Preparation Of Low Molecular Weight Soluble Soybean Polysaccharide Iron Complex(â…¢) And Their Biological Activity

Using soluble soybean polysaccharides （SSPS） with high molecular weight as rawmaterial， the low-molecular-weight SSPSs were prepared by hydrogen peroxide withultrasonic treatment in this paper．The SSPSs with different molecular weight were obtainedby controlling degradation and ultrafiltration，subsequently every different molecular weightSSPS reacted with FeCl3to form its ferrous complex （SSPS-Fe（III））． The structure，moisture-absorbing property，moisture-retention property and antioxidant activity of SSPS-Fe（III）s were studied．Real-time fluorescent quantitative PCR and microcalorimetry wereused to evaluate the effect of SSPS-Fe（III） on growth and metabolism of Escherichia coli，Staphylococcus aureus and Bacillus licheniformis．（1）The process of degrading macromolecular SSPS was investigated by threemethods including ultrasonic，hydrogen peroxide oxidation and hydrogen peroxide withultrasonic treatment．It was found that hydrogen peroxide with ultrasonic treatment had thebest effect for preparing low molecular SSPS． In order to optimize the degradationconditions of SSPS， the orthogonal design was used to analyze the impact of hydrogenperoxide concentration，reaction temperature and reaction time on the molecular weight aftersingle factor experiments．The results showed that， under the ultrasonic power of100W，the optimal SSPS degrading conditions were hydrogen peroxide concentration8%，temperature70℃and time1.5h，Thus the molecular weight of SSPS could be degradedfrom155kDa to10.9kDa．（2） Four different low-molecular-weight soluble soybean polysaccharides wereprepared by the controlling the degradation condition，which were respectively molecularweights of93.9，43.4，18.8and9.6kDa．Another two soluble soybean polysaccharideswere obtained with molecular weights of155and2.6kDa when material SSPS solution wasultrafiltrated．Subsequently every different molecular weight SSPS reacted with Fe³⁺to form itsferrous complex （SSPS-Fe（III））． The structure of SSPS and SSPS-Fe（III） were identified byfourier transform infrared spectrometer． The characteristic absorption peak of910cm^-1demonstrated that the β-FeOOH iron core was formed．The moisture-absorbing property andmoisture-retention property of SSPS-Fe（III）s were also studied in this paper． （3）Studies on the antioxidant activities of six SSPS-Fe（III） complexes with differentmolecular weight showed that they had significant differences in different antioxidantsystems． The SSPS-Fe（III） complex with molecular weight of2.6kDa performed thestrongest reducing power，but it did not have the strongest antioxidant activities in otherantioxidant systems． The SSPS-Fe（III） complex with molecular weight of9.6kDaperformed stronger scavenging activities to hydroxyl and sodium nitrite free radical，andlipid peroxidation inhibition．In the scope of selected concentration，the strongest effect was92.3%，43.4%and74.6%respectively．Compared to five SSPS-Fe（III） complexes，the onewith the highest relative molecular mass of155kDa had weaker antioxidant activity in allantioxidant systems．In conclusion，the SSPS-Fe（III） complex with molecular weight of9.6kDa performed the strongest antioxidant activities，the further research for this complexshould be needed．（4）The effect of the SSPS-Fe（III） complex with molecular weight of9.6kDa on thegrowth of Escherichia coli，Staphylococcus aureus and Bacillus licheniformis was studiedby florescent real-time quantitative PCR． The original copy numbers of three kinds ofmicroorganisms were calculated by amplification curve and standard curve of real-timequantitative PCR．The results showed that the SSPS-Fe（III） complex had a role in inhibitingthe growth of Escherichia coli and Staphylococcus aureus，but promoting the proliferationof Bacillus licheniformis．（5）The effect of the SSPS-Fe（III） complex with molecular weight of9.6kDa on thegrowth thermograms of Escherichia coli，Staphylococcus aureus and Bacillus licheniformiswas studied by using the microcalorimetric method．The analysis of power-time curve，growth rate constant k，total heat Q_total，peak power P_max and time of peak power T_maxshowed that the metabolic heat production of Escherichia coli and Staphylococcus aureuswere inhibited by SSPS-Fe（III） complex，while the SSPS-Fe（III） complex had a role inpromoting the metabolic heat production of Bacillus licheniformis．...