Investigation the effects of Chitosan-natural antimicrobial substances based nano emulsions coating on extending the shelf life of a Cucumber

Cucumber (Cucumis sativus L.), which belongs to the gourd family Cucurbitaceae, is an economically important vegetable crop worldwide. They have a short shelf-life that is mainly related to firmness loss, discoloration, desiccation and fungal rot.The reduction of losses resulting from bacterial and fungal rot is a major objective of postharvest technology for cucumbers, which tries to utilize safe and efficacious methods to control contamination and the growth of spoiling fungi and bacteria. A few studies have shown an interesting inhibitory effect of essential oils (EOs) and their constituents on food-related spoiling and pathogenic microorganisms. Although most essential oils are classified as Generally Recognized as Safe (GRAS) food flavoring, their use in foods as preservatives is limited due to flavor considerations, since effective antimicrobial doses may exceed organoleptically acceptable levels. Besides, it is difficult to formulate solutions with EOs and their derivatives because they are volatile compound which can easily suffer degradation under the action of heat, pressure, light and oxygen. Furthermore, they are insoluble in water, and for certain applications a controlled release is required. In this perspective, encapsulation procedures represent a viable and efficient approach to increase the physical stability of antimicrobial compounds and enhance their bioactivity during food processing and storage. Additionally, the encapsulation of bioactive compounds improve water solubility, controls delivery, improves absorption, reduced toxicity and the cost of using them because a less amount of the active is required. While microencapsulation systems may guarantee protection of antimicrobial compounds against evaporation or degradation, nanoencapsulation systems due to high surface area to volume ratio has a versatile advantage for targeted site-specific delivery and efficient absorption through cells that could lead to higher antimicrobial activity. Also, the nanoencapsulation methods are useful to consolidate antimicrobial agents in material used for food packaging. In recent years, chitosan (CS) is receiving a lot of interest in the encapsulation of bioactive compounds owing to its general recognition as safe (GRAS), biocompatibility and excellent biodegradability, as well as ability to form films, membranes, gels, beads, fibers and particles. Among variety of methods developed to load bioactive compounds into CS nanoparticles (CSNPs), ionotropic gelation has attracted considerable attention due to this process is non-toxic, organic solvent free, convenient and controllable. The CS–TPP nanoparticles has shown its capacity for the loading and delivery of sensitive bioactive compounds such as lipophilic drugs, polyphenolic compounds, proteins, genes and vitamins. This study was performed with the following objectives: i) to encapsulate and optimize two EOs in CS tripolyphosphate (TPP) nanoparticles; ii) to characterize several physicochemical properties of the obtained nanoparticles by ultraviolet and visible (UV–Vis) spectrophotometry, transmission electron microscopy (TEM), and dynamic light scattering (DLS); iii) to evaluate the efficacy of the CSNPs obtained under optimized conditions to inhibit phytopathogenic cucumber bacteria and fungi in laboratory media and as a coating on the cucumbers; iv) to assess the effect of two EOs@CSNPs coating on some physical, physicochemical and microbial characteristics of the cucumbers during storage; and to extend cucumber shelf-life. Zataria multiflora (ZEO) essential oil was encapsulated by ionic gelation technique into CSNPs with an average size of 125–180 nm, as observed by transmission electron microscopy (TEM). Meanwhile, the encapsulation efficiency (EE) and loading capacity (LC) of ZEO decreased upon increasing initial ZEO concentration with a decrease in particle size. In addition, we have prepared Cinnamomum zeylanicum (CEO) essential oil-loaded CSNPs (CEO@CSNPs) with size range of 140–200 nm, loading capacity of 3-4%, and encapsulation efficiency of 2-17% ,in the initial CEO content of 0.25–1 g/g chitosan. The optimal weight ratio of CS to ZEO or CEO was found 1:0.25. In vitro release studies also demonstrated a controlled and sustained release of ZEO and CEO. For coating analyze, cucumbers obtained in commercial maturation stage from organic farming, were transported at low temperature to the laboratory and coating experiments were carried out on the same day. Cucumbers were selected for uniform size, shape and color, and without any signs of mechanical damage or deterioration. Then, fruits washed in sodium hypochlorite solution (1% v/v) and left for 2 h in a safe cabinet to dry. A total of 1000 fruit was used for conducting all experiments. The superior performance of ZEO or CEO when encapsulated by CSNPs under both in vitro and in vivo conditions in comparison with unmodified ZEO against P. drechsleri was revealed. The in vivo experiment showed that the encapsulated oils significantly decreased both disease severity and incidence of infected cucumbers by P. drechsleri, after 1 or 2 days shelf-life at 20°C following removal from storage at 4°C. The in vivo experiment also showed that the ZEO@CSNPs or CEO@CSNPs coating extended the shelf life of cucumber up to 21 days at 8±1°C while uncoated fruits could not reach this far (<15days). Furthermore, it was capable of improving the microbiological and physicochemical quality and preserving the quality of the fruit during the storage period. Coated fruits were firmer, maintained color, water content, and showed lower microbial counts (P