Study On The Multi-stage Gelatinization Behaviors Of Dual Modified Starch With Acid Hydrolysis And Heat-moisture Treatment

The gelatinization behaviors play a key role on the application characteristics and functional properties of starch.Native starch usually require single or dual modifications to improve the machinability and nutritional value,meanwhile,the different modification methods,degree,and sequences affect the molecular and crystal structure of native starch and ultimately alter the physiochemical,crystalline,and rheological properties.The research on these properties of dual modified starch especially the gelatinization behavior could help to understand deeply the effect of dual modifications,provide new insight to clarify the gelatinization mechanism,and thus has certain theoretic value and practical significance.Dual modification of corn starch was carried out by combining acid hydrolysis(AH,6?24 h)and heat-moisture treatment(HMT,15?60 min)in different sequences(AH-HMT and HMT-AH).X-ray diffractometry,differential scanning calorimetry,polarized light microscopy,and Rheometer were used to characterize the differences in molecular structure and physicochemical properties resulting from the sequences.The results showed that AH-HMT sequence had higher thermal stability than HMT-AH sequences with higher onset(To),peak(Tp)and conclusion(Tc)gelatinization temperatures.The AH-HMT sequence also resulted into lower relative crystallinity,swelling power,solubility,gelatinization enthalpy,and pasting viscosity than in those samples produced using HMT-AH sequence.The multiple thermal transitions of acid-hydrolyzed(AH)and heat-moisture treated(HMT)corn starch samples in excess water were measured using differential scanning calorimeter(DSC)and interpreted using a polymer swelling and dissolution theory.The dual treatment of acid hydrolysis and heat-moisture treatment with different extent of reaction generated searches with various degrees of residual crystalline structure.Multiple endothermic transitions(G and M1)were firstly observed in DSC traces even in excess water.The destruction and rearrangement effect of HMT on the the architecture of acid treated starch depended on the hydrolysi degree.In this study,the G and M1 endotherms were proposed to be related with the energy consumption associated with granule swelling and crystallites dissolution respectively.The gelatinization of corn starch was studied using differential scanning calorimetric(DSC)and rheological tests by the same heating rate,temperature range,and starch to water ratio.The viscosity versus temperature was represented using semi-logarithmic coordinates to better demonstrate the viscosity peaks.A three-stage of gelatinization of AH-HMT starches was identified through the comparative analysis of rheological and thermal properties.The first stage of gelatinization correlated with the G endotherm well and was an irreversible process;the second stage of gelatinization and concomitant disruption of the crystalline structure corresponded to the M1 endotherm;while the third-stage of gelatinization was found to be a process of water absorption without energy consumption(no endotherm).The time and temperature dependence were studied by employing heat-moisture treated corn starch and developed a novel gradient gelatinization method with short(5 min)and long(20 and 30 min)isothermal holding within 64-95 ? to determine the relevant temperature thresholds.The increase in viscosity values(??-values)during 5 min isothermal holding demonstrated the temperature-dependent behavior of corn starch gelatinization.The time-dependent nature of which was also evidenced with long-term heat-holding method.70? and 76 ? were proposed as the two critical temperature thresholds,which were associated with amorphous swelling and disintegration of crystalline domains,respectively.Furthermore,the individual influence of time and temperature at different gelatinization stages were discussed based on a multi-stage gelatinization theory.The effect of heat-moisture pretreatment on the preparation of starch nanocrystal(SNC)was analyzed.The SNCs were prepared by hydrolyzing HMT corn starches with H2SO4 at predetermined high temperatures based on the multi-stage gelatinization theory.The hydrolysis process was maintaining at high temperature for maximizing hydrolysis rate;this high temperature pre-gelatinization also imposed the heat sensitivity of final SNC product.The particle size distribution(PSD),XRD,and SEM were also investigated.The results showed that the SNC could be well prepared at 69 ? within 30 min;the yield was 11.6%.SNC products generated agglomeration during drying process and the crystallinity of which was 43%.This new thermostable SNC prepared at 69 ? possessed excellent thermostable properties and had a great potential use in the food and package industry.