Arrowhead (Sagittaria Sagittifolia L.) Storage Characteristics And Its Starch Modification

Arrowhead?Sagittaria sagittifolia L.?is widely distributed in China,but the characteristics such as seasonality,region restriction and high-water content make it difficult to storage and limit its development and production.Starch modification is an important mothed to develop starch resources for its insolubility in cold water,aging and poor film-forming.Based on the principle that ultrasonic pretreatment and hydroxypropyl can effectively improve the properties of starch,this paper chose arrowhead corm as raw materials,studied the nutrient changes at different storage conditions and the effect of different frequency ultrasound treatment on functional characteristics and structure of arrowhead starch,and then produced hydroxypropyl starch by using ultrasonic pretreated starch and evaluated its physicochemical properties and functional characteristics.It was expected to lay a theoretical foundation for the development and utilization of arrowhead starch resources.The main contents and results of this thesis are as follows:?1?At room temperature,the change of moisture content of arrowhead was significant and decreased from 81.39%down to 46.83%at 28^th day amylase activity increased from 0.12up to 0.21 which was significantly from 7^th to 21^st day,starch hydrolyzed fast,reducing sugar and total soluble sugar content of dry matter increased to 37.13%and 112.10?g/mg,respectively and the starch content increased in the early stage because of the after-ripening.When the temperature was 4?,the amylase activity increased steadily,and the content of reducing sugar and total soluble sugar increased at first and then decreased.Comparing with being storaged at room temperature,arrowhead has a fully ripening process and higher quality starch when it was storaged at 4?.?2?The ultrasonic chemical yield and the starch degradation degree almost followed the same order:tri-frequency>dual-frequency>single frequency,and both of them were obtained the highest value?37.6 m L and 89.1?g/mL?.But the ultrasonic chemical yield was12.72 m L when the ultrasonic frequency was 20+40 kHz,which was smaller the 60 kHz?16.77 m L?.However,the starch degradation degree of 20+40 kHz was bigger than 60 kHz.Those results showed that in the same condition,the ultrasonic chemical yield in the liquid occurred more in the case of dual-and tri-frequency ultrasound,but effect of ultrasonic on the starch degradation is not strictly proportional to the amount of ultrasonic chemical yield,it also related to frequency.?3?The effects of different frequency ultrasonic on the physicochemical properties of arrowhead starch were investigated by examining the solubility,swelling power,transparency,retrogradation,freeze-thaw stability,gelatinization property and rheological property of arrowhead starch.The results showed that after ultrasonic treated,the transparency of arrowhead starch decreased,the retrogradation increased,retrogradation velocity was slowing,the freeze-thaw stability became worse;all viscosity indexes were changed in the gelatinization process and the overall effect was thermal stability increased and cold stability decreased;the lag area in rheological properties decreased and the recovery degree is dual-frequency>native starch>tri-frequency>single frequency;the storage modulus increased,which indicated that the interaction force between the molecules increased.Comparing all the indexes of different ultrasound treated starches,it showed that 60 kHz,20+40 kHz and 20+60 kHz ultrasound have more obviously effect on the physicochemical properties of arrowhead starch.?4?After analyzed the apparent morphology and crystal structure of the native starch and ultrasonic treated starch found that:arrowhead native starch granules dispersed evenly,and most of them are round or oval with smooth surface and without cracks and cavities;Amylose content was 36.16%.After being treated by different frequency ultrasound,the starch granules aggregated,the particle size showed double-peaks distribution,the surface of starch granules became coarse and cracked,the amylose content changed,and the characteristic absorption wavelength and A₆₈₀/A₅₄₅ of starch-iodine complex was smaller.The ultrasonic treatment did not destroy the original structure of the starch molecule,and the crystalline structure of the starch was unchanged,but the polarizing cross became fuzzy,which showed that the relative crystallinity of starch decreased.Comparing the changing degree of starch structure after treated by all frequency ultrasound found that 20+60 kHz ultrasound had the most obviously effect on arrowhead starch structure.?5?Study on substitution degree and main physicochemical properties of arrowhead native starch,hydroxypropyl starch produced by native starch and ultrasonic treated starch showed that ultrasonic treatment increased the hydroxypropyl substitution degree and obtained greater substitution degree at 60 kHz and 20+60 kHz,which was 0.0800 and 0.0785,respectively.There was no significant difference in IR spectra and SEM analysis of all hydroxypropyl starch,which showed that ultrasonic treatment and hydroxypropyl have no obvious effect on the structure of arrowhead starch.The introduction of hydroxypropyl group reduced the solubility of arrowhead starch,increased the swelling power and transparency,weaken the retrogradation,enhanced the freeze-thaw stability,at the same time made the thermal stability worse and the cooling stability better,the peak time shorter,the gelatinization temperature decreased,and the energy storage modulus and loss modulus increased.After the ultrasonic pretreatment,all the properties are further strengthened,which indicates that ultrasonic pretreatment increased the reaction property of arrowhead starch and obtained the hydroxypropyl starch with higher substitution degree and better performance.