Effects of Drain and Harvest Dates on Rice Sensory and Physicochemical Properties

Timing of field draining and harvesting of rice with meteorological conditions can allow growers to foster conditions for high head rice yield (HRY). The effects of timing of draining and harvesting on rice sensory and physicochemical properties are not well understood. The objective of this study was to determine the effects of varying drain and harvest dates on the sensory and physicochemical properties of M‐202 grown in California under controlled field conditions. Drain date had a significant (P < 0.05), but very small, effect on amylose and protein contents, with amylose being highest at the late drain date and protein being the lowest at the early drain date. Breakdown and setback were lowest for early and normal drain dates, respectively; however, no significant (P > 0.05) differences in texture were measured as a result of these parameters being low. Drain date did not affect the volatile composition or flavor of the rice. Harvest date had no effect (P > 0.05) on amylose content and a significant (P < 0.05), but very small, effect on protein content. Harvesting at the earliest date (9/30) resulted in rice with higher setback and lower breakdown than at the last date (10/16) and, subsequently, the early harvested rice, when cooked, was harder, more cohesive, and absorbed less saliva in the mouth. However, the differences in texture measured by the panelists were very small and would possibly not be noticed by untrained palates. The lowest levels of the lipid oxidation products 1‐pentanol, hexanal, and nonanal occurred in rice with the lowest harvest moisture content (HMC): rice harvested on 10/13 and 10/16. Differences in levels of lipid oxidation products and branched chain hydrocarbons did not lead to significant (P > 0.05) differences in flavor. In summary, M‐202 demonstrated stable composition, physicochemical properties, flavor, and texture across drain and harvest dates.     

Effect of Moisture Content at Harvest and Degree of Milling (Based on Surface Lipid Content) on the Texture Properties of Cooked Long-Grain Rice

The effects of the degree of milling (based on surface lipids content [SLC]) on cooked rice physicochemical properties were investigated. Head rice yield (HRY), protein, and SLC decreased with increasing milling, while the percent of bran removed and whiteness increased. Results showed that SLC significantly (P < 0.05) affected milled as well as cooked rice properties across cultivar, moisture content (MC) at harvest, and location (Stuttgart, AR, and Essex, MO). Cooked rice firmness ranged from 90.12 to 111.26 N after milling to various degrees (SLC). The decrease in cooked rice firmness with increasing milling was attributed to the lowering of total proteins and SLC. Cooked rice water uptake increased with increasing degree of milling. Water uptake by the kernel during cooking dictated the cooked rice firmness. The increase in cooked rice stickiness with increasing degree of milling was attributed to an increase in starch leaching during cooking because of the greater starch granule swelling associated with a greater water uptake.     

耕作与施肥措施对江淮地区白土理化性质及水稻产量的影响

针对连续旋耕白土田耕层浅薄、下层土壤黏重紧实、养分分布不均衡等问题,探索适合于白土稻田的耕作与施肥措施,以进一步提高江淮地区白土生产力和水稻产量水平。设置2种耕作方式(旋耕和翻耕)及3种施肥措施(单施化肥、化肥+有机肥、化肥+秸秆还田),通过大田定位试验研究不同耕作方式与施肥措施对白土稻田土壤理化性质、水稳性团聚体分布以及水稻产量的影响。结果表明,相较于旋耕,翻耕降低0—10cm土层土壤养分含量,而使10—20cm土层有机质、全氮、有效磷和速效钾含量分别提高3.2%～8.8%,4.5%～9.2%,5.2%～8.2%和8.3%～17.7%。增施有机肥或秸秆还田使土壤有机质和速效钾含量较单施化肥处理分别提高1.3%～8.6%和4.1%～21.1%。翻耕方式下10—20cm土层土壤容重较旋耕降低14.4%～19.5%,土壤大团聚体比例在0—10,10—20cm土层则较旋耕分别降低3.0%～5.4%和3.5%～9.7%;在翻耕的基础上增施有机肥或秸秆还田土壤容重较单施化肥降低2.1%～6.6%,大团聚体比例则提高2.8%～8.4%。翻耕有利于水稻产量的提高,较旋耕的增产幅度在11.7%～18.0%,增施有机肥或秸秆还田使水稻产量提高1.7%～7.5%。因此,江淮地区连续多年旋耕的白土田进行适宜翻耕结合秸秆还田或增施有机肥可改善0—20cm土层土壤理化性质,有利于水稻产量的提升。     

不同密度和氮肥用量对水稻产量、构成因子及氮肥利用率的影响

针对水稻生产中氮肥用量过高、劳动力成本上涨及移栽密度越来越低的现状,设置氮肥、密度互作试验,研究施氮量和移栽密度及其互作效应对水稻产量和氮肥利用率的影响,以期为水稻节氮、省工合理栽培及高效施肥提供理论依据。结果表明,氮肥用量和密度均可显著影响水稻产量,互作效应显著。施氮(N82.5、N165.0、N247.5)后平均分别增产30.6%、47.8%、44.6%;密度为21万蔸/hm2时,籽粒产量最高。有效穗数随施氮量和移栽密度的增加而增加,提高密度后实粒数、结实率和千粒重则出现降低。氮肥利用率随施氮量增加而下降,随密度增加先上升后下降。在资源短缺、环境污染及生产成本上涨的形势下,低氮水平时应适当增加密度,提高移栽密度时则应控制氮肥用量。在本试验条件中,移栽密度为22.1万蔸/hm2的基础上施氮194.9 kg/hm2是实现水稻高产高效、节氮、省工栽培的合理组合。     

Effect of Moisture Content and Temperature on Respiration Rate of Rice

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.     

Effects of Product Temperature and Moisture Content on Viscoelastic Properties of Glutinous Rice Extrudates

The viscoelastic properties of glutinous rice flour extruded at moisture contents of 45–55% and barrel temperatures of 75–95°C have been investigated using a small amplitude oscillatory rheometer. High moisture contents (50 and 55%) resulted in product temperatures 3–5°C lower than the barrel temperatures. It appeared that the moisture content was a key element in influencing the value of G′ and tan δ. Raising product temperature reduced the difference in G′ caused by the moisture content. When the product temperature was >85°C, the extrudates yielded a similar degree of gelatinization despite the difference in moisture content. Meanwhile, both G′ and G″ decreased due to the disintegration of starch granules. The relationship between the energy input, measured as specific mechanical energy, and the viscoelastic properties was also assessed.     

Degree of Milling Effects on Rice Pasting Properties

The effects of degree of milling on pasting properties of medium‐grain (cv. Bengal and Orion) and long‐grain rice (cv. Cypress and Kaybonnet) were quantified using a Brabender ViscoAmylograph and a Rapid Visco Analyser. For all the cultivars tested, surface and total lipid contents decreased as the degree of milling increased. The peak viscosities for all rice increased with the degree of milling and the rates of increase were higher for medium‐grain than long‐grain cultivars. Degree of milling did not have a consistent effect on final viscosity for all the cultivars tested.     

Effect of Nitrogen Rate and the Environment on Physicochemical Properties of Selected High‐Amylose Rice Cultivars

Genetic marker haplotypes for the Waxy and alk genes are associated with amylose content and gelatinization temperature, respectively, and are used by breeders to develop rice cultivars that have physicochemical properties desired by the parboiling and canning industries. Cultivars that provide consistent processing quality across diverse production environments are important to the industry. This study determined if measures of processing quality differed among cultivars, fertility treatments, and production environments. Nine cultivars having high amylose content (>23.0%) but with different Waxy and alk haplotypes were evaluated in three environments and using three nitrogen fertility levels. Although environment and fertility levels significantly (P < 0.05) impacted protein content, gelatinization temperatures, and peak, trough, and final paste viscosities, cultivars performed consistently across production environments and fertility applications. Differences were observed among cultivars in paste viscosity measures and gelatinization temperatures that corresponded with their Waxy and alk haplotypes. However, discriminant analysis revealed subgroupings within the same Waxy and alk haplotypes that were primarily differentiated by trough paste viscosity. The results of this study demonstrated that although these high‐amylose cultivars had consistent ranking across environments and nitrogen fertility regimes, there were differences in rice processing quality traits that were not apparent from their Waxy and alk haplotypes.     

Effects of Milling on the Physicochemical Characteristics of Waxy Rice in Taiwan

Three types of mills and six milling methods were employed to mill two waxy rice varieties (TCSW1, long grain; TCW70, short grain), and the physicochemical and functional properties of rice flour were examined. The results showed that dry-milling maintained a higher level of the chemical components than other milling methods. Wet-milling slightly increased solubility as test temperatures increased, and significantly increased swelling power at 75 and 85°C for TCSW1 and TCW70, respectively. Hammer and semi-dry hammer milling gave higher percentages of coarse particles (100–300 μm); cyclone and turbo milling led to a more even particle-size distribution, and the wet-milling gave the finest particles (10–30 μm). Dry hammer-milled rice had higher gelatinization and pasting temperatures, and semi-dry grinding milling resulted in the lowest pasting temperature, setback viscosity, and enthalpy value among the mills. The final quality of the two waxy rice varieties was profoundly affected by the mill type and milling method.     

Effects of Selected Harvest Moistures and Frozen Storage Times on Selected Yellow Dent Corn: Wet‐Milling Yields and Starch Pasting Properties

The effects of harvest moistures and frozen storage times on corn wet‐milling yields and the pasting properties of the resulting starch were studied. Pioneer hybrid P‐0916‐XR harvested at three moisture contents (49, 35, and 21% wb) were stored frozen for three days or for five months, followed by wet‐milling. The pasting properties of the resulting starch were evaluated with a Rapid Visco Analyzer. The yields of starch and germ increased by 1.2 and 1.9 percentage points, respectively, when harvest moisture decreased from 49 to 21% wb, whereas the yields of steep water solids, total fiber, and gluten decreased by 2.1, 0.7, and 0.6 percentage points, respectively. The frozen corn had lower coarse fiber yields but higher cellular fiber yields. The starch pasting properties showed that peak and breakdown viscosities decreased by 8% (3,824 ± 36 versus 3,520 ± 38 cP) and 13% (2,336 ± 47 versus 2,029 ± 60 cP), respectively, when harvest moisture decreased from 49 to 21% wb, whereas peak time increased by 5% (6.32 ± 0.06 versus 6.62 ± 0.07 min). The setback and final viscosities of starch from long‐term frozen storage (five months) were 14% (1,574 ± 65 versus 1,828 ± 79 cP) and 8% (3,063 ± 27 versus 3,317 ± 101 cP) lower, respectively, than that from control (unfrozen) corn.     

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.     

栽培水氮条件及采后贮存时间对油菜产量及其硝酸盐含量的影响

以油菜为供试作物,用盆栽试验的方法研究不同灌水控制上限、氮素用量对油菜产量及其硝酸盐、亚硝酸盐含量的影响,探讨了不同水氮条件栽培的油菜植株体在贮存期间的硝酸盐、亚硝酸盐含量的变化特点。结果表明,供水越充足(灌水控制上限值越高)、氮素用量越多,油菜产量越高;而油菜收获采摘时硝酸盐和亚硝酸盐含量随灌水控制上限值增高而下降、随氮素用量增加而上升;采摘后8天贮存期间硝态氮含量呈高-低-高-低趋势变化,而亚硝酸盐则呈一单峰态变化,在贮存2~4 d硝酸、亚硝酸盐含量均有峰值出现;水分栽培条件对贮存期间油菜植株体硝酸和亚硝酸含量有显著影响,同一贮存时间、不同水氮处理比较,高灌水控制上限值、低氮素用量处理硝酸盐和亚硝酸盐含量低于低灌水控制上限、高氮素用量处理。     

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.     

不同土壤质地和含水率对炭基肥料氮素矿化的影响

为了探究土壤特性对炭基肥料氮素矿化的影响,采用室内培养和大田小区试验,分析了炭基肥在不同土壤质地(砂质壤土、粉砂质壤土、黏土)及含水率(80%、60%、40%田间最大持水量)条件下,氮素矿化动态变化特征。结果表明:在室内培养条件下,对于不同土壤质地,炭基肥在砂质壤土条件下矿化势最高,其次为黏土,最低的为粉砂质壤土;对于不同田间持水量,在粉砂质壤土条件下,炭基肥矿化势最高的为80%田间最大持水量(80%SMC),其次为60%SMC,最低的是40%SMC;在砂质壤土和黏土条件下,炭基肥的矿化势均表现为60%SMC> 80%SMC> 40%SMC。培养状态下粉砂质壤土、砂质壤土、黏土条件下最大氮素有效性分别是34.12%、56.31%、41.14%,而在大田条件下,炭基肥单季氮素最大矿化率在粉砂质壤土、砂质壤土、黏土3种土壤质地下分别是50.61%、32.27%、34.29%。     

稻秸还田下减量化施氮对小麦产量、养分吸收及土壤理化性质的影响

为明确稻秸还田下减量化施氮对小麦产量、养分吸收及土壤理化性质的影响，以小麦品种“宁麦16”为试验材料开展了试验研究，设置了不施氮对照（CK）、施氮量（常量施氮225kg/hm2，N1；减量20%施氮180 kg/hm2，N2）和氮肥运筹（基肥与追肥的比例为5:5，M1；基肥与追肥的比例为7:3，M2）处理，测定并分析了不同施氮量和氮肥运筹下小麦产量与其构成因素、养分吸收与分配、氮肥利用效率及土壤理化性质。结果表明，稻秸还田下，施氮可使小麦产量显著增加，N2处理小麦产量较N1处理仅降低了80.72kg/hm2，提高基施氮肥比例可使小麦单位面积有效穗数增加。施氮显著促进了小麦籽粒、秸秆和地上部的氮素、磷素和钾素吸收，N2处理小麦氮素、磷素和钾素吸收量低于N1处理；N1和N2水平下，M2处理小麦氮素和磷素吸收量均高于M1处理，而钾素吸收量低于后者。N2处理小麦氮肥农学效率、氮肥偏生产力、氮肥表观利用率和氮素生理效率较N1处理提高，而100kg籽粒吸氮量降低。N1处理土壤碱解氮含量显著高于CK；N2处理土壤有机质、碱解氮和速效钾含量低于N1处理，而土壤有效磷含量高于后者；N1和N2水平下，M1处理土壤有机质和碱解氮含量高于M2处理，而土壤有效磷和速效钾含量表现为M2处理高于M1处理。综合来看，稻秸还田下，常规施氮量基础上减量20%，适当提高基施氮肥比例，可增加单位面积有效穗数，实现小麦高产稳产，提高氮肥利用效率。     

Effects of Germination Duration on Milling,Physicochemical, and Textural Properties of Medium‐ and Long‐Grain Rice

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.