Characterization and End-Use Qualities of Rice Varieties in Kogi State, Nigeria

Received 15 Dec, 2021

Accepted 28 Apr, 2022

Published 18 Aug, 2022

Background and Objective: Oryza glaberrima (Oje-igbale) and Oryza sativa L. Oryza glaberrima hybrid (Adede-agidi) are two rice varieties cultivated in Ibaji LGA of Kogi State, Nigeria and each of them is used for only a singular purpose. Studies were carried out to find out the characteristics of these grains and further processes they could be subjected to contribute to the strive for food security. Materials and Methods: Three samples of each, of the two different rice varieties’ paddy, were procured, cleaned, 2 kg portion parboiled, milled and thereafter analyzed for their physical and cooking, attributes. Un-parboiled paddy (500 g) of the two rice varieties were de-husked, milled into flour and samples were used to determine their physicochemical properties. Results: For the physicochemical properties, the starch content of Oje-igbales was of hard gel consistency (29.32-38.11 mm) and intermediate-amylose content (20.78-24.68 %) depicting it will be a good variety for a long time and high-temperature treatment processes. The starch content of the Adede-agidis’ was of soft gel consistency (66.43-72.52 mm), low-and intermediate-amylose content (18.47-20.23%) depicting it will be suitable for breakfast cereals, fermented rice cakes and baby foods. Conclusion: This research provides knowledge on the characteristics and other end-use qualities of Oje-igbale and Adede-agidi for value addition.

INTRODUCTION

Rice is a staple food in Nigeria, generally considered a semi-aquatic annual grass plant, although it survives as a perennial plant in the tropics. Rice is grown in all ecological and dietary zones of Nigeria, with different varieties possessing adaptation traits of each ecology¹. A hybrid of Oryza sativa-Oryza glaberrima species named Adede-agidi in Ibaji dialect which is high yielding and able to withstand biotic and abiotic stresses of African ecology is the most common variety grown in Ibaji Nigeria. Adede-agidi is used solely in preparing whole cooked rice grains for consumption. A small amount of the Oryza glaberrima species named Oje-igbale in Ibaji dialect is also grown in Ibaji, which is used solely for preparing dumplings. Ibaji, a local government area in Kogi State, Nigeria has headquarters in Onyedega with an area of 1,377 km² and a population of 128,129. Over 90 percent of the inhabitants are farmers who feed their families with their products and make proceeds from them². Adede-agidi is strictly consumed as cooked whole grains eaten accompanied with sauce while Oje-igbale is strictly consumed by milling the de-husked grain into flour and processed into rice dumpling which is eaten accompanied by local soups. Both have the same husk colour but Oje-igbale has red coloured bran instead of white like the Adede-agidi and other common rice grains cultivated in other parts of Nigeria.

Uses and different processing applications of rice include boiled whole grain rice, breakfast cereals, brewers rice, canned rice, baby foods, quick-cooking, convenience and speciality food products, rice flour as a thickener and rice starch, for industrial and other processes³. Rice end-use depend on the inherent characteristics of the rice grain which include amylose content, gel consistency, gelatinization temperature and physical dimensions. There is a need to know other end-use qualities of Oje-igbale and Adede-agidi through characterization for value addition thereby contributing to food security. It is recognized that indigenous foods and dietary diversity among indigenous foods within an ecosystem can be powerful sources of nutrients and thus mediums for better health and food security⁴. The objective of this study was to characterize and determine other end-use qualities of Oje-igbale and Adede-agidi for value addition thereby contributing to food security

MATERIALS AND METHODS

Study area: The study area where samples were collected was from farmers in Ibaji LGA of Kogi State. All the analyses were performed in the Food Processing and Chemistry Laboratory of the Department of Food Science and Technology, University of Nigeria, Nsukka from May to August, 2019.

Materials: Three samples each of Oje-igbale and Adede-agidi rice varieties paddy were purchased from different farmers in different locations in Ibaji LGA of Kogi State and coded, OJ₁, OJ₂ and OJ₃ and AA₁, AA₂ and AA₃, respectively.

Methods: The samples were taken to the Food Processing Laboratory of Food Science and Technology, of the University of Nigeria, Nsukka for parboiling and milling with Engelberg Huller. A portion of the paddy of the two different rice varieties was not parboiled but dehulled and milled to flour for determining functional properties.

Determination of functional properties
Gel Consistency (GC) determination: Gel Consistency (GC) of rice samples was determined according to the method of Bhat and Riar⁵ as reported by Kaur et al.⁶. After sample preparation and analysis, the tubes containing the analyte were laid horizontally over a ruled paper graduated in millimetres and the length of the gel from the bottom of the test tube was measured after 45 min. The sample is categorized according to the standard as shown in the footnote of Table 1.

Amylose content determination: Amylose Content (AC) was determined according to the method described by Villota et al.⁷. The analyte was shaken and allowed to stand for 20 min and the per cent Transmittance was determined at 620 nm using a colorimeter. The amylose content of the samples was determined by a standard curve (graph) and expressed on a percentage basis as shown in Eq. 1:

(1)

Physical properties of the rice varieties
Determinations of grain dimensions: Rice grain dimensions-grain length and width were determined using a digital vernier calliper (0.1-100 mm A&D Company, Limited) according to the method by Odenigbo et al.⁸.

Table 1:

Physicochemical properties of Adede-agidi and Oje-igbale rice varieties

Rice samples	Gel consistency (mm)	Gel consistency behaviour	Amylose (%)	Amylopectin (%)	Classification based on amylose content
AA1	66.43±0.04d	Soft	19.47±0.02b	80.47±0.02d	Low
AA2	68.60±0.01e	Soft	20.23±0.04c	79.22±0.02c	Intermediate
AA3	72.52±0.02f	Soft	18.47±0.01a	81.54±0.02e	Low
OJ1	29.23±0.04a	Hard	20.78±0.00d	79.25±0.04c	Intermediate
OJ2	38.11±0.01c	Hard	24.68±0.02e	78.34±0.01c	Intermediate
OJ3	32.67±0.00b	Hard	24.20±0.05e	75.83±0.04b	Intermediate
Values are means±standard deviation of duplicate determination, means in the same column carrying similar superscripts are not significantly (p<0.05) different, Gel consistency: Soft gel consistency = 61-100 mm, medium = 41-60 mm, hard = 26-40 mm, Amylose content: Waxy (1-2% amylose), very low amylose content (2-9% amylose), low amylose content (10-20% amylose), intermediate amylose content (20-25% amylose), high amylose content (25-33% amylose), AA1-AA3 (Adede-agidi rice variety from three different farmers) and OJ1-OJ3 (Oje-igbale rice variety from three different farmers)

Determination of grain length: Ten milled whole rice grain samples of each variety were randomly selected and the length of the grains was measured using a digital calliper (0.1-100 mm A&D Company, Limited). The mean value of each variable was determined and noted. The value obtained was recorded as each sample’s grain length.

Determination of grain shape: Ten milled whole rice grain samples of each variety were randomly selected and the width of the grains was determined with a digital calliper (0.1-100 mm A&D Company, Limited). The mean value of each variable was obtained and the length/width ratio of the samples was calculated as shown in Eq. 2:

(2)

The value obtained was recorded as grain shape for each sample.

One thousand grain weight (W₁): One hundred milled kernel representative samples (triplicates) for each variety were randomly selected. The weight of each sample was determined using a 500 g capacity weighing scale (Electronic Pocket Scale Model EHA251). The value obtained was multiplied by 10 and the mean weight of the samples obtained was noted as W₁.

Determination of the volume of raw rice grains: The volume of raw rice grain was determined by the displacement method as described by Kaur et al.⁶. One hundred raw rice grains were placed in a measuring cylinder containing 20 mL of water (V₁). The new volume of water after the raw rice grains was added to the measuring cylinder was noted as (V₂). The volume of raw grains (V₃) was obtained by subtracting the volume of water containing raw rice grains from the initial volume of water contained in the measuring cylinder (Eq. 3):

(3)

Where:

V3	=	Volume of raw grain
V2	=	Volume of water after the raw rice grains were added to the measuring cylinder
V1	=	The 20 mL of water which was an initial volume of water in the measuring cylinder before grains were added to the measuring cylinder

Density of raw rice grain: The density of the rice grain samples was obtained by dividing the weight of raw rice grain by its volume (Eq. 4):

(4)

Cooking analysis
Minimum and optimum cooking time: The minimum and optimum cooking time were determined according to the method by Odenigbo et al.⁸.

Quantity of water absorbed: The quantity of water absorbed by rice samples was determined as described by Azuka et al.⁹.

(5)

Volume expansion ratio: The volume expansion ratio was determined according to the method as described by Chukwuemeka et al.¹⁰. The volume expansion ratio is calculated as follows Eq. 6:

(6)

Where:

V8	=	Volume of cooked rice
V3	=	Volume of raw rice

Weight increase: The increase in weight of rice samples was obtained as described by Azuka et al.⁹. The increase in weight was obtained by subtracting the weight of cooked rice grains from the uncooked rice grains as shown in Eq. 7:

(7)

Where:

W2	=	Weigt of cooked rice grain
W1	=	Weight of raw rice

Elongation ratio: The elongation ratio of rice grain samples was determined according to the method of Odenigbo et al.⁸ using ten cooked samples of each variable and ten uncooked rice grains. Their Elongation ratio was obtained as shown in Eq. 8:

(8)

Water Uptake Ratio (WUR): The water uptake ratio was determined according to the method described by Pokhrel et al.¹¹. Four grams of whole milled kernel rice sample was measured in triplicates and cooked in 60 mL of water for 20 min. The sample was removed from heat and the cooked grains were strained and placed on a filter paper to remove excess water and weighed and calculated as shown in Eq. 9:

(9)

Statistical analysis: A Completely Randomised Design (CRD) was used for this study. The data generated from all analyses and sensory evaluations were subjected to statistical Analysis of Variance (ANOVA) using SPSS (version 20). Means were separated using Duncan’s Multiple Range Test¹².

RESULTS AND DISCUSSION

Functional properties of rice varieties: Table 1 shows the functional properties of Adede-agidi and Oje-igbale rice varieties.

The gel consistency value of the Oje-igbale rice varieties ranged from 29.23-38.11 mm while that of Adede-agidi ranged from 66.43-72.52 mm. Significant (p<0.05) differences exist between the gel consistency of the two rice varieties. Gel consistency measures the tendency of the starch content of the cooked rice to harden after cooling, the values of Oje-igbale (29.23-38.11 mm) showed its rice starch to be of hard gel-consistency while the values of Adede-agidi (66.43-72.52 mm) denotes its rice starch to be of soft gel-consistency. Rice varieties of that of hard gel consistency harden when cooked and cooled and are not preferred for consumption as whole grains but find use in canned rice products, prepared convenience products, rice noodle manufacture, dumpling and any other high-temperature treatment processes due to their resistance to splitting into cooking water during boiling rice of soft gel consistency is tender when cooked, hardened slightly when cooled and preferred for consumption which Adede-agidi possess. The hard gel consistency of Oje-igbale, explains why it is not cooked as a whole grain for consumption but used in making dumplings, while the tenderness of Adede-agidi explains why it is preferred for consumption as cooked whole grains. Adede-agidi rice varieties with soft gel consistency can also find application in making baby foods. Results from Oko et al.¹³ showed the gel consistency of the samples to range between 43.00-54.00 mm and were described as rice of medium gel consistency. Different categories of gel consistency are shown in the footnote of Table 1.

The AA₁ and AA₃ had amylose content of 19.47 and 18.47, respectively which makes them low-amylose rice grains while AA₂ had an amylose content of 20.23% which makes it intermediate amylose rice grain. Low-amylose rice grains are desirable in making breakfast cereals, baby foods and risottos while intermediate amylose rice grains can be used in making fermented rice cakes. Amylose content of the Oje-igbale variety ranged from 20.78-24.68% and makes them intermediate-amylose rice grains. Differences between amylose content of the same varieties could be a result of ecology where the grains were planted since the grains were procured from different farmers at different locations. The amylose content in rice is considered the single most important characteristic used in describing and predicting rice cooking and processing qualities¹⁴. High amylose grains cook dry, are less tender and become hard upon cooling while low amylose grains cook moist and sticky and find use in baby cereals and risottos. Intermediate amylose rice is preferred in most rice-growing areas of the world for consumption because it is tender and non-sticky. Rice of the same amylose content is usually differentiated from themselves with their degree of a gel consistency.

Rice varieties of intermediate amylose-hard gel consistency are less tender compared to that of an intermediate amylose-soft gel consistency. Low amylose- soft gel consistency rice varieties (AA₁ and AA₃) are most tender and suitable for use in baby foods, cooked whole grains and breakfast cereals because of their ability to produce a relatively stable gel during storage. They can also be used as popped and puffed rice as a result of expansion in volume^6,15. Varieties with intermediate amylose-soft gel consistency (AA₂) are used in making fermented rice cakes, because of their optimum volume expansion on steaming and their soft texture while intermediate amylose hard-gel consistency grains (Oje-igbales) will find application in canned rice products, rice noodle manufacture, dumpling and any other high-temperature-long time treatment processes.

Physical dimensions: Table 2 shows the dimensions of the uncooked rice grains. The length of Adede-agidi samples ranged from 5.42-5.92 mm, making it a bowl of medium-grain rice. The length of the Oje-igbale variety ranged from 6.48-6.69 mm which makes it long-grain rice. Significant (p<0.05) differences exist in all the dimensions of the raw rice grain varieties.

Table 2:

Dimensions and classification of Adede-agidi and Oje-igbale rice varieties

Rice samples	Length (mm)	Classification	Width (mm)	Length: width ratio	Classification	Weight (g)	Classification	Volume(mL)	Density (g mL–1)
AA1	5.70±0.12b	Medium	2.25±0.01c	2.51±0.01b	Bold	19.02±0.00a	Moderately heavy	11.62±0.02b	1.73±0.00b
AA2	5.42±0.02a	Medium	2.23±0.02c	2.44±0.01a	Bold	20.67±0.02d	Heavy	11.63±0.01b	1.74±0.03b
AA3	5.92±0.02c	Medium	2.27±0.02c	2.62±0.01c	Bold	19.83±0.01b	Moderately heavy	10.49±0.01a	1.83±0.02c
OJ1	6.65±0.02e	Long	2.12±0.02b	3.17±0.02e	Slender	21.72±0.06e	Heavy	13.20±0.02d	1.86±0.00c
OJ2	6.48±0.08d	Long	2.14±0.01b	3.01±0.02d	Slender	20.34±0.02c	Heavy	12.68±0.01c	1.62±0.02a
OJ3	6.69±0.02e	Long	2.01±0.01a	3.35±0.03f	Slender	22.01±0.01f	Heavy	12.64±0.01c	1.73±0.01b
Values are means±of duplicate determination standard deviation, means with different superscript within the same column differ significantly (p<0.05), Length = Extra-long-≥7.0, long-6.00-6.99, medium-5.0-5.99, short <5.0, Shape = Slender->3.0, bold-2.0-3.0, round-<2.0. Weight = Extra-heavy->25 g, heavy-20-25 g, moderately heavy <20 g, AA1-AA3 (Adede-agidi rice variety from three different farmers) and OJ1-OJ3 (Oje-igbale rice variety from three different farmers)

Cooked grains of medium-grain rice varieties are moist and tender and have a greater tendency to cling together than long grain rice and are desirable in making baby foods, whole cooked grains, breakfast cereals and risottos^16,17.

Medium grain rice varieties have low to intermediate amylose content which describes the Adede-agidi varieties. Milled rice of typical long-grain varieties usually cooks dry and fluffy when boiled or steamed^3,15,16. The cooked grains lie separate and are generally preferred for use in prepared products such as canned rice, canned soups, dry soup mixes, frozen dishes and other convenience-type rice-containing foods³. Long-grain and extra-long-grain rice have intermediate to high amylose content which describes the Oje-igbale varieties. Results from Danbaba et al.¹⁶ showed the samples studied to be 6.69-5.44 mm, indicating long-grain to medium grain rice and were within the reported range.

Adede-agidi varieties are bold grains (2.44-2.62 mm) while Oje-igbale rice varieties are slender grains (3.01-3.35 mm). These rice varieties will make use of different post-harvest equipment due to differences in their length-width ratio to reduce the number of broken and obtain high head-rice. Length:width ratio (shape) is said to be probably the most meaningful of the determinations since it is used in sizing rice with slotted sieves or precision graders³. The knowledge of length-width ratio is used in sorting, grading, cleaning, milling and other post-harvest processing operations. Rice with bold grains usually has low amylose while rice with slender grains has intermediate to high amylose content. According to Danbaba et al.¹⁶ ten rice varieties studied reported a range of 2.17-3.25 indicating some were bold grains in shape while others were slender in shape.

The AA₁ (19.02 g) and AA₃ (19.83 g) are moderately-heavy grains, while AA₂ (20.67 g) are heavy grains. The values of Oje-igbales ranged from 20.34-22.01 g making them heavy grains. Heavy grains have high amylose content and absorb more water when cooked while moderately heavy grains have low to intermediate amylose content. Grains higher in weight will sell at a higher price in international trade when rice is sold on a weight basis and will be more profitable to the seller. A range of 16.97-20.05 g was recorded for ten rice varieties studied by Danbaba et al.¹⁶ showing they were moderately heavy and heavy grains.

The volume of the Adede-agidi variety ranged from 10.49-11.63 mL and that of Oje-igbale ranged from 12.64-13.20 mL, a significant (p<0.05) difference existed in the volume of Oje-igbale and Adede-agidi. Grains highest in volume will occupy more storage space during packaging, transportation and sales of agricultural produce. In international trade when rice is traded in volume, grains highest in volume will be beneficial to the seller because they will occupy more storage space while those of low volume will be beneficial to the buyer. In the transportation of rice grains, grains of less volume will attract fewer transportation costs than those of high volume. Results from Danbaba et al.¹⁶ showed the samples were within the reported range (10.05-14.34 mm³).

Table 3:

Cooking characteristics of Adede-agidi and Oje-igbale rice varieties

Rice samples	Elongation ration	Weight increase	Volume expansion ratio	WUR	MCT (mins)	OCT (mins)	VWA (mL)
AA1	1.33±0.01ab	29.35±0.04c	3.45±0.03c	2.32±0.03b	20.50±0.02a	22.49±0.02a	18.34±0.02a
AA2	1.30±0.00a	28.34±0.02b	3.35±0.03b	2.27±0.02ab	19.34±0.02b	21.38±0.00b	22.10±0.02b
AA3	1.35±0.00bc	28.03±0.04a	3.01±0.01a	2.22±0.03a	23.21±0.01c	24.23±0.01c	19.01±0.01c
OJ1	1.41±0.01de	34.35±0.04e	4.35±0.03f	2.68±0.00d	27.85±0.01d	29.87±0.01d	22.94±0.02e
OJ2	1.43±0.02e	34.13±0.04d	4.21±0.01e	2.51±0.01c	32.34±0.02f	34.34±0.01f	22.66±0.01d
OJ3	1.37±0.01cd	36.04±0.05f	3.86±0.00d	2.87±0.02e	29.41±0.01e	31.34±0.01e	23.06±0.05f
Values are means±standard deviation of duplicate determination, means in the same column carrying similar superscripts are not significantly (p<0.05) different, AA1-AA3 (Adede-agidi rice variety from three different farmers) and OJ1-OJ3 (Oje-igbale rice variety from three different farmers)

Cooking quality: The cooking characteristics of the rice varieties include their Elongation Ratio (ER), Weight Increase (WI), Volume Expansion Ratio (VER), Water Uptake Ratio (WUR), minimum and optimum cooking time and Volume of Water Absorbed (VWA).

Cooking characteristics of Adede-agidi and Oje-igbale rice varieties: Table 3 shows the cooking characteristics of Adede-agidi and Oje-igbale rice varieties. Significant (p<0.05) differences existed in the VER within and between rice varieties.

The volume expansion ratio of the two rice varieties exceeded 300% with the Oje-igbales having the highest VER (3.86-4.35). The rice varieties with high VER would produce rice more in volume than those with lower VER when cooked and Food vendors prefer rice varieties with high VER to make more profit from its high expansion.

The elongation ratio (ER) of samples ranged from 1.30-1.43. The ER of rice can be influenced by both the length to width ratio and the amylose content^17,18. The ER is desirable to consumers who love long-grain rice. The result obtained was within the range reported by Sanusi et al.¹⁹, Nehemiah et al.¹⁶ and Odenigbio et al.⁸.

There was a significant (p<0.05) difference between the water uptake ratio of the grains. The Water Uptake ratio (WUR) of the Adede-agidi rice variety ranged from 2.22-2.32. The WUR of the Oje-igbale rice variety ranged from 2.51-2.87. Water Uptake Ratio (WUR) is a measure of the rate at which the rice grains take up water and increase in volume and weight. Grains with high WUR increased more in weight than those with low WUR. High WUR is a result of high amylose content and it is desirable in rice varieties for canning purposes. In other words, Oje-igbale can be a good rice variety for canned rice products. The values obtained were lower than most of the values obtained by Sanusi et al.¹⁹ higher than the results reported by Nehemiah et al.¹⁶ but within the range of the values reported by Odenigbo et al.⁸.

Significant (p<0.05) differences existed in the minimum and optimum cooking time of the Adede-agidi rice variety. Adede-agidis had an optimum cooking time of 21.38-24.23 min while the Oje-igbales had an optimum cooking time of 29.87-34.34 min. The variation in cooking time between and within samples can be a result of the gelatinization temperature since the gelatinization time correlates positively with the cooking time of the rice. The rice which takes a long time to gelatinize contains higher amylose. It has been shown that the higher the gelatinization temperature, the longer it takes to cook rice²⁰ and the cooking time was observed to be dependent on the gelatinization temperature. The differences within samples can be a result of environmental factors where the grains were grown. The Adede-agidis cooked for a short period less than the Oje-igbale which takes a longer time. These characteristics can be attributed to the higher amylose content of Oje-igbale. The values obtained were higher compared to the values obtained by Singh et al.¹⁷, Frei et al.²⁰ and Odenigbio et al.⁸.

Significant (p<0.05) differences existed in the Volume of Water Absorbed (VWA) between and within rice samples. The Adede-agidi rice variety had a VWA of 18.34-22.10 mL/1000 grains. The Oje-igbale rice variety had a VWA of 22.60-23.06 mL. VWA is a direct measure of the amount of water required to cook the rice grains to their optimum eating quality. It was observed that the Adede-agidi rice varieties imbibed less water when cooked than the Oje-igbale variety. This may be attributed to the higher amylose content and water affinity sites of the Oje-igbale rice samples. Its starch content could be exploited in producing rice noodles.

CONCLUSION

The Oje-igbale rice variety is longer, has an intermediate amylose-hard gel consistency and will be suitable in canned rice products, convenience-type rice-containing foods and rice noodle manufacture along with its use as a dumpling. The Adede-agidis being of low amylose-soft gel consistency rice varieties (AA₁ and AA₃) are suitable for use in baby foods, breakfast cereals popped rice and puffed rice, along with its use as cooked whole grain. In making fermented rice cakes, AA₂ with intermediate amylose-soft gel consistency can be used. Oje-igbale also has high OCT and VWA which is not desired in whole-grain cooking, because of more expended heat energy and water, respectively but it is desired in making dumplings to form a stiff paste.

SIGNIFICANCE STATEMENT

This study has provided knowledge on the characteristics and different obtainable end-use qualities of Oje-igbale and Adede-agidi other than their use in making dumplings and being prepared as cooked whole grain, respectively. This knowledge will help and should be used by food industries for value addition in pursuit of food security

ACKNOWLEDGMENT

The authors acknowledge the Department of Food Science and Technology for providing their Food Processing Laboratory and milling equipment used to process and mill the rice.

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