Nine Rice varieties (IRR8, CP306, FARO
15, IRR8, MARUWA, were gotten from the Abakaliki rice mill. The sample were
analysed for their starch, amylose and amylopectin contents, cooking and
sensory qualities.
3.1 CHEMICAL
ANALYSIS
3.1.1 DETERMINATION
OF STARCH CONTENT
The method described by Onwuka,
(2005) will be use to determine the starch content of the sample.
Procedure
Two
point five grammes (2.5g) of the samples with 50ml cold water will be mixed.
After allowing it to stand for one hour (1hr), 20ml concentrated HCL and 150ml
distilled water will be added, then refluxed for 2hrs in a 250ml round bottomed
flask, 5N NaoH will b used to cool and neutralize the mixture, distilled water
will be used to make up the mixture of the mark.
The glucose content will be
determined using anthrone reagent.
Series of glucose solution will be
prepared such that 1ml contains 0.04-0.2mg, these solutions will be used to
calibrate the glucose stand and curve.
Five
milliliter (5ml) of anthrone reagent will be added to 1ml each of standard
solution and a test sample in test tubes and then will be mixed properly.
The tubes will be covered and boiled
in water bath for 20 minutes for the odour to develop. The tubes will be cooled
and the absorbance will be read/red at 620nm against a blank containing only
1ml of water and 5ml of anthrone reagent.
The concentration of the test sample
will be obtained by calculation involving the concentrations and dilutions made
the mass of starch will be consequently obtained from the mass of glucose using
the relation.
Mass
of glucose x 0.9 = mass of starch
3.1.2 AMYLOSE AND AMYLOPECTIN CONTENT
DETERMINATION
The method of Juliano (1971) will be
used. 0.1g of starch will be weighed into a test tube, 1ml of 95% ethanol and
9ml 1N NAOH will be added. The mouth of the tube covered with paraffin to mix
content very well. 0.5ml of aligout will be used in the analysis. 0.1ml of
acetic acid solution and 0.2ml of solution shall be added to make up 10ml of
9.2ml of distilled water and allowed for 20minutes for colour development and
the % amylose shall be calculated as follows.
%
amylose =%Amylose of standard x Absorbance of sample
Absorbance of standard
% Amylopectin = 100 - % Amylose
3.2 PHYSICAL ANALYSIS
3.2.1 SENSORY
EVALUATION
Sensory
evaluation of the cooked rice varieties were carried out 20 untrained panelists drawn from amongst the
students of the department of food science and Technology. in a special room
prepared for the purpose They were requested to express their feelings about
the sample by scoring the following attributes: colour, odour, texture and
taste. Sensory scores we based on a nine point hedonic scale, where 1 is
dislike extremely and 9 is like extremely(Ebuehi et al., 2004).
3.3 COOKING
PROPERTIES
3.3.1 COOKING
TIME
Using Anonymous (1997) method the
cooking time was determined.
- weight 5g of the sample into a beaker
containing 25ML distilled water.
- Note the time cooking stated and the
time it ended.
Cooking time = time cooking - time cooking
(minutes) ended Started
3.3.1 Solids
in Cooking water
This was determined by drying an
aliquot of the cooking water in a tarred evaporating dish to evaporate the
water as steam. The weight of the empty Petri dish was measured and recorded (W1).
This was followed by measuring the weight of the Petri dish and aliquot (W2).
The weight of the Petri dish and the dry aliquot was measured (W3),
The amount of solid in cooking water of empty Petri dish, W2 =
weight of empty dish + dry aliquot (W3).
3.2.2 Grain
Elongation during Cooking
This was determined by first
measuring the initial grain length (Lo) before cooking. The final length (LO)
after cooking was then measured. the grain elongation during cooking was then
calculated as: L1 – Lo, where Lo = initial grain
length before cooking, l1 = final length after cooking.
3.3.3 Gelatinization
time and Gelatinization
temperature
- 2og of the samples is weighed and
poured into 100ml distilled water in a measuring cylinder after which it is
transferred quantitatively into a beaker and heated in a heater that is set at
its maximum range of 10.
The heating continues until the
sample gels and the temperature at which is started gelling was determined by a
thermometer and recorded as the gelatinization temperature.
- The
difference between the time cooking started to the time at which gelatinization
occurs is gelatinization time.
- Water
Absorbed During Cooking the drained cooked sample is weighed
using mettler balanced to determine the water absorbed during cooking. The
difference in the weight of sample after cooking and that before cooking is
taken as the water absorbed during cooking water absorbed
= weight
of - weigh of
Cooked sample fresh
sample
3.3.4 LENGTH AND WIDTH DETERMINATION
The method of FAO (1985) shall be
used 10g of the milled raw rice shall be bulk together. It will be picking at
random and a representative sample shall be selected. Length and width shall be
measured using vernier caliper calibrating in millimeter (mm).