Cereals processing technology

Table 5.2 Physicochemical (quality) characteristics of conventional cooking and
processing long-, medium-, and short-grain rice types
Milled rice Conventional cooking and processing type
characteristics Long Medium Short
Apparent amylose content, % 21–23 15–20 15–20
Alkali spreading value, average 3–5 5.5–7 5.5–7
Gelatinization temperature, a ºC 69–72 64–48 64–68
Gelatinization temperature type Intermediate Low Low
Protein (N 5.95), % 6–8 6–8 6–8
Amylographic paste viscosity, BU b
Peak 650–850 700–900 700–900
Hot 350–400 350–400 350–400
Cool 650–850 650–800 650–800
Breakdown 300–400 350–450 350–450
Setback 150– ‡250 250– 50 250– 50
a Amylographic gelatinization temperature.
b Bu = Brabender units.
Rice production 85
in contact with dilute alkali (indicative of intermediate-gelatinization-temperature
types), and intermediate gelatinization temperatures (69–73ºC). Amylographic
pasting characteristics of typical long-grain varieties usually show
intermediate peak viscosities and relatively high paste viscosities on cooling to
50ºC.
In the United States, specific chemical and physical criteria are used to
describe cooking and processing qualities desired in new varieties of each grain
type. These criteria, based on a series of physicochemical tests, collectively,
serve as indices of rice cooking and processing behavior. New varieties under
development are systematically tested for apparent amylose content, the alkali
spreading reaction of whole-kernel milled rice in contact with dilute alkali, an
indirect measure of gelatinization temperature, amylographic gelatinization and
pasting characteristics. Average and range of test values for these characteristics
are established for commercially acceptable varieties. 32,33
Chemical and physical characteristics of new varieties are always compared
with those of comparably grown leading commercial varieties of appropriate
grain type. If, after a number of years at several locations, properties of new
varieties are similar or superior to those of standard varieties, they are judged to
have satisfactory or superior cooking and processing quality; if not, they are
considered undesirable or of unknown quality.
Typical medium- and short-grain varieties for cooking and processing are
characterized by relatively low amylose content, extensive reaction of wholekernel
rice in contact with dilute alkali, and relatively low gelatinization
temperatures (69–73ºC). Amylograms of typical medium- and short-grain
varieties usually show relatively low cooked paste viscosities on cooling to
50ºC.