Effect of sodium citrate/polyethylene glycol on plasticization and retrogradation of maize starch.

Maize starch was plasticized by mixtures of sodium citrate and polyethylene glycol 200 (PEG200) at varied weight ratios (citric acid/PEG200, 25/0, 20/5, 15/10, 10/15, 5/20 and 0/25). The structure and pasting, aging, moisture absorption and thermal properties of the plasticized starches were studied by means of Fourier transformed infrared, X-ray diffraction, rapid viscosity analysis, tension test and thermogravimetric analysis. Comparing with single plasticizer, co-plasticizers with appropriate proportions are more effective in hindering the retrogradation of starch paste and film. The results also showed that the mechanical property and humidity sensitivity of the starch film worsen after the introduction of PEG200 compared with sodium citrate plasticized starch, but the thermal stability and anti-aging property increase. This is consistent with the association ability of plasticizers with starch observed from FTIR. In addition to the simple additive effect of components on some properties, special formulations also show some synergistic effects, such as the co-plasticizer of 20% citric acid and 5% PEG200 has a better comprehensive property for plasticizing the maize starch bulk than sodium citrate or PEG200 alone. The mixture of sodium citrate and PEG200 can be used as a candidate plasticizer for preparing thermoplastic starch for food and packaging industries.