Evaluation of Cooking, Minerals and Starch Characteristics of Some Rice Varieties

Evaluation of Cooking, Minerals and Starch Characteristics of Some Rice Varieties from Ishiagu Ivo Local Government Area of Ebonyi State

Rice (oryza sativa l) is the main staple food for two third of the world population providing 21% of global dietary energy,14% of protein and 2% of fat(Kennedy and Burlingame 2003).It is primarily utilized for its starch content which is approximately 90% of dry grain weight (Bao et al 2004,Patindol and Wang 2002).Among the major cereal grains, rice is the only grain that is widely eaten as a whole grain after cooking. Generally most is consumed as

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cooked intact grains (Kang et al 2006).According to Gumarnaes et al (2006) rice is hydrophilic specie adapted to a number of ecosystems. It is grown in many countries of the world. In addition to its social importance, it plays an important role in human nutrition as well as agricultural economics.

Pomeranz (1992) reported that rice composition differs according to the variety and processing method used. The texture of cooked grain influences the palatability and thus acceptability to consumers (Kang et al 2006).cooking of milled rice is one of the most important processing step that is done to provide desirable texture in the kernel prior to eating (Yadaw and Jindal 2007).Cooking of milled rice involves the use of water for washing off dirt and boiling of the rice for some minutes at a certain temperature. Starch, protein and lipids are the main rice grain component that affects cooking and eating quality(Kelvin and Blanchard 2002).

Blakeney et al (1996) reported that cooked rice textural properties can differentiate the degree of hardness of the cooked rice similar to that perceived during chewing. The swelling volume reflects water-holding ability of starch and has become a rapid, small scale method to predict the eating quality of wheat, rice and starch noodles. The thermal properties can stimulate the rice cooking and yield valuable information to the rice processor. Quality acceptability and shelf life of starch containing food are profoundly affected by starch retrogadation.

According to Frie (2003) rice starch is usually digested quite rapidly, compared to other starchy foods such as noodles, sweet potato or cassava. This leads to a prompt and pronounced increase in blood glucose level (high glycemic index) after ingestion of rice similar to that of white bread or pure glucose. Because of the widespread use of rice starch in food and non-food industries, the processing quality of rice starch is also an important factor in the assessment of starch functionality. Like other cereal starch, rice starch is composed of linear chain of & 1-4 linked glucose and amylopectin which has &1-6 branches in addition to the & 1-4 links (Satin, 2000).

Rice starch typically comprises of 20-30% amylase and 70% amylopectin and the physiochemical properties responsible for rice eating quality are mainly dependent on the structure and functionality of these two molecules and their relative abundance (Patindol and Wang 2002, Satin 2000). Amylose is mainly a linear form of starch. The amount of amylose in the rice grain determines how sticky the rice will be when cooked. As amylose content increases the rice grain become less sticky and more. Some varieties do not have amylose in them because of a mutation in a gene called waxy gene. These varieties called waxy or glutinous rice are sticky when cooked and are mainly eaten in South East Asia (IRRI, 2007).

Juliano (1990) also carried out a study on water uptake behavior of raw and cooked rice and found out that cooked rice has lower water absorption capacity than raw and thus retained better shape, fluffiness, less sticky, more consistent and loss less solids during cooking.

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According to Zhou et al (2002) different properties define rice kernel eating quality. The eating quality is determined by physiochemical properties (Chrastil 1990, 1992, 1994, Nomhorm et al 1997, Perdon et al 1997, champagne et al 1999) mainly water absorption, cooking quality, whiteness, dullness and gelatinization of starch. On the other hand Lisle et al (2000) reported that neither amylase content, amylopectin structure and protein composition explained the difference in cooking quality of rice.

Quality evaluation of cooked rice involves the application of sensory test and physiochemical determination based on the chemical composition, cooking quality, gelatinization time and temperature and physical properties of cooked rice (Mastic and Ogata 1998).

Yousat(1992) reported that minerals like calcium, magnesium, phosphorus are present in the rice along with some trace of iron, copper, zinc and manganese. According to Sanjiva (1999), the difference in the quality of rice maybe attributed to the difference in their colloidal structure. Furthermore the extent of swelling of any variety during cooking could be used as index of its quality.

Consumer preference is based on the evaluation of quality attributes which is determined not only by chemical and physical properties of grains but also by aspects related to the appearance of the product after cooking such as stickiness and texture (softness and fluffiness). The cooking and textural properties largely dependent on the chemical composition of cultivars rather than their physical characteristics (Mohaptra, Bal 2009). Cooking time is important as it determines the tenderness of cooked rice as well as stickiness to great extent (Anonymous 1997).

It has been established that the physical and chemical properties influence the cooking quality of rice vary with varieties and different rice varieties are grown especially in Ivo Local government area of Ebonyi State because of this it is therefore important to evaluate their cooking characteristics which helps to determine the quality of processed rice.

Aims and Objective of the Research

1. To determine the functional properties of raw and cooked rice.

2. To determine the starch characteristics of the varieties of rice.

3. To determine the cooking sensory evaluation of rice.

4. To determine the of mineral content of the raw and cooked rice.


Literature Review

Rice is the main staple food for two third of the world population providing 21% of global dietary energy,14% of protein and 21% of fat ( Kennedy and Burlingame 2003).Rice belongs to the tribe Oryzeae, consist of 11 genera and 70 species (Vaughan 1994 )and along with the cereal corn, wheat, barley, sorghum and oat is a member of the grass family, poaceae. (Henry et al 2009).Only two species of rice are cultivated , the Asian species oryza sativa and the African species oryza glaberrima. Except for these domesticated species, the remainder of the genus oryza are commonly referred to as wild relatives of rice( Vaughan 1994).North American native species, zizania is named as wild rice after being brought under cultivation and domestication 20 years ago (Hayes, Stucker and Wandrey 1989).

The domestication of the two cultivated oryza sativa and oryza glaberrima is an example of parallel evolution which started 10,000 years ago independently and currently in different parts of Asia and Africa (Khush 1997) of these two species oryza sativa is cultivated all over the world where as oryza glaberrima is cultivated in west Africa only. The oryza genus is classified into four complexes, oryza sativa ,oryza officinals,oryza ridleyi and oryza meyeriana (Vaughan 1994).

Oryza sativa is composed of two major biotypes or subspecies indica and japonica and represent evolutionary adaptation to environment variable (Kennedy and Burlingame 2003).Although there are many overlapping traits these sub species( Garris et al 2005,OECD 1999).Typically indica rice are genetically highly diverse non-sticky rice that grow throughout lowland tropical and temperate Asia(Gao et al 2005).In contrast,the japonica are sticky rice grown in upland areas of temperate East Asia and higher elevation in South Asia, colder climate species and are not genetically as variable as indica (Gao and Innan 2008,Garris et al 2005,Lu et al 2002.)

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Rice Production and Use

Rice is one of the key crops in agriculture and in the world food system, providing a source of carbohydrate to supply the main food energy for half the human population. In Some Asian countries,as much as 80% of the daily caloric and 20% protein come from rice (Bao and Bergman 2004).Rice is mainly consumed as whole milled and or boiled grain ( Kang et al 2006,Khush 2000).

In addition to mainly used for its starch which accounts for 90% of the grain weight ,both the rice grain and crop have versatile uses in food and non-food industries. It is used to make noodles, puffed rice, fermented sweet rice, snacks food ,in the production of beer, rice wine and vinegar( OECD Environment 2004).Rice starch is used in many non food application such as adhesives ,coatings , pharmaceuticals, fillers, viscosity modifiers, and a host of enzymes. (Fitzgerald 2004).Rice starch is used for livestock feeds, concrete blocks and media for enzymes and mushrooms Maclean et al 2002.Hulls and husks are used for fuel, bedding and incubation material, seed bank medium, tiles, fiber board, ceramics, cement, fiters and charcoal bliquettes and gas cooking production. Rice straw is used as fuel for cooking and roofing materials (Maclean et al 2002).The whole rice plant are desirable for human consumption such as poor grade paddy rice, broken rice, hulls, bran and rice flour, hulls/polishing of parboiled rice are used in animal feed (OECD Environment 2004).

Currently rice is growing in 100 countries and more than 10% of the total cultivated land (Blankeney 1996,Juliano 2004).which equates to 150 million hectares producing more than 500 million tones of paddy rice every year (Blakeney 1996).Since 1960,per capital energy supplied by rice globally has increased by 40%   (Waters et al 2003).World population is growing at a substantial rate and so is the demand for rice (Blakeney 1996, Tuley 1991).

Since domestication research and selective breeding on high yield, disease resistance and farming practice have brought substantial increase in production. Growing human population coupled with adverse and unpredictable environmental conditions and declining yield have become the greatest threats for production today   Khush 2001.

Rice Processing

Steeping/parboiling 90C for 30mins
Steeping/soaking 1-2days
Raw paddy (50C)



Paddy dehusking/milling
Sun drying 2-3 days

Paddy grain basically consist of husk or hull and a grain of brown rice. Brown rice consist of a bran layer including pericap, seed coat and aleurone layer   a germ and scutellum connected on the ventral side of the grain and an edible portion or endosperm www.google .com .Husk and bran are not edible, therefore it must be paady. Bran is more difficult to remove from brown rice, because it is tightly attached to the kernel   Clement and Seguy 1994.

Cleaning Operation

The paddy rice is passed through coarse screen to remove all straw, stones and other objects that are larger than the rice .The rice passes over screens to remove weed, sand and dirts, stones and other objects smaller than the rice. Air separation systems are sometimes used in the process     http;//www.sagevfood.com.

Okaka 2009 reported that cleaning of rice is done by a machine, the rubble separator that is equipped with sets of fans and sieves which blow off dust. Impurities still left may be removed by a second rubble separator. A set of disc separators segregate rice grain from large grains,straw and stings while the other disc separator separates other smaller grains,sand and small stones. Magnetic separators remove nails and other metallic contaminant which otherwise damage machinery.

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Paddy Rice Parboiling

According to Okaka 2009 parboiling is a hydrothermal process which consist of steeping paddy rice in hot or cold water, steaming and draining /drying to suitable moisture content for safe storage. Pandey 1998 reported that parboiling of paddy is a hydrothermal process in which starch granules within the rice are gelatinized by the application of steam and water. This helps in the recovery of head rice. The three major steps in parboiling are soaking, steaming and drying, and these have a great influence on the final characteristics and quality of parboiled rice. Parboiling helps to loosen the hulls, but in addition enhances the nutritive value of the milled rice ,so treated because water dissolve the vitamins and minerals concentrated in the bran and hulls and redistributes them in the endosperm. Okaka 2009.

Drying Of Parboiled Paddy Rice

This refers to the removal of relatively small amount of moisture content and it involves both heat and mass transfer operation simultaneously. Thus drying is the process that removes moisture from rice grain mass for safe storage and preservation of quality, nutritive value and viability and facilities for further processing (google.com/status paper html). The three methods of drying include;

SUNDRYING; According to pandey 1998 most of the rice in the traditional mills is sundried on a drying floor/The drying floor is normally cemented floor consisting of layer of bricks bats with cement plaster on it. The parboiled is spread on the floor 10-30mm thick layer by labour with the help of of a plank or by feet. After four hours of drying in the sun , paddy is heaped and covered by mats or tempering period of 2-3 hours. Then it is spread again in the sun for two hours in the sun to dry it to a desirable moisture content.

MECHANICAL DRYING; According to pandey (1998) it is the process of utilizing mechanical means for drying grains by ventilating natural or heated air through the grain mass to accomplish removal of moisture from the paddy parboiled rice .It removes moisture from wet paddy by concentratedor heated air at a predetermined rate of flow, air, temperature or relative humidity.

CHEMICAL DRYING ;According to Pandey (1998) this method involves the spraying of common salt solution with specific gravity of 1.1-2.2 on the ears of the parboiled paddy rice. This treatment reduces the moisture content from 29%-14.5% after 4 days google.com/status paper .

Evaluation of Cooking, Minerals and Starch Characteristics of Some Rice Varieties from Ishiagu Ivo Local Government Area of Ebonyi State


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