Moisture content is a key factor responsible for inducing rice yellowing

Differences in volatile compounds and the changes in physicochemical properties during the yellowing of glutinous rice were analyzed for investigating its association with water content during storage. The physicochemical analysis indicated that the yellowing led to an enhanced rice viscosity and reduced pasting temperature. More importantly, rice yellowing at higher moisture content resulted in a greater difference in the pasting properties between fresh and the yellowed rice. The changes in the rheological properties of rice appeared to be more sensitive to the initial moisture content, in particular at high moisture condition. In addition, the parameter tanδ might be a key indicator in highlighting the association of rice yellowing with its corresponding dynamic rheological properties. Specially, the volatile compounds detected by gas chromatography-ion mobility spectrometry (GC-IMS) and gas chromatography-mass spectrometry (GC-MS) showed that most of volatile compounds were decreased following the rice yellowing process, which was independent to the initial moisture content of the storage, and the increased level of the storage moisture enhanced the loss of the volatile compounds. Nevertheless, the newly formed volatile compounds during the rice yellowing still noted, and the increase of 1,2,4-trimethyl-bnzene and the decrease of phenol may be the potent to indicating of rice yellowing.