Preparation Of Debranched Hydroxypropylated Pea Starch In Ionic Liquid

Debranched hydroxypropylated pea starch(DHPS)with high degree substitution was prepared under alkaline conditions using pea starch(PS)as a raw material,pullulanase as a debranching agent,propylene oxide as an etherifying reagent,and 1-butyl-3-methylimidazolium chloride as a solvent.The effect of debranching and etherification conditions on the debranching degree of pea starch and the hydroxypropylation of debranched pea starch(DPS)were investigated.On the basis of single factor experiment,the technology parameters for the debranching of pea starch and the hydroxypropylation of debranched pea starch were further optimized with the response surface methodology.The debranching degree of debranched pea starch was determined by a DNS method,and the hydroxypropyl content of debranched hydroxypropylated pea starch was determined by a spectrophotometric method.The experimental results showed that the debranching degree of pea starch first increased and then decreased as increasing the debranching time,debranching temperature and pH,and had a better value.The debranching degree of pea starch increased with increasing the amount of pullulanase.The optimum reaction conditions for preparing debranched pea starch were as follows: debranching time 2.0h,debranching temperature 55℃,pH 4.5,amount of pullulanase 60U/g.The hydroxypropylation of debranched pea starch indicated that the molar substitution degree of debranched hydroxypropylated pea starch could reach 1.34 using an ionic liquid of 1-butyl-3-methylimidazolium chloride as a solvent during a homogeneous reaction of 3h under alkaline conditions.As increasing the etherification time,etherification temperature,amount of propylene oxide and sodium hydroxide,the substitution degree of debranched hydroxypropylated pea starch first increased rapidly,and then rose slowly.The optimum reaction conditions for preparing debranched hydroxypropylated pea starch were: etherification time 3.0h,etherification temperature 90℃,amount of sodium hydroxide 10%,amount of propylene oxide 257.7%.Investigating the effect of debranching and hydroxypropylation on the blue value,freeze-thaw stability,viscosity stability,swelling power,acid resistance,alkali resistance and the surface hydroxyl numbers of pea starch indicated that after pea starch was modified by debranching and hydroxypropylation,its freeze-thaw stability,acid resistance,alkali resistance and swelling power were obviously changed.The blue value of debranched pea starch was much greater than that of pea starch,whereas the blue value of debranched hydroxypropylated pea starch was less than that of debranched pea starch and pea starch.After pea starch was debranched,its retrogradation was enhanced.After pea starch was debranched and further hydroxypropylated,its the surface hydroxyl numbers increased.The structure,thermal property,particle morphology of debranched pea starch and debranched hydroxypropylated pea starch were measured by the infrared spectrometer,differential scanning calorimeter,thermogravimetric analyzer,X-ray diffraction,polarizing microscope and scanning electron microscope.The results showed that Maltese crosses were observed on the pea starch particles,but these crosses completely disappeared on particles of debranched pea starch and debranched hydroxypropylated pea starch.The crystalline structure of pea starch was a C-type,debranching pea starch particles was a CB-type,but the structure of debranched hydroxypropylated pea starch became amorphous.The surface of pea starch granules was smooth,and its shape displayed an oval one.However,the surface of debranched pea starch granules was rough,and its shape exhibited an irregular one.A lot of fragments and small pores appeared on some of debranched hydroxypropylated pea starch granules.