Study On Physicochemical And Film-forming Properties Of Shange Yam Starch And Its Application In Fresh-cut Carambola Fruit

Starch is a main component of Shange yam(Dioscorea opposita Thunb).The physicochemical properties of Shange yam starch,the optimized process of film-forming from Shange yam starch,the antimicrobial properties of edible coating of Shange yam starch and application in keeping quality of fresh-cut carambola fruit were investigated in this paper.The objectives of this study were to providing a theoretical basis for the development and utilization of yam starch,as well as to providing a practical guidance for industrial production of edible film of yam starch,and also to providing a scientific basis for applying the edible coating of yam starch in keeping quality of fresh-cut carambola fruit.The major results were showed as follows:1.The Shange yam starch was mainly composed of amylose and amylopectin.The granule structure of Shange yam starch belonged to C-type,with uniform particle size and smooth granule surface,most of Shange yam starch granules were oval shape,while few starch granules were round or irregular shape.Shange yam starch had high starting gelatinization temperature,bad thermal stability and high retrogradation tendency.Shange yam starch exhibited pseudoplastic fluid with shear thinning,large thixotropy,shear structural recovery and weak gel.The solubility and swelling of Shange yam starch increased with the increasing of gelatinization temperature,which exhibited low clarity and freeze-thaw stability,strong retrogradation stability.2.The effects the concentrations of Shange yam starch,glycerol dosage,drying temperature and the addition of carboxy methyl cellulose sodium(CMC)on film-forming characteristics,and the optimized filming technology using response surface methodology were investigated.The results showed that when the concentration of yam starch was 4%,the edible film of Shange yam starch exhibited the optimal comprehensive index with maximum tensile strength and minimize water vapor permeability.The tensile strength and elongation at break of the edible film of Shange yam starch increased with the increase of glycerol dosage.There were highest values of tensile strength and elongation at break and transparence,while lowest value of solubility in edible film of Shange yam starch when glycerol dosage was 1.5%.There were not ideal properties of edible film from Shange yam starch when drying temperature was too low or high.When the drying temperature was at 80?,the edible film of Shange yam starch exhibited the optimal comprehensive index.In addition,the edible film of Shange yam starch had low flexibility and easy to break when the addition of CMC is low.While the decreases of mechanical properties,the decreases of solubility and light transmission,and the increase of water vapor permeability in the edible film of Shange yam starch were observed when the addition of CMC exceeded was 0.4%,thus the appropriate CMC concentration for edible film of Shange yam starch was 0.4%.Shange yam starch concentration 3.95%,1.54%glycerol,drying temperature 80.80? and 0.39%CMC were the optimized film-forming parameters of Shange yam starch by orthogonal experiment3.The evaluation of antimicrobial properties of edible film of Shange yam starch at different pH with different kinds and different concentrations of antibacterial agents,the application of the edible film from Shange yam starch for keeping quality of fresh-cut carambola fruit were investigated.The results showed that edible film of Shange yam at pH 6 with 0.015%Nisin and 0.05%Natamycin exhibited obvious antimicrobial properties of bacteria like staphylococcus aureus and bacillus subtilis,and fungi such as aspergillus niger and penicillium.In addition,as compared to the control fresh-cut carambola fruit storage at(5±1)?,the treatment of edible film of Shange yam starch could reduce respiration rate,retard the increase of cell membrane relative permeability,keep higher firmness,higher contents of total sugars,total soluble solid and titratable acid,retard color change from green to yellow,decrease weight loss and decay,maintain the original flavor and quality of fresh-cut carambola fruit,and extend the storage life of fresh-cut carambola fruit.