| Capsicum frutescens L,also known as pepper,rich in a large amount of capsaicin,vitamins,minerals,high-quality protein,is one of the most widely grown and largest vegetables in China.By 2020 it was the second largest exporter in the world,and has an important position in the development of China’s vegetable industry.Due to the high water content and special cavity structure,capsicum is easy to lose water and wilt during storage and is infected by pathogenic fungi.At present,the commonly used means of preservation are physical preservation and chemical preservation.Physical preservation has high cost,time-consuming and laborious,while chemical preservation has potential risks such as reagent residue,environmental pollution and harm to human health.Therefore,natural preservatives have become a research hotspot because of their green safety and strong antibacterial properties.Litsea cubeba is an important woody oil resource in China,and the essential oil extracted from it has been widely used in fruit and vegetable preservation,medical and health care fields because of its important roles in antioxidant and bacteristasis.However,the essential oils have high volatility,heat is easy to decompose,with obvious pungent odor and other limitations.In the process of application,its antibacterial effect is greatly weakened,so that the application and promotion is also greatly restricted.Nano-embedding technology refers to an emerging technology that selects polymer substances to embed the target to form nanocapsules,which can well mask the pungent odor of essential oils,avoid unstable and volatile defects of essential oils,and reduce the loss of active ingredients.In this paper,taking the essential oil of Litsea cubeba as raw material,exploring its inhibition effect on common postharvest pathogenic fungus of pepper,and using chitosan and gum arabic as composite wall materials,the nanoparticles of Litsea cubeba essential oil were prepared,which were applied to the preservation of pepper,and the effect of nanoparticles of Litsea cubeba essential oil on pepper was studied by measuring the corresponding indicators of pepper.And the results of the study are as following:1.Four types of pepper postharvest pathogenic fungi(Colletotrichum nigrum,C.gloeosporioides,Rhizopus spp.and Phytophthora capsici)were tested with Litsea cubeba essential oil.The inhibition effect was as follows: C.nigrum.<C.gloeosporioides < Rhizopus spp.=Phytophthora capsici.The higher the concentration of essential oil was,the stronger the inhibition effect was.When the concentration of essential oil was 0.5 μL/m L,the inhibition rates of the four pepper postharvest pathogenic fungi were 73.47%,89.45%,100%,100.00%,respectively.When the concentration of Litsea cubeba essential oil was 4 μL/m L,the inhibition rate of the essential oil against the four postharvest pathogenic fungi reached100.00%.The minimum inhibitory concentration(MIC)of Litsea cubeba essential oil against Phytophthora capsici and Rhizopus spp.were 0.3125μL/m L,and the MIC for C.gloeosporioides and Colletotrichum nigrum were 0.625 μL/m L and 1.25 μL/m L,respectively.2.Litsea cubeba essential oil nanoparticles were successfully prepared: chitosan and gum Arabic were used as wall materials to encapsulate Litsea cubeba essential oil nanoparticles.The effects of p H value,wall material mass ratio,wall material concentration and other factors on the formation of nanoparticles were analyzed,the optimal preparation conditions were selected as: p H 4.0,ratio of chitosan and acacia gum 1:3,concentration of chitosan and acacia solution 0.2%,ratio of emulsifier(Tween 80:Span)80)1:1,the mass ratio of emulsifier to essential oil is 1:1,and the amount of essential oil was 0.2% to characterize the prepared nanoparticles.The particle size of Litsea cubeba essential oil was 297.47 nm,and the PDI was 0.219< 0.3,Zeta potential was 32.81> 30;It was observed by negative staining transmission electron microscopy that the prepared nanoparticles had good dispersion and no obvious agglomeration phenomenon.Fourier transform infrared(FTIR)spectroscopy shows that essential oil of Litsea cubeba was successfully embedded.The sustained release behavior simulation experiment showed that the release rate of essential oil nanoparticles was 61.17% after 30 hours of storage at 37 conditions,which was 32.28% lower than the release rate of pure essential oil(90.33%),indicating that the nanoparticles prepared by this method were successfully embedded and the essential oil achieved sustained release effect.By measuring the MIC of 4 kinds of postharvest pathogenic fungi in pepper,the results showed that the MIC of litsea cubeba essential oil nanoparticles against Colletotrichum nigrum was higher than that of free litsea cubeba essential oil.The MIC of litsea cubeba essential oil nanoparticles against C.gloeosporioides,Phytophthora capsici and Rhizopus spp.were consistent with that of free essential oil.Moreover,blank nanoparticles had no inhibitory effect on the tested pathogenic fungi.3.The successfully prepared Litsea cubeba essential oil nanoparticles were applied in the preservation of pepper,and the changes of fruit weight loss rate,respiration intensity,decay rate and defense enzyme activity were measured.The results showed that pepper was stored for 25 days;Compared with CK2(blank treatment)CN(blank nanoparticle treatment)and EO(Litsea cubeba essential oil),the weight loss rate decreased by 31.80%,30.25%,6.68%,respectively.The decay rate decreased by 34.38%,36.36% and 18.18%;respiration rate decreased by 39.10%,38.21%,17.41%.Vc content increased by 27.02%,23.71% and 11.74%,respectively.Chlorophyll content increased by 22.55%,24.36% and 5.83%,respectively.The relative conductivity decreased by 30.49%,30.28% and 14.91% respectively.MDA content decreased by 27.55%,23.53% and 10.50%,respectively.Contents of total phenols and flavonoids and activities of three defense enzymes(SOD,PAL,POD)increased and then decreased during storage,which were higher than the blank treatment group on the whole.It can be seen that Litsea cubeba essential oil nanoparticles have good fresh-keeping effect,which is more significant than free Litsea cubeba essential oil. |
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