18A-25 |
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T. WU1, S. Zivanovic1, S. R. Baxter2, and J. Weiss3. (1) Dept. of Food Science & Technology, Univ. of Tennessee, 2509 River Drive, Knoxville, TN 37996, (2) Dept. of Food Science and Human Nutrition, Univ. of Maine, 5735 Hitchner Hall, Orono, ME 04469-5735, (3) Dept. of Food Science, Univ. of Massachusetts, Amherst, 234 Chenoweth Lab., Box 31410, Amherst, MA 01003-1410 High intensity ultrasound (HIUS) has shown to be an effective way to improve functionality of food biopolymers. However, little is known as to the effects of HIUS treatments on molecular weight and conformation of the highly functional aminopolysaccharide chitosan. The objective of this research was to investigate degradation kinetics and molecular conformation of sonicated chitosan by utilizing gel permeation chromatography (GPC) coupled with refractive index (GPC-RI) and multiangle laser light scattering (GPC-MALLS) detectors. High molecular weight chitosan was purified by precipitation and dialysis. Solutions containing 1% chitosan in 1% acetic acid were sonicated for 0, 1, 2, 10, 30, and 60 min. at 25° C using an ultrasonic homogenizer at power levels of 16.5, 28, and 35.2 W/cm2. GPC separations were performed at 30°C on 3 ultrahydrogel columns with 0.2M ammonium acetate buffer (pH=4.5) as mobile phase. Pullulans with molecular weight from 59 to 788 kDa were used as calibration standards for GPC-RI. The average weight molecular weight (Mw) of chitosan decreased from initial 401 kDa, to 220, 112 and 105 kDa after 60 minutes sonication at power levels of 16.5, 28, and 35.2 W/cm2, respectively. Under the same conditions, radius of gyration (Rg) of chitosan molecules decreased from an initial 58 nm, to 38, 27, and 26 nm. By plotting log(Rg) as a function of log(Mw), the resulting slopes decreased from initial 0.48 to 0.41, 0.36, and 0.32 indicating alterations in random coil and spherical molecular conformation after sonication. Molecular weight determined by GPC-RI was significantly higher than when analyzed by GPC-MALLS probably due to lack of adequate standards for chitosan. Our results confirmed that the molecular weight of chitosan was reduced and more uniform molecules were produced under high intensity ultrasound treatment. Additionally, the results showed that the GPC-RI overestimated the molecular weight.
Session 18A, Carbohydrate: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |