首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
This study evaluated the physicochemical properties of high‐temperature, single‐pass dried rough rice. Pureline cultivars Wells (long grain) and Jupiter (medium grain) and hybrid cultivar CL XL729 (long grain), at initial moisture contents of 17.9–18.1% were dried in a single pass to approximately 12.5% moisture content with drying air temperatures of 60, 70, and 80°C and relative humidities of 13–83%. Immediately after drying, the samples were tempered for 1 h at the drying air temperatures in sealed plastic bags. Color, degree of milling, pasting viscosity, and thermal properties of the milled rice were evaluated. Results showed that color, degree of milling, and thermal properties were not affected by drying treatments. However, peak and final viscosities increased with increasing drying air temperatures in all three cultivars.  相似文献   

2.
The objective of this research was to determine the influence on drying characteristics and resultant milling quality of storing high moisture content (MC) rough rice (Oryza sativa L. ‘Bengal’ and ‘Cypress’) under various conditions and durations before drying. Immediately after harvest, drying experiments were performed with samples of both cultivars using two drying air conditions: 52°C with 25% rh and 60°C with 17% rh. Rough rice from each cultivar also was stored for 27 and 76 days at ‐9 or 4°C. After storage, all samples were dried under the same two drying air conditions as at harvest. Head rice yields (HRY) were determined for all dried samples. There were no significant differences between the drying rates or resultant HRY of Bengal or Cypress rice samples stored for either 27 or 76 days at both storage temperatures and then dried compared with the HRY of samples dried immediately after harvest. This research shows that it may be possible to store high MC rice for extended periods of time without detrimental effects on HRY.  相似文献   

3.
The surface lipids and free fatty acids (FFA) content of head and broken rice samples generated through milling after various drying treatments were studied. Long grain cultivars Francis, Wells, and Cypress, and medium grain cultivar Bengal were dried under three air conditions (mild 25°C, 50% rh; moderate 45°C, 40% rh; and stressed 65°C, 20% rh) for two durations (10 and 30 min). Immediately after drying, the rough rice samples were placed in a conditioning chamber to continue drying slowly to ⋍12.5% moisture content (MC), which occurred within three to five days. After dehulling, a McGill No. 2 mill was used to mill the samples for 30 sec. The head rice yield (HRY) for all rice samples were within the range of 40–68%. Rice surface lipid was extracted with isopropanol (IPA) and the lipid and FFA content of the IPA extracts were determined. Broken rice kernels had significantly greater surface lipid and FFA content than head rice kernels. The surface FFA contents of broken kernels were within the range of 0.045–0.065% of broken rice mass, while that of head rice was 0.027–0.040%. Broken ricehad greater b values indicating greater yellow color than did head rice.  相似文献   

4.
Rice yellowing is a problem for the rice industry. The objective of this research was to determine the effect of various temperatures and exposure durations at certain moisture content levels on yellowing in rice. Preliminary experiments were performed on stored Oryza sativa L. ‘Cypress’ rice. These experiments showed that exposure temperature and duration had a great effect on yellowing, but that the effect of moisture content was not significant (P > 0.15). With this information, similar experiments were performed on freshly harvested ‘Cypress’ and ‘Bengal’ rice. Color degradation, as measured by hue angle and chroma, was observed when at temperatures >50°C for exposure durations >12 hr. Temperatures >55°C with exposure durations >12 hr also resulted in dramatically lowered peak viscosity, but not all samples that showed yellowing had lowered viscosity. For the conditions of these experiments, temperature and exposure duration were the most important factors in color and viscosity change.  相似文献   

5.
One cause of yellowing or stackburn of rice may be elevated respiration rates caused by storage at either high moisture content (MC) or temperature. The effect of MC and temperature on the respiration rate of Oryza sativa L. ‘Bengal’ and ‘Cypress’ rice harvested in the fall of 1998 was investigated. For respiration rate measurement of rough rice at different temperatures, rice samples at high, medium, and low MC were sealed in quart jars and equilibrated to temperatures of 20–80°C. The respiration rate was quantified by measuring the rate of CO2 accumulation in the free air space. To determine the effect of MC on respiration rate, rough rice was tested at 12–25% MC. Respiration was greatly affected by MC and temperature. The response of respiration to temperature was dependent on MC and varied between rice cultivars. Respiration rates increased as MC increased from ≈15 to 25%. Maximum respiration was at 50°C when MC was high (20–25%). At 15% MC, respiration increased from 20 to 70°C, while respiration of 12% MC rice, although very low, appeared to increase up to 80°C. A model was developed from this data to predict the respiration rate of rice over the MC range tested.  相似文献   

6.
Thermomechanical analysis (TMA) and differential scanning calorimetry (DSC) were used to investigate the thermal transitions of long‐grain rice kernels. Three distinct thermomechanical transitions were identified as rice kernels were heated from 0 to 200°C. The identified transitions were a low temperature transition with onset at ≈45°C, an intermediate temperature transition at ≈80°C, and a high temperature transition at ≈180°C. Low temperature transition with onset from ≈60°C at 5% moisture content (MC) to 30°C at 20% MC was identified as the glass transition of the rice kernels. Intermediate temperature transition from 60 to 100°C, depending on MC, may be caused by rapid evaporation of moisture in the rice kernels. High temperature transition was associated with melting of the crystalline structure of rice starch. The temperatures of all three transitions decreased as MC increased, confirming that moisture acted as a plasticizer in rice kernels.  相似文献   

7.
Long‐grain rice cultivars Francis and Wells and hybrid XL8 Clearfield were harvested from two locations at three harvest moisture contents (HMC) in 2003. The rough rice was dried, fractionated into thin, medium, and thick fractions, and milled. Physicochemical properties of unfractionated and fractionated samples were determined. The effects of HMC and location on thickness distributions were investigated and the weighted‐average physicochemical properties of the thickness fractions were compared with those of unfractionated rice. Generally, the growing location and HMC affected kernel thickness distributions, green kernel content, fissured kernel content, and head rice yield (HRY). As kernel thickness within samples increased, amylose content increased and the protein content and α‐amylase activity decreased. Thick fractions had greater peak viscosities than medium and thin fractions. The thin, medium, and thick fraction physicochemical property weighted averages provided good predictions of most unfractionated rice sample properties. However, this approach was not entirely accurate for predicting HRY, milled rice total lipid content, and bulk density.  相似文献   

8.
Germinated brown rice is popular in Asia for its increased γ‐aminobutyric acid (GABA) content and sweeter and softer texture compared with conventional brown rice. However, most studies investigated germinated rice properties on medium‐grain or aromatic rice. The objective of this study was to compare differences between a medium‐grain (Jupiter) and a long‐grain (Wells) rice under similar germination conditions on their milling, physicochemical, and textural properties over the course of germination. Rough rice was soaked in water at 25°C for 12 h and then incubated at 30–34°C for four germination durations. Wells had a higher breakage percentage and a greater weight decrease than Jupiter during germination. Wells had a significantly lower GABA content before germination and at the first two germination durations than Jupiter, but the GABA content in Wells significantly increased at the third germination duration to become significantly higher than that of Jupiter. There were no significant changes in gelatinization temperatures and pasting properties of germinated rice from both cultivars at different germination durations. The cooked rice hardness from Wells decreased at the longest germination duration, whereas Jupiter showed a more significant decrease in cooked rice stickiness from germination. The results demonstrate that the impacts of germination on physical, chemical, and textural properties of rice were affected by grain type and germination duration.  相似文献   

9.
《Cereal Chemistry》2017,94(5):798-800
Internal stresses owing to moisture and temperature gradients often result in the development of rice kernel fissures. Fissured rough rice kernels tend to break upon milling and potentially reduce the market value of rice. This work was conducted on the premise that fissures may be healed by soaking in water at a specific temperature and duration. Fissured rough rice kernels of a long‐grain cultivar, Wells, were selected by X‐ray imaging. Fissured kernels were soaked in a water bath at six soaking temperatures (22, 60, 65, 70, 75, and 80°C) and three soaking durations (1, 2, and 3 h) and then gently dried for characterization. X‐ray images revealed that soaking at 75°C for 3 h healed up to 70.0% of the fissured kernels. Soaking at 22, 60, or 65°C did not result in healing. For normal kernels, soaking at different temperatures for 3 h created fissures. Bending tests using a texture analyzer showed that brown rice breaking force increased from 18.5 N (fissured kernels) to 43.7 N (healed kernels). Soaking rough rice in water at a temperature slightly above its onset gelatinization temperature may potentially heal fissures.  相似文献   

10.
Rice quality can vary inexplicably from one lot to another and from year to year. One cause could be the variable temperatures experienced during the nighttime hours of rice kernel development. During the fall of 2004, a controlled temperature study was conducted using large growth chambers, testing nighttime temperatures of 18, 22, 26, and 30°C from 12 a.m. until 5 a.m. throughout kernel development, using rice cultivars Cypress, LaGrue, XP710, XL8, M204, and Bengal. As nighttime temperature increased, head rice yields (HRY) significantly decreased for all cultivars except Cypress and Bengal, for which HRY did not vary among nighttime temperature treatments. Kernel mass did not vary among temperature treatments for any cultivar. Grain dimensions generally decreased as nighttime temperature increased. The number of chalky kernels increased with an increase in nighttime temperature for all cultivars but Cypress. The amylose content of Cypress and LaGrue was significantly lower at the nighttime temperature of 30°C, while total brown rice lipid and protein contents did not vary among temperature treatments for all cultivars.  相似文献   

11.
Milling data of four long-grain rice cultivars were analyzed to determine the uniformity in the slope of their curves for head rice yield (HRY) versus the corresponding degree of milling (DOM). The data set for each cultivar comprised samples that had been subjected to various drying air conditions and durations and milled over a range of moisture contents. All treatment combinations were split and milled for either 15, 30, 45, or 60 sec in a McGill no. 2 laboratory mill to obtain HRY versus DOM data. Linear relationships between HRY and DOM, as observed in past research, were confirmed. This implies that as rice is milled to greater extents (higher DOM), the HRY decreases linearly. Within the bounds of the experimental levels tested, neither the drying air condition nor drying duration affected the rate at which HRY changed with DOM. However, the cultivar and the moisture content at which the rice was milled significantly (P < 0.05) influenced this rate. At higher milling moisture contents, the decrease in HRY per unit of increase in the DOM was greater than at lower moisture contents. While not conclusive, there was an indication of a relationship between the average kernel thickness of a cultivar and the HRY versus DOM slope.  相似文献   

12.
During storage, the milling, physicochemical properties, and eating quality of rice change, which is generally termed “aging.” Aged rice is preferred by processors because of better processing characteristics, and therefore there are attempts to develop accelerated aging processes. In this study, the effects of various heat treatments and their influences on the milling, physicochemical, and cooking properties of two long‐grain rice cultivars during storage were investigated with a randomized complete block design with an 8 × 5 × 2 full‐factorial treatment design. Two long‐grain rice cultivars, Wells and XP723, were treated with eight different heat treatments, including two levels of UV irradiation, two levels of autoclaving, three levels of convection oven heating, and one control, and then stored for 180 days at room temperature. The heat treatments significantly influenced all properties, including head rice yield (HRY), surface lipid content, peak gelatinization temperature, pasting properties, and cooked rice texture. All properties except HRY exhibited a significant two‐way interaction of cultivar and heat treatment. The severe autoclaving treatment resulted in rice of significantly different protein compositions when compared with the control. Storage impacted all properties except HRY and peak gelatinization temperature. Autoclaving (particularly severe autoclaving) produced samples with more distinct characteristics for most properties. Cooked rice hardness and stickiness exhibited not only significant main effects but also significant two‐ and three‐factor interactions.  相似文献   

13.
Germinated brown rice is considered a more nutritious and palatable cooked product than conventional brown rice. However, germination usually decreases rice milling yield and alters some physicochemical properties. Parboiling is commonly used to increase milling yield and retain nutrients, but it also changes rice color and texture. The objective of this study was to investigate the effect of parboiling on milling, physicochemical, and textural properties of a medium‐grain and a long‐grain rice after germination at varying durations. Germinated rice samples of three germination durations were prepared with one germination time before the optimum time at which 70% of rice revealed hull protrusion, the optimum time, and one time after. Germinated rice was then immediately parboiled at 120°C for 20 min and was then immediately dried. The milling, physicochemical, and textural properties of parboiled germinated rice from both cultivars were determined. Parboiling significantly decreased the percentage of brokens, whiteness, and the apparent amylose content and increased γ‐aminobutyric acid content (GABA) in the nongerminated rice and rice at the first germination duration for both cultivars. Parboiling reduced pasting viscosities for both cultivars, but Jupiter still exhibited higher pasting viscosities than Wells. Cooked parboiled germinated rice was overall softer than nonparboiled rice because of kernel splitting, but Wells remained harder and less sticky than Jupiter. In conclusion, it is beneficial to combine parboiling with germination to enhance nutritional values and improve milling properties without affecting textural properties for both rice cultivars.  相似文献   

14.
Many rice cultivars and hybrids have unique physical characteristics that affect milling performance. The purpose of this study was to quantify the rate of bran removal during milling for several rice cultivars and hybrids common to the southern United States, and compare the quantity of lipids remaining on the kernel surface to that located throughout the kernel. This was accomplished by analyzing two sample sets. The first comprised cultivars Cocodrie, Cypress, and Lemont, and hybrids XL7 and XL8, which were milled for 0 (brown rice), 20, 30, 40, 50, 60, and 70 sec in a laboratory mill. In the second set, cultivars Cocodrie, Cypress, and Wells, and hybrids XL7 and XL8 were milled for 0, 20, 40, and 60 sec. The surface lipid content (SLC) and color of head rice samples were measured as indications of the degree of milling (DOM). The total lipid content (TLC) of ground head rice was also measured to determine the total amount of lipids present throughout the entire kernel. Results showed that at a given milling duration, SLC and color varied across cultivars and hybrids. In particular, the SLC levels of hybrids were lower than those of cultivars, particularly for Cocodrie, for all milling durations. This research indicated that it may be necessary to mill different cultivars and hybrids for varying durations to attain comparable DOM levels. Milling to a consistent DOM level is necessary to ensure equitable head rice yield comparisons across cultivars and hybrids.  相似文献   

15.
《Cereal Chemistry》2017,94(4):683-692
In‐bin, on‐farm drying systems for rough rice present challenges for maintaining kernel quality when drying fronts stall and the top layer of grain maintains its harvest moisture content (MC) for extended periods. This high MC, in addition to ambient temperatures in early autumn in the Mid‐South United States, creates ideal conditions for quality losses to occur. This study evaluated the effects of rough rice storage at MCs of 12.5, 16, 19, and 21% for up to 16 weeks at temperatures of 20, 27, and 40°C on milling yields, kernel color, and functionality of three long‐grain cultivars. Head rice yield was negatively impacted only after other reductions in quality had occurred. Temperature‐specific discoloration patterns were observed at 27 and 40°C in 2014; the uniquely discolored kernels seen in 2014 at 27°C were absent from samples in 2015 under identical conditions. Peak viscosity, breakdown, and final viscosity tended to increase over storage duration at 20 and 27°C and all storage MCs but plateaued after 8 weeks. Storage of rice at 40°C and all MCs greatly reduced peak viscosity after 6 weeks. To prevent quality losses, in‐bin dryers should be monitored closely to avoid exceeding the thresholds of storage MC, temperature, and duration identified here.  相似文献   

16.
Field studies were conducted from 2011 to 2013 near Stuttgart, Arkansas. The impacts of nitrogen rate (0, 45, 90, 135, and 180 kg of N/ha) and harvest moisture content (HMC) (23, 19, and 15%, wet basis) on physicochemical properties and milling yields were determined. Trends were similar for the cultivars evaluated: Cheniere, CL XL745, and Wells. Milled rice yields were only minimally impacted by either N rate or HMC level. Increasing N rate reduced kernel length and thickness of brown rice, chalkiness of brown rice and head rice, and viscosities of head rice flour, and it increased brown rice and head rice crude protein content and head rice yield (HRY). In terms of milling yields and head rice functionality, these data suggest that N rates as low as 90 kg of N/ha could be utilized, should production recommendations be changed. Significant interactions between N rate and HMC level were infrequent and were associated with the 0 kg of N/ha rate, unrealistic for rice production. Decreasing HMC from 23 to 19% reduced kernel length and thickness and increased crude protein content and chalkiness; further decreasing HMC to 15% also increased kernel fissuring and decreased HRY.  相似文献   

17.
The effect of moisture content (MC) on the glass transition temperature (Tg) of individual brown rice kernels of Bengal, a medium‐grain cultivar, and Cypress, a long‐grain cultivar, was studied. Three methods were investigated for measuring Tg: differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical analysis (DMA). Among these methods, TMA was chosen, because it can also measure changes in the thermal volumetric coefficient (β) of the kernel during glass transition. TMA‐measured Tg at similar MC levels for both cultivars were not significantly different and were combined to generate a brown rice state diagram. Individual kernel Tg for both cultivars increased from 22 to 58°C as MC decreased from 27 to 3% wb. Linear and sigmoid models were derived to relate Tg to MC. The linear model was sufficient to describe the property changes in the MC range encountered during rice drying. Mean β values across both cultivars in the rubbery state was 4.62 × 10‐4/°C and was higher than the mean β value of 0.87 × 10‐4/°C in the glassy state. A hypothetical rice drying process was mapped onto the combined state diagram generated for Bengal and Cypress.  相似文献   

18.
The relationship of glass transition temperature Tg and moisture content (MC) gradient of rice kernels to head rice yield (HRY) variation was investigated. Mathematical models describing heat and moisture transfer inside rice kernels during drying were developed and solved using the finite element method. Moisture distributions inside a kernel were simulated and verified using thin-layer drying experiments, and the intra-kernel MC gradients during drying were accordingly determined and analysed. Results showed that in the glassy region, rice did not incur measurable HRY reduction after drying. However, when rice was dried in the rubbery region and then cooled down immediately without being tempered following drying, HRY decreased markedly after MC gradients exceeded certain levels. It was found in this study that the time when the percentage point of moisture removal reached a maximally allowable level before HRY decreased dramatically coincided with the time at which the curve of kernel MC gradients versus drying duration reached its peak. Such a relation was verified with the HRY data of two varieties (Cypress and M202) as measured in this study and cited from literature. The HRY trends for these two varieties were well explained through the behaviour of glass transition and MC gradients of rice.  相似文献   

19.
Rice endosperm often develop a yellow discoloration during commercial storage in conditions of high temperature and moisture, thereby reducing the value of the grain. This postharvest yellowing (PHY) appears to be coincidental with fungal presence. To study the yellowing process in a controlled manner, we developed a technique to induce PHY on a small, laboratory scale. Milled rice kernels were rinsed with water and incubated in clear test tubes or microfuge tubes at 65–80°C. This allowed direct observation of the color change and measurement using a colorimeter. Every rice cultivar tested (long and medium grain japonicas and indicas) showed some level of PHY, which increased with temperature yielding a maximum color change at 79°C. Most color change occurred within one day. The moisture parameters required for yellowing to occur were measured. Using sterilization and culture techniques, we found no indications of direct fungal involvement in the yellowing process.  相似文献   

20.
《Cereal Chemistry》2017,94(3):497-501
The objectives of this research were to characterize dry matter loss of hybrid long‐grain rough rice during storage under reduced‐oxygen conditions and develop a new approach to predict the dry matter loss by using storage temperature and relative humidity data as input. Two long‐grain hybrid rice cultivars, CL XL745 and XL760, harvested in the year 2015 were stored in rough‐rice form in sealed glass jars at moisture contents of 12.5, 16, 19, and 21%, (wet basis) and temperatures of 10, 15, 20, 27, and 40°C for a total of 16 weeks, with samples taken at 2, 4, 6, 8, 10, 12, and 16 weeks of storage. Results revealed no differences in dry matter loss connected with the rough‐rice moisture content levels and temperature during the storage duration. However, the dry matter loss was statistically different based on rough‐rice cultivar. Experimental data were fitted to a dry matter loss equation for long‐grain rice found in literature. The dry matter loss equation developed for conditions of grain storage without oxygen limitation did not accurately predict rough‐rice dry matter loss under reduced‐oxygen conditions. Equation constants generated for reduced‐oxygen storage conditions were significantly lower than the typical constants used for long‐grain rice in literature. Hence, integration of rice cultivar and storage conditions such as oxygen supply is crucial for accurate determination of kinetics of dry matter loss during storage of hybrid long‐grain rough rice.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号