Preparation And Modification Of Waxy Potato Starch Nanocrystals

In this paper,starch nanocrystals were prepared from waxy potato starch with/without glucoamylase enzymatic pretreatment by sulfate acid hydrolysis,and the esterification of octenyl succinic anhydride and the crosslinking of sodium trimetaphosphate were carried out.A comparative experiment about the production of starch nanocrystals?SNCs?with/without glucoamylase enzymatic pretreatment by sulfate acid hydrolysis from waxy potato starch?WPS?was employed in the present study.The research focused on the enhancement of the preparation efficiency while improving the dispersion of SNCs at the same time.The results showed that the enzymatic hydrolysis was efficient under the enzymatic hydrolysis pretreatment condition of glucoamylase addition amount of 1000 U/g?starch?,enzymolysis time 6 h.Some cracks and pores were obtained on starch granules surface for enzymatic pretreated WPS.The factor of enzymatic hydrolysis time was proposed by LOS method to conform to the first-order dynamic model.The enzymatic pretreatment resulted in the decrease of acid hydrolysis duration.When the WPS was carried out with enzyme hydrolysis pretreatment,particles with the minimum size were obtained after 5 days?P-SNC5?nevertheless this occurred just after 6 days without pretreatment.SNCs obtained after 5 days with enzymatic pretreatment possessed the relative crystallinity of 46.1%,higher than the counterpart of native starch?33%?,with the changed X-ray patterns?B to C?.FTIR infrared spectrum detection revealed that the absorbance centered on 1104 cm^-1 for SNCs was increased slightly in intensity than the counterpart of other samples,probably ascribed to the formation of sulfate ester on the surface of SNCs.Zeta potential?particle size distribution and dispersion stability observation graph showed P-SNC5 had a smaller particle size distribution and better dispersion stability with the suspension pH of 7.0.SEM and TEM observed that the grape-like aggregates of SNCs were found with the particle size of 50¹00 nm.The esterified starch nanocrystals were prepared with octenyl succinic anhydride in alkaline conditions.The study found that the degree of substitution?DS?of starch nanocrystals gradually increased from 0.047 to 0.1292,with the increase of OSA addition?up from 12.5%to 75%?.According to X-ray diffraction analysis,the relative crystallinity of starch nanocrystals increased with the increase of DS,and the crystalline type was still C-type starch.The FTIR detection showed two new characteristic peaks of C=O and-COO^-groups at 1732 cm^-1 and 1572 cm^-1,and the strength were greater as the increase of DS,which demonstrated the successful introduction of octenyl succinate group on nanocrystalline surface.The dispersion experiments of starch nanocrystals showed that the modification of esterification caused the decrease of polarity,and it had a certain amphipathicity,which was stable and dispersed in water and some organic solvents such as trichloromethane and acetone.SNCs were more readily dispersed in organic solvents with the increase of substitution.The X-ray photoelectron spectroscopy analysis further proved that more octenyl succinates are connected to the nanocrystal surface with the improvement of esterification.In order to study the effect of the addition of sodium trimetaphosphate on the crosslinked starch nanocrystalline,the cross-linked starch nanocrystals were prepared by different addition of sodium trimetaphosphate with the suspension pH of 11.5 with SNCs obtained with enzymatic pretreatment.The degree of substitution of cross-linked nanocrystals was calculated by the determination of phosphorus content in samples.It was found that as the addition of sodium trimetaphosphate increased?from 3%to 12%?,the DS of products increased(from 1.68×10^-5 to 2.23×10^-5).According to the X-diffraction pattern of the samples,the polymorph was transformed from C-type of the original starch nanocrystalline to B-type crystallization after the crosslinking modification.The enhancement of absorption peak at 1017cm^-1 confirmed the introduction of P-O-C groups in nanocrystalline particles by infrared spectrum analysis.The strength of peak increased with the enhancement of degree of cross-linking.Meanwhile,the swelling degree of crosslinked starch nanocrystals decreased with the increase of substitution.The results showed that the greater the crosslinking substitution was,the more network structure modified samples had.