Analysis of chemical reactions on pure starch induced by dielectric barrier discharge plasma at atmospheric pressure

Dielectric barrier discharge (DBD) plasma techniques at atmospheric pressure have gained in importance in the food industry over the last years, for example for sterilisation of food, enhancement of food durability and degradation of pesticides and food allergens. In this work, DBD plasma-induced effects on the chemical composition of one of the most important nutrients, starch, are investigated. Plasma treatment was performed in ascending time steps for 30 s, 1 min, 2 min, 4 min, 8 min, and a maximum of 16 min and the treatment duration-dependent modifications of the chemical composition of starch were investigated via both Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). These analyses have revealed a reduction of absorbed water in starch molecules as indicated by a decrease in FTIR peak intensity at 1643 cm-1 by a factor of about 2 as well as the formation of new carboxyl bonds that can be related to oxidation, esterification, or breaking of glucose rings. Such modifications have occurred quite rapidly, i.e., within the first few minutes of plasma treatment. Auxiliary heat treatment experiments at a temperature of about 75 °C, corresponding to plasma gas temperature, have shown that this effect resulted from chemical reactions between reactive oxygen species provided by the plasma and starch molecules. In contrast, the reduction of absorbed water was shown to be induced by plasma heating as supported by a detected loss in sample mass by 12.5 ± 1.9%. Furthermore, the plasma-induced modification of starch molecules did not result in the production of substantial quantities of nitrogen-containing compounds as verified via XPS. The presented results thus contribute to a better understanding of mechanisms of plasma-food interactions, for example for food decontamination or the improvement of shelf life.