Relating Rice Milling Quality Changes During Adsorption to Individual Kernel Moisture Content Distribution

Several varieties of rough rice that were either stored for an extended period of time or freshly harvested were conditioned to initial moisture contents ranging from 10 to 17%. After the individual kernel moisture content distributions were measured, the samples were soaked in water at temperatures ranging from 10 to 40°C. The samples were then dried and milled. The bulk critical moisture content, at which head rice yield began to decline due to moisture adsorption, ranged from 12.5 to 14.9%, depending on the variety, harvest moisture content, and storage conditions. The kernel critical moisture content, determined from each sample from the cumulative kernel moisture content frequency distribution, increased with increasing sample initial moisture content.     

Effects of microwave heat, packaging, and storage temperature on fatty acid and proximate compositions in rice bran

The effect of microwave heat, packaging methods, and storage temperatures on proximate and fatty acid compositions of rice bran during 16 weeks of storage was examined. Freshly milled raw rice bran was adjusted to 21% moisture content and microwave heated for 3 min. Raw and microwave-heated brans were packed in zipper-top bags and/or vacuum-sealed bags and stored at 4-5 and/or 25 degrees C for 16 weeks. The moisture content decreased significantly from an initial 8.4 to 6.4% in microwave-heated samples regardless of packaging methods and storage temperatures. Protein, fat, linoleic, and linolenic contents did not change significantly in all raw and microwave-heated samples during 16 weeks of storage. The microwave-heated rice bran packed in zipper-top bags can be stored at 4-5 degrees C for up to 16 weeks without adverse effect on proximate and fatty acid composition quality under the conditions employed in this study.     

Kinetics and mechanism of free fatty acid formation on the surface of milled rice

The presence of free fatty acid (FFA) is an important factor in determining rice quality for brewing. FFA formation in milled rice during storage was monitored, and a two-parameter semiempirical kinetic model giving product concentration as a function of time is proposed to describe FFA formation on milled rice during storage. The model was tested using sets of data obtained from partially milled rice samples stored at 24, 37, and 50 degrees C and fully milled rice stored at 37 degrees C and 70% relative humidity. The predicted values provide very good fits (R(2) >or= 97%) of the experimental data at all storage temperatures. A two-substrate reaction mechanism representing a two-phase process is also presented. Milled rice FFA at a given storage time varied with storage temperatures. The kinetic model and mechanisms proposed could be useful in describing and predicting FFA contents of milled rice during storage and transportation.     

Prevention of hydrolytic rancidity in rice bran during storage.

The effect of microwave heating, packaging, and storage temperature on the production of free fatty acids (FFA) in rice bran was examined. Freshly milled raw rice bran was adjusted to 21% moisture content and heated in a microwave oven at 850 W for 3 min. Raw and microwave-heated rice bran were packed in zipper-top bags or vacuum-sealed bags and stored at 4-5 or 25 degrees C for 16 weeks. FFA content of bran was measured at 4-week intervals. Total FFA increased rapidly over the 16-week period from the initial value of 2.5% in raw bran stored at 25 degrees C to 54.9% in vacuum bags and 48.1% in zipper-top bags. However, total FFA of raw bran stored at 4-5 degrees C increased at a slower rate from an initial value of 2. 5 to 25.4% in vacuum bags and 19.5% in zipper-top bags. After 16 weeks of storage, total FFA of microwave-heated bran stored at 25 degrees C increased from 2.8 to 6.9 and 5.2%, respectively, for samples stored in vacuum bags and zipper-top bags. Total FFA of microwave-heated samples stored at 4-5 degrees C did not change significantly with storage time. Results showed that hydrolytic rancidity of rice bran can be prevented by microwave heating and that the recommended storage condition for microwaved rice bran is 4-5 degrees C in zipper-top bags.     

Effects of Rough Rice Storage Conditions on the Amylograph and Cooking Properties of Medium-Grain Rice cv. Bengal

Rough rice (cv. Bengal) was stored at four moisture contents (8.8, 10.7, 12.9, and 13.6% MC) and three temperatures (3, 20, and 37°C) for up to six months. The amylograph overall paste viscosity of the milled rice increased during storage. This increase was most apparent in all samples stored at 37°C. For rice stored at 20 and 37°C at all MC levels, a 30–50% increase in peak viscosity (PV) was observed during the first three months of storage. PV subsequently leveled off for rice stored at 12.9 and 13.6% MC but declined for samples stored at 8.8 and 10.7% MC. The final viscosities also increased during storage. The water-absorption ratio of the samples during cooking in excess water increased by an average of 15% over six months of storage. The amylograph and cooking properties were significantly affected (P < 0.05) by rough rice storage duration, temperature, MC, and their respective interactions.     

Effects of Postharvest Elevated‐Temperature Exposure on Rice Quality and Functionality

Rapid drying with high‐temperature air has gained interest in the rice industry, but the effects of elevated‐temperature exposure on physicochemical properties of rice are of concern. This study investigated the effects of exposing rough rice to elevated temperatures for various durations without removing moisture. Physicochemical property response was evaluated in terms of head rice yield (HRY), germination rate (GR), milled‐rice yellowing, pasting properties, and gelatinization temperatures. Two long‐grain cultivars (pure‐line Wells and hybrid CL XL729) at initial moisture contents (IMCs) of 17.9 and 18.6%, respectively, and dried moisture content (DMC) of 12.5%, were hermetically sealed and exposed to 40, 60, and 80°C for various durations. Exposure to 80°C of IMC samples of Wells and CL XL729 resulted in a significant (2.3–2.5 percentage point) reduction in the HRYs. A 2 hr exposure of both cultivars at IMC level to 60°C completely inhibited GR, and exposure to 80°C of the cultivars at both moisture content (MC) levels immediately inhibited GR. Exposure to 80°C for almost all durations and 60°C for durations over 4 hr produced significant yellowing in both cultivars at IMC. Significant yellowing in both cultivars at DMC was also observed during a 28 day storage following 80°C exposure. In general, peak viscosities of both cultivars at IMC increased only after extended exposure to 40 and 60°C, but peak viscosities of the cultivars exposed to 80°C increased sharply and immediately upon exposure. No significant differences were observed in gelatinization temperatures of either cultivar at either MC level from elevated‐temperature exposure. Results from this study suggest that extreme‐temperature exposure of rough rice affects HRY, GRs, yellowing, and pasting properties of rice, but the extent of impact is MC dependent.     

Effect of Sucrose on Glass Transition,Gelatinization, and Retrogradation of Wheat Starch

Differential scanning calorimetry (DSC) was used to study the effect of sucrose on wheat starch glass transition, gelatinization, and retrogradation. As the ratio of sucrose to starch increased from 0.25:1 to 1:1, the glass transition temperature (T_g, T_g′) and ice melting enthalpy (ΔH_ice) of wheat starch‐sucrose mixtures (with total moistures of 40–60%) were decreased to a range of −7 to −20°C and increased to a range of 29.4 to 413.4 J/g of starch, respectively, in comparison with wheat starch with no sucrose. The T_g′ of the wheat starch‐sucrose mixtures was sensitive to the amount of added sucrose, and detection was possible only under conditions of excess total moisture of >40%. The peak temperature (T_m) and enthalpy value (ΔH_G) for gelatinization of starch‐sucrose systems within the total moisture range of 40–60% were increased with increasing sucrose and were greater at lower total moisture levels. The T_g′ of the starch‐sucrose system increased during storage. In particular, the significant shift in T_g′ ranged between 15 and 18°C for a 1:1 starch‐sucrose system (total moisture 50%) after one week of storage at various temperatures (4, 32, and 40°C). At 40% total moisture, samples with sucrose stored at 4, 32, and 40°C for four weeks had higher retrogradation enthalpy (ΔH) values than a sample with no sucrose. At 50 and 60% total moisture, there were small increases in ΔH values at storage temperature of 4°C, whereas recrystallization of samples with sucrose stored at 32 and 40°C decreased. The peak temperature (T_p), peak width (δT), and enthalpy (ΔH) for the retrogradation endotherm of wheat starch‐sucrose systems (1:0.25, 1:0.5, and 1:1) at the same total moisture and storage temperature showed notable differences with the ratio of added sucrose. In addition, T_p increased at the higher storage temperature, while δT increased at the lower storage temperature. This suggests that the recrystallization of the wheat starch‐sucrose system at various storage temperatures can be interpreted in terms of δT and T_p.     

辐照生姜的贮藏性状研究

8 0～ 2 5 0Gyγ射线辐照处理生姜 ,可以导致生姜贮藏初期Vc损失 ,但辐照处理能够抑制生姜的发芽和呼吸代谢作用 ,从中长期贮藏的角度来看 ,反而有利于Vc含量的维持。辐照处理还引起生姜贮藏过程中还原糖含量的增加 ,以 1 5 0和 2 5 0Gy剂量处理升高幅度最明显。2 5 0Gy辐照处理使生姜蛋氨酸和精氨酸含量明显下降 ,但对其余 1 6种氨基酸含量影响较小。生姜受到辐照后 ,短期内出现呼吸高峰 ,然后呼吸强度迅速下降 ,并维持在较低水平。 80～40 0Gy剂量辐照处理使生姜根茎肉质部电解质渗透率升高 ,但同样剂量的辐照没有引起生姜组织酯酶同工酶酶谱的变化     

Viability of Oryza sativa L. seeds stored under genebank conditions for up to 30 years

Germination ability, equilibrium relative humidity (eRH), and moisture content of ‘control’ seed samples representing 183 rice accessions stored in the active (2–4 °C) and base (?10 °C until 1993, then ?20 °C) collections of the T. T. Chang Genetic Resources Center were determined after storage for 20.5–30.5 years. Germination of seeds that had been stored in the base collection was generally high (>70 %), whereas germination was more variable for seeds stored in the active collection. Samples with lower viability after storage in the active collection were likely to have lower viability after storage in the base collection. There were significant differences in the moisture content-eRH relationship of the seeds depending on whether the seeds had been stored in the active or base collection. Based on re-test data for regular seed samples regenerated in 1979–1980 and stored in the active collection for up to 31 years, estimates of the time for ability to germinate to fall to 50 % (p ₅₀) ranged from 54 to 997 years. For the same seed samples stored in the base collection for approximately 31 years, ability to germinate has been maintained and germination increased due to improved procedures. The ability to germinate of base collection samples was also generally higher than that of ‘safety duplicate’ samples of the same seed lots that had been sent to the National Center for Genetic Resources Preservation, USA in 1981 and stored at ?18 °C. This may have been due to uptake of moisture either during processing for dispatch or as a consequence of poor packaging material. The results are discussed in relation to long-term seed storage and genebank management.     

Moisture Redistribution and Phase Transitions During Bread Staling

Standard white breads were stored with or without crust at 25°C in hermetic pouches. During two weeks of storage, the crumb moisture content and water activity (a_w) decreased significantly when stored with crust. When stored without crust, moisture content and a_w remained relatively unchanged. The causes of the initial firming of both breads over zero to seven days were not conclusive. But when stored beyond seven days, bread stored with crust was significantly firmer in texture and higher in amylopectin recrystallization than bread stored without crust. Moisture redistribution from crumb to crust played a significant role. This was accompanied by a decrease in freezable water in the bread crumb stored with crust. This loss in freezable water coincided with changes in the thermomechanical profile only in the case of sample stored with crust intact (and with a significant total and freezable water loss). Bread crumb stored without crust did not change in total and freezable water and showed less change in thermomechanical transitions. The transition occurring at ≈60°C (T₂) correlated with amylopectin recrystallization but it could also have been caused by moisture loss during the analysis. Moisture migration from crumb to crust greatly reduced the total and freezable water in the crumb region, resulting in a significant reduction in the magnitude of the mechanical transition at ≈0°C (T₁) as well as an increase in the storage modulus.     

Detection of changes in taste of japonica and indica brown and milled rice (Oryza sativa L.) during storage using physicochemical analyses and a taste sensing system

Changes in the taste of japonica, hybrid, and indica brown and milled rice, stored for 10 months at low (5 degrees C, 65-70% relative humidity) and room temperatures were observed by physicochemical analyses and a novel method using a taste sensing system. During storage, some properties increased or decreased while others were fairly constant. The main taste components of cooked rice such as sweetness (sucrose) and umami tastes (glutamic acid and aspartic acid) were reduced during storage, whereas glucose and fructose increased. The increase of fat acidity and consequent decrease of the pH value of the cooking solution may contribute to the off-taste of cooked stored rice. A taste sensing system with 10 lipid membrane sensors was also used to classify new and old rice samples using principal component analysis. Fresh and room temperature stored japonica and indica rice could be clearly distinguished; however, it was not possible to differentiate the samples stored at low temperature.     

Effect of Changing Temperature on the Deterioration of Soya Beans

Deterioration rates as indicated by carbon dioxide evolution for soya bean (Glycine max L. Merr.) stored under changing temperature conditions were quantified and compared with those predicted using equations. Experiments included soya bean moisture contents of 18, 22, and 26% (wet basis), constant storage temperatures of 15, 20, 25, and 30°C, and cyclical storage temperatures that changed between 15 and 25°C and between 20 and 30°C on a 24 h basis. Also, the growth of micro-organisms was identified after 10 days from the treatments by using the pour plate method.The results indicated an increase in deterioration by increasing storage temperature and moisture content of soya bean. Equations of carbon dioxide weight versus time for each moisture content and storage temperature were fitted. The longest allowable storage time to reach 0·5% dry matter loss (1132 h) occurred at lower moisture content and lower constant storage temperature, while the shortest allowable storage time (170 h) occurred at higher moisture content and higher constant storage temperature. The allowable storage times for soya bean stored under cyclical temperatures were close to the allowable storage time for soya bean stored at a constant temperature equal to the average cyclical temperature. Microbial infection levels increased with increasing storage temperature and moisture content. The increasing rate of micro-organism growth decreased by increasing the storage temperature over 25°C. However, this increasing rate of micro-organism growth for soya bean exposed to a cyclical storage temperature was usually lower than that for soya bean held at constant storage temperatures of about 20°C (the average of 15 and 25°C) and 25°C (the average of 20 and 30°C).     

Storage of Wheat Grains at Elevated Temperatures Increases Solubilization of Glutenin Subunits

Grains of two wheat (Triticum aestivum L.) cultivars, Sunco and Sunsoft, were stored at 4°C and 30°C for 270 days to examine changes in proteins during storage. When whole meal flour extracted from the grains was analyzed using an unfractionated protein extraction procedure, no significant changes were found in protein content or SDS‐PAGE profile for either cultivar in samples stored at 30°C compared with those stored at 4°C. Fractionation of the flour samples from stored grain into soluble and insoluble proteins revealed increases in soluble protein content for both cultivars stored at 30°C compared with 4°C. The soluble protein content, expressed as a percentage of the total protein, increased by 1.5% (P = 0.032) for Sunco and by 8.0 % (P = 0.158) for Sunsoft during storage at 30°C compared with those samples stored at 4°C. Analysis by SDS‐PAGE and subsequent protein identification revealed that the most evident change that occurred during storage at 30°C was an increase in the content of high molecular weight glutenin subunits (HMW‐GS) in the soluble fraction. The potential effect of changes in solubility of HMW‐GS on functional properties is discussed.     

Physicochemical Properties of Rice Dried in a Single Pass Using High Temperatures

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.     

End-Use Quality of Flour from Rhyzopertha dominica Infested Wheat

The objective of this study was to evaluate how Rhyzopertha dominica infestation of stored wheat grain affects the rheological and baking properties of bread made with the milled flour. Wheat samples were infested with R. dominica and stored for up to 180 days at room temperature. Every 45 days, samples of wheat were collected and evaluated for insect population and flour yield. Flour milled from these wheat samples was evaluated for color reflectance, pH, fat acidity, and rheological properties which were measured by a farinograph. Loaves of bread were baked using a straight-dough procedure. Volume, height, and weight of the loaves were evaluated. None of the analyses performed on the control wheat flours showed any changes during the storage period, and they were similar to the initial wheat. The insect population increased during storage of the wheat up to 90 days, and the flour yield decreased with the storage up to 180 days. Flours from insect-infested wheat absorbed more water than did flours from control wheat. Dough stability and dough development times of infested flours decreased. Bread volume showed a progressive decline throughout the storage experiment. In conclusion, flour from insect-infested wheat exhibited changes in rheological properties such as dough stability, dough development times, water absorption, and mixing stability; bread had an offensive odor; and volume and loaf characteristics were negatively affected.     

Influence of Storing Rough Rice with High Moisture Content on Subsequent Drying Characteristics and Milling Quality

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.     

Factors That Influence the Microwave Expansion of Glassy Amylopectin Extrudates

The microwave expansion of glassy, unexpanded amylopectin pellets was studied. Amylopectin was extruded at three levels of specific mechanical energy (483, 809, and 846 kJ/kg), and 35–40% moisture content, without expansion at the die. Glassy pellets were obtained by drying and equilibrating the extrudates at five water activities (a_w 0, 0.11, 0.33, 0.67, and 0.75). The pellets were characterized by measuring volume, porosity, and moisture content. The pellets were then expanded in a constant power microwave oven to determine the degree of expansion. When subjected to microwave heating, regardless of extrusion condition and initial a_w, the pellets expanded from the center where the highest temperature was recorded and then expansion advanced in the whole volume. Maximum expansion was reached after 30 sec of heating, after which samples started to burn from the center. Samples simultaneously expanded and lost moisture, both processes being faster and more intense for pellets of higher initial a_w. No expansion was observed for the pellets stored at a_w 0, while collapse was observed for pellets stored at a_w 0.73. A linear correlation between pellet expansion temperature and glass transition temperature was obtained. A hypothesis for the microwave expansion of glassy extrudates was formulated and represented on a state diagram.     

前期不同水分状况对土壤氧化亚氮排放的影响

田间采集的新鲜土壤样品分别在室温下风干(土样D)和淹水(土样S)保存110d后,将二者的含水量分别调至20%、40%、60%、80%、100%持水量(WHC,Water Holding Capacity),在25℃下培育138h,设置不通和通入10%(v/v)乙炔的处理。结果显示,在20%～80%WHC下培育时,土样S的氧化亚氮(N2O)排放量为土样D的2.48倍～6.36倍(p<0.01),而在100%WHC水分含量下培育时,土样S的N2O排放量仅为土样D的19%(p<0.01),通入乙炔不但未使土样D的N2O排放量增加,反而显著减少。通入乙炔的处理,培养结束后硝态氮的含量增加。随培育水分含量的升高,土样S和土样D的二氧化碳排放量增大。供试土样可能存在异养硝化作用。前期水分的差异显著影响土壤N2O排放量,故在田间测定土壤N2O排放量时,要考虑土壤前期水分的差异。     

Dry Matter Loss for Hybrid Rough Rice Stored Under Reduced‐Oxygen Conditions

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.