Influence of Gradient Milling on Cooking and Sensory Attributes of Chinese Black Rice: Insights into Volatile Flavor Compounds

This study investigated the impact of gradient milling on the cooking properties and sensory characteristics of Yangxian black rice. The results showed that as the degree of milling increased, the gelatinization time decreased (36.85-23.54 min) and the water uptake ratio of whole black rice (188.29%) was significantly lower compared to that of refined grains (194.05%). Low-field nuclear magnetic resonance (NMR) was further used to monitor the water concentration and distribution of black rice during soaking and cooking. It was found that the bran layers of black rice, as a physical barrier, impeded the water penetration into the kernels for a given soaking and cooking duration. The sensory evaluation conducted by a panel of trained volunteers demonstrated a high score for all sensory attributes in slightly milled black rice, corroborating findings from the taste analyzer. Through correlation analysis of volatile components determined by gas chromatography-mass spectrometry (GC-MS), smell scores in sensory evaluation, and electronic nose response values, 2-pentyl-furan (54.84-12.72 ng/g) and guaiacol (19.39-5.51 ng/g) were found to be the predominant volatile flavor contributors in cooked black rice. Overall, this study provides valuable insight into the intricate relationship between milling degrees and the cooking properties, sensory characteristics, and volatile flavor compounds of Yangxian black rice.