Antimicrobial Efficacy Of Liposome Encapsulated Citral And Its Effect On The Shelf Life Of 'Shatangju' Mandarin

Citrus is one of the most cultivated genera of fruits worldwide,which has been accepted as healthy and nutritious food.However,fresh fruit are prone to be contaminated by microorganisms during storage and transportation,resulting in a significant reduction of both the overall quality of the fruit and the percentage of edible fruit.Application of traditional preservatives is the primary method for disease control of postharvest fruit,which however carries a risk to consumer health due to the possibility of chemical residue on the product.In this study,liposome encapsulated citral was developed as a sustained-release antimicrobial agent.The properties of the liposome were characterized by dynamic light scattering.The antimicrobial activity of the liposome encapsulated citral was tested in vitro.In addition,in vivo tests were conducted in order to evaluate the ability of the liposome encapsulated citral for controlling postharvest decay and extending the shelf life of fresh 'Shatangju' mandarin.The microstructure and dispersion properties of the liposome were characterized after investigation by transmission electron microscope(TEM)and dynamic light scattering(DLS).The average particle size was found via DLS to be 105.7 ± 2.08 nm,PDI was 0.236 ± 0.010 and the zeta potential was-43.2 mV.Encapsulation efficiency of citral by the liposome was 61.75 ± 1.58%.In addition,there was no visible sign of stratification after the samples were kept at room temperature up to one month,it could be inferred that the liposome encapsulated citral possess favorable dispersibility and stability.After 3-week storage,the Retention value of citral remained about 20%,suggesting that liposome efficiently entrap citral.The antimicrobial activity of the liposome encapsulated citral was tested in vitro against four microorganisms: Escherichia coli,Staphylococcus aureus,Bacillus subtilis and Penicillium italicum.E.coli and S.aureus are representatives of pathogenic bacteria commonly occurring in ‘shatangju' mandarin;B.subtilis is involved in the softening of fruit during ripening by producing pectinolytic enzymes;P.italicum was selected because it is the main fungus causing citrus disease.The results show that the antibacterial activity of citral against gram-positive bacteria was greater than against gram-negative bacteria.Liposome encapsulated citral exhibited larger inhibition zone when compared to an exposure to an equivalent dose of free citral.The MICs of liposome encapsulated citral against these four pathogens were significantly lower than those of free citral.Comparative growth inhibition curves found that the antibacterial effect of free citral was sharply weakened after the third day,and citral after encapsulation by liposomes showed a more significant antibacterial activity than free citral.The experiment was performed for 72 h.After that,the growth of S.aureus and P.italicum was almost completely inhibited,and it could exert its long-lasting bacteriostatic effect.On the fourth day,it could still reduce the bacterial content of E.coli and Bacillus subtilis,which were 0.27 and 0.65 CFU/mL.In addition,in vivo tests were conducted in order to evaluate the ability of the liposome encapsulated citral for controlling postharvest decay and extending the shelf life of fresh 'Shatangju' mandarin.Compared with the control group,citral liposome treatment can effectively inhibit the growth of yeast and mold on the surface of granulated orange fruit.After storage for 24 d at 25 °C and 60-70% RH,the total is only 497.67 CFU/g,which is far lower than the control group at 1519.46 CFU/g.The liposome encapsulated citral significantly reduced decay incidence,presenting a reduction of 43.33% and 42.04% compared to control and free citral treated fruit,respectively,after storage.Weight loss of liposome encapsulated citral treated fruit significantly lower than that of control and free citral treated fruit,moreover,liposome encapsulated citral treated can keep the fruit in a good appearance.In summary,liposome encapsulated citral was successfully prepared with good dispersion,stability and antimicrobial activity,which demonstrated great potential to be an effective antimicrobial agent to extend the shelf-life of 'Shatangju' mandarins.