| Starch is the most important carbohydrate energy source for human beings,and one of the most important food components that provide energy for human body.Widely distributed in nature,starch is a common part of higher plants,the main storage form of plant carbohydrates,and the main source of human physiological activities.However,due to the poor water-solubility,easy aging,poor shear resistance and heat resistance of starch,it is not suitable for direct application in food processing,so it needs to be modified by adding non-starch polysaccharide or hydrocolloid to improve its properties.In this paper,yam powder was obtained by a series of means such as washing,peeling,peeling and drying,and then yam starch was extracted by itself.Due to the difference in natural characteristics of natural starch,gallic acid was added to modify yam starch.Then the original yam starch and modified yam starch were mixed with chitosan to comprehensively study the effect of chitosan on starch gelatinization,rheology and other physicochemical properties.At the same time,we prepared modified yam starch and chitosan composite film on this basis,and then used the film for fresh pork preservation.The main research contents and results are as follows:(1)The effects of chitosan on gelatinization,swelling and rheology of yam starch were studied.Chitosan with different concentrations(0.1%,0.2%,0.6% and1.0%,W/V)was mixed with yam starch(6%,W/V),and it was found that the low concentration of chitosan promoted the dissolution of amylose.With the increase of the concentration of chitosan,the solubility of amylose wrapped by chitosan decreased.The gelatinization parameters(PV,TV,FV and SB)of modified yam starch were significantly changed.These changes may be due to the interaction between appropriate starch and gallic acid,which promotes the formation of ordered starch structure and increases the resistance to hydrothermal treatment.The rheological results show that the sample has typical gel properties and the mixture has shear thinning behavior of non-Newtonian fluid.The XRD curves of yam starch modified by gallic acid are similar to those of natural starch,indicating that the modification has no effect on the crystal structure of the samples.The infrared results showed that the ordered molecular structure increased at the near-range level after gallic acid treatment,and the ordered molecular structure was not destroyed in this process.The outer region structure of the modified mixture became more ordered,and the gallic acid modification could promote the formation of double helix structure.(2)This chapter explored yam starch and the preparation of starch film after the compound of modified yam starch and chitosan,and then measured the thickness,color,permeability,tensile strength and other aspects of the composite film.May safely draw a conclusion that,added under the condition of the same concentration of chitosan,modified yam starch film thickness is thinner than the original thickness of yam starch film,due to natural cationic polysaccharide,chitosan is the only nature gallic acid modified yam starch after adding chitosan modified starch complex rarefy,so makes the complex preparation film thinning.The results of color difference experiment showed that the three color difference parameters increased first and then decreased with the increase of chitosan due to the dark color of chitosan itself and the Maillard reaction of yam starch and other substances during heating.The transmittance of the composite membrane has a similar change with the addition of different concentrations of chitosan.The transmittance of the composite membrane has a similar change with the addition of different concentrations of chitosan.The transmittance increases first and then decreases.The transmittance is the lowest when the concentration of chitosan is 0.1%,and reaches the maximum when the concentration of chitosan is 0.6%.After the yam starch was modified by gallic acid,the tensile strength of the composite film also increased with the increase of the concentration of chitosan.Similarly,the composite film also became more brittle.The surface of starch film was smooth,which indicated good compatibility between yam starch and chitosan.(3)Starch film was prepared by yam starch,modified yam starch and chitosan and applied to fresh pork.After the fresh pork is kept fresh by the plastic film prepared with modified starch,the effect of keeping fresh plays a very good role to some extent in terms of smell,elasticity,viscosity and water condition.With the increase of the concentration of chitosan,the L value increased,and reached the maximum value under the same condition as the unmodified yam starch at 0.6%,but the brightness of the film prepared by the modified yam starch was higher.When the concentration of chitosan in 0.6%,p H value is less than 6.5,belongs to fresh meat.The results showed that the preservative effect of yam film was the best when the concentration of chitosan was 0.6%.The fresh-keeping effect of modified starch was better than that before modification,and the fresh-keeping effect was better when the concentration of chitosan was 1.0%.The membrane prepared by the modified starch and chitosan complex had better blocking effect on oxygen than that before modification,which made the myoglobin in fresh pork have poor ability to bind oxygen.Therefore,the film prepared by modified starch has a lower ferritin value. |
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