International Journal of Food Science
Volume 2020 (2020), Article ID 8810553, 9 pages
https://doi.org/10.1155/2020/8810553

Research Article

Effect of Parboiling Conditions on Physical and Cooking Quality of Selected Rice Varieties

Ayenew Meresa, Ayalew Demissew, Seifu Yilma, Getu Tegegne, and Kiber Temesgen

Amhara Agricultural Research Institute (ARARI), P.O. Box 527, Bahir Dar, Ethiopia

Correspondence should be addressed to Ayenew Meresa; ayenew.meresa@arari.gov.et

Received 12 June 2020; Revised 18 August 2020; Accepted 2 September 2020; Published 9 September 2020

Academic Editor: Jaime Yanez

Copyright © 2020 Ayenew Meresa et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Most locally cultivated rice varieties in Ethiopia have low physical (low head rice yield, high broken rice yield, and high percentage of chalkiness) and cooking qualities (low water uptake ratio and swelling ratio). Parboiling, a process which involves soaking, steaming, and drying, has been identified as a key technique to improve cooking and milling quality of rice. The current study is aimed at elucidating the effect of parboiling on physical and cooking qualities of three rice varieties (Gumara, Edget, and Narica4) collected from Fogera National Rice Research and Training Center, Amhara region, Ethiopia. Each rice variety was subjected to different soaking temperatures (40°C, 50°C, 60°C, 70°C, and 80°C) and steaming time (10, 20, 30, 40, and 50 minutes). The treatment effect results indicated that parboiling has a significant effect () on head rice yield and percentage of broken rice with increased soaking temperature and steaming time as compared to the control. For instance, percent head rice yield increased as soaking temperature (from 40 to 80°C) and steaming time (from 10 to 50 min) increased: for Gumara, from 4.07 to 93.6%, for Edget, 9.47 to 96.53, and from 3.20 to 91.67 for Narica4. Percentage chalkiness had decreased as soaking temperature and steaming time increased: 97.33% to 0.00% for Gumara, 97.80% to 0.00% for Edget, and 100.00% to 0.13% for Narica4 as compared to 100% for control of all varieties. The minimum cooking time was identified as 16-23 min for Gumara, 16-23 min for Edget, and 15-20 min for Narica4 rice varieties. The result of the present study clearly showed that parboiling with high soaking temperature and steaming time increased the head rice yield, water uptake ratio, decreased percentage chalkiness, and enhanced the overall quality of the rice varieties.

1. Introduction

Rice (Oryza sativa L.) is a sole cereal crop cooked and consumed mainly as whole grain and hence considerations on grain quality are much more relevant than other food crops [1]. Rice supplies high-value carbohydrates accounting for more than 50% of the daily calorie intake, and it is consumed by more than 67% of the world’s population [2, 3].

According to the Central Statistical Agency [4] of Ethiopia report, the number of farmers engaged in rice production was about 115 thousand in 2012/13, and it has increased to about 161 thousand in 2017/18 [5]. Similarly, the area covered showed an increment from about 41 thousand ha in 2012/13 [4] to about 53 thousand ha in 2017/18 [5] along with increased production from about 121 thousand tons in 2012/13 [4] to 151 thousand tons in 2017/18 [5]. Although the production shows an increment through time, there is a substantial postharvest loss during rice milling. Furthermore, the local rice has low market price due to its poor cooking quality due to high breakage during milling, chalky grains, low head rice, and low water absorption capacity.

Parboiling is a hydrothermal process consisting of soaking, heating, and drying operations modifying the qualitative and processing behavior of rice [6, 7]. Soaking is a hydration process in which the diffusion-controlled water uptake migrates into the rice kernel [8], and continuous heating leads to nonreversible swelling and fusion of starch granules. Due to the reason that starch granules are gelatinized, followed by relevant reassociation, different changes occur in rice that plays an important role in various postharvest handling and processing operations, such as storage, milling, cooking, and eating qualities [9]. Due to the diversity in genetic and environmental factors [10, 11], different rice varieties vary in their cooking and sensory characteristics [12].

Locally milled rice in Ethiopia is poor in quality, usually consumed in rural areas, and cannot compete with imported rice both in terms of price and quality. The poor cooking quality of the local rice makes urban consumers to prefer imported rice to local ones. Hence, there is a need to improve the quality of locally produced rice in terms of physical and cooking attributes of the grain in order to make it competitive with imported ones.

2. Materials and Methods

2.1. Sampling

About 50 kilograms of paddy rice of each selected rice variety (Narica-4, Edget, and Gumara) harvested in 2017 and stored for six months was collected from Fogera National Rice Research and Training Center, where the milling activity was also performed. Experiments on parboiling processes, physical quality analysis, and the cooking quality analysis were conducted at the Food Science and Post-Harvest Handling Research Directorate laboratory, Amhara Agricultural Research Institute, Bahir Dar, Ethiopia.

2.2. Experimental Design

The experiment consisted of two treatments with five levels and one control. Soaking temperature (°C) and steaming time (minutes) were the treatments of the experiment. Five temperatures (40, 50, 60, 70, and 80°C) at a constant soaking time and five steaming durations (10, 20, 30, 40, and 50 min) were the levels of the treatments. A complete randomized design was employed for the levels and each was replicated three times.

2.3. Parboiling Process

The laboratory parboiling procedure was conducted according to the method described by Danbaba et al. [13] with some modification. A laboratory water bath (Clifton unstirred bath, England) with temperature regulation of ±2°C was used for soaking rice grains before steaming to produce parboiled rice. About 14 kg of rice sample was put in a perforated dish and soaked in a water bath. Soaking was done in hot water of five different temperatures (40, 50, 60, 70, and 80°C) at constant soaking time. Then the soaked sample was steamed for five steaming durations (10, 20, 30, 40, and 50 min) over boiling water. After steaming, the parboiled paddy was spread on a tray with a thickness of about 2 cm at ambient condition for about 4 days to dry until equilibrated to 12-14% moisture content. The dried parboiled rice sample was dehusked (TYPE 25 M, Oya Tanzo Manufacturing Co., Ltd, Japan), polished (CBS550BS, SATAKE, Japan), and packed with plastic bags till analysis.

2.4. Determination of Physical Characteristics

2.4.1. Moisture Content

Grain moisture content was measured in triplicates using a digital moisture meter (Riceter J301, KETT, Japan).

2.4.2. Husking/Milling Quality

From 1.2 kg of paddy rice, it was done by the removal or separation of husk and bran to recover the edible portion of rice. The milling quality (husking efficiency or recovery percentage) was calculated according to the international rice research institute method [14] as follows:

2.4.3. Percentage of Broken Rice

Broken rice is an estimate of those kernels that are less than ¾ of their normal length after milling (dehusking). This was determined by weighing 50 g samples of polished rice and separating into broken and unbroken fractions. This was done manually with careful handpicking and repicking. Each portion was weighed and expressed as a percentage of the initial weight of rice. This was conducted by the method followed by Adu-Kwarten et al. [15].

2.4.4. Percentage of Head Rice

From a 50 g sample of cleaned and milled rice, the head rice was manually separated and weighed. Milled rice grains with a length greater than three quarters of complete grains were classified as head rice. The head rice yield was calculated using the method followed by Fofana et al. [16] with some modifications by calculating head rice percentage instead of head rice ratio.

2.4.5. Percentage Chalkiness

Percentage of rice chalkiness was calculated from three replicates of 50 g samples, according to the method outlined by WARDA [17]. The amount of chalk in the milled rice was measured using seed viewer florescent (QUG/A2-SL, UK) for transmission of light. A perfect rice grain is translucent, allowing the transmission of light, whereas opaque or chalky areas in a chalky grain prevent this transmission. Chalkiness is expressed as the proportion of opaque relative to translucent areas in rice grains.

2.4.6. Determination of Cooking Properties

(1) Minimum Cooking Time (MCT). This was done according to Singh et al. [11]. About 2 g head rice samples was taken in a test tube and cooked in 20 ml distilled water in a boiling water bath. The cooking time was determined by removing a few kernels at different time intervals during cooking and pressing them between two glass plates until no white core was left

(2) Water Uptake Ratio. Water uptake ratio of cooked rice was determined by the increase in weight of rice after subjecting it to MCT as described above. Eight grams of rice was cooked with 100 ml water in a 200 ml cylinder on an electric heater [18]. Water uptake ratio was calculated as

(3) Swelling Ratio. Milled rice (8 g) was placed into a wire mesh cooking basket. The height of the raw rice in the cooking basket was measured using a digital caliper (SS17DV150, China) (H1). The samples were cooked according to the cooking times determined above. The cooking basket was subsequently removed and stood erect for 2 minutes for the water to drain off. The height of the cooked rice in the cooking basket was measured using a digital caliper (H2). This determination was carried out in triplicate [16]

2.4.7. Data Analysis

Data were analyzed using the SAS software version 9.0 and one-way analysis of variance (ANOVA) followed by Duncan’s multiple range test for the multiple comparison analysis was carried out. Statistical significant test was carried out at 0.05 probability level.

3. Result and Discussion

3.1. Physical Characteristics of Rice Varieties

The mean moisture content for paddy Gumara rice ranged from 12.47% to 15.13%, from 14% to 15% for Edget, and for Narica4, it ranged from 12.10% to 14.73% (Table 1). There was significant difference between the combination of each soaking temperature and steaming time treatments () for the three varieties (Table 1). In general, the moisture contents of the tested rice varieties were comparable with those reported by Bleoussi et al. [19] (14%), Farhan et al. [20] (10-12%), Adu-Kwarten et al. [15] (14%), Prasad et al. [21] (13-14%), and Ayamdoo et al. [22] (15%).

Table 1: Physical property of rice varieties at different soaking temperatures and steaming time.

Soaking T (°c)
Steaming time(min)
Gumara rice
Edget rice
Narica4 rice

Husking quality %
Moisture content %
% head rice
% broken
% chalkiness
Husking quality %
Moisture content %
% head rice
% broken
% chalkiness
Husking quality %
Moisture content %
% head rice
% broken
% chalkiness

40
10
78.1
15.13a
4.07Θ
95.93!
97.33β
79.30
14.57bcd
13.13ϘΦ
86.87±!
97.80β
80.00
13.37dfe
3.20Θ
96.80!
100.00α

40
20
82.7
14.70bdc
8.80⁹
91.20±
96.53γβ
79.50
14.27cde
11.60ϘΦ
88.40±!
96.80βγ
80.20
13.03gf
5.079Θ
94.93±!
99.67αβγ

40
30
77.8
13.23ih
10.93⁹⁸
89.07#±
96.47γβ
80.00
14.17de
9.47Ϙ
90.53!
96.00γδ
80.20
12.33h
6.209Θ
93.80±!
99.60αβγ

40
40
78.1
14.67dc
12.67⁷⁹⁸
87.33#ͷ ± $
96.33γβ
79.90
14.70abc
19.00Δ
81.00#
96.07γδ
80.00
12.10h
8.07⁹⁸
91.93±#
99.33αβγ

40
50
77.8
14.50efd
13.33⁷⁹⁵⁸
86.67#ͷ ± $
96.07γβδ
79.60
14.47bcd
67.47⁶⁷
32.53ͻ
97.00βγ
80.20
13.43dfe
14.67⁷
85.33$
99.33αβγ

50
10
78.6
13.23ih
9.87⁹⁸
90.13#±
96.00γβδ
79.70
14.23de
12.13ϘΦ
87.87±!
96.53βγ
80.10
14.33ba
5.139Θ
94.87±!
99.60αβγ

50
20
78.3
14.97bac
14.07⁷⁶⁸
85.93^#ͷ$
95.60γεβδ
79.70
14.53bcd
14.47Φ
85.53±
95.60γδε
80.60
14.57a
6.009Θ
94.00±!
99.47αβγ

50
30
78.6
14.50efd
15.93⁷⁶⁸
84.07^ͷ$
95.47γεβδ
79.50
14.43bcd
51.07⁸
48.93^
94.53ε
80.20
14.73a
19.67⁶
80.33ε
99.40αβγ

50
40
78.5
14.57efdc
17.00⁷⁶
83.00^ͷ
94.47γεδ
79.90
14.33bcde
69.00⁶⁵
31.00ͻ<
94.40ε
76.60
13.67dce
20.00⁶
80.00ε
99.67αβγ

50
50
79.0
14.33efd
17.73⁶
82.27^
93.87εζδ
80.10
14.30bcde
70.20⁶⁵
29.80<
95.07εδ
81.20
14.63a
25.20⁵
74.80^
99.40αβγ

60
10
78.3
14.60efdc
11.33⁹⁸
88.67# ± $
93.53εζ
79.70
14.40bcde
28.80Θ
71.20$
94.33ε
80.00
14.67a
6.87⁹
93.13±
99.53αβγ

60
20
78.5
14.33efd
14.80⁷⁶⁸
85.20^#ͷ$
92.20ζ
78.70
14.23de
45.53⁹
54.47ͷ
94.20ε
76.10
13.83dc
13.80⁷
86.20$
99.13βγ

60
30
78.5
14.47efd
17.53⁷⁶
82.47^ͷ
92.00ζ
78.00
14.43bcd
71.40⁵
28.60<
92.20ζ
80.20
13.50dfe
23.73⁵
76.27^
99.13βγ

60
40
75.7
12.47k
26.33⁵
73.67ͻ
92.07ζ
78.00
14.33bcde
72.27⁵
27.73<
92.00ζ
80.10
13.03gf
32.00⁴
68.00ͻ
99.67αβγ

60
50
78.7
14.50efd
42.80³
57.20<
89.13η
80.00
15.00a
88.93⁴
11.07>
0.60η
80.20
13.83dc
33.07⁴
66.93ͻ
99.13βγ

70
10
78.7
14.23ef
27.73⁵⁴
72.27ͻ
1.53θ
74.50
14.73ab
65.93⁷
34.07ͻ
0.87η
80.10
13.47dfe
13.27⁷
86.73$
99.80αβ

70
20
77.8
12.77kj
46.87³
53.13<
0.00θ
79.90
14.23de
71.40⁵
28.60<
0.33η
79.90
14.10bc
25.80⁵
74.20^
99.73αβγ

70
30
78.7
14.20f
55.80²
44.20>
0.00θ
79.80
14.73ab
89.87⁴³
10.13+>
0.27η
78.70
13.67dce
50.87³
49.13
99.73αβγ

70
40
73.5
12.90ij
57.40²
42.60>
0.00θ
79.70
14.50bcd
92.07⁴³²
7.93+ > <
0.13η
89.60
13.27gfe
49.40³
50.60
98.93γ

70
50
78.4
14.63edc
60.00²
40.00>
0.00θ
79.90
14.53bcd
93.33¹³²
6.67+¢-
0.00η
79.60
13.43dfe
61.40²
38.60<
0.93δ

80
10
78.6
15.07ba
42.80³
57.20<
0.00θ
79.30
14.47bcd
95.07¹⁰²
4.93=¢-
0.00η
78.90
13.23gfe
81.47¹
18.53>
0.60δε

80
20
78.4
13.13ihj
74.40³
25.60⁺
0.00θ
79.70
14.50bcd
96.53¹⁰
3.47=¢
0.00η
79.60
13.70dce
82.67¹
17.33>
0.67δε

80
30
78.5
13.37h
75.40¹
24.60⁺
0.00θ
80.20
14.53bcd
96.93¹⁰
3.07=¢
0.00η
80.10
14.03bc
81.67¹
18.33>
0.80δε

80
40
78.5
12.90ij
91.87⁰
8.13⁻
0.00θ
79.90
14.43bcd
97.20⁰
2.80⁼
0.00η
78.80
13.53de
83.13¹
16.87>
0.27δε

80
50
78.4
13.23ih
93.60⁰
6.40⁻
0.00θ
79.40
14.00e
97.93⁰
2.07⁼
0.00η
79.20
13.53de
91.67⁰
8.33⁺
0.13ε

Control
78.4
13.73g
31.47⁴
68.53
100.00α
80.10
12.83f
29.53Θ
70.47$
99.87α
80.10
12.87g
9.87⁸
90.13#
100.00α

CV
-
1.56
7.70
4.04
2.10
-
1.53
3.50
5.33
1.41
-
1.89
5.24
2.56
0.53

value

40.09
313.59
313.59
4401.95

8.80
716.53
716.53
11451.8

32.48
889.31
889.31
33357.00

Means with the same alphabet, number, symbol, and Greek letter as superscript within same columns are not significantly different at 5% significance level.

Table 1 shows that there was significant difference () within each soaking temperature and steaming time treatment combination for the three rice varieties with respect to head rice yield. In general, the head rice yield of the three rice varieties had increased as the soaking temperature and steaming time increased. Gumara, Edget, and Narica4 rice varieties soaked at 80°C and steamed for 50 minutes gave the highest yield and best quality rice with a mean value of 93.60%, 97.93%, and 91.67%, respectively. According to Musa et al. [23], head rice yield is the current standard to assess commercial rice milling quality, and hydrothermal treatment increases head rice yield which then increases the quality indexes of processed rice [24].

The mean value of broken grains decreased as the soaking temperature and steaming time increased for all the three rice varieties. For instance, at 80°C and 50 min treatment, the percentage of broken rice was 6.4% (68.53% for control), 2.07% (70.47% for control), and 8.33% (90.3% for control) for Gumara, Edget, and Narica4 rice varieties, respectively. Different researchers also reported the good effect of parboiling in reducing the percentage of broken rice during milling. For instance, Ayamdoo et al. [22] reported that broken grains significantly decrease from 47% of control samples to 9.5% of parboiled rice. Prasad et al. [21] also reported that percentage of broken rice was significantly reduced from 27.25% for control to 6.31% for parboiled treatment.

The mean percentage value of chalkiness for Gumara rice variety ranged from 0 to 97.33%; for Edget, it ranged from 0 to 97.80% and Narica4 from 0.13 to 100% as compared to almost 100% for the control of all rice varieties. There was a significant difference () with respect to chalkiness in all rice varieties within the treatment combinations. Less mean percentage chalkiness value for Gumara rice variety (1.53%-0.0%) between 70°C, 10’ and 80°C, 50’; Edget variety (0.87%-0.0%) between 60°C, 50’ and 80°C, 50’; and Narica4 rice variety (0.93%-0.13%) between 70°C, 50’ and 80°C, 50’ was recorded. Generally, the result this study shows that as the soaking temperature and steaming time increased, the percentage chalkiness decreased. As a result, the endosperm translucency, which is an acceptable quality parameter for rice, was enhanced. The translucency character of the endoderm increases during parboiling treatment, mainly due to the pregelatinization of its starch [25]. This character of the endosperm mostly determines the appearance of the grain, and this is inversely related to the amount of chalkiness. Parboiling and cooking processes disappear partially or totally the chalkiness of rice, which may have no direct effect on cooking and eating qualities. But a large amount of chalkiness downgrades the physical quality, reduces milling recovery, and can determine attractiveness on a competitive price on the market [15, 26–28].

As indicated in Table 2, Edget rice had the highest percentage head rice (60.4%) compared to the other two rice varieties. Similarly, less percentage of broken rice (39.6%) and chalkiness (55.18%) was recorded for Edget rice. The result of varietal effect indicated that there was no significant difference between Gumara (34.41) and Narica4 (32.84) () rice varieties in terms of head rice yield and percentage of broken rice.

Table 2: Overall effects of varieties on physical properties.

Variety
Husking quality %
Moisture content
% head rice
% broken
% chalkiness

Edget
78.62ba
14.38⁰
60.40!
39.60β
55.18b

Gumara
78.28b
14.01¹
34.41±
65.59α
58.41b

Narica4
80.02a
13.62²
32.84±
67.16α
76.68a

CV
3.66
4.24
25.41
18.82
30.87

value
2.65
31.63
159.84
159.84
27.34

Means with the same alphabet, number, symbol, and Greek letter as superscript within columns are not significantly different at 5%.

As indicated in Table 3, soaking temperature significantly affected () the percentage of head rice, broken rice, and percentage chalkiness of the rice. As soaking temperature increased, percentage of head rice increased and percentage of broken rice reduced. Chalkiness at 40°C, 50°C, and 60°C was not significantly different from the control () but significant differences were observed at higher temperatures (70°C and 80°C). Similarly, as steaming time increased, percentage of head rice increased and percentage of broken rice reduced. In addition, steaming time significantly affected () the percentage chalkiness of rice.

Table 3: Effect of soaking and steaming time on the physical properties of rice varieties (Gumara, Edget, and Narica4).

Moisture content
% head rice
% broken
% chalkiness

Soaking T°(°C)
40
13.91b
13.84⁴
86.16!
97.62α

50
14.38a
24.50³
75.50±
96.60α

60
14.11ba
35.28²
64.72#
88.59α

70
13.96b
57.41¹
42.59$
26.82β

80
13.84b
85.49⁰
14.51ͷ
0.16γ

Control
13.14c
23.62³
76.38±
100α

CV
4.24
25.41
18.82
30.87

value
5.79
314.20
314.20
241.63

Steaming time (min)
10
14.25a
28.05³
71.95!
65.16β

20
14.06a
35.45²
64.55±
64.66β

30
14.02a
45.10¹
54.90#
64.37β

40
13.69b
49.83¹
50.17#
64.22β

50
14.18a
58.09⁰
41.91$
51.38γ

Control
13.14c
23.62³
76.38!
100α

CV
4.24
25.41
18.82
30.87

value
5.87
53.76
53.76
4.12

Means with the same alphabet, number, symbol, and Greek letter as superscript within columns are not significantly different at 5% significance level.

3.2. Cooking Properties of Rice Varieties

The minimum cooking time for Gumara ranged from 16 min (at 40°C, 10’) to 23 min (at 80°C, 50’), for Edget 16 min (at 40°C, 10’) to 23 min (at 80°C, 50’), and for Narica4 15 min (at 40°C, 10’) to 20 min (at 80°C, 50’) (Table 4). The trend revealed that when soaking temperature and steaming time increased, the cooking time also increased. The results obtained were similar with that reported by Farhan et al. [20] (20.67 min for nonparboiled rice to 25.00 for parboiled rice), Tetens et al. [29] (15.42-17.20 min for raw and for parboiled rice 20.70-23.05 min), Otegbayo et al. [30] (56 min for parboiled and 49 min for nonparboiled rice), and Kar et al. [31] (22 min for parboiled and 15 min for raw rice). Cooking time of parboiled rice was longer than the nonparboiled rice because of the strong cohesion between endosperm cells that makes the tightly packed starch granules to hydrate at a slower rate, which leads to a decreased in-water penetration into the grain [30].

Table 4: Cooking property of rice varieties at different soaking temperature and steaming time.

Soaking T (°c)
Steaming time (min)
Gumara
Edget
Narica4

Minimum cooking time
Water uptake ratio
Swelling ratio
Minimum cooking time
Water uptake ratio
Swelling ratio
Minimum cooking time
Water uptake ratio
Swelling ratio

40
10
16
3.27bc
2.46θ
16
3.12a
2.11ηθ
15
3.70igh
4.59ε

40
20
16
3.33bac
2.46θ
16
3.25a
1.88ι
15
4.31edf
3.02ι

40
30
16
3.34bac
2.47ηθ
16
3.23a
2.29η
16
3.61ih
3.22ιθ

40
40
17
3.34bac
2.53ηζθ
16
3.15a
2.33ηζ
16
3.67igh
5.08βαγ

40
50
17
3.35bac
2.55ηζθ
18
3.15a
2.10ηθ
16
3.93ghf
5.22α

50
10
17
3.26bac
2.57ηζθ
18
3.18a
2.20η
16
3.98eghf
3.25ιθ

50
20
17
3.33bac
2.58ηεζθ
18
3.16a
2.14η
17
4.77bac
4.88εβδαγ

50
30
17
3.35bac
2.58ηεζθ
18
3.18a
1.11λ
17
4.08egdf
5.16βαγ

50
40
17
3.36bac
2.59ηεζθ
18
3.18a
1.50κ
17
4.75bac
4.09ζ

50
50
18
3.37bac
2.60ηεζθ
18
3.21a
1.73ι
17
5.08a
4.76εβδγ

60
10
19
3.36bac
2.61ηεζθ
19
3.20a
1.82ι
17
4.96a
4.58ε

60
20
19
3.38bac
2.58ηεζθ
19
3.21a
2.65εδ
17
4.07egdf
5.17αγ

60
30
20
3.38bac
2.60ηεζθ
19
3.15a
2.76εδγ
17
5.03a
4.92εβδαγ

60
40
20
3.39bac
2.60ηεζθ
19
3.24a
2.60ε
17
3.68igh
2.94ι

60
50
20
3.38bac
2.61ηεζθ
19
3.23a
2.86βδγ
17
4.78bac
4.88εβδαγ

70
10
20
3.42bac
2.63εζδ
21
3.36a
3.04βα
18
3.97eghf
3.47ηθ

70
20
20
3.42bac
2.62ηεζδ
21
3.30a
3.15α
18
4.82ba
3.83ηζ

70
30
20
3.42bac
2.64εζδ
22
3.33a
2.90βγ
19
4.41dc
3.36ιθ

70
40
21
3.43ba
2.64εζδ
22
3.35a
2.53εζ
19
4.35ed
3.14ιθ

70
50
21
3.44ba
2.67γεζδ
22
3.35a
1.41κ
19
3.95eghf
4.62εδ

80
10
21
3.45a
2.67γεζδ
22
3.36a
2.75εδγ
19
4.35ed
4.61ε

80
20
22
3.46a
2.73γεβδ
23
3.33a
2.31ηζ
20
3.64ih
4.08ζ

80
30
22
3.46a
2.81γβ
23
3.37a
2.66εδ
20
3.45i
4.13ζ

80
40
22
3.46a
2.86β
23
3.38a
3.07βα
20
3.57ih
5.06βδαγ

80
50
23
3.47a
3.00α
23
3.40a
2.98βαγ
20
3.70igh
4.63εδ

Control
16
3.23c
2.77γβδ
16
3.11a
2.09ηθ
15
4.45bdc
4.71εδγ

CV
-
3.07
3.15
-
7.53
5.71
-
5.13
5.46

value

1.24
6.45

0.42
50.21

16.30
31.73

Means with the same alphabet and Greek letter as superscript within columns are not significantly different at 5%.

As shown in Table 4, the result of water uptake ratio for Gumara rice variety shows that there was no significant difference among each soaking temperature and steaming time treatment combination () from (40°C, 20’) to (80°C, 50’). But the mean value of water uptake ratio within the treatment combination is ranged from 3.33 at (40°C, 20’) to 3.47 at (80°C, 50’) with the control value of 3.23. There was no significant difference throughout the treatment combination, including the control for Edget variety (). The mean value within the treatment combination is ranged from 3.12 at (40°C, 10’) to 3.40 at (80°C, 50’) with the control value of 3.11. There was a significant difference between the treatment combinations of Narica4 rice variety (). The mean value within the treatment combination is ranged from 3.45 at (80°C, 30’) to 5.08 at (50°C, 50’) with the control value of 4.45. Among those three varieties, Narica4 rice variety achieved the highest mean value of the water uptake ratio. In this study, for Narica4 rice variety, no clear trend was observed with the changes in the water uptake ratio at different storage of treatment combination; however, the results clearly showed that parboiling drastically increased the water uptake ratio of the rice. Hence, for Gumara and Edget varieties, increasing the soaking temperature and soaking time increases the mean value of water uptake ratio. Similar to the result obtained by Otegbayo et al. [30], the water absorption of the parboiled rice was higher (13.56 ml/g) than that of the nonparboiled rice (10.31 ml/g). Kurien et al. [31] reported that water absorption capacity, as reflected by the swelling ratio, is significantly low for parboiled rice as compared with raw rice cooked for the same period (at 10 min, raw (2.22) to parboiled (2.06)). However, the samples of raw and parboiled rice cooked to an equivalent degree of softness show that parboiled rice can absorb more water without losing its shape (from 2.06 at 10 min to 3.55 at 40 min) [32]. Mustapha [33] indicates that parboiled rice has higher water absorption, which may be a result of the steaming pressure during parboiling, which in turn, affects starch gelatinization.

The mean value of swelling ratio for Gumara rice variety was ranged from 2.46 at 40°C, 10’ to 3.00 at 80°C, 50’ with the control mean value of 2.77 (Table 4). The data revealed that there was a significant difference () within the treatment combination, including the control. The trend of this data for specific Gumara rice variety indicates that the swelling ratio had increased as the soaking and steaming time were increasing. Also, the mean value of Edget rice variety was ranged from 1.11 to 3.15, and that indicates there was a significant difference (). There was no clear trend observed for the swelling ratio data of Edget variety. Narica4 rice variety has mean value ranged from 2.94 at 60°C, 40’ to 5.22 at 40°C, 50’ with the control mean value of 4.71. In this study, for Narica4 rice variety, no clear trend was observed with the changes in the swelling ratio at different storage of treatment combination; however, the results clearly showed that parboiling drastically increases the swelling power of the parboiled rice. Kurien et al. [32] reported that the swelling ratio is significantly low for parboiled rice as compared with raw rice cooked for the same period (at 10 min, raw (2.57) to parboiled (2.32)). However, the samples of raw and parboiled rice cooked to an equivalent degree of softness show that parboiled rice can absorb more water without losing its shape (from 2.32 at 10 min to 4.54 at 40 min) [32].

There was a significant difference () in minimum cooking time, water uptake ratio, and swelling ratio among the three varieties (Table 5). The minimum cooking time was recorded for Gumara (19 : 00 min), whereas the highest water uptake and swelling ratio were recorded for Narica4 variety which were 4.20 and 4.28, respectively (Table 5). As indicated in Table 6, some soaking temperatures had significantly affected () the water uptake ratio and swelling ratio of the tested rice. But all steaming times, including the control, did not significantly affected () the water uptake ratio and swelling ratio.

Table 5: Overall effects of varieties on cooking properties of rice varieties.

Variety
Minimum cooking time (min)
Water uptake ratio
Swelling ratio

Edget
19.42a
3.25²
2.35#

Gumara
19.00b
3.38¹
2.63±

Narica4
17.46c
4.20⁰
4.28!

CV
3.26
8.96
17.25

value
74.93
199.19
301.48

Means with the same alphabet, number, and symbol as superscript within columns are not significantly different at 5%.

Table 6: Effect of soaking temperature and steaming time on cooking properties for Gumara, Edget, and Narica4 rice varieties.

Water uptake ratio
Swelling ratio

Soaking T°(°C)
40
3.45b
2.95¹

50
3.68a
2.92¹

60
3.71a
3.21¹⁰

70
3.69a
2.98¹

80
3.52ba
3.36⁰

Control
3.59ba
3.19¹⁰

CV
8.96
17.25

value
5.82
5.84

Steaming time (min)
10
3.59a
3.02⁰

20
3.65a
3.07⁰

30
3.59a
3.04⁰

40
3.57a
3.04⁰

50
3.65a
3.24⁰

Control
3.59a
3.19⁰

CV
8.96
17.25

value
0.71
1.27

Means with the same alphabet as superscript and number within columns are not significantly different at 5% significance level.

4. Conclusion and Recommendation

The study explored the effect of parboiling on physical and cooking qualities of three rice varieties, Gumara, Edget, and Narica4. Higher soaking temperatures and steaming times increased the head rice yield, water uptake ratio, and swelling ratio and decreased chalkiness and broken rice which are indicators of good quality rice. On the other hand, the swelling ratio for Edget rice and water uptake ratio and swelling ratio for Narica4 variety had no clear trend at treatment conditions. Higher treatment conditions increased the cooking time of parboiled rice varieties compared to the cooking time of nonparboiled rice. In general, parboiling with prolonged soaking temperature and steaming time improved the physical and cooking quality of local rice varieties.

Data Availability

The husking quality (%), moisture content (%), head rice yield (%), broken rice (%), chalkiness (%), minimum cooking time (min), water uptake ratio, and swelling ratio data used to support the findings of this study are included within the article.

Conflicts of Interest

The authors declare that they have no competing interests.

Authors’ Contributions

MA and DA conceived and designed the experiments. MA, DA, YS, TG, and TK collected and analyzed the data. MA, DA, and SY contributed to the writing of the manuscript.

Acknowledgments

The authors would like to extend our gratitude to Amhara Agricultural Research Institute (ARARI) for the financial support and Fogera National Rice Research and Training Center for supplying raw materials and allowing to us to use rice dehusking and polishing machine.

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