Studies On Delaying Ripening And Senescence Of Harvested Guava(Psidium Guajava L.cv.Zhenzhu) Fruits By 1-MCP Treatment And Its Action Mechanism

Guava(Psidium guajava L.)is an important fruit crop of the subtropical and tropical regions in the world and is also one of famous subtropical fruit varieties in Fujian Province of China,of which Fujian Province focuses on the development.But the guava fruits are easy to deteriorate,such as soften,yellow and decay after harvest,bringing great difficulties to its long-distance transportation and consumption,which will seriously influence the quality and commodity value of fruits.’Zhenzhu’guava(Psidium guajava L.cv.Zhenzhu)fruits,the chief guava cultivar in Fujian Province of China,were treated with AnsiP-STM for 12 hour,a new anti-ethylene product of Taiwan LiTong company,at room temperature and stored in the condition of(25±0.5)℃,85%relative humidity in this study.The rusults were as follows:1.In this experimentation,the ’Zhenzhu’ guava fruits were treated with 0,0.3,0.6,0.9μL/L 1-methylcyclopropene(1-MCP).The results showed the treatment of 1-MCP lowered the respiration rate and respiratory peak of ’Zhenzhu’ guava fruit,that it could delay the increase of cell membrane relative leakage rate of fruit,inhibiting the decrease of hue angle(h°)value of fruit surface,maintaining higher fruit firmness,higher contents of titratable acid in fruit and chlorophyll in pericarp,retarding the change of apparent color of fruit,together with decreaseing fruit weight loss and fruit decay.Among the above fruits treated with different concentration of 1-MCP,the effects are distinctly different,in which the fruits pre-treated with 0.9 μL/L 1-MCP showed the best fruit quality.So it was chosed as the optimum conditions of 1-MCP treatment for the harvested guava fruits in this study.2.The treatment of 0.9 μL/L 1-MCP could keep higher firmness of sarcocarp and endocarp in ’Zhenzhu’ guava fruits,efficiently lowering the activities of cell wall degrading enzymes,such as pectinesterase(PME),polygalacturonase(PG),cellulose,P-galactosidase,etc.and retard the decrease of contents of cell wall material,covalent-bound pectin,hemicellulose and cellulose and the increase of content of water-soluble pectin.From the results,it could be concluded that 1-MCP could obviously decrease cell wall metabolism and fruit softening in sarcocarp and endocarp of harvested’Zhenzhu’ guava fruits,and prolong fruit storage life.3.The treatment of 0.9 μL/L 1-MCP decreased the lipoxygenas(LOX)activities in sarcocarp and endocarp of ’Zhenzhu’ guava fruit,maintaining higher relative contents of unsaturated fatty acids,such as oleic acid,linoleic acid,a-Linolenic acid,etc.and lower relative contents of Saturated fatty acids,such as myristic acid,palmitic acid,stearic acid,arachidic acid,etc..As a result,the index of unsaturated fatty acids(IUFA)and unsaturated degree of fatty acids were decreased.From the results,it could be concluded that 1-MCP treatment delaying ripening and senescence of ’Zhenzhu’ guava fruits may be due to decreases of activities of LOX,which may reduce the oxidation and decomposition of unsaturated fatty acids of membrane lipids.Thus,it may reward a transition of membrane lipid from predominantly liquid crystalline to gel-phase lipid,increasing the liquidity in the membrane and resulted in maintaining integrity of cell membrane structure and compartmentalization within the cell.4.The treatment of 0.9 μL/L 1-MCP maintained higher activities of active oxygen scavenging enzymes,such as superoxide dismutase(SOD),peroxidase(POD),catalase(CAT)and ascorbate peroxidase(APX)and contents of endogenous antioxidant substances such as ascorbic acid(AsA)and glutathione(GSH),and obviously decreased the O2-production rate and malondialdehyde(MDA)content in sarcocarp of ’Zhenzhu’ guava fruit.From the results,it could be concluded that 1-MCP treatment enhanced active oxygen scavenging capacity,which reduced the accumulation of reactive oxygen species that can undermine cell membrane structure,and delayed membrane lipid peroxidation of’Zhenzhu’ guava fruits,which retarded their ripening and senescence.5.The treatment of 0.9 μL/L 1-MCP maintained higher activities of cytochrome c oxidase(CCO),H+-ATPase,NAD+ kinase and kept higher contents of adenosine triphosphate(ATP),NADP(H)and lowered the contents of adenosine diphosphate(ADP),adenosine monophosphate(AMP),NAD(H)in sarcocarp of ’Zhenzhu’ guava fruit.As a result,it maintained a higher level of energy charge during the whole storage.From the results,it could be concluded that 1-MCP treatment kept higher activities of cytochrome c oxidase(CCO),H+-ATPase,NAD+ kinase to meet the energy requirements of the normal metabolism in sarcocarp of ’Zhenzhu’ guava fruit and maintained the extra and intracellular concentration of the ions to keep the integrity of cellular membrane structure,which retarded fruit ripening and senescence.