67D-3 |
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S. R. BAXTER1, S. Zivanovic2, J. R. Mount2, and J. Weiss2. (1) Department of Food Science and Technology, University of Tennessee, 2605 River Dr. Room 100 FSPB, Knoxville, TN 37996, (2) Dept. of Food Science & Technology, Univ. of Tennessee, Food Chemistry & Biophysics Labs., 2605 River Dr., Knoxville, TN 37996-4591 Chitosan is a glucosamine polymer produced by deacetylation of chitin from crustacean shells. The functional properties of chitosan, such as thickening, film-formation and antimicrobial activity, are related to its molecular weight and degree of acetylation (DA). High intensity ultrasonication has the potential to modify molecular weight of chitosan and thus alter or improve chitosan functional properties. The objective of this research was to determine molecular weight and DA of chitosan molecules as a function of sonication intensity and treatment time. High molecular weight shrimp chitosan was purified by alkaline precipitation and dialysis from aqueous solution. A 1% chitosan in 1% aqueous acetic acid was sonicated for 0, 0.5, 1, 5, 15, and 30 minutes at 25°C. A Misonix 3000 ultrasonic homogenizer was used to sonicate 50mL samples at power levels of 1.71W/cm2, 3.63W/cm2, and 4.96W/cm2 with pulsed output (1s sonication, 1s break). The DA was determined by HPLC-PDA at 210nm, monitoring acetyl groups released after complete hydrolysis and deacetylation of the samples. Molecular weight was determined by intrinsic viscosity through successive dilutions of sonciated solutions and confirmed by size exclusion chromatography. The DA of purified chitosan was 23.9%. Results indicated that neither power level nor sonication time enhanced deacetylation of chitosan molecules. Furthermore, intrinsic viscosity measurements demonstrated a first order, logarithmic relationship between the intrinsic viscosity and the sonication time with first order rates increasing with ultrasonic intensity. Ultrasonication at 4.96W/cm2 for 30 minutes reduced the intrinsic viscosity of the solution by 75.7% compared to the untreated solution. This reduction in intrinsic viscosity translates to an approximate decrease in molecular weight of 33%. The molecular weight change was also confirmed using size exclusion chromatography. Our results confirm the hypothesis that high intensity ultrasonication can be utilized to reduce molecular weight of chitosan while not reducing the degree of acetylation.
Session 67D, Food Chemistry: Lipid and carbohydrate chemistry
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