Date of Award
Master of Science
Food Science and Technology
John Mount, Qixin Zhong
Chitosan, a deacetylated product of chitin, is a copolymer of 2-amino-2-deoxy-D glucopyranose and 2-acetamido-2-deoxy-D glucopyranose. Chitosan has many functional properties and has various applications in food, agriculture, pharmaceutical, cosmetic industries. However, little is known about the fate of chitosan and its films during prolonged storage. Although it has been reported that chitosan films treated with dry heat or saturated steam became brown, data available on physical characterization of chitosan films is still conflicting.
This study was conducted to determine chemical stability and mechanical properties of chitosan films as affected by (1) type of acid used for film preparation (acetic, lactic, citric, and hydrochloric acid), (2) final pH of the films (regular vs. neutralized), (3) storage conditions (temperature of 4, 22, and 80°C, and relative humidity 20 and 70%), and (4) time (up to 5 months). Development of colored compounds was observed with a Hunter colorimeter and UV-Vis spectrometer, while polarized microscope was used to observe micro-structural changes in the film. Accumulation of hydroxymethyl-furfural (HMF) was monitored by high performance liquid chromatography. Neutralized films stored at high temperature and high humidity showed more darkening and higher HMF levels than regular films stored at lower temperature under dry conditions. Polarized microscopy showed presence of birefringent crystals only in the films stored at high temperature.
Effects of type of acid and storage conditions on mechanical properties of chitosan films were evaluated on films stored for a period of 1 year. Dynamic mechanical analysis showed that citric acid films were brittle while lactic acid films were flexible even at room temperature. Thermal degradation of the films started at temperatures around 200 °C regardless on type of acid used for film preparation. Glass transition temperature (Tg’) of chitosan films appeared to be between 40 ºC to 50 ºC.
Our study has shown accumulation of HMF and development of crystallinity at higher temperature and high humidity in chitosan films, whereas films stored at lower temperatures (4 ºC and 22 ºC) had low levels of HMF and no crystals were observed. Among all the films tested, acetic acid films were found to be the best for food application with least HMF accumulation and better overall mechanical properties compared with lactic, citric, and hydrochloric acid films.
Rajpal, Gagan, "Color and Mechanical Properties of Chitosan Films during Storage. " Master's Thesis, University of Tennessee, 2007.