| In order to develop a new environmentally friendly packaging materials and improve theapplication value of polysaccharide film, the aim of this study was to combine naturalantibacterial (essential oils) and antioxidants (tea extracts) agent into edible chitosan-basedfilm and evaluate the effects of essential oils, emulsifier, tea extracts, plasticizers on physical,mechanical, optical and structural properties of chitosan film. Moreover, in order to improvethe value of edible film in the foods preservation, the study investigated the effects of chitosancomposite film on whole and fresh-cut Chinese water chestnuts. This article included thefollowing aspects:(1) The combined effects of0,0.5%,1%and2%lemon essential oils (LO) andemulsifiers on the physical, mechanical and structural properties of chitosan film wereinvestigated. The results showed that lemon essential oil decreased apparent viscosity, watercontent and water vapor permeability (WVP), and increased the color and opacity of thecomposite film. The tensile strength and elongation at break of2%lemon essential oilcomposite films increased50.0%and62.5%compared with the control. Moreover, theaddition of Tween80significantly increased WVP and solubility in water of thechitosan-essential oils film and led to the decrease of tensile strength and elongation at break.The film containing Span80showed lower transparency. The morphology (SEM) wasdifferent depending on the LO contents and emulsifier types used. FTIR showed that LO didnot affect significantly the chemical structure of chitosan film, but the emulsifiers (Tween andSpan) resulted in the formation of new bonds in1737cm-1due to its nCOO-stretchingvibration.(2) The combined effects of plant essential oils (lemon, thyme, cinnamon) on the physicaland structural properties of chitosan-based films were investigated. Results showed that theapparent viscosity and average particle size of lemon essential oils were significantly lower than thyme and cinnamon essential oils. The combined use of two kinds of essential oilsdecreased the particle size compared with single essential oil. In addition, thyme oil has thestrongest antioxidant and antibacterial ability, followed by cinnamon essential oil and lemonessential oil. The combined use of two kinds of essential oils balanced the antioxidant abilityof single essential oil. Three plant essential oils increased the thickness and color anddecreased the water content, water vapor permeability and solubility of chitosan film. Thewater vapor permeability of lemon/cinnamon oils composite films was lowest than others, thevalue was7.52*10-11g.m-1s-1Pa-1. In addition, the tensile strength of lemon oils compositefilm was highest. SEM analysis showed that the oil droplets were homogenously distributedacross the flm. The emulsification was obviously observed in chitosan/lemon/cinnamonessential oils composite films due to the electrostatic interaction of limonene andcinnamaldehyde. From the sensory evaluation, three plant essential oils significantly increasethe flavor of chitosan film detected by the electronic nose. Wherein, lemon essential oils had agood flavor and more easily to be accepted.(3) The effects of green tea extracts (GTE) and black tea extracts (BTE) on the physical,structural and antioxidant properties of chitosan films were studied. Results showed that theaddition of tea extracts significantly increased the antioxidant ability of films and decreasedwater vapour permeability. The DPPH radical scavenging ability of chitosan-tea compositefilm was94.9%. The antioxidant ability of chitosan-tea composite film was improved with theincreasing tea extracts concentration. In addition, the antioxidant ability of GTE films wasstronger than that of BTE films in all food simulants (0%,20%,75%and95%ethanol). Theequilibration time in different food simulants decreased with the increased ethanolconcentration. SEM showed that chitosan and tea extracts had good compatibility, however,the addition of tea extracts decreased the elongation at break of chitosan film which changedthe structure and interaction in the matrix and led to the decrease of thermal stability.(4) The effects of plasticizer such as glycerol and polyethylene glycol200on the physical,mechanical, antioxidant and structural properties of the chitosan films were studied. Resultsshowed that water vapor permeability and flexibility of chitosan/green tea films wereincreased with the increasing glycerol concentration, meanwhile the solubility and swellingdegree decreased. Moreover, the release time of antioxidants from films was delayed with theincrease of glycerol concentration. The presence of Tween20had a complex effect on theseproperties which depended on the blend ratio of glycerol and Tween20. DSC, X-ray diffraction and FTIR spectra analysis indicated that there was strong interaction in film matrix,which could be reflected by the physical and mechanical properties of composite films. Onthe whole, the best composition of chitosan composite film was2%chitosan,0.5%GTE and45%glecerol. In addition, compared with the two plasticizers, the mechanical strength of1:1ratio composite films was the highest with the tensile strength and puncture force were31.05MPa and19.26N, respectively. The chitosan/glycerol films had the lower swellingdegree and better water barrier properties than chitosan/polyethylene glycol200films.However, with the addition of GTE, the lowest water vapor permeability was found inchitosan/polyethylene glycol200films. In a word, the differences in chitosan composite filmswere related to the number of hydroxyl groups contained in the plasticizer and the blend ratioof green tea polyphenols.(5) The microstructure, water properties, quality characteristics and preservation ofChinese water chestnut were studied. Results showed that the arrangement of cell tissues wasclose and a large number of starch granules (5-10μm for each one) were dispersed in the cell.The free-water was the main part in Chinese water chestnut, accounting for95.1-98.3%. Andthe holding capacity of cell was weak and the relaxation time was long. In addition,disaccharide (sucrose,65.28mg/g) was the main sugar in the water chestnut and the content ofmonosaccharide (fructose4.96mg/g, glucose6.72mg/g) was lower. After storage, the tissuebrowning was serious in the fresh-cut Chinese water chestnut. Compared with acetic acid,citric acid, oxalic acid, vitamin C, thyme oil and sodium chloride etc., potassium sorbate andgreen tea polyphenol had the best effects on the browning prevention of water chestnuts.However, compared with0.2%potassium sorbate, green tea polyphenols and1.5%chitosancoating, combined use of chitosan and potassium sorbate/green tea polyphenols had the besteffects on the moisture content, decay and browning.(6) The effects of chitosan, shellac and sodium alginate edible coating on the texture,quality attributes and internal changes of Chinese water chestnut (Eleocharis tuberosa) wereinvestigated. For the whole fruit, results showed that the weight loss, respiration rate,peroxidase (POD) activity, cell membrane permeability and decay rate decreased, however,hardness and quality parameters increased with the application of coating during cold storage.For the fresh-cut fruit, results showed that chitosan coating had better effects than sodiumalginate on preventing the browning, but had little effects on the decay and weight loss. |
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