Simultaneous parboiling and drying of hige moisture paddy by infrared radiation (IR) heating. | |
| Author | Charun Likitrattanaporn |
| Call Number | AIT Diss. no.FB-11-03 |
| Subject(s) | Drying apparatus Infrared heating Heat--Radiation and absorption Rice--Postharvest technology |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science in Food Engineering and Bioprocess Technology, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. FB-11-03 |
| Abstract | In this study, infrared radiation (IR) heating was used for simultaneous parboiling and drying of high moisture paddy under vibrating conditions. The IR heating and vibrating apparatus was designed and fabricated. Various parameters, including height of IR heater, IR power and the sample bed depth were investigated for optimum mixing and uniformity of heat distribution. Physico-chemical properties such as milling yield, color and pasting properties of IR treated paddy were evaluated and compared to commercial parboiled rice which was selected from different rice millers. The conventional steam parboiled rice was prepared and compared to the parboiled rice under simultaneous parboiling and drying process by IR heating. The qualities of commercial parboiled rice from 11 different rice millers were evaluated. The samples were taken from 5 well known rice producing provinces; Nakorn Pathom, Supanburi, Ayutthaya, KhampangPetch and ChachangSao. The parboiling processes of all millers used high temperature soaking, high pressure steaming and high temperature drying. Paddy was soaked in 60-70oC water in batch type soaking tanks for several hours. A steaming tower with a locked rotary valve at both the loading and unloading ports applied 7 kg/m2 steam pressure for steaming high moisture paddy. A fast drying system, the fluidization-bed dryer is used for the first stage drying and is followed by a mixed-flow dryer for second stage drying. Long grain rice varieties such as Chi-nat-1, Suphan-Buri-1, and Supan-Buri-90 were processed for premium grade parboiled rice. The qualities of parboiled rice included less yellow discoloration (near white rice or b-value range 19-23), off parboiled rice flavor and no impurities. An IR heating and vibrating apparatus was designed and developed to meet the demands of parboiled rice production. It consisted of three main parts: the heating source, sample tray and vibrating table. The heating source consisted of 3 carbon shield IR lamps (220V, 700W). The maximum heating was 46.67kW/m2 IR intensity. The sample tray was a rectangular tray (150x300 mm) and 60 mm deep. It was divided into 8 small compartments and clamped on the vibrating table. The vibrating mechanism consisted of an eccentric joint with a speed controlled motor and helical springs to perform vibration. The vibration was transmitted to the sample tray by a 10mm eccentric link and an adjustable speed controlled motor which gave vibrating amplitude supported by 4 helical springs. The various parameters of IR heating and vibrating apparatus were evaluated. The mixing and moving of grain in each compartment was the first observation. The best stirring condition resulted from a 25-26 Hz speed controlled motor. The grain in the sample tray jumped out if speed was 2 Hz above or below that level. Three IR power levels (700, 1400 and 2100 W), three exposure times (10, 15 and 20 minutes), three IR heights (100, 150 and 200 mm) and three grain thicknesses (10, 15 and 20 mm) were investigated. The results showed that IR height at 150 or 200 mm was more convenient for operating due to ample space above the tray to remove or install it during testing. The 15 mm grain thickness had efficient mixing and moving compared to the 10 mm sample that was quickly moving and slightly jumping. The grain was moving very slowly in the four corners of the compartment during the 20 mm experiment. All IR power raised the air temperature in the grain bed to 70oC within 10 minutes for the 700 W sample; within 7 minutes for the 1400 W sample and only 4 minutes for the 2100 W sample. The grain bed ivtemperature substantially increased and approached 100oC if the grain was totally dry. All samples under IR power and for all exposure times showedmilling yield below 40%. It was less after longer exposure time (especially 20 minutes) and higher IR power. White-belly was found in 2 to 10 % of samples. The sample tray was enclosed by tempered glass in order to increase air temperature to 100oC inside the tray during simultaneous parboiling and drying. According to preliminary experiments using microwave and IR heating with a closed chamber, it was found that milling could improve to nearly zero breakage and chalkiness for both microwave and IR heating. However, several over-dried grains were found under microwave heating due to limitations of radiation distribution that caused uniformity problems. Therefore, tempered glass was introduced to the IR heating and vibrating apparatus for closing the sample tray. The air in the grain bed increased rapidly to 100oC within 4 minutes at 2100 W. The milling yield was ultimately improved and no chalkiness was measured under 2100 W IR heating. However, other levels of IR power still faced some chalkiness in the grain. Using an IR heating and vibrating apparatus to study a simultaneous parboiling and drying process, physico-chemical properties such as milling yield, color and pasting properties of paddy were evaluated. The IR height was set at 150mm, the grain bed depth was 15 mm and the motor speed control was set at 25 Hz. IR radiation intensity levels of 46.67 kW/m2 (2100 W), variable exposure times (10, 13, 15 and 18 minutes) and rice samples at fixed initial moisture contents of 30% and 32% wb were used.It was discovered that the radiation intensity of 46.67 kW/m2 and 32% wb moisture content yielded a similar quality level to conventional steam parboiled rice. The head rice yield (HRY) of IR paddy slightly decreased with increasing exposure time. The HRY of IR heating was more than 60% compared to 67.68-69.34% HRY of conventional steam parboiled rice. 23-25 b-value of IR samples showed lighter yellowness than the 29.7 b-value of conventional steam parboiled rice. The pasting properties of all IR samples showed lower viscosity compared to the milled rice samples but was higher than with conventional steam parboiled rice. Initial moisture content of paddy effected the degree of starch gelatinization (SG) by differential scanning calorimetry (DSC). Under IR heating at 18 minutes exposure time, the 32% wb IMC sample showed starch gelatinization (SG) at 80.15% compared to SG at 59.02% of 30% wb IMC samples. Hence, operation on simultaneous parboiling and drying by IR heating and exposure time of 18 minutes retained higher parboiled flavor as a result of higher degree of starch gelatinization. However, the sample showed lower HRY but yellowness was within the acceptable range. The IR heating and vibrating apparatus was successfully used for parboiling paddy to meet the requirements of moving grain during heating and gelatinization of grain. The IR heating samples showed low moisture content which did not significantly reduce energy costs. However, two advantages were revealed: investment in a steam generator was not necessary and less drying stages were required. The results suggest that simultaneous parboiling and drying by IR heating should be developed and applied in parboiled rice processing industry in the future. |
| Year | 2011 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. FB-11-03 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Food Engineering and Bioprocess Technology (FB) |
| Chairperson(s) | Athapol Noomhorm; |
| Examination Committee(s) | Rakshit, Sudip Kumar;Anal, Anil Kumar;Soni, Peeyush; |
| Scholarship Donor(s) | Royal Thai Government;Rajamangala University of Technology Thanyaburi (RMUTT), Pathumthani, Thailand |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2011 |