Effects of chemical structure of common monosaccharides and polyols on plasticization and antiplasticization of starch films.

摘要

Monosaccharides have several hydroxyl groups and a compatible structure with starch polymers likely resulting in effective plasticization in starch films. Two groups of plasticizers (polyols and monosaccharides) were used to compare their plasticizing efficiency. Fructose, glucose, mannose, galactose, glycerol, sorbitol, ethylene glycol and maltitol were selected at 13.031 mmol per 100 g of pea starch. Edible starch films were produced after heat gelatinization and dehydration of the 3% starch dispersion. The microstructure, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) characteristics, thickness, moisture content, tensile strength, modulus of elasticity, elongation-at-break, water vapor permeability, and transparency of films were determined. Microstructure of the film solutions showed that some swollen starch granules and their remnants existed in the film. Compared to the FTIR spectra of pure starch films, the spectra of plasticized films showed that more hydrogen bound hydroxyl groups and more water molecules were attracted around starch polymer chains. Monosaccharide-plasticized films were comparable to the polyol-plasticized films in parameters determined from the tensile test, but were more resistant in moisture permeation than the polyol-plasticized films. It was assumed that the structural compatibility of monosaccharides with starch might result in a denser polymer-plasticizer complex, smaller size of free volume, and less segmental motions of starch chains. In conclusion, monosaccharides were identified as effective plasticizers for starch film.;According to the study results, the recommended plasticizer concentration for plasticization of the starch films is as follows: Fructose is in the range of 4.34 to 10.87 mmol at almost entire RH. Mannose and glucose should be from 4.34 to 8.69 mmol at RH below 50%. Otherwise, the crystallization occurs. Glycerol can have a broader range. Sorbitol is like glucose. Its concentration will be below 8.69 mmol in case of crystallization occurs. (Abstract shortened by UMI.).;Effect of plasticizer content (4.34 to 10.87 mmol per g of dry starch) and storage relative humidity (RH) (11.3% to 75.4%) on moisture content (MC), tensile strength (TS), elongation (E), modulus of elasticity (EM), and water vapor permeability (WVP) were evaluated using response surface methodology. EG was dropped, because during the experiments the EG film became brittle at low EG concentration level and low RH conditions. MC was influenced strongly by RH. Glycerol-plasticized films had the highest MC, indicating that water molecules played a more important role in plasticizing starch films. Monosaccharidc-plasticized films and polyol-plasticized films had similar TS values. However, monosaccharide-plasticized films had higher E values and lower EM values than polyol-plasticized films, meaning monosaccharides had better efficiency in plasticizing starch films. Recrystallization happened in glucose- and sorbitol-plasticized films when they were stored in high RH. Sorption isotherm studies showed similar adsorption and desorption profiles for all three monosaccharide-plasticized films and hysteresis. Flory-Huggins model fitted experimental data best for starch films, while BET model fitted the data marginally.