Preparation Of High Methoxyl Pectin And Its Application In Nanoemulsion

Pectin is a complex polysaccharide existing in plant cell walls.Ultra-high methoxy pectin(UHMP,degree of esterification DM>90%)prepared by pectin esterification with a relatively homogeneous structure is a unique molecular template.Staring from the esterification of pectin,HMP with various DM range was firstly prepared by optimizing reaction conditions and its structural features and physiochemical properties were characterized.Furthermore,nanoemulsion was prepared using UHMP by low energy method and the factors affected nanoemulsion stability was investigated.Firstly,series of HMP samples with various esterification range were prepared by altering reaction conditions(reaction time,temperature,solid-to-liquid ratio(SLR)and HCl concentration),Under the condition of 60°C,1:50 SLR and 0.1 M HCl,HMP with DM of70-80%,80-90%,and>90%was obtained after 2 h,4 h and 12 h respectively.Including the raw pectin(DM=63.18%),the four pectin samples were investigated in following studies.Secondly,the physicochemical properties of four HMP samples were characterized.Results of molecular weight(MW)distribution showed that the number-average molecular weight(M_n)was decreased with the increase of the DM.Particularly in the case of HMP with DM of>90%,the M_n was decreased from 64.00 kDa(raw pectin)to 15.00 kDa.Significance analysis of the results of sugar composition showed there is no significant difference(p>0.05)in the content of the five monosaccharides in different HMP samples,therefore the acidic hydrolysis in the esterification reaction only broke the molecular chain of pectin resulting in a decrease in MW without other side reactions to pectin fragments.Effects of concentration,pH and temperature on the viscosity of different HMP samples were studied.With the same DM,higher HMP concentration produced greater viscosity.At the same HMP concentration,higher DM lowered solution viscosity,and the pectin was less sensitive to pH and temperature.Solubility test showed that pectin with higher DM and less MW presented better solubility.Thirdly,dynamic interfacial tension test suggested that the dynamic interfacial tension of the system decreases with the increase of DM and UHMP could be faster absorbed onto O/W interface with a saturated aqueous concentration of 3%(w/v).The low energy method was used to prepare the nanoemulsion using HMP with various DM.The particle size distibution showed that HMP with higher DM had smaller particle size of the prepared emulsion.The particle size of the emulsion prepared by the raw pectin was around 900 nm,while the emulsion prepared by UHMP was about 370 nm.Finally,the long-term stability of the nanoemulsion prepared by UHMP through low energy method employing various surfactant-oil ratio(SOR)was studied.The stability of emulsion was evulated by particle size,polydispersity index(PDI),zeta-potential,creaming index(CI)and viscosity.After 8-weeks storage at room temperature,the emulsion produced by 20%and 30%SOR had a clear free oil layer floating up,while the emulsion of 40%and50%SOR remained stable.The size of droplet and PDI decreased significantly after storage for 7 days and stable during the following storage time(49 days),indicating that the particle size of the emulsion system gradually became uniform.Zeta-potential decreased slightly during storage while CI value was not significantly(p>0.05)changed.By fixing SOR of 50%,the effect of pH(pH 2~8)and storage temperature(25~85?)on the properties of nanoemulsion was investigated.The emulsion was stable under different pH values suggested by slightly decreased droplet size and the constant CI.The clear free oil layer was not observed.The droplet size of the emulsion treated at 85?was almost the same to that of the emulsion stored at room temperature for several weeks,which indicated that the emulsion had good thermal stability.