Effects of Combine Harvesting on Head Rice Yield and Chaff Content of Long and Short Grain Paddy Harvest in Sri Lanka

Paddy harvesting is the process of collecting the mature rice crop from the field which consists of activities such as cutting, handling, threshing and cleaning. Cutting, threshing and cleaning plays an important role to reduce postharvest losses. Lower performance of traditional harvesting process, labour shortage, reduced turn-around time and use of high yielding varieties have inevitably forced farmers to shift into mechanical grain harvesting in Sri Lanka. Rice milling is carried out to produce an edible polished or white rice product from harvested rough rice. Head rice yield is considered for marketing purposes because broken rice has low price in the market. Field survey was conducted in Polonnaruwa, Ampara and Hambanthota districts to identify most popular types of combine harvesters operating in the above districts. Paddy samples were collected from harvest of two most popular models of combine harvester in triplicate. Paddy sample of 1m² area from every paddy field were harvested separately by manual harvesting followed by manual threshing and cleaning in laboratory as control sample of relevant paddy field. Moisture content of the paddy grains were measured in the paddy field using digital moisture meter before harvesting. Paddy samples were subjected to sun drying until the moisture content come down to 14±1% before the quality analysis in the laboratory. Each paddy sample was analyzed for moisture content, chaff percentage and head rice yield percentage (HRY). Paddy was milled using laboratory scale rubber roll sheller and abrasive polisher. Chaff content percentage was measured by adding 100 ml of paddy to water and volume of chaff was measured using graduated cylinder. HRY was calculated dividing the weight of grain partials, which are larger than the ³/₄ of the grain, by weight of paddy sample. HRY between the two combine harvesting machine models evaluated were not significantly different at p<0.05 and also it was not significantly dependent on the harvesting methods such as combine harvesting and manual harvesting. The chaff content was significantly higher in model-2 in comparison to control sample for long grain paddy while model-1 was not significantly different with control sample for short grain paddy.     

我国高水分稻谷干燥工艺设备的研究设计及应用

提出了适合我国国情的高水分稻谷逆顺流多级变温组合干燥工艺方案,设计了HNST系列环保型连续式逆顺流高水分稻谷保质干燥机,阐述了其干燥原理、主要结构和性能特点。实践证明,该机型热效率高、节能显著、环保、干燥后粮食品质好、连续生产,可使粮食一次降至安全水分、自动化程度高、可操作性强、通用性及适用性好、便于系列化和标准化生产,具有广阔的市场推广前景。     

优质稻谷保鲜干燥方法研究

将水分为16.0%～18.6%的新收割优质稻谷采用包装打围、中间散存的方式储藏,分别使用热风就仓干燥,自然风就仓干燥和低温储藏干燥等方法进行干燥处理,同时也使用低温烘干机和自然晾晒等方法进行干燥处理。结果表明:各种干燥处理都达到了满意的效果,达到预期干燥水分,干燥均匀,未增加裂纹粒(爆腰粒),发芽率、黄粒米率、整精米率、脂肪酯值和粘度等重要品质指标未发生明显变化,品质新鲜。通过试验找到了稻谷保鲜干燥方法,可与保鲜储藏稻谷的方法配套,为保鲜大米加工常年提供新鲜稻谷原料。     

Application of simulation in determining suitable operating parameters for industrial scale fluidized bed dryer during drying of high impurity moist paddy

A systematic approach has been developed for selecting the suitable drying parameters to be used for drying of high moisture and high impurity paddy with an industrial fluidized bed paddy dryer (10–20 t h⁻¹ capacity) based on targeted specific air flow rate and residence time during two typical paddy drying seasons. A mathematical model was developed by modifying an existing model and was simulated and validated with observed industrial drying data as well as data reported in the literature. Comparison between the observed and simulated results showed that the mathematical model is capable of predicting outlet paddy moisture content and air temperature well. Suitable operating parameters were determined for reducing any initial paddy moisture content (mc) down to 24–25% dry basis (db), the safe mc level after fluidized bed drying to maintain rice quality, to achieve maximum possible throughput capacity of the dryer with corresponding energy consumption. Based on these criteria, bed thickness at 10 cm, specific air flow rate of 0.05 kg kg⁻¹ s⁻¹ (for corresponding bed air velocity of 2.3 m s⁻¹), air temperature of 150 °C and residence time of 1.0 min were found to be suitable drying conditions for reducing paddy mc from 30 to 24.30% (db) in one season while the maximum throughput capacity of 15.7 tonne per hour (t h⁻¹) might be achieved. The specific electrical and thermal energy were 0.48 and 6.15 MJ kg⁻¹ water evaporated, respectively. On the other hand, the dryer capacity was found to be limited to 7.4 t h⁻¹ during drying paddy of higher initial mc (35% db). This approach might provide easy and comprehensive guidelines for selecting suitable sets of operating parameters for any industrial fluidized bed dryer at its possible maximum throughput capacity for drying of freshly harvested high moist paddy with a high level of impurities.     

Comparison of performances of pulsed and conventional fluidised-bed dryers

Consumption of energy, outlet moisture content and quality of the dried commodity are important parameters of paddy-dryer performance. The fluidised-bed paddy-dryer has been commercialised for several years and in this paper, paddy drying by pulsed and conventional fluidised-bed dryers are compared. Experimental results have shown that the variation of moisture content at the exits of both dryer types in test runs was very small. Heat utilisation was more effective when such dryers were used to dry paddy at moisture contents above 24% dry basis and up to 50% of the thermal energy was saved by recycling 70–80% of the air. Paddy qualities i.e. head-rice yield and colour of the dried white rice were similar with both dryers and almost the same as the original undried values, or slightly higher in the case of head-rice yield, depending upon the drying conditions. Below 28% dry basis, it is recommended that inlet-air temperature should be lower than 145 °C in order to maintain white colour. The cooked rice obtained from paddy dried at a temperature of 145 °C was harder than naturally dried control samples. A mathematical model based on energy and mass balance predicted values in good agreement with experimental results for both the pulsed and conventional fluidised-bed dryers. Calculated thermal and electrical energy consumptions indicated that the pulsed flow dryer was more economical than the conventional dryer.     

Mathematical modeling and performance analysis of thin layer drying of bitter gourd in sensible storage based indirect solar dryer

An indirect forced convection solar dryer integrated with porous sensible heat storage medium was developed. The effect of porous thermal storage and mass flow rate of air on the performance of the system for drying bitter gourd was studied. The experimental setup consists of a blower, solar flat plate collector with corrugated absorber plate (2 m²) and a drying chamber. The thermal storage medium (pebble) is placed below the corrugated absorber plate, in the air passage as a porous medium. The experiments have been carried out with various mass flow rates of air and different drying models have been used for explaining the drying behaviour of sliced bitter gourd. The result shows that, (i) the initial moisture content 92% (w.b) of bitter gourd was reduced to 9% (w.b) in 7 h in the proposed drying system, while it was 10 h for open sun drying, (ii) the maximum specific moisture extraction rate was observed as 0.215 kg/kWh at the mass flow rate of 0.0636 kg/s and the corresponding specific energy consumption was 4.44 kWh/kg, (iii) the collector and drying efficiency of the system were 22% and 19% respectively. The two term model and Midilli–Kucuk model are most suitable for indirect solar dryer and open sun drying in terms of statistical parameter respectively. The drying inside sensible heat storage based indirect dryer was more consistent and produced better quality product as compared to open sun drying.Industrial relevance

• •Every year post harvest losses are increasing rapidly due to the lack of storage facilities.
• •Solar dryers are the most suitable technology that can be easily availed at low cost and in small scale and it can be used as an income generation option for farmers and women in rural areas.
• •The role of solar dryers in food processing industries is significant especially in developing countries in the following areas
  • oFor preserving fruits and vegetables
  • oDairy industries
  • oAgricultural crop drying
  • oTimber drying
  • oIndustrial waste drying
• •The utilization of thermal storage medium in the solar dryers is being focused much for the reasons of extending the availability of the system for operation and to achieve better quality of the products.

     

低温循环式烘干机对南方高水分稻谷干燥的实践

中国南方湿稻谷含水率往往高达24％～35％,如果干燥不及时则会造成霉变或发芽等损失,如果干燥不当则易产生爆腰而造成碾米时的碎米率增大.谷粒的特殊结构使稻谷成为一种较难干燥的谷物.文章介绍了一种配有电脑自动水份测定仪的低温循环式烘干机这种低温循环烘干机对湿稻谷的平均干燥速率为0.8％～0.9％/h,每吨湿稻谷的烘干成本为50元左右,收购稻农的湿谷进行集中烘干可以获取30元/t的利润;与场地晾晒稻谷相比,集中烘干稻谷可以获取442元/t的经济效益.     

Effects of fluidized bed drying temperature and tempering time on quality of waxy rice

Waxy rice, which is soft and sticky in nature, can be used as a raw material to produce many food products. After being harvested, high-moisture waxy paddy must be dried to appropriate moisture content to prolong its storage life and to achieve higher head rice yield. Fluidized bed dryer could be used to dry waxy rice at high-temperature. However, due to the high heat and mass transfer rates during drying, stresses are generated in a rice kernel, leading to crack and low head rice yield. Tempering is thus recommended to reduce the moisture-induced stresses in the kernel after rapid drying. In this study, the effects of fluidized bed drying temperature (90, 110, 130 °C) and tempering time (30–120 min) on the quality of waxy rice, i.e., head rice yield, thermal properties, pasting properties, color, translucent kernel and microstructure, were investigated. The results showed that head rice yield of waxy rice after drying was significantly lower than that of the reference sample even when tempering was performed. Higher drying temperatures led to higher head rice yield while the tempering time did not have any effect on the head rice yield except when the drying temperature of 90 °C was used. Drying at higher temperatures also affected the starch granule morphology and the pasting properties. Waxy rice changed its appearance from opaque white to translucent when being dried at 130 °C.     

Accelerated aging of jasmine brown rice by high-temperature fluidization technique

After being cooked, newly harvested brown rice becomes a pasty mass and swells only slightly. To modify these undesirable brown rice properties, the paddy needs to be stored for at least 3–6 months. However, problems arise since brown rice has short shelf-life (3–6 months) due to accumulation of free fatty acids (FFA) leading to rancidity during storage. In the present study, high-temperature fluidized-bed drying technique in combination with tempering step was tested to alleviate the above-mentioned problems. The quality of rice dried at temperatures of 130 and 150 °C and tempered for 30 up to 120 min was compared to that of brown rice stored at ambient temperature (approximately 30 °C) for 7 months. The experimental results showed that the cooking and eating properties of the fluidized bed dried brown rice, i.e., hardness, solid loss, volume expansion and elongation ratio, changed in a similar fashion to those of the conventionally aged brown rice. The drying temperature and tempering time affected significantly the brown rice properties. The texture of cooked thermally treated brown rice was significantly firmer than that of the conventionally aged brown rice. In addition, it was found for the thermally treated brown rice that the contents of free fatty acids increased only slightly during storage while the glycemic index reduced from high to low-medium level.     

Effect of superheated-steam drying compared to conventional parboiling on chalkiness,head rice yield and quality of chalky rice kernels

Four rice cultivars (Ayutthaya 1, Khao Bahn Nah 432, Plai Ngahm Prachin Buri, and Prachin Buri 2) that usually have a major problem with chalkiness were processed by applying superheated-steam drying and conventional parboiling methods. The main objectives were: (1) to determine the possibility of applying superheated-steam drying to solve the chalkiness and low head rice yield problems and (2) to compare the properties of rice produced using superheated-steam drying and the conventional parboiling process. Both the initial moisture content and superheated-steam drying temperature significantly affected head rice yield. The higher moisture helped to increase starch gelatinization leading to a stronger rice structure and subsequently an increased head rice yield. The rice samples dried in the superheated-steam dryer using an initial moisture content of paddy at 32% w.b. for 6 h under a steam pressure of 1.2 bar and at three drying temperatures (120, 140, 160 °C) had higher milling quality than the conventionally parboiled rice samples. The darker color of the superheated-steam-dried samples was their main drawback. Both parboiling and superheated-steam drying could clearly lessen the percentage of chalky rice kernels compared to the raw paddy. The parboiled rice and superheated-steam-dried rice had more nutrients than normal white rice.     

稻谷热风与真空干燥特性及其加工品质的对比研究

比较稻谷热风与真空干燥特性及对其加工品质的影响,为有效改善稻谷加工品质提供依据。通过对初始水分为26.5%的稻谷进行热风和真空干燥试验,研究热风干燥和真空干燥对稻谷的干燥特性和其加工品质的影响。结果表明:干燥温度越高,稻谷的平均降水速率越大,且真空干燥平均最大降水速率大于热风干燥平均最大降水速率;热风干燥在干燥开始后的5～10min降水速率出现最大值,真空干燥在干燥开始后的5～15min降水速率出现最大值。随着干燥温度的升高,稻谷的爆腰率上升,出糙率和整精米率下降;相同的干燥温度下,真空干燥稻谷的加工品质优于热风干燥稻谷的,其中爆腰率最为明显。对于高水分稻谷采用真空干燥可以提高稻谷的加工品质。     

基于多品质指标的响应面试验优化稻谷流化床干燥工艺

为优化稻谷流化床干燥工艺,采用三因素三水平Box-Behnken响应面分析法,研究干燥温度、降水幅度、缓苏时间对稻谷流化床干燥降水速率和干燥稻谷爆腰增率、垩白粒率、脂肪酸值、硬度、黏着性等品质指标的影响。结果表明：随着干燥温度和降水幅度水平的增加,稻谷降水速率、爆腰增率、垩白粒率和米饭硬度增加,脂肪酸值和米饭黏着性降低;随着缓苏时间延长,稻谷降水速率、爆腰增率、脂肪酸值和米饭硬度降低,米饭黏着性增加。而在较低的干燥温度条件下,缓苏时间延长,稻谷的爆腰增率和垩白粒率降低并不明显。Box-Behnken响应面分析法优化的流化床最优干燥参数为降水幅度2.50%（干基）、干燥温度45 ℃、缓苏时间3 h,此时隶属度综合分达最大值0.75。验证实验结果与拟合值无显著性差异（P＜0.05）,优化结果可靠有效。     

An investigation into lactose crystallization under high temperature conditions during spray drying

Lactose crystallization was studied at high temperature conditions in a Buchi B-290 mini spray dryer. The inlet gas temperature was 200 °C, and an insulating material was used to reduce the heat loss from the drying chamber (outlet temperature 157 °C), thus increasing the gas and particle temperatures. At these conditions, lactose crystallinity was found to increase significantly compared with a case where it was spray dried at 170 °C in a non-insulated drying chamber (outlet temperature 90 °C), but the process yield was lower for the former case (0.16% yield) than for the low temperature conditions (47% yield). There is some evidence that high-temperature spray drying of lactose is more likely to give more β-lactose anomer. Different analytical techniques (Fourier Transform Infrared Spectroscopy, modulated differential scanning calorimetry, moisture sorption test, Raman spectroscopy) were used to investigate the degree of crystallization and possible lactose anomer formation during this spray drying at high inlet gas temperatures.     

稻谷分程干燥工艺优化

为了得出最佳稻谷分程干燥工艺条件,实验选取Ⅰ阶段热风温度、Ⅰ阶段终了含水率、Ⅱ阶段暂存时间和Ⅲ阶段热风温度4个因素,首先进行单因素试验确定优化区间,后通过主成分分析法对多个稻谷干燥品质指标综合建立稻谷干燥品质评价模型,再以综合指标作为评价标准进行响应面试验得出稻谷分程干燥最佳工艺条件。最终优化结果:Ⅰ阶段热风温度为76.30℃,Ⅰ阶段终了含水率为19.99%,Ⅱ阶段暂存时间为11.34 d,Ⅲ阶段热风温度为35.53℃,验证得到综合F值为1.284,其中爆腰率为51%、整精米率为64%,计算平均干燥速率为1.21%/h。     

Effects of drying conditions in hybrid dryer on the GABA rice properties

In this study, pre-germinated rough rice was dried under various conditions using a hybrid dryer that incorporated heat pump dryer with fluidized bed drying (FBD) system in order to compare with the single-stage drying by hot air dryer. The main objective was to investigate the effect of drying conditions on the cooking and physical properties, nutrients and sensorial qualities of GABA rice products. It appeared that the FBD at 100–140 °C led to noticeable increase of head rice yield. The germination process caused the decline of gelatinization enthalpy of brown rice flour, the change of pasting properties, the reduction of cooking time and escalation of the total phenolic content, antioxidant activity and GABA content. The FBD at higher temperature significantly raised the degree of starch gelatinization and caused longer cooking time, higher hardness and adhesiveness of cooked GABA rice. Three-stage drying comprising FBD at 60 °C for 10 min in the first stage followed by FBD at 100 °C in the second stage and then heat pump drying at 45 °C together with tempering step between drying stages was recommended due to its superior GABA rice product quality.     

不同通风方向对稻谷降水效果影响的数值模拟研究

基于数值模拟方法,对高水分稻谷的就仓降水通风实验工况进行了数值模拟仿真,分析了在垂直机械通风过程中粮食温度和水分的变化规律,对实验数据与计算机模拟结果进行了对比分析。同时,探究了垂直向上和垂直向下通风时的降水效果。研究发现,数值模拟方法可以有效和形象地反映通风过程中粮堆内部的变化规律,在其他条件相同时,沿着粮堆温度梯度方向通风,降水效果更加明显。本研究对粮库的储粮通风操作具有一定的指导意义。     

稻谷等温干燥-缓苏过程数值模拟及优化

利用稻谷干燥热湿传递数学模型,对稻谷等温干燥-缓苏过程进行数值模拟,对比分析了缓苏条件下干燥稻谷籽粒内部水分分布变化规律。结果表明：与热风温度60?℃下单纯干燥过程相比,缓苏降低了稻谷内部的水分梯度峰值,缩短了干燥时间,同时将籽粒干燥终了水分梯度降低接近50%。通过参数研究,发现缓苏温度、缓苏比和缓苏时间是缓苏过程的重要参数,并提出干燥-缓苏过程的优化机制,即在稻谷籽粒干燥缓苏过程初期设置短时缓苏、中期单纯干燥、后期长时缓苏,可有效地降低水分梯度过程最大值和终了值,缩短缓苏时间和减少次数。本研究为稻谷干燥缓苏提供了理论和技术支持。     

Process of Producing Parboiled Rice with Different Colors by Fluidized Bed Drying Technique Including Tempering

Steamer is utilized to gelatinize rice starch. High pressure or long steaming time is conventionally applied to obtain the dark brown color of the product. A new alternative method to produce dark brown parboiled rice was proposed in this work. High temperature fluidized bed drying technique including tempering was therefore explored to determine the operating condition to meet the requirement of light and dark brown parboiled rice along with high head rice yield. In addition, the couple of heat and mass transfer model was developed to determine the effective moisture diffusion coefficient, the temperature and moisture distributions within a grain kernel during drying. The effective diffusion coefficient was well correlated with grain temperature by Arrhenius equation. The drying temperature and moisture content after drying caused the drop of head rice yield. When the parboiled paddy at the intermediate moisture contents of 22 and 27% d.b. was tempered, the head rice quality was improved while the parboiled rice color was browner. To obtain high drying capacity, high head rice yield, and light brown color, the parboiled paddy should be dried at a maximum allowable temperature of 150 °C and tempered for 30 min. The tempering time should be extended to 60 min for the dark brown parboiled rice.     

Quality maintenance and economy with high-temperature paddy-drying processes

Drying processes result in some loss of product quality. Three drying systems for paddy were investigated for their effects on head-rice yield and whiteness. Fluidised-bed drying, tempering and ambient air ventilation units were the main components, but they were arranged differently in each drying system. Heat- and mass-transfer equations were applied to predict the change in moisture content for each drying system. Both the experiments and simulations indicated that the two sub-drying systems (system No. 2) with tempering and ventilation as elements of each stage yielded higher drying capacity and thermal efficiency than the single drying system (system No. 1), in which paddy was treated with the drying, tempering and ventilation units only once. The proportion of full kernels and value of the whiteness obtained from both drying systems were not significantly different. System No. 3, where grains after the first tempering were dried immediately by the second fluidised-bed dryer with no ventilation unit, produced poor head-rice yield and colour and was unacceptable for producing white rice.     

Moisture diffusivity and shrinkage of broad beans during bulk drying in an inert medium fluidized bed dryer assisted by dielectric heating

Drying behavior of broad beans (Vicia faba) was studied in a pilot scaled fluidized bed dryer with inert particles assisted by dielectric heating. The effective diffusion coefficient of moisture transfer was determined by Fickian method at four different air drying temperatures of 35, 45, 55 and 65 °C. Correlations for moisture diffusivity as a function of moisture content and temperature of the drying medium were developed. The values of moisture diffusivity were obtained within the range of 1.27 × 10^?9–6.48 × 10^?9 m²/s and the activation energies for FBD and FBD + DE were found to be 27.71 and 17.10 kJ/mol, respectively. The shrinkage behavior of the broad beans was also investigated by considering the volume ratio of (V/V_O) to be function of moisture content alone and fitting a polynomial of the third order. The dielectric heating power was also found to be effective on the rate of drying.