Evaluation of Eating Quality in Japonica Rice: A Multi-Trait Analysis of Starch Properties, Protein Content and Taste Value

Rice eating quality is a core determinant of consumer preference and commercial value. Although it is chemically determined by the accumulation and distribution of the substances in rice seeds, the comprehensive physicochemical basis underlying this trait in japonica rice remains insufficiently clarified. To identify the key physicochemical indicators that predict and regulate japonica rice eating quality, the taste value of 59 japonica rice varieties was evaluated, and the protein content (PC), apparent amylose content (AAC), starch pasting properties, gelatinization characteristics, and textural attributes were systematically measured. The results indicated that japonica rice has an average taste value of 72.0 with a range between 54.0 and 87.8. The taste value was significantly negatively correlated with PC, onset (To), peak (Tp) and conclusion (Tc) gelatinization temperatures, but was significantly positively correlated with appearance score, mouthfeel score, hot paste viscosity (HPV), and cool paste viscosity (CPV). PCA further indicated that AAC, HPV, CPV, peak viscosity (PV), and setback value (SB) were the major contributors to the first principal component, explaining 38.5% of the total variation. Stepwise regression analysis showed that the best regression equation for predicting taste value was: Taste value = 142.526 − 5.226 PC − 0.425 To (R2 = 0.455; p < 0.001), confirming PC and To as the core parameters accounting for 45.5% of the taste value variation. Path analysis further indicated that PC and To affected japonica rice eating quality through direct and indirect pathways. These findings suggest that low PC, low gelatinization temperature, high HPV, and high CPV can serve as good physicochemical indicators for the breeding of high-eating-quality japonica rice.