Abstract:
As a crucial process in the production of frozen fried rice, little research had been conducted on the impact of freezing methods on the quality of fried brown rice. In this study, fried brown rice was frozen using four different methods: refrigerator freezing (RF), micro-freezing (MF), liquid nitrogen freezing (LF), and individual quick freezing (IQF). A variety of analytical techniques were employed, including low-field nuclear magnetic resonance imaging, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), texture analysis, and differential scanning calorimetry (DSC), to compare and analyze the moisture state, microstructure, short-range order of starch, crystal structure, retrogradation characteristics, and texture properties of fried brown rice. The results showed that the freezing rate of the three freezing methods was from fast to slow: LF (6.34 ℃/min)>MF (1.95 ℃/min)>RF (0.27 ℃/min). The LF group exhibited a significantly higher proportion of T
21 strongly bound water (10.21%) compared to the other three groups, along with notably lower hardness values (2544.03 g). This phenomenon could be attributed to accelerated freezing rates, which resulted in increased ice crystal formation, reduced average ice crystal dimensions, collectively indicating that LF treatment caused the least microstructural damage to fried brown rice. The results of FTIR, XRD, and DSC analyses indicated that as the freezing rate increased, the peak intensity ratio (R
1047/1022) and relative crystallinity decreased, along with the rate constant k decreased, which in turn slowed the recovery rate of fried brown rice. Consequently, the quality of fried brown rice treated with LF was the highest, followed by MF and IQF, while the quality of fried brown rice treated with RF was the lowest. The research findings demonstrated the effects of various freezing methods on the moisture content, texture characteristics, and retrogradation properties of fried brown rice. This study provided a theoretical basis for the industrial production of frozen fried brown rice.