| Natural starch can be developed as renewable and biodegradable natural macromolecule compound because of its rich in sources.Our country is an agricultural country whose starch resources are very abundant.However,the development of modern starch industry in China relatively lags behind,and the kind of products is very limited.Moreover,the natural starch has some defects such as the low light transmittance,poor freeze-thaw stability,overly sensitive to the pH change,and is easy to retrograde,which limits the the application of natural starch in the modern food and non-food processing industry.In order to solve these problems,researchers use the method such as chemical,physical or biological engineering to modify the natural starch according to the structure of starch and the physical and chemical properties,which makes it have the character that is suitable for particular purpose.The modified starches could overcome some problems which exist in the natural starches.To increase the use value and economic benefit of the natural starch and utilize the resource advantage of starch in our country fully,we must conduct the multi-level modification for starch.Therefore,it is of great significance to accelerate the deep processing study of starch.This study uses the new additive sodium phytate and environmentally friendly oxidant hydrogen peroxide to modify the wheat starch and researches the influence mechanism on modified wheat starch by sodium phytate and hydrogen peroxide,which could explore the feasibility that sodium phytate acts as a new type modifier for wheat starch.The main contents and results of this study are as follows:1)The wheat starch was used as the raw material to be modified by use of sodium phytate and hydrogen peroxide,which is based on the chemical modification of crosslinking and oxidation.The four kinds of modified starches including the oxidized(OWS),cross-linked(CLWS),cross-linked oxidized(COWS)and oxidized cross-linked(OCWS)were obtained.Firstly,the optimal reaction conditions for starch modification were determined.In the single factor experiment,temperature,crosslinking time,crosslinking pH value,starch milk concentration and sodium phytate dosage were included.When the temperature of the reactional system is 50℃,the crosslinking time is 6 h,the crosslinking pH value is 7,the starch concentration is 30%,the amount of the crosslinking agent is 2%,the high level of the combined phosphorus content can be reached.Secondly,the orthogonal order experiment was used to determine the main order of the main factors affecting the content of phosphorus in cross-linked wheat starch: cross-linking p H > addition of sodium phytate > starch concentration > crosslinking reaction time > reaction temperature.Thirdly,the binary linear regression equation between phosphorus content and each influencing factor was obtained by quadratic universal orthogonal experiment,which is Y=-0.12+0.049X1+0.023X2+0.3778X3+0.00013 X1X2+0.063X1X3+0.0063X2X3-0.089X12-0.00172X22-10.8X32.The simplified equation which eliminated item was not significant in the variance analysis is that: Y= 0.0241X2+0.432X3-0.00172X22-10.8X32-0.0477.2)After the processes of cross-linked oxidized and oxidized cross-linked,the native wheat starch was modified effectively with respects to physicochemical properties and functional characteristics,as determined by Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),differential scanning calorimetry(DSC),rapid visco analyzer(RVA),and scanning electron microscope(SEM).The Fourier infrared spectroscopy(FT-IR)analysis showed that the sodium phyate and hydrogen peroxide were introduced into wheat starches successfully.The XRD result indicated that cross-linked phosphates from sodium phytate were primarily located in the amorphous regions of starch granules.DSC analysis presented that peak temperature(Tp)64.41℃ of the COWS was the highest,which indicated that starch molecular linked more closely each other after being modificated by sodium phytate and hydrogen peroxide.It needed more heat to destroy the binding force,which lead to the higher peak temperature.The result of RVA testified that viscosity indexes of CLWS were noticeably increased compared with the other four starches,of which three oxidized starch samples showed lower RVA profiles because of oxidation.Modified by different treatments,the starch samples exhibited a multiple morphological characteristics including the A-type and B-type wheat starch granules that showed much closer contaction with each other by the cross-linking reaction under the SEM observations.The characteristics including solubility,swelling power,light transmittance and freeze-thaw stability(FTS)of all five treated and untreated wheat starches presented that COWS presented the highest solubility by 0.57 and the CLWS showed the best swelling power by 12.63(g/g).The paste clarity of COWS was improved to 47.72% higher when compared to the native starch(7.54%)and the water loss rate of COWS(21.62%)was the lowest,which is beneficial to the produce of quick-frozen food.Our results showed that the dual-modified starch by sodium phytate and hydrogen peroxide could significantly alter the functionality and enhance the connection between the A-type and small B-type granules rather than altering the internal structure of starch granules.The present study should provide fundamental information of dual-modified wheat for their potential industrial applications.3)At present,the packaging products with plastic materials had caused serious environment pollution.The good biodegradability and non-toxic safe food packaging materials has gradually become research hotspot in the modern food packaging industry.In this study,five wheat starch film samples were obtained by using the five kinds of wheat starches,through adding glycerol,sorbitol and sodium carboxymethyl cellulose.Firstly,the optimal technological conditions of the preparation of wheat starch films were determined: the concentration of wheat starch was 6.0 g/100 mL,addition of glycerol was 5.0 g/100 m L,and amount of sodium carboxymethyl cellulose(CMC-Na)was 0.3 g/100 mL,and addition of sorbitol was 0.5 g/100 mL.Secondly,the physical and chemical properties of starch film samples including membrane thickness,solubility,water permeability and tensile stress study were studied.It is verified that the cross-linked oxidized starch film showed the excellent characteristics,such as low thickness,low solubility and strong tensile stress,which opens a new pathway of research for the comprehensive utilization of double modified starch by sodium phytate and hydrogen peroxide. |
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