Juliano et al. - 1993 - Grain Quality Evaluation of World Rices

Setback viscosity was viscosity cooled to 50 °C minus peak viscosity.
Amylograph consistency was viscosity cooled to 50 °C minus final
viscosity at 94 °C or the increase in paste viscosity during cooling. A
model VA 1 Viscoamylograph was used from 1962 to 1988, when a
Viscograph type VS6E with electronic thermoregulator was acquired.
Table 3 shows the typical Amylograph values for the various
amylose types.
Cooked rice hardness and stickiness
We measured cooked rice with an Instron model 1140 food tester as per
the method of Perez and Juliano (1979). Twenty grams of milled rice
was cooked in a predetermined optimum amount of water (26 ml for
waxy rice, 34 ml for low-amylose, 38 ml for intermediate-amylose, and
42 ml for high-amylose) in 150-ml beakers for 20 min in Toshiba RC4B
automatic electric cookers. There was an excess of 200 ml of water in the
outer pot, with four samples per cooker. Cookers were not disturbed
for at least 10 min after cooking. The cooked rice was then drained and
cooled in plastic bags. All samples since 1989 were cooked with 42 ml
water to obtain more consistent results among samples with borderline
amylose contents.
Duplicate 17 g of cooked rice were placed in the Ottawa Texture
Measuring System (OTMS) 50-cm 2 cell. It was modified with four side
liners to reduce the cell cross-section to 15% of the original (7 cm 2 ). A
2.2- × 2.5-cm plunger was used. Each sample was pressed with 145 g
weight for 1 min before extrusion. Hardness was the maximum force
(in kg) needed to extrude the rice through the cell’s 7-cm 2 perforated
base with 5.2 -mm diam holes at the crosshead speed of 10 cm/min
and the same chart speed. The 0-50 kg load cell was used. Hardness
values were 15% of the value obtained with the standard cell. An OTMS
10-cm 2 cell was used from late 1982 onward and hardness values were
multiplied by 0.7 to express them into kg/7 cm 2 .
For the stickiness test, cooked rice (17 g) was pressed onto the
platform with the OTMS plunger (6.9 × 6.9 cm) for 10s with a clearance
of 0.4 mm. This allowed the rice to squeeze out around the edges.
Stickiness, expressed in gram-centimeters, was the product of the force
in grams required to lift the plunger and the distance in centimeters
that the plunger traversed. It was measured directly by planimetry
from the Instron chart paper. The 0-5 kg load cell was used. Chart speed
was 100 cm/min and the crosshead speed was 5 cm/min.
Because of the very high correlation between amylose content and
Instron stickiness, few samples were measured after 1977-79. Due to
Materials and methods 9