Carboxymethylation of corn starch and characterization using asymmetrical flow field-flow fractionation coupled with multiangle light scattering.
Asymmetrical flow field-flow fractionation (AsFlFFF) was coupled online with multiangle light scattering (MALS) to study the changes in the molecular weight and the size distribution of the corn starch during carboxymethylation. A corn starch was derivatized with sodium chloroacetate in alcoholic medium under alkaline condition to produce carboxymethyl starches (CMS) having various degrees of substitution (DS). The change in thermal characteristics and granule structure of the native corn starch and CMS were compared using Thermogravimetric analysis and scanning electron microscope. The ionic strength of the carrier liquid (water with 0.02% NaN(3)) was optimized by adding 50mM NaNO(3) to minimize the interactions among the starch molecules and between the starch molecules and the AsFlFFF membrane. A field-programmed AsFlFFF allowed determination of the molecular weight distribution (MWD) of starches within about 25min. It was found that carboxymethylation of starch results in reduction in the molecular weight due to molecular degradation by the alkaline treatment. The weight-average molecular weight (M(w)) was reduced down to about 4.4x10(5) from about 7.2x10(6) when DS was 0.14. It seems AsFlFFF coupled with MALS (AsFlFFF/MALS) is a useful tool for monitoring the changes taking place in the molecular weight and the size of starch during derivatization.
Department of Chemistry, Hannam University, Daejeon 305-811, South Korea.
Seungho
S
Lee
Sun Tae
ST
Kim
Bhoj Raj
BR
Pant
Hai Doo
HD
Kwen
Hyun Hoon
HH
Song
Sung Kwang
SK
Lee
Sachin Vilas
SV
Nehete
D031521:Fractionation, Field Flow / Q000379:methods*; D008027:Light; D008745:Methylation; D008855:Microscopy, Electron, Scanning; D008970:Molecular Weight; D009566:Nitrates / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry; D012542:Scattering, Radiation; D017550:Spectroscopy, Fourier Transform Infrared; D013213:Starch / Q000737:chemistry*; D013696:Temperature; D013818:Thermogravimetry
D009566:Nitrates; C003320:sodium nitride; C031618:sodium nitrate; D013213:Starch; D009584:Nitrogen