Starch-aroma Inclusion Complexes: Formation Mechanism And Application

Starch,especially the linear amylose,is capable of complexing with various aroma compounds to form inclusion complexes（ICs）.During the complexation process,the non-covalent interaction of aroma compounds and starch induces amylose to form a single left-handed helix named V-amylose.The size of the hydrophobic helical cavity matches well with the molecular size of aroma compounds.Therefore,the construction of amylose ICs can be an ideal strategy to encapsulate aroma compounds and solve the low stability and high volatility during processing and storage.In this thesis,the complexation mechanism of single/binary aroma compounds and starch was systematically investigated.The relationship between the chemical structure of aroma compounds,complexation mechanism,and ICs properties was established.In addition,more innovative carriers of starch-aroma ICs were constructed,for example the pre-formed V-amylose carriers.The starch-aroma ICs with different types and preparation processes were optimized.Furthermore,the advantages and disadvantages of the preferred carriers and commercialβ-cyclodextrin in slow-release thymol,antibacterial properties,preservation of fruits and vegetables were compared.These contents help to create starch-aroma ICs with good application prospects.The main research contents and results of this thesis are as follows:（1）The complexation mechanism of high amylose maize starch with nine C10 aroma compounds with different chemical structures was studied.The results showed that increasing the cross-section of aroma compounds increased the number of glucose units per turn in the amylose helix from 6 to 8,and formed four crystalline structures:V_6I,V_6I-V₇,V₇,and V₈.Compared with lactonic and aromatic aroma compounds,the ICs complexing with linear alkyl and cycloalkyl aroma compounds have more ordered crystal structures,larger proportions of single helices,and higher dissociation temperatures.In addition,aroma compounds with longer alkyl chains,stronger hydrophobic functional groups,and smaller cross-sections interacted more strongly with the helical cavity of amylose,contributing to the formation of compact V-amylose ICs.（2）Due to the different binding affinity of linear and cyclic aroma compounds to starch,decanal and thymol were used as templates of linear and cyclic aroma compounds,respectively,to study the complexation mechanism of starch and aroma compounds in binary aroma systems.The results showed that the encapsulation efficiency and loading capacity of thymol were higher than that of decanal,and the binding ability of thymol to starch was stronger than that of decanal.However,the loading efficiency of decanal in the binary aroma systems（2.7%）was higher than that of a single decanal system（1.6%）.The synergistic effect between the two aroma compounds reached the maximum in the same mass of decanal and thymol system,in which the starch-binary aroma ICs had higher loading efficiency（11.8%）and ordered structure.Complexation with more aroma compounds also facilitated the stabilization the helical structure of V-amylose.（3）A preparation method（water-ethanol method）of pre-formed V-amylose carrier with helical cavity was constructed and optimized.The results show that the starch-ethanol complexation temperature significantly affected the ordered structure of the V-amylose carrier.Increasing the complexation temperature from 30°C to 90°C improved the crystallinity from25.2%to 40.2%,and the enthalpy changed from 6.11 J/g to 14.57 J/g,leading to perfect V-amylose crystallites and increase in relative crystallinity from 25.2%to 40.2%.The V-amylose carrier prepared at 90°C has the highest thymol loading capacity（34.0 mg/g）due to the best ordered structure.In addition,this preparation method is simple and efficient,and no additional annealing treatment is required.（4）The complexation process of the above two different starch-aroma ICs（traditional high temperature-water method and pre-formed V-amylose）was optimized by the reaction solvent and starch-aroma complexation temperature.The results show that the loading capacity of thymol was in the order of pre-formed method in solid phase>traditional high temperature-water method>pre-formed method in ethanol phase.Increasing the complexation temperature increased the accessibility of thymol to starch chains and promoted the formation of starch-thymol ICs.The ICs formed by pre-formed V-amylose bonding with thymol by solid-phase method mainly presented V_6I structure,with high crystallinity and good short-range ordered structure.But the traditional high temperature-water method forms V₇ crystals.In addition,the ICs prepared by the solid-phase pre-formed and traditional high temperature-water methods released about 45%and 75%of thymol,respectively,after storage at 25°C for two weeks.Therefore,the pre-formed V-amylose carrier combined with solid-phase encapsulation is an ideal method to improve the thymol loading capacity and achieve sustained release.（5）The loading capacity of pre-formed V-amylose carriers prepared by the water-ethanol,alkali-ethanol,and salt-ethanol methods and commercialβ-cyclodextrin for thymol was compared.The release behavior,antibacterial ability,and application in the preservation of strawberries of these thymol carriers were investigated.The results showed that compared with other carriers,the pre-formed V-amylose carrier constructed by the water-ethanol method had the best crystalline structure,thymol loading capacity,sustained release and antibacterial ability,and extended the shelf life of strawberries from 2 days to 6 days under daily storage conditions.In contrast,commercialβ-cyclodextrins were sensitive to high humidity environments,and the encapsulated thymol was rapidly released upon storage.Overall,the pre-formed V-amylose by the water-ethanol method is a promising aroma carrier and has the potential to replace commercialβ-cyclodextrin.