| Edible films can reduce moisture loss and nutrient consumption, preventmicrobial contamination, and prolong the shelf life of food products. Edible filmsprovide bright application prospects in improving the market competitiveness of foodproducts and have attracted broad attentions nowadays. Among many naturalbiopolymers for forming edible films, starch is one of the most promising rawmaterials due to its abundance, low cost, simple treatment, biodegradability and goodvapor barrier ability.Kudzu as a natural medicine and healthy food is widely distributed in China.Kudzu is mainly used to extract medicinal ingredients now, whereas a great amount ofstarch rich in its root is just discharged, which not only spoils the environment butalso wastes resources. If the starch can be recovered and effectively utilized, it willget more comprehensive values. Therefore, in order to expaned the application filedsof kudzu starch and promote the healthy development of kudzu industry, thephysiochemical properties of kudzu starch based edible films were studied in thispaper. The main research methods and contents are as follows:（1） The influences of film–forming processes （pasting temperature from80°Cto100°C, gelatinization time from5min to60min, starch concentration from1%to6%） on mechanical property and water vapor permeability of kudzu starch edible filmwere studied; The effects of glycerol content （from0%to40%） and relative humidity（50%,75%, and100%） on the comprehensive properties （including FT–IR, XRD,TG–DTA, water sorption isotherms and so on） of the films were also evaluated. Theresults showed that:①The film showed the best performance when we chose thepasting temperature of100°C, gelatinization time of15min, starch concentration of3%, and glycerol content of30%.②FT–IR displayed that the shift of peakcorresponding to C–O in C–O–C group was affected by dual factors of glycerol content and relative humidity.③The intensity of B–type crystal diffraction enhancedgradually as glycerol content increased, and glycerol could form V–type crystal withkudzu starch; the intensity of diffraction peak relating to V–type crystal weakenedwith the increase of relative humidity.④TG curve of kudzu starch film presented3degradation steps representing water evaporation, degradation of the glycerol–richphase, and starch degradation, respectively. The activation energy value relating to themain starch degradation step was found to be negative linear with glycerol content.（2） The effects of surfactant （tween20and span80） on the surface tension andwettability of kudzu starch/ascorbic acid film–forming solution, the release behaviorof ascorbic acid from film to water, as well as the crystal structure, microstructure,mechanical property, water vapor permeability and solubility of the film wereevaluated. It was found that:①Each surfactant effectively decreased the surfacetension of the film–forming solution （P<0.05）.②Only adding tween20improved thewettability of film–forming solution on both glass and paraffin wax substrates,smoothened the film’s surface, and enhanced the film’s solubility; Adding span80alone reduced the contact angle of film–forming solution on paraffin wax substratebut enhanced the surface roughness of the film; the use of blended–surfactantincreased the film’s water vapor permeability;③The diffusion coefficient ofwater–soluble ascorbic acid from kudzu starch/ascorbic acid film to water was about2.22×10–11m2s–1, and each surfactant could delay the release of ascorbic acid.④The addition of surfactant decreased the B–type crystal structure of the film, andadding tween20promoted the formation of V–type crystal.（3） Effects of acid types （acetic acid, lactic acid and malic acid at concentrationof1%） and storage conditions （25°C and–20°C, respectively） on the properties ofkudzu starch/chitosan composite film were investigated, including the fluidity offilm–forming solution, antibacterial activity, functional group interaction, crystalstructure, water sorption ability, mechanical property, water vapor barrier ability,solubility and color index of the resulting film. The data displayed that:①Thefilm–forming solution belonged to shear–thinning fluid. When chose acetic acid,lactic acid, and malic acid as solvent, the pseudoplasticity of film–forming solutiondeclined, newtonianism increased, and consistency decreased following the aboveorder.②The antibacterial effect of the composite film was stronger against E. colithan against S. aureus.③The film–forming component was compatible with eachother as evidenced by FT–IR and XRD spectra.④The composite film choosing acetic acid as solvent presented the strongest mechanical property, the smallestsolubility, and the lightest yellowness. The film mading from lactic acid solutiondisplayed the greatest flexible property. The film using malic acid as solvent showedthe best antibacterial activity and water barrier property, and the lowest water sorptionability.⑤Storage time significantly affected film’s water content, mechanicalproperty, water barrier ability, color and solubility （P <0.05）; subzero temperaturedelayed the color changes of the film during storage. However, storage temperaturedid not influence the crystallization, water content, mechanical property and solubilityof the film （P>0.05）.（4） The overall performance of kudzu starch/chitosan/ascorbic acid compositefilm with addition of0.1%tween20was evaluated, including surface tension, contactangle and fluidity of the film–forming solution, the antibacterial activity, releasebehavior of ascorbic acid, mechanical propertiy, water vapor permeability, solubility,and color index of the film.①Surface tension of kudzu starch/chitosan/ascorbic acidfilm–forming solution was significantly lower than the value of kudzu starch/ascorbicacid film–forming solution under the same experiment condition （P<0.05）; the contactangle of the film–forming solution on the glass substrate was less than30°, and thecontact angle was less than90°on solid paraffin substrate; acid solvent type did notsignificantly affect the surface tension and wettability of film–forming solution（P>0.05）.②The release of ascorbic acid from film choosing acetic acid as solventwas mainly controlled by film swelling process, and the release behavior of ascorbicacid from film made from lactic acid or malic acid was affected by thefilm–dissolution as well.③As compared with kudzu starch/chitosan composite film,the antibacterial ability was better, and the color was darker of kudzu starch/chitosan/ascorbic acid film.The results showed that kuzu starch can form relatively desired compositepackaging film by effectively blending with a variety of additives, and this manuscriptprovided some theoretical supports for expanding the application area of kuzu starch. |
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