TABLE OF CONTENT
1.1 CHAPTER
ONE INTRODUCTION
1.2 OBJECTIVES OF THIS WORK ARE
2.0 CHAPTER TWO LITERATURE REVIEW
2.1 ORIGIN OF RICE
2.1.2 FLOW CHAR ON RICE PROCESSING
2.1.3
NUTRITIONAL COMPOSITION OF RICE
2.2 NUTRIENTS
AND NUTRITIONAL IMPORTANCE OF RICE
2.3 COOKING
QUALITY
2.4 COOKING PROPERTIES OF RICE
2.4.1 COOKING TIME
2.4.2 VOLUME EXPANSION
2.4.3 GRAIN ELONGATION DURING COOKING
2.4.4 WATER UPTAKE
2.4.5
AMOUNT OF WATER-EVAPORATED DURING COOKING
CHAPTER ONE
INTRODUCTION
Rice
is the most important cereal for human consumption. It is the staple for over three billion
people, constituting over half of the world’s population (faostat 2006,
purseglove 1972)
Rice (oxyza sativa) is a staple food of
billions of people and is consumed mostly as intact except hulls, bran and
germ. It is food that is very rich in
carbohydrate and is also an important tropical cereal which also supplies a
quarter of the entire calorie intake of the human race. Rice is believed to have originated from south
Asia and Africa. Most cultivated
varieties of rice are in diploid species oryza sativa and oryza glaberin.
Rice is grown in all the ecological
and dietary zones of Nigeria, with different varieties processing adaptation
traits for each ecology (Sanni et al 2005).
Rice is an economic crop, which is important in household food security,
ceremonies, nutritional diversification, income and employment. It is utilized mostly at the household level,
where it is consumed as boiled or fried or ground rice with stew or soup. Rice is cooked by washing and boiling in
water which leads to loss of some nutrients.
The proximate composition of rice has been previously reported (Abulude
2004)
Despite the fact that different
varieties of rice are widely cultivated in Nigeria, for example, ‘Ofada’ and
‘Abakaliki’ rice , there is an up surge in the influx of foreign or imported
rice varieties into the country. A
popular foreign and parboiled rice variety in Thailand, widely consumed and
imported into Nigeria, is ‘Aroso’ rice
Starch have been widely used as thickeners for
many years. The primary sources of
starches are the corn, wheat, potato and tapioca. Rice starch are the little known secret of
the starch world comprising a very small percentage of the total starch usage.
(Swany 1982)
There are two types of starch in
rice, amylose and amylopectin. Amylose is a long, straight starch molecule that
does not gelatinize during cooking, so rice which contains more of this starch
tends to cook fluffy, with separate grains. Long grain white vice has the most amylase and the least amylopectin, so it
tends to be the fluffiest more when cool, going in tightly together and forming
crystals that melt when the rice is reheated Rice that that is high in amylopectin is a has a
lower glycemic index number (Bhattacharva 1997)
Amylopectin is a highly branched
molecule that makes the rice sticky when it’s released from the grain during
cooking. Medium grain rice has more amylopectin making it a good candidate for
visottos, salads and rice pudding, which are served cold. And short grain rice
has even more amylopectin and little to no amylose, so its used most often for
Asian cooking, when you want grains to be sticky so they are easier to eat with
chopsticks. Then there’s glutinous rice, which is vary sticky when cooked with
the highest amount of amylopectin and no amylose (Houston (1997)
Rice starch has by far the smallest
particle of all commercial starches. The average Rice starch granule is between
2-8 microns. rice starch is also known to have the whitest colour of all the
starches. Rice starch is easily digested. The relevant literature quotes a
digestibility rate of between 98 and 100%. Rice starch are known for the soft
gel and creamy mouthfeel. They have widely used as fat replacers in wide range
of food product, waxy rice starches can be used at low level in food to create
the sensation of richer and higher fat product.
The objectives of this work are to determine
(1)
Cooking properties of rice
(2)
Sensory evaluation on some rice varieties
(3) The amount of starch on different variety
of rice.
CHAPTER TWO
History of rice
Starting in 2500BC, rice has been a
source of food for people. Rice production originated in china, and was spread
to countries such as Srilanka and India. It is believed that rice was bought to
west Africa and Greece in 300BC, by Alexander the Great’s armies. In 800 AD.
People in East Africa traded with people form India and Indonesia and were
introduced to rice, it was a common belief in the middle Ages that rice fields
were a breeding ground for malaria. People believed that mosquito easily layed
their eggs in the water of the rice fields.
Rice was introduced to Greece and
neighboring Mediterranean (344-324B.C.E) and then gradually to Europe and
Africa (IRR 1997) there have been debates about the introduction to Asia rice
into Africa oryza sativa was believe to have been introduced to Africa
primarily from malayoolynesia a few centuries B.C.E or form sri Lnaka and
Indonesia. The other possibilities for the introduction of rice into Europe are
form Persia, Central Asia, or directly form China. Later the Portuguese brought
rice to Brazil and the Spanish introduced rice to Central and south America
Oryza Sativa was introduced to Egypt form India and finally to west Africa by
Portuguese spice traders between the 15th and 17th
century (Grist 1986).
Origin and diffusion of rice are
still unsettled (Huke 1990) Asian cultivated rice originated in the region from
south china to the changes ins south and south east Asia, including the river
valleys and deltas of the Brahaneputra of northern India, the irrawaddy of
Burma, the making of vietenam and the Yangtse of china based on the number of
wide rice specie and evidence of rice glumes in the burnt day from the late
Neolithic period (Ting, 1949) concluded that rice might have in south china and
spread northwards (Capeland 1924) and some Japanese rice scientists asserted that
rice might have originated from south or south east Asia, including India,
china, Thailand and Indonesia.
Thermolumine scene and carbon 14
test of the pottery shards with the imprints of rice grains in Thailand
indicates that rice could be dated back to at least B.C.E (IRR, 1997). The
second oldest pieces of archacological evidences for rice origin are from
maharaga of India (6500-4500 B.C.E) and pentonshan of china (7150-6250 B.C.E)
(Abro et al., 1999.
RICE VARIETIES
African
varieties: African rice (Oryza
glaberrima) new rice for Africa, ofada rice.
Austrilian
varieties: Amaroo, kyeema, langi and
opus e.t.c
Bangladeshi
varieties: chinigura, kalijira, kataribhog, payam rice, e.t.c
Cambodian
varieties: neangkhon, bonla pdao,
senkrob.
Canadian
varieties: wild rice e.t.c
Chinese
varieties: forbidden rice e.t.c
Indonesian
varieties: peta, Rajelele (Semi-aromatic) Temang gung black rice.
Iranian
Varieties: Domsianh, Binam, Hasani,
e.t.c
Italian
varieties: Arborio, ariete and
Baldo.
World wide there are more than
40,000 different varieties of rice, species name Oryza sativa. There are four
major categories of rice world wide indica, japonica, aromatic and glutious.
Improved varieties that have the following essential characteristics are, high
yields, good grains quality and resistant to rice blast disease most improved
varieties are also resistant and tolerant to drought, cool temperature, iron
toxicity in the soil (Odomena, 2006).
Nutritional composition of rice, rice,
white, long-grain vegetable, raw nutritional value of per 100g (3.502).
|
ENERGY
|
1,527K,
(365K CAL
|
|
Carbohydrates
|
80g
|
|
Sugars
|
0.12g
|
|
Dietary
fiber
|
1.3g
|
|
Fat
|
0.66g
|
|
Protein
|
7.13
|
|
Water
|
11.61g
|
|
Thiamine
(vitamin b1)
|
0.070lmg
(6%)
|
|
Ribo
flavine (vitamine B2)
|
0.0149mg
(1%)
|
|
Niacin
(Vitamin B3)
|
1.62mg
(11%)
|
|
Pantothenic
acid (B5)
|
1.014mg
(20%)
|
|
Vitamin
B6
|
0.164mg
(13g)
|
|
Calcium
|
28mg
(3%)
|
|
Iron
|
0.80mg
(6%)
|
|
Magnesium
|
25mg
(16%)
|
|
Phosphorus
|
115mg
(16%)
|
|
Potassium
|
115mg
(2%)
|
|
Manganese
|
1.088mg
(52%)
|
|
Zinc
|
1.09mg
(11%)
|
Source:
Usda nutrient database
Rice is a good source of protein and
a staple food in many parts of the world, but it is not a complete protein. It
does not contain all the essential amino acid in sufficient amounts for good
health.
Rice is rich in starch moderate in
protein, poor in fat, iron and calcium provides about 350 kcal (1.47m) per 100g
day weight (Wadswort 1993) Rice is a complete food, it does not contain some
amount of thiamin, riboflavin and niacin but lacks in vitamin (A,D,C) The level
of vitamin is considerably low in polished rice than in brown rice due to high
content of b- complete vitamin in the bran and germ that are removed during
milling.
SOURCE AND UTILIZATION OF STARCH
Starch
is one of the most important natural organic compound, abundant in nature. It
is found in the roots or fruits (Duprat et
al, 1980; Buleon et al., 1990).
The most common sources of food starch are corn, potato, wheat, tapioca and
rice (Woolfe, 1992; Henry and Westby, 1998). Developed countries (Canada, USA,
Europe and Japan) have 77% of the global starch market (Sansavani and Verzoni,
1998).
STARCH
Starch is a polysaccharide (meaning
“many sugars”) made up of glucose units linked together to form long chains.
The number of glucose molecules joined in a single starch hundred thousand,
depending on the type of starch. Starch is the storage form of energy for
plants, just as glycogen is the storage form of energy for animal. Starch
exists as granules varying in diameter from 2 to 130 microns. The size and
shape of the granule is characteristic of the plant from which it came and
serves as a way of identifying the source of a particular starch (Swamy 1982).
CHEMICAL COMPOSITION OF STARCH
Starch is predominantly composed of
two polysaccharides macromolecules, amylose (20-30%) and amylopectin (70-80%).
Amylose is mainly linear with very few branches, while amylopectin is highly
branched. The organization of amylopectin and amylase is the basis for the
semi-crystalline structure of the starch granule (Bell et al., 1998). The ratio
of amylose to amylopectin is one of the key factors determining industrially
important properties.
CHEMICAL STARCH MODIFICATION
Starch modification is the changing
of starch so that it obtains the characteristics that deviate from the nature
starch. The products are called derivatives. Chemically modified starches are
starches that have been modified with chemicals.
TYPES OF STARCH MOLECULES
- amylose
- amylopectin
Amylose averages 20 to 30% of the
total amount of starch in most native
starches. There are some starches, such as waxy starch, which contain only
eamylppectin. Others may only contain amylose. Glucose residues united by a 1,4
linkage form the linear chan molecule of amylose. Amylose is the linear
fraction and amylopectin is the branched
fraction. The is because the linear chains can orient parallel to each
other, moving close enough together to bond. Probably due to the ease with
which they can slop past each other in the cooked paste, they do not contribute
significant to viscosity. The branched amylopectin molecule give viscosity to
the cooked paste. This is partially due to the role it serves in maintaining
the swollen granule. Different rice have different relative amounts of amylose
and amylopectin. These different proportions of the two types of starch within
the starch grains of the plant give each starch it’s characteristic properties
in cooking and gel formation.
Rice starch composes approximately
90% of milled rice. It is made up of two
major glucose polymers, amylose which is a slightly branched, primary long
chain and amylopectin, which is highly branched. The amylose content of rice
starch ranges form 0 to 30% (w/w) cooked rice texture and rice starch
functional properties are reported to be primarily impacted by amylose content
(Bhatta charya, soubhagy. Indudhara swamy 1982)
STARCH PROPERTES
Because
of its structure starch bears some special properties which make it a unique
natural polymer. The following list contains the most important properties of
starch, which are highly dependent on the origin and the chemical.
Physical modification of the polymer
- thickener
- Rheology enhancer
- Film former
- Sticking – adhesive (cohesive
- Water binding capacity
- Water retention
- Flocculent
- Shear stability
(Muhrbek 1987 )
Starch components and molecular weights
of rice oryzenin
|
Rice
|
Mx105
|
Rice
|
Mx105
|
|
Oryzenin
(protein medium – grainrice)
|
|
Medium
- grainrice
|
|
|
Control
4c
40c
|
1.03
1.12
2.01
|
Control
4c
40c
|
29.9
31.0
32.0
|
|
|
|
|
|
|
Long
grain rice
Control
4c
40c
|
1.22
1.44
2.01
|
Long
grain rice
Control
4c
40c
|
25.2
25.6
31.2
|
|
Amylase
|
|
Starch
|
|
|
Medium-grain
rice
|
|
Medium-gran
rice
|
|
|
Control
|
1.24
|
Control
|
24.9
|
|
4c
|
1.18
|
4c
|
25.3
|
|
40c
|
1.03
|
40c
|
27.5
|
|
|
|
|
|
|
Longer
grain rice
|
|
Long
grain rice
|
|
|
Control
|
1.55
|
Control
|
19.7
|
|
4c
|
1.46
|
Control
|
20.3
|
|
40c
|
1.10
|
40c
|
22.7
|
(sources
J. Chrastil, 1990)
Starch composition of milled rice
largely determines the cooking and eating characteristics of rice. Starch
consists of amylase and amylopectin. Amylase is a long, straight starch
molecule that does not gelatinize during cooking long grain white rice has the
most amylase and the least amylopectin. Amylopectin is a highly brached
molvecue that makes the sticky when it’s released from the grain during
cooking. Medium grain rice has more amylopectin.
Rice can thus be generally
categorized into
1. Waxy
(or glutinous) rice, which is mainly amylopectin and has an opaque endosperm.
These high amylopectin starches endosperm. These high amylopetin starches are
available with a range of viscosity and stability characteristics
2. Non-waxy
rice, which is mainly amylase and usually has a translucent endosperm.
Volume expansion and water
absorption of milled rice during cooking increases with increased amylase
content. Cooked high-amylose rice is less tender, but drier and flakier (not
sticky) than intermediate or low amylase rice, but becomes harder on cooling.
After cooking, low amylase rice remain glossy, stocky and moist (Damion and
Ben, 2006)
Amylose content (Effect of Cooking)
This is considered one of the most
important quality factors of rice since it is known that amylase content is a
good index of water absorption and textural properties of rice. The texture of
cooked rice and its gloss are principally determined by the amylase,
amylopectin ratio of the starch. Increasing the amylase content improves the
capacity of the starch granule to absorb water and expand in volume without
collapsing because of the greater capacity of amylose to hydrogen bond or
retrograde. Thus, the amylase content is an index of resistance to
disintegration during cooking. It has been shown that an increase in amylose
content improves the firmness of cooked parboiled rice, the correlation
coefficient ® between amylase content and firmness being 0.62. amylase content
of milled rice is determined by the colourmetric method is the starch-iodine
blue test which is used for screening amylose content of sample with less than
30% amylase. The most widely used method involves digesting 100mg of rice flow with lml, 95% ethanol and
9ml of NaoH heating the sample for 10m in a boiling eater bath and diluting the
gelatinized starch with distilled water, 5ml of the starch solution is pipettes
into a 100ml volumetric flask lml of in acetic acid and 2ml of iodine solution added made up to volume
and absorbance read at 620m. amylose content is determine by reference to a
standard curve.
The
amylase content of some Nigeria rice varieties has been shown to very between
19% and 28%. Various workers have shown that parboiling does not effect the
amylase content of rice (Adeyimi 2006)
Amylose content affects rice cooking and
eating quality
|
Amylase
content
|
Term
|
|
0.2%
|
Waxy
|
|
8.20%
|
Low
amylose
|
|
21.-25%
|
Intermediate
|
|
>25%.
|
High
amylose
|
- 100
amylose rice are moist, skicky, and glossy hen cooked
- They spit and disintegrate when over
cooked
- High
amylase rice cook dry and fluffy but become hard when cool
- Intermediate
amylose rice are fluffy when cooked and remain soft when cool(Andrew 2006)
EFFECT
OF COOKING
Cooking quality is one of the
important aspects of food quality. However, nutrition’s a food material may be,
it will not be accepted by the consume unless it satisfies specific culinary
characteristic amylose dispersion is responsible for greater absorption and
retention f water and thus the expansion of rice grain (Chungcharoen 1987).
GRAIN SHAPE
Long Grain
The category known as long grain
contains milled rice that is approximately three times longer than it is wide.
A conventional U.S long grain rice has an intermediate gelatinization
temperature and from 19 to 23% apparent amylose content (Houston 1972).
After cooking it is firm and fluffy,
consumers in areas of the world such as North and South America, southern
China, Europe, and the middle East often prefer this type of rice. California
long grain rice generally has slightly highly apparent amylose content and
lower gelatinization temperature compared to southern grown U.S long rice.
Medium Grain: The medium grain rice category describes milled rice
that is from 2.1 to 2.5 times longer than it is wide U.S. medium grin rice
after cooking is soft, moist and sticky in texture. This type of rice is in
general preferred by people from Japan, Northern China and North and south
Korea (Houston 1992) medium grain rice is generally lower in amylose content
and has a lower gelatinization temperature compare to U.S conventional long
grain
Short Grain: Rice that is
less then two times longer than it is wide classified as short grain. In general
short grain rice has cooking quality, amylose content and gelatinization
temperature similar to that of rice in the medium grain category. Because this
type o rice is used for making sushi some call it sushi rice.
RICE PRODUCTS
Virtually all the rice produced in
Nigeria is used for human consumption. The increase in consumption has been
predicted to continue at a rate faster than the rate growth in population rice
apart form being eaten as a while grain can be used in food industry in the
processing of some products such as infant foods, break fast foods, snacks,
rice flour and for production of alcoholic beverages such as beer and rice wine
etc (Ihekoronye and Ngoddy 1985)
Break fast food and baby foods” rice
are pre-cooked, dried, flaked formed and expanded and toasted into ready to-eat
break fast foods. The rice flour can be made into baby food since is absolutely
gluten free. Some people are allergic to gluten and may turn rice based product
(wade 1972).
Noodles: The resultant rice flour can equally be made into
noodles, a mixture of rice and egg being
made into dough and expressed through holes. The noodle is improved by the use
of local gums, okra gums and gum Arabic (NIFEST, 1999).
Beverages: Various
aleoholic beverages are manufactured From rice. Rice is also used in the
brewing industry for the manufacture of beer and in the production of wine.
(Yashizawa and Kishi 1985)
RICE QUALITY
Rice breeders considers rice quality
as the most important factors after yield, that determine the accept ability
and price of processed rice. The physio-chemical characteristics of rice
determine it quality. The term quality refers to milling quality appearance and
market acceptability, cooking eating qualities. Storage and nutritional
quality. Rice quality changes continuous through the entire post-harvest
system. Some of the changes are negative, but grain milling quality can also
improve during storage (Bradley, 2007).
FACTOR AFFECTING QUALITIES OF RICE
Rice qualities are affected by many
factors, which may vary according to the standard on which it will be sold
(grist 1986). The degree of milling, percentage of damage kernel and percent of
broken are all important factors.
Milling degree: Milling degree is an
important factor for quality. This depends on the size and shape, i.e on the
variety, conditions under which it was grow, the degree of ripeness and amount
of exposure. Milling removes the bran layer. Rice bran is about 20% oil and is
subject to very aggressive enzyme activity.
Broken Rice: Broken rice get soft and mushy cooked from a
nutrition standpoint, broken are the same as whole grain. But the texture is
poor and broken tend to have more bran, which affect flavour (Liu et al., 1998).
Nature of Starch: The nature of
the starch affects texture and retro graduation properties of rice. The nature
of rice starch differs depending on variety, growing area, and crop year. There
are two different types of starch. Amylose is a long chained starch without a
lot of branding and amylopectin is a shorter but much more highly branched
chairs of element.
The amylopectin/amylose ratio does
not exist a very important factor.
Age of Rice: Age creates
changes in nature of starch. Rice gets harder with age as if the percentage of
amylose is increasing. The rice gets former and less sticky most older rice
losses moisture and so the cracking problem during cooking occurs if there is
any brain on the surface of the rice due to loose milling, then rancidity
problems causes poor flavour.
Moisture: The moisture
of the rice prior to cooking also affects texture. If the moisture is below 13%
the quick involvement of water will cause cracking. The lower the moisture, the
greater the cracking. Rice that cracks will have a poor cooking texture.
Cracking of Rice: This is
probably the biggest factor affecting the quality of cooked rice. The quick
migration of moisture through rice causes cracking kernel. Quick changes in
temperature can cause cracking. The cracking can occur in milling where milling
temperature gets high or as a result of pressure applied in milling. Also
cracking releases enzymes that affect flour.
CHAPTER THREE
MATERIAL AND METHOD
Different varieties of Rice (Oryzae
Sativa) will be gotten from the Abakaliki rice mill. They will be packed and
representative samples will be drawn from the bagged sample from distal, middle
and proximal end using a sample probe. The sample will be analysed for starch
content, amylose and amylopectin determination e.t.c.
Chemical Analysis
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
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
Protein Determination
The crude protein in the sample were
determined by the routine semi-micro Kje ideahl, procedure/technique as
described by (AOAV 1984)
0.5ml of each finely ground dried
sample was weighed carefully into the kjeldahl digestion tubes to ensure that
all sample materials got to the bottom of the tubes. To this were added
lkjeidah catalyst table and 10ml of conc. H2Co4. these were set in
the appropriate hole of the digestion Block heaters in a fume cupboard. The
digestion was left on for 4 hours, after which a clear colourless solution was
left in the tube. The digest was cooled and carefully transferred and made up
into 100ms volumetric flask, it was distilled and filtered. Thoroughly rinsing
the digestion tube with distilled water
and the flask was made up to mark with distilled water.
The percentage nitrogen in this
analysis was calculated using the formula.
%
N = Titre
value x Atomic mass of nitrogen x Normality of HCL used X 4
The crude protein content is determined by multiplying
percentage nitrogen by a constant factor of 6.25 i.e. % N x 6.25.
EXTRACT DETERMINATION.
The crude fat was determined using
AOAC (1984) method. 1 gm of each dried sample was weighed into fat extraction
thimble and pug lightly with cotton wool. The thimble was placed in the
extractor and fitted with reflux condenser and a 250ml soxhlet flask which has
been previously dried in the oven, cooled in the desiccater and weighed. The
soxhlet flask is then filled to ¾ of its volume with petroleum ether (b.pt. 40
-600C) and the soxhlet flask. Extractor plus condenser set was
placed on the heater. The heater was put on for six hour with constant running
water form the tap for the ether to boil gently. The Ether is left to siphon
over several times soy over at least 10-12 times until it short of siphoning.
It is after this is noticed that any ether content of the Extractor is
carefully drained into the ether stock bottle. The thumble containing sample is
then removed and dried on a clock glass on the bench top. The extractor, flask
and condenser is replaced and the distillation continues until the flask is practically
dry. The flaks which now contains the fat or oil is detached its exterior
cleaned and dried to a constant weight in the oven. If the initial weight of
dry soxhlet flask is wo and the final weight of oven dried flask + oil (fat is
w1, percentage is obtained by the formula:
W1 – wo x 100
Wt
of sample taken 1
ASH DETERMINATION
The method described by Pearson.
(1980) was used 2.og of the sample was gently weight into a clean curable. The
sample was then gently heated in a murtle furnace at a temperature of 5500C
for 3 hours all the organic matter was burn off leaving a white grey ash. The
curable was placed in a desiccators to cool and weight was taken again. The
percentage ash content was calculated.
%
Ash w3 - w1
W2
- w2
W1 = weight
of empty curable
W2 = weight
of crucibles + sample
W3 = weight
of curable + Ash
MOISTURE CONTENT DETERMINATION
The moisture content was determined
using AOAC (1984) method. The hot even method is used in the moisture content
determinations. Petri dishes were washed and properly dried in he oven at 1000C
for a period of 30 mins and cooled in a dessicator. The weight of the Petri
dishes were determined by using the mettler weighing balance and labeled (w1)
5.g of the rice samples is carefully weighed into the dishes reweighed (w2)
and put in the oven at 1000C for 3 hours after which it is removed
cooled in the dissector and weighed again (w3)
The percentage moisture is
calculated form the weight loss of the sample
Thus % moisture
Wt
of dish + sample – wt of dish + sample after
x 100
Wt
of sample 1
Mathematically w2 - w3 x 100
w2 - w1 1
= Difference in weight x 100
Weight of sample 1
= Difference in weight x 100
Weight of sample 1
Physical Analysis
Sensory evaluation
Sensory
evaluation of the cooked rice varieties was carried out of 20 untrained
panelists in a special room prepared for the purpose (Ebuehi et al., 2004) they were instructed to
taste the rice sample and to rinse their mouth after each sample taste. 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.
Cooking Properties
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
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
Increased method
The volume of cooked and raw rice
was measured by water displacement method
- weight
20g of raw rice into a graduated cylinder containing 100ml of distilled water
and the change in volume noted.
- 20g
of the cooked rice of which the water used in cooking have completely drained
off is put into a cylinder containing distilled waters and change in volume
noted. It is determined using the expression increase in = volume displaced
after cooking – volume displaced by
raw sample.
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).
LENGTH AND WIDTH RATIO
The method of Singh et al (2004)
shall be used. Length and width wise arrangement of milled rice shall be done
and their cumulative measurements (1nmm) shall be taken. The value L/W shall be
determined by dividing length width. A mean of 10 replication will be reported.
VOLUME EXPANSION
The volume of cooked and raw rice
shall be measured by water displacement method. 5g of raw rice shall be placed
in a graduated cylinder containing 25ml of distilled water and the change in
volume will be noted.
The 5g of the cooked rice after
which the water used in the cooking is completely drain off and the cooked
sample shall be place in the cylinder containing the same 25ml distilled water
and change in volume shall be measure.
Volume expansion is determined using
expression
Volume
expansion = volume displaced after cooking – volume displaced by raw
sample.