IRRI SERVICE LABORATORIES

provides quality and efficient integrated laboratory testing services and expertise

Viscosity

An aqueous suspension of a ground sample of rice flour is prepared in the disposable canister and placed into the Rapid Visco Analyser (RVA, Newport Scientific Pty. Ltd), which simultaneously heats and stirs the contents. The starch in the heated sample gelatinizes and forms a continually changing paste, which is monitored, resulting in a pasting curve. Rice starch granules are generally insoluble in water below 50 °C.


The maximum viscosity during heating (peak viscosity), minimum viscosity after the peak (trough), final viscosity (FV), and their relationship provide an indication of the pasting properties of the flour sample tested and hence, its processing value for different purposes.

Breakdown = Peak – Trough

Lift off/Setback from trough = Final – Trough

Setback from peak = Final – Peak


The setback (final minus peak viscosity) is considered as an indicator of the firmness of cooked rice with higher values, indicating firmer texture.


The RVA is used to determine the pasting quality of rice, which can vary significantly between different varieties. Each year, a selection of the milled late-generation breeding lines is screened with this test. The RVA is also used to make hot water-soluble amylose.


Note: To determine viscosity, the sample weight required is at least 10 g of rice flour placed in a plastic bottle. In order to keep the integrity of the customers' samples, senders are requested to place them in secure plastic boxes.

References:
RVA-software manual Thermocline for windows. Version 2.4, Sept. 2004. Copyright Newport Scientific Pty. Ltd. 1999.
AACC Approved Methods 11th edition, 61-02.
Sreenivasulu, N. (2018). Rice Grain Quality: Methods and Protocols. New York, NY: Humana Press.