Study On The Efficient Preparation Of Starch Nanocrystals And The Construction And Application Of Starch-based Nanocomposite Coating

Due to the advantages of wide sources,low price,and good biocompatibility,starch has a very wide range of applications in agriculture,paper industry,and other fields.In recent years,with the continuous development of nanoscience and nanotechnology,the research on starch has deepened to the nanoscale.Among them,starch nanocrystals with high crystallinity and high mechanical strength have gradually attracted the attention of scholars.Considering the low efficiency of the traditional preparation method of starch nanocrystals and the high damage rate of vulnerable fruits and vegetables under the treatment of postharvest mechanical equipment,this work mainly focuses on the improvement of the preparation method of starch nanocrystals,the construction of starch-based self-reinforced nanocomposite coatings,and the effect of the coating on the loss reduction and quality preservation of the Huangguan pear during the roller conveying process.In this study,we take the Huangguan pear as a representative of vulnerable fruits and vegetables,and roller conveying as a representative postharvest processing machinery in order to achieve the mechanical treatment of the vulnerable fruits and vegetables.Among them,the starch-based self-reinforced nanocomposite coating is prepared by starch as a film-forming substrate and starch nanocrystals as a reinforcing agent and barrier agent.Since starch nanocrystals and starch are very similar in chemical structure,there is a good interfacial interaction between the two,so when rigid starch nanocrystals are added to the flexible starch matrix,a better reinforcement effect can be achieved,which is the so-called self-roinforced effect.The main research contents and conclusions of this work are as follows:(1)The method of ball milling pretreatment combined with acid hydrolysis can greatly improve the preparation efficiency of starch nanocrystals.Compared with the traditional acid hydrolysis method,the ball milling pretreatment combined with acid hydrolysis method can shorten the preparation time of starch nanocrystals from 5 days to 3 days,and the preparation yield increased from 15.8% to 19.3%.(2)The method of heat-moisture pretreatment combined with acid hydrolysis can further improve the preparation efficiency of starch nanocrystals.Through single factor analysis and response surface experiment analysis,the best heat-moisture treatment conditions were determined.Compared with the traditional acid hydrolysis method,heat-moisture pretreatment combined with acid hydrolysis method can shorten the preparation time of starch nanocrystals from 5 days to 4 days,and the preparation yield increased from 15.8% to 26.7%.(3)In order to prepare a starch-based film with better physical and chemical properties,the best film-forming substrate was selected from 9 different types of starch.By characterizing the the physiochemical properties of the corresponding starch films including mechanical properties,water vapor permeability,color and other indicators,it was determined that the cross-linked cassava starch film had the best comprehensive performance as a film-forming substrate.(4)The self-reinforcing effect can be used to prepare starch-based nanocomposite films reinforced by starch nanocrystals.According to the characterization of mechanical properties,water vapor permeability and other indicators,the obtained nanocomposite films had significantly improved physical and chemical properties,and 6% content of starch nanocrystals was the most appropriate amount.Applying it as a coating material on the surface of the Huangguan pear in the roller conveying process can significantly improve the loss reduction and quality preservation effect of the pears.(5)Sodium hexametaphosphate was used to cross-link the starch nanocrystals,and the self-reinforcing effect can be used to prepare starch-based nanocomposite films reinforced by cross-linked starch nanocrystals.The obtained nanocomposite film was compared with the starch nanocrystals in the previous content.The starch-based nanocomposite film had further improved physical and chemical properties,and the content of 10% cross-linked starch nanocrystals was the most appropriate addition amount.The research on the coating of pears proved that when the coating was applied on the surface of the conveyed Huangguan pear,it can further improve the loss reduction and quality preservation effect.This research can provide theoretical basis and method support for the automatic conveyor of vulnerable fruits and vegetables.