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Introduction
Rice (Oryza sativa) is one of the most important dietary staple foods worldwide, and especially so for Asian people. At present, there is significant interest in its nutritional balance, as exemplified by research into fortified rice and glycemic index. Previous studies revealed some health effects of rice and its products1. Studies of rice pigmentation have identified that grains with red-brown or dark purple coloration may have useful nutritional benefits, including anti-oxidative and anti-inflammatory properties2. Moreover, colored rice is rich in nutrients, including vitamins and minerals, which vary depending on coloration as well as environmental conditions1,3,4. In Thailand, there are many varieties of rice. Therefore, consumers have many choices. Local rice varieties are becoming more popular due to increased consumer demand for organically-grown and healthier products. However, information on the local rice varieties grown in each Tambon (subdistrict), community or part of Thailand is still outdated; primarily only commercial rice consumption and composition data has been investigated. Even though the rice-growing area of southern Thailand is not the biggest of Thailand’s rice-growing areas, there are 82 local southern rice varieties5; some, such as Sang Yod Phattalung are popular and are finally developing to commercial premium quality in the national Thai rice market. Three southern border provinces of Thailand – Narathiwat, Yala and Pattani – located close to the marginal body of water in the western Pacific Ocean and Malaysia, experience environmental variation in growing conditions such as climate and soil properties when compared to rice production areas elsewhere in Thailand. These factors may influence the grain quality and nutrient content of local rice varieties. Narathiwat is home to one of the local rice-growing areas in the three Southern border provinces of Thailand. The local variety, named Hawm Gra Dang Ngah (HGDN), originated in Narathiwat. HGDN’s rice features a red pericarp, and sub-varieties, established hundreds of years ago continue to be grown in the region. More recently, a pure line designated HGDN PTNC09002-59 has been produced6. This study is the first pilot report to describe the physical and nutritional characteristics of local HGDN in 4 large rice-growing areas. This research is key to developing nutritional qualities, breeding and further supporting growing local HGDN rice in Narathiwat, and ultimately developing this variety to commercial premium quality.
Materials and Methods
Rice Samples and Chemicals
HGDN rice samples used in this study were locally grown in 4 Tambons: Phron, Bangkhunthong, Praiwan and Salamai, in Takbai amphoe (district), Narathiwat, Thailand. The samples were collected from 4 households per Tambon during February-March 2019. The pre-harvest and post-harvest activities were carried out manually. Paddy were dried in the sun for 3 days before packing in sacks.
Physical Characteristics of Paddy and Dehusked Rice
Grain Dimensions
In order to classify the types of paddy and dehusked rice7, the grain dimensions of paddy and dehusked rice were determined. The length and width were measured by digital Vernier caliper and the ratio of length and width was calculated. These figures are shown in Table 1.
Table 1: Classification of the Types in Paddy and Dehusked Rice7
| Types of grain | Paddy (length:width ratio) | Dehusked rice(length:width ratio) |
| Long | ≥ 3.4 | ≥ 3.1 |
| Medium | 2.3-3.3 | 2.1-3.0 |
| Short | ≤ 2.2 | ≤ 2.0 |
1000-Grain Weight
1000-grains weight of both paddy and dehusked rice, selected at random, were weighed using a digital scientific scale.
Color of Paddy and Dehusked Rice
The color of both paddy and dehusked rice was determined using a Hunter-Lab Colorimeter (Ultrascan Color Flex, USA). The colorimeter was calibrated with white board. It was set with standard condition of illumination D65 and observation 10°. The color parameters (L*, a* and b*) according to The International Commission on Illumination (CIE) were then read. Four biological replicates were performed for each sample.
Nutritional Values
The proximate analyses for full standard nutritional values of dehusked HGDN rice, according to Thailand nutrition labeling, were performed using standard procedures8.
Statistical Analysis
All the analyses were carried out with at least five replicates and expressed as a mean and standard deviation. Data were statistically analyzed by one-way analysis of variance (ANOVA) and significant differences between two means were identified by Duncan’s multiple range test using SPSS statistics program version 26.0. The probability value of less than 0.05 was considered significant. A comparison of nutritional values (mean and standard deviation) between local HGDN and pure line selection HGDN PTNC09002-59 was performed.
Results
Physical Characteristics of Paddy and Dehusked Rice
Table 2 shows the physical characteristics of paddy including grain dimensions, 1000-grain weight and color parameters. Significant differences (p<0.05) within each column are indicated with different superscript letters. The values of length and width of each Tambons’ paddy were in the range 8.28-8.83 mm. and 2.41-2.60 mm, respectively. The paddy grain of Phron was medium whereas others were long. The values of 1000-grain weight were in the range of 20.30-28.06 g. The color parameters of L*, a* and b* express the brightness, red and yellow, respectively. The L*, a* and b* values were in the range 51.68-53.35, 5.63-6.09 and 16.78-17.10, respectively. The a* and b* values did not show significant differences (p<0.05) between any Tambons.
The physical characteristics of dehusked rice are shown in Table 3. The values of length and width of each Tambons’ dehusked grain were in the range 6.17-6.69 mm. and 1.92-2.27 mm, respectively. The dehusked grain types of Bangkhunthong and Salamai were long, while Phron and Praiwan corresponded to the medium type of dehusked grain. The values of 1000-grain weight were in the range of 16.19-19.53 g. The values of L* were in the range 42.09-44.89 which shows no significant difference (p<0.05) between Bangkhunthong, Phron and Salamai. The value of a* was in the range 9.78-10.57 and all Tambons showed no significant differences (p<0.05). The value of b* was in the range 12.38-13.41 and showed the same values in Bangkhunthong and Salamai. The physical characteristics of paddy and dehusked rice are presented in Figure 1.
Table 2: Physical Characteristics of Paddy.
| Tambons | Paddy | 1000-grain weight (g) | Color parameters | ||||
| Length (mm) | Width (mm) | Types of grain | L* | a* | b* | ||
| Bangkhunthong | 8.83±0.47a | 2.57±0.23ab | Long | 24.55±8.51ab | 52.26±1.38ab | 6.09±0.58a | 17.10±1.23a |
| Phron | 8.67±0.51ab | 2.60±0.21a | Medium | 20.30±1.14b | 51.68±1.66b | 5.63±0.77a | 16.78±2.17a |
| Praiwan | 8.42±0.64ab | 2.41±0.20b | Long | 25.20±7.86ab | 53.35±1.86a | 5.99±0.58a | 17.33±1.36a |
| Salamai | 8.28±0.70b | 2.44±0.22ab | Long | 28.06±8.09a | 52.46±1.89ab | 6.01±0.65a | 16.60±1.10a |
Mean value ± standard deviation of five replicates.
Mean values with different letters (a-c) in the same column are significantly different (p<0.05).
Table 3: Physical Characteristics of Dehusked Rice.
| Tambons | Dehusked rice | 1000-grain weight (g) | Color parameters | ||||
| Length (mm) | Width (mm) | Types of grain | L* | a* | b* | ||
| Bangkhunthong | 6.66±0.25a | 1.92±0.26c | Long | 18.50±1.35ab | 43.79±1.87a | 9.84±1.07a | 12.72±0.75ab |
| Phron | 6.29±0.43b | 2.10±0.20b | Medium | 16.19±0.92c | 44.26±1.58a | 9.78±1.22a | 12.38±1.22b |
| Praiwan | 6.69±0.28a | 2.27±0.15a | Medium | 17.23±0.99bc | 42.09±1.41b | 10.57±0.48a | 13.41±0.66a |
| Salamai | 6.17±0.52b | 1.97±0.24bc | Long | 19.53±4.49a | 44.89±2.43a | 10.50±0.67a | 12.72±1.08ab |
Mean value ± standard deviation of five replicates.
Mean values with different letters (a-c) in the same column are significantly different (p<0.05).
 |
Figure 1: Physical Characteristics of Paddy (left) and Dehusked (right) Rice in (A) Bangkhunthong, (B) Phron (C) Praiwan and (D) Salamai. |
Nutritional Value
The nutritional values of dehusked HGDN rice in 4 Tambons are presented in Table 4. Significant differences (p<0.05) within each row are indicated with different superscript letters.
The total energy determined per 100 g sample in each of the 4 Tambons were in the range 356-362 kcal. The dehusked HGDN rice in Phron showed the highest total energy (362.56±0.66). The nutritional value of total fat was in the range 2.44-3.07 g. The dehusked HGDN rice grown in Phron showed higher energy, and that grown in Salamai showed higher total fat, than those grown in the remaining areas. The amounts of protein, carbohydrate, dietary fiber and total sugar were in the ranges 6.83-8.73 g, 74.2-77.5 g, 4.1-5.0 g and 1.11-1.36 g, respectively. There was no cholesterol found in any dehusked HGDN rice. Samples from each Tambon showed significant differences in the amount of protein, carbohydrate and total sugar; however, there were not significant differences in the amount of dietary fiber.
The amounts of vitamins found were: vitamin B1 (0.41-0.50 mg), and vitamin B2 (0.077-0.093 mg). The number of minerals such as calcium and iron were 9.67-13.31 mg and 0.87-1.01 mg, respectively. Overall, the dehusked HGDN rice grown in Bangkhunthong showed the highest levels of vitamins and minerals. The moisture content was in the range 11.68-13.22 g.
Local HGDN was found to have higher total fat, carbohydrate, dietary fiber and ash than HGDN PTNC09002-59. Interestingly, calcium content detected in local HGDN was only a quarter that of HGDN PTNC09002-59, as shown in Table 5.
Table 4: Nutritional Values of Dehusked HGDN Rice in each of 4 Tambons (units per 100 g/dry weight)
| Compositions | Bangkhunthong | Phron | Praiwan | Salamai |
| Energy (kcal) | 356.24±1.07c | 362.56±0.66a | 359.00±0.49b | 358.55±0.99bc |
| Total fat (g) | 2.73±0.12b | 2.44±0.08c | 2.95±0.07ab | 3.07±0.10a |
| Protein (g) | 8.73±0.01a | 7.65±0.00c | 8.22±0.03b | 6.83±0.03d |
| Carbohydrate (g) | 74.20±0.07d | 77.50±0.14a | 74.90±0.21c | 75.90±0.07b |
| Dietary fiber (g) | 4.99±0.14a | 4.10±0.07a | 5.00±0.04a | 4.70±0.11a |
| Total sugar (g) | 1.26±0.04b | 1.18±0.01c | 1.36±0.00a | 1.11±0.00d |
| Vitamin B1 (mg) | 0.501±0.00a | 0.490±0.06a | 0.430±0.03a | 0.410±0.00a |
| Vitamin B2 (mg) | 0.077±0.00c | 0.086±0.00b | 0.093±0.00a | 0.080±0.00c |
| Calcium (mg) | 13.31±0.53a | 10.93±0.01b | 10.36±0.76b | 9.67±0.40b |
| Iron (mg) | 1.01±0.09ab | 0.87±0.04b | 0.93±0.01ab | 1.01±0.00a |
| Ash (g) | 1.19±0.00b | 0.75±0.01d | 1.10±0.00c | 1.34±0.00a |
| Moisture (g) | 13.22±0.03a | 11.68±0.02c | 12.89±0.07b | 12.88±0.01b |
Mean value ± standard deviation of five replicates.
Mean value with different letters (a-c) in the same row are significantly different (p<0.05).
Table 5: Comparison of Nutritional Values between Local HGDN and Pure Line Selection HGDN PTNC09002-59.
| Compositions | Local HGDN (This study) | Pure line selection HGDN PTNC09002-596 |
| Total fat (g) | 2.79±0.27 | 2.42 |
| Protein (g) | 7.85±0.81 | 8.96 |
| Carbohydrate (g) | 75.62±1.43 | 71.40 |
| Dietary fiber (g) | 4.69±0.42 | 1.52 |
| Calcium (mg) | 11.06±1.58 | 47.02 |
| Iron (mg) | 0.95±0.07 | 1.12 |
| Ash (g) | 1.09±0.25 | 0.87 |
Discussion
The grain type of paddy and dehusked rice was in the ranges of medium and high. In each Tambon, the most common type of paddy was long, except Tambon Phron. On the other hand, the most common type of dehusked rice was balanced between medium and long. The paddy and dehusked rice of pure line selection HGDN PTNC09002-59 were medium. The physical characteristics of local HGDN grown in Takbai differ from those of HGDN PTNC09002-59. However, the investigation of local rice varieties’ physical characteristics by Phodjanawichaikul9 showed similar ranges in the ratios of length and width to the values found for paddy and dehusked rice in this study. The color parameters of paddy and dehusked pigmented rice showed less difference within Tambons. The red-brown color of local dehusked HGDN had lower values of L* and higher values of a* compared to the previous study of HGDN10, which was provided by Pattani, Thailand; therefore, local dehusked HGDN color was darker and redder in this study. Its pigment was in the color range of local rice Sang Yod Phattalung, popular rice in Phatthalung, located to the north of Narathiwati10. Given the red-brown pericarp, the differences in grain color could depend on the quantities and proportions of polyphenols, which mainly consist of the anthocyanins cyanidin-3-O-β-D-glucoside and peonidin-3-O-β-D-glucoside in the grain2. These components of pigmented rice elevate the potent antioxidant activity, provide health benefits and have the potential for nutraceutical development. However, further study should include consideration of environmental variations in growing conditions such as climate and soil properties. The Narathiwat Meteorological Department data reported the last 3-year rainfall in Amphoe Takbai during sowing in November and harvest in March was an optimal amount of water in the middle range of 10.1-35.0 mm11.
All Tambons were found to contain comparable nutrient levels. The comparison of the nutritional content of local HGDN was within the range of protein, carbohydrate and ash observed by previous studies6,9,10, 12; however, all of 4 Tambons showed higher amounts of dietary fiber and total fat. This data has shown local HGDN grew in Takbai still requires more research and breeding programs to develop nutrient content.
Rice is also a good source of vitamin B1 (thiamine) and vitamin B2 (riboflavin)1. Local HGDN has high levels of thiamine compared to previous studies of thiamine content, which found ranges of 0.144-0.447 mg13 and 0.16-0.32 mg14. Thiamine is useful in treating vitamin B1 deficiencies such as muscle weakness and neuritis1,15. Phosaeng and colleagues showed that the thiamine content in grains depended on the rate of biosynthesis and bioaccumulation during grain development13. Riboflavin content of local HGDN in each Tambon was in the range 0.08-0.09 mg/100g. However, the only previous report of vitamin B2 content was found in Pathum Thani 1 brown rice, which contained 0.12 mg/100g16. Other reports showed low levels of riboflavin in raw Brazilian long-grain white rice (<0.02 mg/100g)17,18 and Basmati rice from India (0.033 mg/100g)18,19. Riboflavin is a co-enzyme in many reactions, such as its role as an electron carrier in cell respiration (related to releasing the energy of carbohydrate, fat and protein in the growth process), and the composition of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) in the metabolism of many nutrients20.
Conclusion
Local HGDN from 4 Tambons in the largest local HGDN rice-growing area of Takbai, Narathiwat, in this pilot study indicated that red-brown grain contains comparable nutrient levels among 4 Tambon. Moreover, the recorded values of carbohydrate, total fat, dietary fiber, thiamine and riboflavin are higher than previous reports. Local HGDN will be an excellent source of energy and vitamin B. The nutrient content data presented here will provide new information about local HGDN, thus supporting agricultural industry in Takbai to continue growing HGDN for commercial use, and providing further information to Takbai, Narathiwat Provincial Agricultural Extension Office in order to increase promotion of local HGDN for commercial sale in the Thai rice market. This study also contributes basic knowledge of the nutritional values of food products derived from HGDN, providing a basis for the development via breeding of new local HGDN to complement the pure line selection HGDN PTNC09002-59.
Acknowledgments
The authors are grateful for a supplementary financial support grant provided by the Anandamahidol Foundation. In addition, the authors would like to thank Mr. Sommay Janpan (Former Chief of Takbai District Agricultural Extension Office), his team and all the agriculturers who contributed to this work by producing grain samples and supporting the authors for all their activities, and Associate Professor Dr. Jiraporn Chompikul (ASEAN Institute for Health Development) for statistical suggestions.
Funding Sources
This study was fully funded by a supplementary financial support grant from Anandamahidol Foundation.
Conflicts of Interest
The authors declare no conflict of interest.
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