The Establishment And Application Of The Method For Characterization Of Starch Hydrophobicity

Starch helical cavity is composed of methylene and glucoside oxygen groups,resulting the hydrophobicity of helical cavity.The hydrophobicity is the important parameter for analyzing the helical structure of starch and the capability to form inclusion complexes.It provides direct evaluation method for the encapsulation and emulsibility of starch.At present,the domestic and foreign researches on starch hydrophobicity mainly focus on qualitative analysis,but the researches about method of quantitative analysis are absent.In this paper,we introduced salicylic acid into the starch helix,and established the method to characterize the starch hydrophobicity based on the change of fluorescence intensity,and discussed the verification and application of the method.Screening the optimum fluorescent guests.A sealed-heating procedure was carried out to prepare inclusion complexes of high-amylose maize starch with 1-naphthol,2-naphthol and salicylic acid.X-ray diffraction(XRD)and thermogravimetric analysis(TGA)were carried out to elucidate the structures of inclusion complexes.XRD analysis showed that the three fluorescence guests could form V-type inclusion complexes with high-amylose maize starch.The relative crystallinity of inclusion complexes was 34.20%,29.49% and 28.05% respectively,and both higher than high-amylose maize starch.The relative crystallinity of inclusion complexes of high-amylose maize starch with salicylic acid was among the highest.TGA showed that the thermal degradation temperature of 1-naphthol,2-naphthol and salicylic acid was increased by 110 oC,85oC and 65 oC respectively after encapsulation of starch,which indicated the formation of inclusion complexes of three kinds of fluorescent guests with high-amylose maize starch.The encapsulation rates of inclusion complexes of high-amylose maize starch with the three fluorescent guests were: salicylic acid > 1-naphthol > 2-naphthol.It was found that the encapsulation efficiency of starch with salicylic acid was the highest.In order to further investigate the structure of inclusion complex of starch with salicylic acid,fourier transform infrared spectroscopy(FT-IR)was studied.The research found that the C=O stretching vibration peak shifted from 1658 cm-1 to a higher wavenumber 1673 cm-1 and the peak intensity of benzene ring C=C stretching vibration at 1614 cm-1significantly decreased,which indicated that the salicylic acid moleculars were embedded into the helical cavity.Thus,salicylic acid was the optimum fluorescent guest to characterize the starch hydrophobicity.The study of fluorescence properties of salicylic acid as fluorescence guest and conditions optimization.The results showed that salicylic acid was sensitive to the polarity of environment.With the decline of solvent polarity,the fluorescence intensity of the salicylic acid increased obviously.Therefore,the hydrophobicity of media environment was characterized by the change of fluorescence intensity of salicylic acid.The optimization of complexes preparation conditions and solvent system was investigated.Specific conditions: the solvent was ultrapure water,the concentration of salicylic acid was 2×10-7 mol/L,starch: salicylic acid =2:1(w/w),heating temperature was 120 oC and heating time was 90 min.Establishment of starch hydrophobicity characterization method of basing on the enhancement of fluorescence intensity.The fluorescence spectra of physical mixture and inclusion complex of high-amylose maize starch and salicylic acid were determined.Results showed that the fluorescence spectra of salicylic acid unchanged by physical mixing with high-amylose maize starch,but the fluorescence intensity significantly increased from 2419 a.u.to 4312 a.u.at 406 nm by embedding with starch.Then,the fluorescence spectra of inclusion complexes of salicylic acid with amylose of different chain length showed that the enhancement of the fluorescence intensity of salicylic acid was positively correlated with the starch hydrophobicity.Therefore,in this paper,a method to characterize the starch hydrophobicity by the enhancement of fluorescence intensity of salicylic acid was established.The accuracy and universality of the method for starch hydrophobicity characterization was verified.The relative standard deviation(RSD)of the data determined by the method was less than 5%,which proved that the favorable precision and repeatability of the method.The correlation between the hydrophobicity and the structure of starch was analyzed to verify the universality of the method.Results showed that the starch hydrophobicity was positively correlated with amylose content and chain length within certain range,but not with the fine structure of amylopectin.The results determined were consistent with the theoretical analysis,and the method could be used to characterize the hydrophobicity of starch from different sources.The application of the method of characterization of starch hydrophobicity.With the increase of amylose chain length,the starch hydrophobicity increased,and the color of starch-iodine complex was gradually deepened until dark blue.In the process of starch retrogradation,the hydrophobicity of starch was decreased,and the capability of complexation with iodine was decreased synchronously.Therefore,the difference of color reaction of starch with iodine was explained by the variability of starch hydrophobicity,and it provided a new inspection to explain the color reaction of starch with iodine.The capability of starch to form inclusion with hydrophobic guests can be evaluated by the characterization of starch hydrophobicity.The experiment results showed that the hydrophobicity of waxy,normal and high-amylose maize starch was consistent with the capability to form inclusion complexes with stearic acid.