Analysis of chalk in rice by two-dimensional correlation spectroscopy

To extract the characteristic information of chalk in rice, the chalky milled rice were analyzed systematically by mid-infrared (IR), near-infrared (NIR) spectra analysis and two-dimensional (2D) correlation spectroscopy. 24 non-chalky and 24 chalky rice samples for four types milled rice were prepared in laboratory. NIR diffusing reflection and IR attenuated total reflection (ATR) spectra of all samples were collected at room temperature. The synchronous 2D NIR-NIR correlation spectra was calculated to show the differences between chalky and non-chalky rice more remarkably. The 2D IR-NIR correlation spectra was used to confirm the near-infrared characteristic peak. According to the IR spectra, a lot of starch was found in rice samples. Besides, in the NIR spectra, peaks at around 4332 and 4732 cm−1 could be considered as the key factors to discriminate chalky rice kernels. And the higher peak intensity ratio of 5168/5624 cm−1 was found compared to the non-chalky sample. In addition, significant differences emerged in the 2D NIR-NIR correlation by the intensity and number of the auto-peaks and cross-peaks in synchronous spectra. There was three auto-peaks near 4484 cm−1, 4752 cm−1and 4958 cm−1 in chalky rice sample. While only one auto-peak near 4958 cm−1 in non-chalky rice sample. Besides, chalky rice sample has one cross-peak between 4484 and 4958 cm−1, while it was absent in non-chalky rice. The technique for chalky rice kernels detection of milled rice kernels was rapid and non-destructive, which could be used to provide technical support for rice quality improvement breeding. •Two-dimensional correlation spectroscopy was used to analyze chalky and non-chalky rice.•The differences of characteristic peaks between the two in infrared and near-infrared spectra were found.•Chalky and non-chalky rice can more distinguishable by NIR spectrum using 2D correlation analysis.