FTIR analysis of thermal and plasma treatments on riceberry brown rice

Abstract

Riceberry brown rice (RB) is known as source for valuable nutrients. Recently our group has used plasma treatment on RB to effectively shorten their cooking time and soften their texture. During the plasma treatment, rice was also subject to elevated temperature. This sometimes has led to confusion whether the thermal effect dominate. In this study, we have carried on these issues by using Fourier Transform Infrared spectroscopy (FTIR) to follow changes in vibrational characteristics of RB after being plasma treated. The plasma treatment was performed using a low-pressure inductively coupling argon plasma system. This is done in comparison to conventional thermal treatment at 45°, 60°, and 75°C for 120 minutes. The O-H stretching group was found to increase in the plasma treated samples; while decreasing in all the other thermal treated samples. The decrement has varied monotonically with temperature. There is also significantly increasing of C-O-C skeletal mode of α-glycosidic linkage, C-O-H bonding, and C-O-C asymmetric stretching glycosidic bonds in the plasma treated samples; while the decrement was observed in the thermal treated samples. This is understood as a consequence of cross-linking effect; leading to increase in glycosidic bonds along with H₂O abstraction during the plasma treatment. It can be concluded that the plasma treatment has caused more inclusive effects which cannot be accounted for by the action of the thermal treatment alone.