Study On Dry-Heating Treatment Of Sweet Potato Starch And Pectin

Dry-heating treatment refers to a physical modification method in which starch is treated at a relatively anhydrous(Moisture content below 10 %)and certain temperature.The internal structure of starch can be changed without any chemical reagents during dry-heating treatment,and then the properties of starch can be changed.It is a safe method of starch pretreatment.In this paper,the effects of pectin concentration,pH value of blends,dry-heating treatment time and dry-heating treatment temperature on the viscosity and anti-digestibility of sweet potato starch were analyzed by using the method of synergy effect between pectin and dry-heating treatment.The parameters of sweet potato starch were optimized by response surface analysis.The effect of pectin synergistic dry-heating treatment on the molecular structure,gelatinization properties and digestive properties of sweet potato starch was investigated using sweet potato starch and dried heat-treated starch as controls.The specific contents are as follows:1.The viscosity of sweet potato starch and pectin blend increased first and then decreased with the increase of pectin concentration,pH in blends,heat treatment time and the dry-heating treatment temperature.The peak viscosity was at 2 % of pectin concentration,7of blends pH,2 h for dry-heating treatment and 120 ? for dry-heating treatment temperature,which indicated that pectin synergetic dry-heating treatment was not easy to make starch samples swell and fracture,and the viscosity increased.After the starch swelled and ruptured,the viscosity decreased.The content of anti-digestive starch after pectin synergistic dry heat treatment was the highest under this condition,reaching 15.44 %.2.Taking the starch peak viscosity and anti-digestibility as the examination factors,The optimum process conditions for the pectin-co-dry heat-treated sweet potato starch were optimized through Box-Behnken's combined experimental design and response surface analysis.The pectin concentration was 2.2 %,the dry heat treatment time was 2.1 h,and the dry heat treatment temperature was 122 °C.Under this condition,the peak viscosity of sweet potato starch after pectin co-dried heat treatment was 1905 ± 8 cp,and the digestive resistance was 18.48.% ± 0.73 %.3.According to the molecular structure analysis of dry-heated treatment with pectin of sweet potato starch,the grain morphology of starch after dry-heat treatment showed no significant change compared with the original starch,and the dry-heated treatment with pectin analysis showed that the starch granules adhered to each other.The ultraviolet absorption spectra of starch and iodine absorption shows that after dry-heated treatment with pectin,a stable complex is formed between starch and iodine,and the maximum absorption wavelength of starch and iodine is red-shifted.The maximum absorption wavelength is 630nm;After dry-heated treatment with pectin,the proportion of large particles increased,reaching 5.03 %;Dry-heated treatment with pectin can also effectively inhibit the leakage of amylose in starch samples.4.The analysis of pasting properties of dry-heated treatment with pectin of sweet potato starch showed that the starch gelatinization opening temperature,peak temperature and gelatinization end temperature and the enthalpy of heat increase afterdry-heated treatment with pectin;The storage modulus and the loss modulus of the post starch are both increased.The hardness and elasticity of the starch gel are higher than that of the original starch,and therecover ability is also the best;dry-heated treatment with pectin of sweet potato starch can effectively improve the acidity and thermal stability of the starch and Reduce the rate of precipitation of sweet potato starch.5.The analysis of vitro digestibility of dry-heated treatment with pectin of sweet potato starch showed that the hydrolysis rate of modified sweet potato starch decreased.The hydrolysis rate of un-gelatinized sweet potato starch samples was lower than that of standard samples,and the sample resistance after dry-heated treatment with pectin was analyzed.The content of digested starch was higher than that of dry-heated treatment with pectin,and its value was as high as 68~91 %.The content of anti-digestion starch in starch treated with gelatinized pectin was 9.09 % and 7.09% higher than that of dry-heated treatment with pectin,respectively.