamon essential oil on ‘Hongyang' kiwifruitsAfter treatment with 0.0400% cinnamon essential oil,‘Hongyang' kiwifruits were stored at(4 ± 1°C),the obvious effects on controlling the metabolism and quality of kiwifruits were observed.The treatment could effectively inhibit the decomposition of antioxidant substances and antioxidant enzymes on kiwifruits.