Research On The Properties Of An Edible Film Prepared By Gum Ghatti

Gum ghatti(GG)was the research object of this paper and the film-forming ability of it was explored by supplementing antibacterial agents.The purpose of this paper was to develop a new type of edible antimicrobial film,which not only had a good barrier,but also had certain antibacterial properties,could be used for aquatic product preservation.The contents and conclusions were as follows:(1)The effect of GG concentration,plasticizer type and content on the film physical properties(thickness,moisture content,water solubility,surface hydrophobicity,water permeability,oxygen permeability,color)and mechanical properties(tensile stress,elastic modulus and elongation at break)was researched,and T_g values were determined by differential scanning calorimetry(DSC),microscopic characterization was analyzed by X-ray diffraction analysis(XRD)and scanning electron microscopy(SEM).The results showed that physical property of gum ghatti films were influenced by GG content,plasticizer type and concentration.WVP of gum ghatti films were no more than 0.5 g mm/m² h k Pa.GG-Gly films were more permeable than GG-Sor films for each plasticizer concentration investigated.Tensile stress of gum ghatti films decreased significantly with the increase of plasticizer content and ranged from 10 MPa to 25 MPa.The T_g values decreased with the increase of plasticizer content,and when the GG content and plasticizer concentration were identical,T_gvalue of GG-Sor film was lower than that of GG-Gly film.Through SEM observation,it could be concluded that plasticizer and GG had better compatibility,and GG-Gly film was more regular,smooth and dense than GG-Sor film.XRD diffraction showed that gum ghatti film had amorphous crystalline structure,its crystallinity increased with the concentration of plasticizer decreased.(2)In order to increase the antibacterial ability of gum ghatti film,lactic acid streptococcus(Nisin)was selected as a natural antibacterial agent in this test.Its minimum inhibitory concentration and antibacterial ability was determined.The effect of Nisin on the antibacterial properties,physical properties,mechanical properties and microstructure of gum ghatti film were determined and analyzed.As a result,Nisin had a better ability in inhibiting Staphylococcus aureus and Bacillus subtilis than that of Proteus vulgaris,Escherichia coli and Pseudomonas aeruginosa bacteria.The antibacterial effect of gum ghatti film on Staphylococcus aureus,Bacillus subtilis,Bacillus subtilis and Pseudomonas aeruginosa increased with the increase of Nisin,but not obvious effect was observed on Escherichia coli.The thickness,surface hydrophobicity and WVP values of films were decreased with increasing Nisin concentration.Nisin concentration had significantly effect on tensile stress,elastic modulus.However,Nisin concentration had little effect on the elongation at break(P>0.05).Gum ghatti film had a smooth surface and uniform texture,which indicating that Nisin and GG molecules have good compatibility.(3)The adsorption isotherms of gum ghatti film at temperature of 5,15 and 25?were studied by static weighing method.Thermodynamic properties,such as net adsorption heat,differential entropy and expansion pressure(?),were obtained by calculation.The state diagram of gum ghatti film at 25?was established.The results were as follows:the moisture adsorption of gum ghatti films showed a III type isotherm,Halsey model was the most suitable model to describe the moisture adsorption characteristics.Throughout the adsorption process,the q_st and S_d of GG film(gum ghatti film without plasticizer or bacteriostatic agent,the same below)were always lower than that of GG-Gly film(gum ghatti film with glycerol as plasticizer,the same below)and GG-Gly-Nisin film(gum ghatti film with glycerol as plasticizer and Nisin as bacteriostatic agent,the same below).The?value of GG films was lower than GG-Gly film and GG-Gly-Nisin film.The adsorption of water in each group was in accordance with the theory of entropy and enthalpy and the adsorption process was enthalpy driven and non spontaneous process.T_g values of GG films increased with water content decreased,and at the same moisture content,T_g value of GG film was greater than GG-Gly film,GG-Gly-Nisin film had the highest T_g.According to the state diagram,the critical wet basis moisture content and critical water activity of GG-Gly film was lowest at10?,which indicated that glycerol decreased the storage stability of gun ghatti film.(4)By using the method of coating preservation,GG was applied to the storage of penaeus vannamei,and compared with gum ghatti film containing Nisin.The storage temperature was 4?and the p H value,TVB-N,colony count(TAC)and color changes of shrimp were explored.The purpose of this part was to investigate the preservation capacity of gum ghatti film on coating Penaeus vannamei.The results showed that GG film could effectively reduce the spoilage rate of Penaeus vannamei,prolong the freshness.The addition of Nisin on gum ghatti film solution showed the best effect,which not only protected the color,but also suppressed the declining rate of other freshness indexes effectively.