Transcript Document

Course
Module 6
Lesson 1
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
What are the three chemical characteristics of milled rice that determine quality?
Gel consistency
measures the
tendency of the
cooked rice to
harden on cooling.
Gelatinization
temperature
determines the
time required for
cooking the rice
High amyclose content?
Rice grains cook dry, are less tender, and
become hard upon cooling.
Low-amylose content?
Rice grains cook moist and are sticky
Course
Module 6
Lesson 1
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
What are the three chemical characteristics of milled rice that determine quality?
FREQUENTLY ASKED QUESTIONS (FAQs)
1.
What are the specific physicochemical tests used
to determine the cooking and eating qualities of
rice?
•
•
•
•
•
Alkali test
Amylose test
Gel consistency test
Kernel elongation test
Aroma test
Course
Module 6
Lesson 1
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
What are the three chemical characteristics of milled rice that determine quality?
FREQUENTLY ASKED QUESTIONS (FAQs)
2.
Why is endosperm appearance a major breeding
consideration?
The appearance of milled rice is important to the consumer,
which makes it also important to the producer and the miller.
The consumer prefers rice with a clear endosperm and pays a
premium rice for it, even though capacity disappears during
cooking and does not affect eating quality. Grain with opaque
areas in the endosperm, caused by the loose packing of the
starch and protein particles, breaks more readily during milling
than clear grain, greatly reducing its market value.
Course
Module 6
Lesson 1
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
What are the three chemical characteristics of milled rice that determine quality?
FREQUENTLY ASKED QUESTIONS (FAQs)
3.
Of what importance are grain length, shape and
endosperm appearance to the breeder?
Most breeders attempt to estimate the milling behavior of
pedigree selections n the basis of grain length and shape
and on endosperm appearance. Grain traits that
contribute to increased breakage, singly and in
combination with other traits, include grain length,
excessively slender or bold shape, partial flatness, and
appreciable white belly.
Course
Module 6
Lesson 1
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
What are the three chemical characteristics of milled rice that determine quality?
FREQUENTLY ASKED QUESTIONS (FAQs)
4.
How does the limited association of gelanization
temperature and amyclose content help the
breeders?
It allows the breeders, in certain cases, to use the
simple gelatinization temperature test to estimate the
amylose content, which is considerably more difficult
to measure directly.
Course
Module 6
Lesson 1
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
What are the three chemical characteristics of milled rice that determine quality?
FREQUENTLY ASKED QUESTIONS (FAQs)
5.
How is gelatinization temparature related to the
physical cooking properties of rice?
Gelatinization temperature directly affects the physical properties of the starch
granule, which in turn influences the quality ratings of cooked rice. Rice with a
high gelatinization temperature becomes excessively soft and tends to
disintegrate when overcooked. Under standard cooking procedures, this type of
rice tends to remain undercooked. It requires more water and time to cook than
those with low or intermediate gelatinization temperature. Thus, gelatinization
temperature correlates positively with the time required to cook rice. Soaked
milled rice of high gelatinization temperature elongates less during cooking than
rices with low or intermediate gelatinization temperature.
Course
Module 6
Lesson 1
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
What are the three chemical characteristics of milled rice that determine quality?
FREQUENTLY ASKED QUESTIONS (FAQs)
6.
Why test for gel consistency?
Varietal differences in gel consistency exist among varieties
of similar high amylose content (more than 25%). The gel
consistency test separates the high-amylose rices into three
categories:
• very flaky rices with hard gel consistency (length of gel
= 40 mm or less)
• flaky rices with medium gel consistency (length of gel =
41 to 60 mm)
• soft rices with medium gel consistency (length of gel >
61 mm).
Course
Module 6
Lesson 1
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
What are the three chemical characteristics of milled rice that determine quality?
FREQUENTLY ASKED QUESTIONS (FAQs)
7.
Why should paddy rice be stored for at least 4
months after harvest before tasting panels evaluate
promising lines?
Aging increases water absorption and volume expansion during cooking,
resulting in a more flaky cooked rice than freshly harvested grains.
Course
Module 6
Lesson 2
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
Why is amyclose content important and how is it measured?
If
then
Amylose content
is high,
the rice grains will show high volume expansion
(not necessarily elongation) and a high degree
of flakiness. The rice grains cook dry, are less
tender, and become hard upon cooling.
Amylose content
is low,
the rice grains will cook moist and sticky.
Course
Module 6
Lesson 2
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
Why is amyclose content important and how is it measured?
CLASSIFICATION RANGES
20-30% amyclose
content is classified as
High
25% amyclose content is classified as
Intermediate. Intermediate amyclose rice is
preferred in most rice-growing areas of the
world except where low -amyclose japonicas
are grown.
10-20% amyclose
content is classified as
Low
Course
Module 6
Lesson 3
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
Why is gelatinization temperature important and how is it measured?
Gelatinization
temperature determines
the amount of time it
takes for a particular
variety of rice to cook.
Course
Module 6
Lesson 3
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
Why is gelatinization temperature important and how is it measured?
High
Varieties with a gelatinization temperature greater than 74°C. If
GT is very high, then the rice will become excessively soft and
disintegrate when overcooked. It will also require more cooking
and water than rice with a lower GT.
Intermediate
Varieties with a gelatinization temperature
between 70°C – 74°C. Most tropical Indica
varieties have intermediate or low
gelatinization temperature.
Low
Varieties with a gelatinization
temperature below 70°C. Most
Japonica varieties have a low
gelatinization temperature.
Course
Module 6
Lesson 4
:
:
:
Grain Quality
Determining the Chemical Characteristics of Milled Rice
Why is gel consistency important and how it is measured?
Hard and soft gel consistencies
Gel consistency
If
then
Classification
Length of gel (mm)
Gel
consistency
is hard,
the cooked rice tends to be less
sticky. Harder gel consistency is
associated with harder cooked rices
and this feature is particularly evident
in high-amylose rice.
Hard
27-35
Medium Hard
36-40
Medium
41-60
Soft
61-100
Gel
consistency
is soft,
the cooked rice has a higher degree
of tenderness. This is a preferred
characteristic