Evaluation of Hardness and Retrogradation of Cooked Rice Based on Its Pasting Properties Using a Novel RVA Testing

With rice being one of the most important crops worldwide, rapid and objective quality evaluation methods based on physicochemical measurements of rice are necessary. We compared the pasting properties of various rice samples using three different heating and cooling programs (maximum temperatures were 93, 120, and 140 degrees C, respectively) in a newly developed high-temperature-type Rapid Visco Analyzer (RVA, RVA 4800). Furthermore, we investigated the relationship between the different pasting properties measured by the three programs, with starch microstructure measured by iodine scanning analysis, the physical properties of the cooked rice measured by a Tensipresser after 2 h at 25 degrees C or after 24 h at 6 degrees C, and prolamin ratio measured by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The consistency value (final viscosity-minimum viscosity) yielded by a new program of maintenance for 2 min at 120 degrees C using RVA 4800 had a higher positive correlation with retrograded surface hardness H1(R) (r = 0.92), retrograded overall hardness H2(R) (r = 0.90), and the absorbance at lambda max (A lambda max) of cooked rice (r = 0.88) and resistant starch (r = 0.80) than those by the conventional program at 93 degrees C. We developed estimation formulae for H1(R) for various kinds of rice, of which the determination coefficient was 0.86. It led to an easy and rapid assay method for the cooking properties of the various rice samples.

Automated summary

In this study, different heating and cooling programs were used to compare the pasting properties of various rice samples using a high-temperature-type Rapid Visco Analyzer. A new program at 120 degrees Celsius showed higher positive correlations with retrograded surface and overall hardness, absorbance of cooked rice, and resistant starch compared to the conventional program at 93 degrees Celsius. Estimation formulae were developed for predicting retrograded surface hardness for various kinds of rice, providing an efficient method for assessing the cooking properties of different rice samples.