Two main species of cultivated rice in the world are Oryza sativa (Asian rice) and Oryza glaberrima (African rice). The Oryza sativa species, which is grown worldwide, is far more widely utilized compared with the Oryza glaberrima species, which is grown in West Africa. Recently, the annual rice production has reached almost 480 million tonnes, and this demand is expected to rise to 550 million tonnes in 2035. Thus, this increases the need to characterize and maintain the quality of rice and hence to determine the price of rice appropriately. Obviously, modern technologies that can provide fast and accurate measurement are essential in the large-scale industrial rice processing. In this chapter, several technologies and instruments used for rice processing are reviewed. The principle of the measurement for each technology is briefly described. The strength of this chapter is to introduce the application of microwave technology during rice processing, such as rice dying process, rice moisture detection, broken rice measurement and rice insect control. The pros and cons of the microwave method will be discussed in detail. Hence, some standard test laboratory for monitoring of carbohydrate, protein, fat and trace elements content is also described in this chapter.
- rice physical properties
- rice chemical properties
- broken rate
There are more than 40,000 different types of rice in the world. However, commonly, rice is categorized by its physical shape and sizes or length either long grain, medium grain or short grain. Rice consists of two main species, which are
2. Various manufactured brand of rice grain
There is existing variety of rice in the market, but most of the users are not experienced in distinguishing between the rice in terms of its physical and chemical properties. In this chapter, up to 10 types of commercial rice grain have been chosen to show the distinction between their properties, as well as the techniques used to characterize its properties. The basic physical properties (moisture content,
|Manufactured brand of rice||Weight before heat (g)||Weight after heat ||Weight losses ||Moisture content ||Average length ||Average width |
|1. Sakura Super Thai Brown Rice||10.005||8.556||1.449||14.48||7.52||1.76|
|2. Jasmine Nutririce||10.003||8.524||1.479||14.79||7.29||2.04|
|3. Floral Glutinous||10.004||8.389||1.615||16.14||7.06||1.95|
|4. Maharaja Basmathi||10.009||8.377||1.632||16.30||6.79||1.52|
|5. SUMO Calrose||10.008||8.320||1.688||16.87||4.92||2.80|
|6. Bird of Paradise Thai Fragrant||10.010||8.303||1.707||17.05||7.18||1.86|
|7. Sakura Super Basmathi Pakistan||10.008||8.248||1.76||17.59||7.06||1.80|
|8. Giant Super Special White Rice||10.002||8.228||1.774||17.74||7.33||2.06|
|9. Sun Rise Australian Fragrant||10.005||8.203||1.802||18.01||7.22||1.90|
|10. Phkarkhnei Cambodi Organi||10.002||8.150||1.852||18.52||7.58||1.92|
3. Applications of scientific methods and microwave equipments in rice processing
3.1. Rice drying and sterilization processing
The moisture content,
In fact, the interaction between agri-foods materials containing water with microwave can be described by the complex relative permittivity,
where the real part,
The water removal rate of the rice grain is increased with the microwave power. However, the higher microwave power will increase the percentage of the broken milled rice and higher rate of oxidation as well as nutritional losses of the milled rice. Typically, the microwave oven power will be adjusted to 55°C of heating temperature in order to reduce the
There are two microwave frequencies allocated by the US Federal Communications Commission (FCC) for industrial, scientific and medical (ISM) use, which are 915 MHz and 2.45 GHz. Normally, most of the microwave heating applications are devoted to 2.45 GHz, since it provides a suitable compromise between power deposition and penetration depth, as well as it is an unlicensed operating frequency. For instance, the manufactured microwave heating system for agri-food products is shown in Figure 4.
3.2. Rice moisture sensing
There are two methods of determining moisture content,
In contrast, the indirect method requires the measurement of the electrical property of the rice grain using fabricated instrument, so-called moisture meter. The change in electrical properties can be directly correlated with a change in the actual moisture content,
As mentioned above, the polarization of water molecules contained in the rice grain is sensitive and showed a significant response when exposed to microwaves, and this will allow the microwave sensor to be used as a measuring technique to sense the moisture content,
In this section, some of the microwave sensors related to the grain moisture measurement are presented. A microwave microstrip ring resonator as miniaturized and nondestructive sensor for single wheat grain microwave estimation were reported by Abegaonkar et al.  as shown in Figure 5. The ring resonator was designed on an alumina substrate with a
In this study, a wheat grain was overlaid on the ring resonator and its corresponding measured resonant frequency
Kim et al.  proposed a prototype microwave transceiver grain moisture meter based on free-space transmission method for rice grain
A multilayer microstrip moisture sensor was developed by Jafari et al.  for measuring the
You et al.  proposed cylindrical slot antennas as sensors for rice quality (
Both sensors were designed to operate at 1 GHz for
The comparison of the measured
3.3. Broken rice detection
The rice grain has a length <3/4 but more than 1/4 of the average head grain length are categorized as a broken rice as shown in Figure 12. Normally, the bulk rice, which contains broken grain for 0–5, 5–20, 20–35 and 35–50%, is classified as a premium grade, grade 1, grade 2 and grade 3, respectively. Using conventional broken rice sorting machine, the mechanical filter techniques are implemented. Since broken rice has a size smaller than head rice, the broken rice can be filtered by the wire net with small size of mesh in the machine. Recently, the image processing technique is popularly used for grading and classification of rice, in which the optical scanning is used to differentiate the size and color of the rice grain [12–14].
The optical techniques are able to recognize the ratio of broken rice and the impurities in bulk rice sample based on the pixel image area and pixel intensity for each rice grain. By using the developed image processing software, the dimensional features of the rice kernels such as length, perimeter and projected area were extracted from the captured images. Empirical equations that relate the BR percentage and characteristic dimension ratio, which is computed from the dimensional features, were developed for percentage of BR estimation. The result showed that the BR percentage can be estimated with average error of 2%. For instance, in the work done by Lloyd et al
In this section, an alternative broken rice measurement using microwave techniques is introduced. The measurement technique is based on the change in air gap density in the bulk rice, since the air gap between broken grains is smaller than the normal rice grains. The electromagnetic wave is generated from microwave sensor and radiated into the bulk grain sample. In fact, the air gap density in the grain sample is inversely proportional to the density of radiated field, which is covering inside the grain sample .
Besides moisture measurement, the cylindrical slot sensors in Figure 8(a) and Figure 8(b) (Section 3.2) can also be implemented for percentage of BR determination. In this BR percentage measurement, the sensors were operated at 13.5 GHz based on the measured magnitude of reflection coefficient |γ| from a vector network analyzer. The short wavelength or high-frequency signal is required to enhance the air gap sensitivity for broken rice measurement and reduce the penetration of energy into the rice grains . Figure 14 shows the variation in measured reflection coefficient |γ| of the rice grain with the percentage of broken rice in the samples at 13.5 GHz.
3.4. Rice insect detection and control
In addition to the above applications, microwave method can also be used to control and eliminate the rice weevils (in Figure 16) without affecting the texture of the rice grain. It is because each agri-food or biological specimen has unique energy absorption properties, which is mainly influenced by its loss factor
For instance, the values of
3.5. Rice nutrition test
3.5.1. Determination of total carbohydrate content by using phenol-sulfuric acid method
Hundred milligrams of each rice sample was weighed and hydrolyzed with 5 mL of 2N hydrochloric acid in a boiling water bath (80°C) for 1 h. The sample was left to cool at room temperature and neutralized with solid sodium carbonate, and then, distilled water was added to top the sample up to 100 mL. Meanwhile, the standard glucose solution was prepared by dissolving 100 mg of D-glucose with distilled water in a 100-mL volumetric flask. Ten milliliter of the standard glucose solution was further diluted to 100 mL, and the standard solution was used as working standard. A series of working standard of glucose solution was prepared by transferring 0.2, 0.4, 0.6, 0.8 and 1 mL of the working standard solution into five different volumetric flasks and topped up with distilled water (except the 1 mL sample) until the mark of 1 mL. On the other hands, 0.1 mL of the digested rice samples was pipetted and added with distilled water to bring the digests to 1 mL. Then, 1 mL of phenol solution (5%) and 5 mL of sulfuric acid (96%) were added to each digest, working standard and blank solution. All the digests, working standards and a blank solution were placed on a shaker and shook for 20 min to obtain homogeneous solutions. The amount of total carbohydrate content for all the digests, working standards and the blank was measured using an ultraviolet-visible spectrophotometer at 490 nm, and the absorbances were recorded as tabulated in Table 2.
|No.||anufactured rice grain||Concentration of rice sample (mg/mL)||Total carbohydrate content (%)|
|5||Sun Rise Australian Fragrant||0.083||83|
|6||Bird of Paradise||0.055||55|
|7||Phkarkhrrel Cambodi Organi||0.043||43|
|8||Sakura Super Thai||0.086||86|
|9||Sakura Super Pakistan||0.073||73|
|10||Giant Super Special Rice||0.051||51|
As given in Table 2, the carbohydrate contents for the ten different rice samples were ranged from 43 to 88%. Floral rice sample gave the highest carbohydrate content (88%), while Phkarkhrrel rice sample had the lowest carbohydrate content (43%). The average carbohydrate content for the 10 different rice samples was 70.2%. This result was similar to the finding that obtained by Deepa and coworkers  on various Indian rice samples. The carbohydrate content of their analysis was ranged from 61.7 to 91.7% with the average value of 73.5%.
3.5.2. Determination of protein content by using Kjeldahl method
To determine the protein content in rice samples, 0.15 g of each sample was refluxed with 1 mL of mixed catalyst (96% sodium sulfate anhydrous and 3.5% copper sulfate) and 3 mL of concentrated sulfuric acid. When the sample solution was turned into green-blue, 30 mL of distilled water, 10 mL of 45% sodium hydroxide, 10 mL of 0.5 N hydrochloric acid and a few drops of methyl red indicator were added into the mixture. The ammonia solution produced from the reaction was distilled and collected in a conical flask. The distillate was titrated with 0.5 N sodium hydroxide solution in order to determine the protein content.
The results of the protein content analysis for the 10 different types of rice sample were ranged from 1.40 to 11.11% as shown in Table 3. The highest protein content was found in Jasmine rice (11.11%), and the lowest was the Sun rice (1.40%). The average protein content for the 10 different types of rice sample was 6.25%. This result is similar to the results obtained by Kenedy and Burlingame  who had done a comprehensive protein analyses on thousands of rice varieties from different regions of the world. The protein content for the rice samples ranged from 4.50 to 15.90%, with the mean value of 8.8%.
|No||Manufactured rice||Volume of NaOH to titrate blank (mL)||Volume of NaOH to titrate HCl (mL)||% Nitrogen||% Protein (% nitrogen נ5.95)|
|5||Sun Rise Australian Fragrant||8.75||8.80||0.2333||1.40|
|6||Bird of Paradise||8.75||8.90||0.7000||4.17|
|7||Phkarkhrrel Cambodi Organi||8.75||8.90||0.7000||4.17|
|8||Sakura Super Thai||8.75||9.00||1.1667||6.94|
|9||Sakura Super Pakistan||8.75||9.05||1.6333||8.33|
|10||Giant Super Special Rice||8.75||9.10||1.6333||9.72|
3.5.3. Determination of fat content by using Soxhlet method
For analyzing the fat content, 1 g of each sample was placed in a porous thimble and the extracting solvent (150 mL of hexane) was placed in a dried, weighed distillation flask. The extraction was repeated continuously for a period of 1 h. The extracted fat presented in the distillation flask was dried in an oven at 100°C for 30 min. The flask was reweighted, and the increase in weight of the flask was taken as the weight of the fat present in the rice sample. Table 4 lists the fat content for the ten different types of rice sample. The highest fat content was found in the Bird of Paradise rice (4.79%), and the lowest was Jasmine rice (3.0%). The average fat content for the 10 different types of rice samples was 3.65%. However, the fat content obtained in this analysis is slightly higher compared to the results obtained by Oko et al.  with the average fat content of 2.5 and 1.5%, respectively.
|Manufactured rice grain||Weight of round bottom flask (g)||Weight of round bottom flask and extracted fat (g)||Weight of sample (g)||Extracted fat (g)||Fat (%)|
|1. Maharaja Basmathi||95.2746||95.3135||1.0306||0.0377||3.77|
|2. SUMO Calrose||94.8465||94.8798||1.0001||0.0333||3.33|
|3. Jasmine Nutririce||94.8440||94.8747||1.0383||0.0307||3.00|
|4. Floral Glutinous||94.8337||94.8760||1.0004||0.0423||4.23|
|5. Sun Rise Australian Fragrant||95.2816||95.3184||1.0312||0.0368||3.57|
|6. Bird of Paradise||95.2751||95.3239||1.0185||0.0488||4.79|
|7. Phkarkhrrel Cambodi Organi||94.8476||94.8786||1.0235||0.0310||3.01|
|8. Sakura Super Thai||95.2832||95.3253||1.0150||0.0421||4.15|
|9. Sakura Super Pakistan||95.2675||95.3015||1.0002||0.0340||3.40|
|10. Giant Super Special Rice||95.2782||95.310||1.0225||0.0328||3.21|
3.6. Rice trace element test
3.6.1. Chemicals and reagents
All chemicals and solvents were of analytical-reagent grade. Nickel(II) sulfate and chromium(III) chloride-6-hydrate were purchased from Hamburg Chemicals. Copper standard solution and calcium standard solution, magnesium sulfate heptahydrate and lead nitrate were purchased from Merck. Zinc chloride and cadmium nitrat-4-hydrate were purchased from Riedel-de Haen Chemicals. Nitric acid, perchloric acid and sulfuric acid were purchased from R & M chemicals.
3.6.2. Preparation of acid digested rice samples
One gram of each rice sample was accurately weighed in a sample container and transferred into a 250-mL conical flask. A mixture of concentrated acids containing nitric acid (67 mL), perchloric acid (22 mL) and sulfuric acid (13 mL) was added to each of the rice sample. The mixture was digested according to the wet digestion method  for 20 min at room temperature until a clear yellow solution was obtained. The digested rice samples were further digested with a reflux system for 40 min. The digested rice samples were allowed to cool down at room temperature for about 20 min until all the nitric fumes were evaporated. The digested rice samples were then boiled using a hot plate by increasing the temperature gradually until all perchloric fumes were evolved. The boiling process was stopped when a final volume of about 10 mL of clear liquid solution was obtained. The clear liquid solutions were then transferred into a 100-mL volumetric flask and topped up with deionized water. The concentration of trace elements in the rice samples was measured by using Shimadzu AA-6200 flame-AAS. Each analysis was conducted in triplicate, and the uncertainty in measurements was <10%.
3.6.3. Preparation of standard solutions
Stock solution (100 ppm) of a metal salt was prepared by dissolving appropriate amount of the metal salt with 20 mL of deionized water in 100-mL volumetric flasks. A mixture of acids containing nitric acid (5 mL), per chloric acid (1.7 mL) and sulfuric acid (0.8 mL) was added to the metal salt and topped up with deionized water to 100 mL. A series of standard solutions (2, 4, 6, 8, 10, 12, 14, and 16 ppm) were prepared by diluting from this stock solution and used to obtain the standard calibration curves. A blank standard solution containing same amount of concentrated acids but without rice sample was prepared as control.
3.6.4. Results and discussion
The results of trace element contents for 10 different types of rice sample are summarized in Table 5. These results indicated that the average content of Mg, Ca, Zn and Cu in the rice samples was 62.7, 8.3, 12.3, 7.5 mg kg−1, respectively, while the Cr, Cd, Ni and Pb were not detected. All the 10 different types of rice sample showed the highest average Mg content ranging from 22 to 287 mg kg−1, followed by Zn (9–18 mg kg−1), Ca (0–14 mg kg−1) and Cu (0–14 mg kg−1). Comparing the results in Table 5 with the heavy metal content of rice samples from foreign countries, we found that there was not much difference in the heavy metal content between the two different sources. For example, the average Cd, Cr, Cu, Ni, Pb and Zn content in the rice samples from Taiwan was 0.02, 0.07, 2.20, 0.26, 0.01 and 14.6 mg kg−1, respectively .
|Manufactured rice||Trace Eelement Llevels (mg kg-1)|
|1. Maharaja Basmathi||23.0||9.0||10.0||9.0||nd||nd||nd||nd|
|2. SUMO Calrose||287.0||3.0||12.0||3.0||nd||nd||nd||nd|
|3. Jasmine Nutririce||42.0||14.0||18.0||14||nd||nd||nd||nd|
|4. Floral Glutinous||33.0||1.0||14.0||1.0||nd||nd||nd||nd|
|5. Sun Rise Australian Fragrant||31.0||6.0||14.0||6.0||nd||nd||nd||nd|
|6. Bird of Paradise Thai Fragrant||22.0||nd||9.0||nd||nd||nd||nd||nd|
|7. Phkarkhnei Cambodia Organi||35.0||13.0||13.0||13.0||nd||nd||nd||nd|
|8. Sakura Super Thai Brown Rice||29.0||10.0||11.0||10.0||nd||nd||nd||nd|
|9. Sakura Super Basmathi Pakistan||34.0||11.0||11.0||11.0||nd||nd||nd||nd|
|10. Giant Super Special White||91.0||8.0||11.0||8.0||nd||nd||nd||nd|
In this chapter, the emerging microwave and laboratory measurement techniques for rice processing and rice testing were presented. Up to 10 brands of manufactured rice grain in the market were analyzed in terms of physical and chemical properties. A wide range of microwave applications can be implemented in the rice industry. Besides microwave heating, the microwave technique used for rice insert control is considered new and attractive since this method leaves no chemical residues on the rice grain product. Microwave technology has provided a rapid and accurate measurement to test the quality of the rice in order to increase the rice production.
International Rice Research Institute (IRRI). Rice Quality. 2009. [Report]. Retrieved on November 24, 2012. Available from http://www.betuco.be/rijst/Rice%20Quality.tif
American Society of Agricultural and Biological Engineers (ASABE). ASAE S352.2 Moisture measurement – unground grain and seeds. 1998; St Joseph, MI, USA.
Bhattacharya K R: Rice Quality: A Guide to Rice Properties and Analysis. New Delhi, India: Woodhead Publishing; 2011. ISBN: 9781845694852
Yu X R, Su Y, Wang Y, Zheng T S, Zhao S M, Huang S Z: Study on microwave drying of grain. Proceedings of the 7th International Working Conference on Stored-product Protection.14-19 October. Beijing, China. 1998: 1096-1101.
Abegaonkar M P, Karekar R N, Aiyer R C: A microwave microstrip ring resonator as a moisture sensor for biomaterials: application to wheat grains. Measurement Science Technology. 1999; 10(3): 195–200. doi:10.1088/0957-0233/10/3/014
Kim K B, Kim J H, Lee S S, Noh S H: Measurement of grain moisture content using microwave attenuation at 10.5 GHz and moisture density. IEEE Transactions on Instrumentation and Measurement. 2002; 51(1): 72–77. doi:10.1109/19.989904
Jafari F, Khalid K, Yusoff W M D W, Hassan J: The analysis and design of multi-layer microstrip moisture sensor for rice grain. Biosystem Engineering .2010; 106(3): 324–331. doi:10.1016/j.biosystemseng.2010.04.005
You K Y, Salleh J, Abbas Z, You L L: Cylindrical slot antennas for monitoring the quality of milled rice. Progress in Electromagnetics Research Symposium Proceedings. 12–16 September. Suzhou, China. 2011: 1370–1373.
Mun H K, You K Y, Dimon M N: Rice grain moisture determination using microstrip wide-ring and microstrip coupled-line sensors. American Journal of Applied Sciences. 2015; 12(3): 112–120. doi:10.3844/ajassp.2015.112.120
You K Y, Mun H K, You L L, Jamaliah S, Abbas Z: Small and slim coaxial probe for single rice grain moisture sensing. Sensors. 2013; 13(3): 3652–3663. doi:10.3390/s130303652
Nelson S O: Dielectric properties of agricultural products – measurements and applications. IEEE Transactions on Electrical Insulation. 1991; 26(5): 845–869. doi:10.1109/14.99097
Yadav B K, Jindal V K: Monitoring milling quality of rice by image analysis. Computersand Electronics in Agriculture. 2001; 33(1): 19–33. doi:10.1016/S0168-1699(01)00169-7
Lloyd B J, Cnossen A G, Siebenmorgen T J: Evaluation of two methods for separating head rice from brokens for head rice yield determination. Applied Engineering in Agriculture. 2001; 17(5): 643–648. doi:10.13031/2013.6902
Courtois F, Faessel M, Bonazzi C: Assessing breakage and cracks of parboiled rice kernels by image analysis techniques. Food Control. 2010; 21(4): 567–572. doi:10.1016/j.foodcont.2009.08.006
Mun H K, You K Y, Dimon M N: Broken rice detection based on microwave measurement technique using microstrip wide-ring sensor and microstrip coupled-line sensor. Australian Journal of Crop Science. 2013; 7(13): 2079–2090. ISSN: 1835-2707[CE7]
Nelson S O: Dielectric Properties of Agricultural Materials and Their Applications. U.S.: Elsevier; 2015. ISBN: 9780128023051.
Deepa G, Singh V, Naidu K A: Nutrient composition and physiochemical properties of Indian medicinal rice–Njavara. Food Chemistry. 2008; 106: 165–171.
Kennedy G, Burlingame B: Analysis of food composition data on rice from a plant generic resources perspective. Food Chemistry. 2003; 80: 589–596.
Oko A O, Onyekwere S C: Studies on the proximate chemical composition, and mineral element contents of five new lowland rice varieties planed in Ebonyi State. International Journal of Biotechnology. 2010; 6: 949–955.
American Society for Testing and Materials (ASTM). Standard Guide for Preparation of Biological Samples for Inorganic Chemical Analysis, Water and Environmental Technology. Annual Book of ASTM standards. 2000; 11.01, D 4638-95a. doi:10.1520/D4638-11
Haw T L, Sue S W, Gwo C L: Heavy metal content of rice and shellfish in Taiwan. Journal of Food and Drug Analysis. 2004; 12(2): 167–174.