Antimicrobial Activity Of Carvacrol And Its Application On The Preservation Of Pitaya Fruit

As a typical tropical fruit,pitaya has unique flavor and rich nutrition such as sugar,organic acids,dietary fiber,protein,vitamins and betaine(especially in red-fleshed pitaya).Pitaya fruit is popular with consumers due to its biological activities,such as anti-oxidation,anti-aging,lowering blood fat,and anti-tumor.However,pitaya fruit is highly susceptible to fungal infection during postharvest,causing quality deterioration and resulting in the loss of its market values.The traditional storage techniques,such as refrigeration and chemical storage,are costly,inefficient and have side effect like pesticide residues.Carvacrol,as an efficient,safe and natural antimicrobials,has great potential for utilization and development in the storage of fruits and vegetables.This research was intended to isolate and identify the dominate pathogens which cause rotting of pitaya in Zhejiang province during storage.The antibacterial mechanism of different concentration of carvacrol treatments was investigated,and the effect of carvacrol fumigation combined with controlled atmosphere storage on the quality and physiological and biochemical attributes was also studied.Meanwhile,the feasibility of the application of carvacrol in the storage and fresh-keeping technology of pitaya was discussed.The results will provide theoretical basis and reference for development and application of postharvest preservation technology in pitaya.Major results were as follows:(1)In this study,the pathogenic strains were isolated from pitaya fruit through tissue separation method,proved by Koch's postulate and identified by morphological observation and analysis of r DNA-ITS sequence and phylogenetic tree.The results showed that HS-2caused spoilage of pitaya fruit in Zhejiang Province,which was identified as Colletotrichum fructicola.(2)Carvacrol essential oil(CVR)was investigated for its activity to control C.fructicola.The results showed that treatment with CVR could effectively inhibit mycelial growth,spore germination and germ tube elongation of C.fructicola in vitro,significantly reducing the onset and spot diameter of anthracnose in pitaya fruit.Membrane permeability and leakage of cellular components in the hyphae of C.fructicola increased as the concentrations of CVR increased.CVR treatment caused abnormalities of hyphal morphology and disorganization of intracellular organelles by SEM and TEM.In addition,CVR treatments induced the generation of reactive oxygen species(ROS),which caused oxidative injury to the cell membrane via lipid peroxidation.The antifungal mechanism of CVR against C.fructicola might be attributed to induced ROS production,increased membrane permeability,resulting in abnormalities of ultrastructure,and loss of intracellular contents.(3)The effects of pitaya treated with carvacrol fumigation combined with controlled atmosphere storage(7?)on the quality,physiological and biochemical properties were studied.The results showed that CVR treatment could significantly decrease the respiratory rate and inhibited the increase of MDA content,delay TSS,TA and V_C.Meanwhile,it could increase the activities of antioxidant-related enzymes,including SOD,POD,PPO and CAT and activities of disease-resistant enzymes,including PAL,CHT,and GLU during storage.Therefore,the method of CVR+MA can be recommended as an effective and safe fresh-keeping technology for pitaya fruit.