Study On Preparation And Properties Of Emulsifier For Lotus Root Amylopectin-Whey Protein Isolate Complex

Lotus root is a common perennial aquatic edible plant,which is planted in Jiangsu,Shandong,Hebei and Anhui etc in China.Lotus root contains rich nutritional components,such as amylopectin,cellulose,carbohydrates,vitamins,phosphorus,ascorbic acid and so on.Among these components,lotus root amylopectin(LRA)is one of the most important nutrient.Whey protein isolate(WPI)was extracted from milk.Besides the rich nutritional value and high biological activity,WPI was often used as a emulsifier to improve the texture and taste of food.Research showed that the formation of WPI-LRA emulsifier was affected by many factors,such as the concentration of starch,temperature and time of dry-heat reaction.In this work,the effects of LRA,temperature and time of dry-heat reaction on the formation of WPI-LRA complex emulsifier were investigated.On this basis,the functional properties of the emulsion stabilized by WPI-LRA complex and the encapsulation effect of the system on vitamin E(VE)and peppermint oil were preliminarily discussed.The specific contents and results are as follows:(1)The optimum preparation conditions of WPI-LRA conjugate emulsifier.The effects of LRA,dry-heat reaction time and dry-heat reaction temperature on the emulsifying activity(EA)and emulsifying stability(ES)of WPI-LRA complex were investigated.On this basis,response surface model(RSM)was used to optimize the preparation conditions of WPI-LRA complex.Results showed that the optimum value of EA reached 74.8% under the conditions of dry-heat reaction time 13.5 h,dry-heat reaction temperature 44.8°C and 24.1% of LRA.The optimum value of ES reached73.1% under the conditions of dry-heat reaction time 13.6 h,dry-heat reaction temperature 43.0°C and 23.8 % of LRA.(2)The functional properties of WPI-LRA complex emulsifier.The EA and ES of emulsions stabilized by WPI-LRA conjugate were increased when pH < 7 or at a higher NaCl concentration.Moreover,no significant change was observed in Zeta potential,and the particle size of the composite was generally higher than that of the pure LRA.When the mass fraction of LRA was 24%,the storage stability of the emulsion stabilized by WPI-LRA conjugate reached a maximum,and the particle size of emulsion was stable within 6 days,which was also consistent with the results obtained in the second chapter.Moreover,at high temperature(60~100°C),the thermal stability of the emulsion stabilized by WPI-LRA conjugate was obviously higher than that of theemulsion stabilized by WPI.The particle size of the emulsion stabilized by WPI-LRA conjugate was not changed at high temperature,but the particle size of the pure protein emulsion was increasing,resulting in the unstable emulsion.The free radical scavenging rate(58.8%)of WPI-LRA was significantly higher than that of untreated WPI(39.2%),which also proved that the system was better.FT-IR showed that the addition of LRA increased the content of-OH group in conjugates,but did not change the structure of WPI absorption characteristic peaks.(3)Effect of emulsion stabilized by WPI-LRA conjugate encapsulation on antibacterial properties of peppermint oil.The mixed oil phase of soybean oil(SO)and peppermint oil(PO)can prevent the occurrence of austenite ripening in emulsion.When PO:SO=1:5,the nano-emulsion with particle size of 176 nm could be obtained by homogenizing 7 times at high pressure.When core-wall ratio(CRW)was 3:3,the values of particle size and PDI were both small,which was the most suitable condition to prepare emulsion.The stability experiments showed that the size of the three oil-phase emulsions(1:1;1:5;5:1)were increased during storage.Meanwhile,the initial particle size and the final particle size were increased with the increase of PO.There was a slight oil droplet suspension phenomenon during storage.The antibacterial experiments showed that the two emulsions had no effect on the minimum inhibitory concentration(MIC)of enterobacter sakazakii(BS)and staphylococcus aureus(SA),but the emulsion group containing PO could inhibit the growth of BS and SA more than the pure PO group.(4)Encapsulation of VE in emulsion stabilized by WPI-LRA conjugate.VE was a lipid-soluble antioxidant and a necessary micronutrient for human and animals.In this paper,the complex of WPI-LRA was used as emulsifiers to analyze the effects of different particle sizes on the oxidative stability,extent of lipolysis and bioavailability of VE.Results showed that the oxidation stability of VE was increased with the decrease of particle size.In vitro gastrointestinal simulation experiments showed that the extent of lipolysis and the bioavailability of VE were inversely proportional to the particle size.In conclusion,the emulsion system established in this study is of great significance for improving the physical and chemical properties of VE.