Determining the gelatinization temperature of milled rice flour

Jennifer M.C. Dang (1) and Mark L. Bason (2)
Perten Instruments of Australia, 13/2 Eden Park Drive, Macquarie Park NSW 2113, Australia
(1) jdang@perten.com, (2) mbason@perten.com

Summary of the AACCI Approved Methods Technical Committee Report: Collaborative Study on a Method for Determining the Gelatinization Temperature of Milled Rice Flour Using the Rapid Visco Analyser (1).

Gelatinization temperature (GT) is commonly measured to assess the cooking and processing quality of rice. Traditional methods of estimating rice GT using the amylograph and differential scanning calorimetry (DSC) are time-consuming and, in the case of the amylograph, require large quantities of samples, which is not well suited to rice breeding requirements. The Rapid Visco Analyser (RVA) is commonly used in laboratories to measure the pasting properties of rice and provides the advantages of speed, ease of use and small sample size requirements.

A faster and simpler method to accurately determine rice GT using a small quantity of sample has been sought by rice breeders and others in the industry. A collaborative study was conducted by the AACCI Rice Milling and Quality Technical Committee to assess a new method optimized for determining the GT of milled rice flour using the RVA.

Twelve laboratories analyzed three rice flour samples (Pecos, Dixiebell and Jacinto), representing low-, medium- and high-GT varieties, to evaluate the performance of the method. In addition, seven laboratories returned amylograph data and six returned DSC data. Analysis of variance was performed on the data to obtain precision statistics for the method.

The RVA GT method involved holding a concentrated slurry of rice flour (6.00 ± 0.01 g, corrected to 12% moisture basis) in 24.0 ± 0.1 g of distilled water at 50°C for 5 min, heating it from 50 to 95°C at 3ºC/min (Table 1), and measuring the viscosity of the sample throughout. The GT, observed at the point of rapid increase in viscosity, is defined as the temperature at which the viscosity first increases by at least 24 cP (=24 mPa.sec = 2 Rapid Visco units [RVU]) within 6 sec (Figure 1). Because high viscosities were obtained, the tests were manually stopped when viscosity reached ≈1,200 cP (100 RVU), which occurred between 10 and 15 min into the test.

Table 1. Test configuration for the RVA GT methoTable 1. Test configuration for the RVA GT method
a12 cP = 1 Rapid Visco Unit (RVU) 

RVA Figure 1
Figure 1. Example of rice flour testing using the RVA method

Within-laboratory repeatability (Sr) values were ≤0.15ºC for the method and between-laboratory reproducibility (SR) values were ≤0.25ºC (Table 2). RVA GT results were similar to but more precise (lower RSDr and RSDR for each sample and overall) than those obtained from parallel testing using the amylograph and DSC (Table 2).

The RVA method showed good precision for use in determining the GT of milled rice flour, and has been approved as official AACCI method 61-04.01 (2). The method is simple to perform, rapid and requires only a small amount of sample, making it well suited to the requirements of rice breeders.

Table 2. Precision statistics for the gelatinization temperature of rice flour by RVA, Amylograph and DSC methods a,bTable 2
aAmylograph and DSC results are included for comparison.
bSr = repeatability standard deviation (ºC), RSDr = repeatability relative standard deviation (%), SR = reproducibility standard deviation (ºC), RSDR = reproducibility relative standard deviation (%), GT = gelatinization temperature (ºC), To = gelatinisation onset temperature (ºC).

References

1. Dang, J.M.C., and Bason, M.L. 2014. AACCI Approved Methods Technical Committee Report: Collaborative Study on a Method for Determining the Gelatinization Temperature of Milled Rice Flour Using the Rapid Visco Analyser. Cereal Foods World, 59(1): 31–34.

2. AACC International. Approved Methods of Analysis, 11th Ed. Method 61-04.01. Gelatinization Temperature of Milled Rice Flour. AACC International: St. Paul, MN, U.S.A. http://dx.doi.org/10.1094/AACCIntMethod-61-04.01.