Mechanical and thermal characteristics of pea starch films plasticized with monosaccharides and polyols

Edible starch films were produced from pea starch and various plasticizers (mannose, glucose, fructose, and glycerol and sorbitol) at the ratio of 4.34, 6.50, 8.69, and 10.87 mmol plasticizer per gram of starch. After film specimens were conditioned at 50% relative humidity, mechanical properties (tensile strength, elongation, and modulus of elasticity), water vapor permeability (WVP), moisture content, and thermomechanical properties (G' and tan delta) were determined as a function of plasticizer concentration. At all concentration levels, monosaccharides (mannose, glucose, and fructose) made the starch films stronger (higher tensile strength) and more stretchable than polyols (glycerol and sorbitol), while WVP of monosaccharide-plasticized starch films were lower than those of polyol-plasticized starch films, especially at higher plasticizer concentration levels. Except for 4.34 mmol/g of mannose-plasticized film, all the other films showed similar modulus of elasticity at the same plasticizer concentration. Polyol-plasticized films had lower T than the monosaccharide-plasticized films. Glucose- and sorbitol-plasticized films needed more activation energy to go through glass transition than others. After all, research results showed that not only the polyols but also the monosaccharides were effective in plasticizing starch films. It is concluded that molecular size, configuration, total number of functional hydroxyl group of the plasticizer as well as its compatibility of the plasticizers with the polymer could affect the interactions between the plasticizers and starch molecules, and consequently the effectiveness of plasticization.