Harvest Moisture Content Research Articles

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

ABSTRACTTiming 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 harvest time and drying on supersweet sweet corn seed quality

A supersweet sweet corn hybrid, Pacific H5, was grown under field conditions in South-East Queensland to study the effects of harvest time and drying conditions on seed quality. Cobs were harvested at different times to obtain seed with two moisture percentage ranges (20-30% and 40-50%) and dried to 12% moisture under different combinations of drying temperatures (30 degrees C, 40 degrees C and 50 degrees C) and air velocities (1.25 m/s, 2.75 m/s and 4.30 m/s). Dried seed was stored at 30 degrees C with bimonthly monitoring of seed quality for 12 months. For standard as well as cold test germinations, statistical analysis yielded significant main effects for temperature, air velocity and harvest moisture content and significant interactions for drying temperature by harvest moisture and drying temperature by air velocity. Germination at the beginning of storage was unaffected by drying temperatures up to 40 degrees C regardless of harvest moisture but was lower at 50 degrees C for higher moisture. However, germination at the end of the storage period of 12 months was greatest for seed harvested at higher moisture and dried at temperatures up to 40 degrees C. Germination was not affected by air velocity for drying temperatures up to 40 degrees C but at 50 degrees C it generally decreased with increase in air velocity. To slow down seed deterioration during storage, it is recommended that sweet corn seed should be harvested at a higher moisture range (40-50%) and dried at 40 degrees C and 4.30 m/s air velocity. The drying temperature can be raised to 50 degrees C for seed harvested at a low moisture range (20-30%) provided the air velocity is kept low (1.25 m/s).

HARVEST LOCATION AND MOISTURE CONTENT EFFECTS ON RICE KERNEL-TO-KERNEL BREAKING FORCE DISTRIBUTIONS

One medium-grain rice variety, six long-grain varieties, and two long-grain hybrids, harvested from 13.4% to 26.0% moisture content (MC) from Keiser, Arkansas, Stuttgart, Arkansas, and Alvin, Texas, were used to determine the influence of harvest location and MC on kernel-to-kernel breaking force distributions (BFDs). Harvest moisture content (HMC) affected BFDs, however, a greater influence was imposed by the growing location. Breaking force distributions were generally characterized by primary and secondary modal populations, although in many instances a clear demarcation between these populations was not apparent. Head rice yield (HRY) was plotted against the percentage of kernels in a sample having breaking forces greater than 20 N, which was used as an estimate to define “strong” kernels. The strongest correlations between HRY and the percentage of strong kernels were found for growing location/variety lots having HRYs of 45% to 65%. Little to no correlation was observed for groups of samples having HRYs greater than 65%. One of the issues preventing a better HRY versus strong kernel percentage correlation was that the force level separating “weak” from “strong” kernels could not be accurately and consistently identified due to a lack of clear delineation between the modal populations.

INDIVIDUAL RICE KERNEL MOISTURE CONTENT VARIABILITY TRENDS

Variation in individual kernel moisture content (MC) distributions in rice panicles were measured for rice cultivarsBengal, Cypress, and Drew. Rice panicles were harvested at different stages of maturity from foundation seed fields at twolocations with widely varying soils in Arkansas during the autumns of 1998, 1999, and 2000. The objective was to quantifyvariability of individual rice kernel MCs as affected by maturity, planting location, and year. Individual kernel MCdistributions were multi-modal until the average harvest MC (HMC) reached about 16%, at which point the distributionstended to be primarily single-modal. For all cultivars, HMC significantly affected kernel MC standard deviation (SD). ForCypress and Drew, individual kernel MC SD was also significantly affected by year and location with significant interactionsbetween HMC and year and HMC and location. Regression equations that accounted for the variation in individual kernelMC at varying kernel maturity stages were generated for each cultivar.

INFLUENCE OF DRYING ON RICE FISSURE FORMATION RATES AND MECHANICAL STRENGTH DISTRIBUTIONS

Tests were conducted to determine the effects of drying conditions on the rate of fissure formation after drying and the resultant mechanical strength distributions of individual rice kernels. Long-grain varieties Cypress, Drew, and Wells at 21% harvest moisture content (HMC) were dried at 40°C, 45°C, 50°C, 55°C, and 60°C and constant 17% relative humidity (RH) to 12% MC. Immediately after drying, the samples were placed in sealed plastic bags at 21°C. Fissure enumeration, milling tests, and individual kernel breaking force measurements were made at 1, 24, 48, and 120 h after drying ceased. Head rice yields (HRYs) decreased as drying temperature increased. Very few fissures were visible immediately after drying. Most fissures appeared within 24 h of drying cessation and corresponded to HRY reductions. There was no difference in the kernel thickness distributions of fissured and non-fissured kernels taken from the dried samples. The drying treatments produced samples having greater variation in kernel breaking forces than that of control samples. Thus, the breaking force distributions (BFDs) were affected by drying treatment, but were also affected by post-drying durations. The percentage of strong kernels in a sample, defined as those brown rice kernels withstanding a 20 N force in a three-point bending test, was strongly correlated with HRY (R2 = 0.804, 0.835, and 0.915 for Cypress, Drew, and Wells, respectively).

Effects of Rough Rice Moisture Content at Harvest on Peak Viscosity

During rice kernel development, kernel size and chemical composition change with maturation, and the kernel moisture content progressively decreases (Del Rosario et al 1968; Lee and Chang 1985). Therefore, kernel moisture content is an important indicator of rice kernel development. Lee and Chang (1985) found that when starch and protein synthesis were nearly completed, the rice kernel moisture content was ≈27–29% (wb). The composition of rice kernels harvested after this point reportedly did not change dramatically, although the starch content increased slightly, causing a proportional decrease in protein content in the kernel (Del Rosario et al 1968; Kim et al 2001). Rice kernel-to-kernel development on panicles is nonuniform, which in turn produces a range of kernel moisture contents within a bulk at harvest (Chau and Kunze 1982; Kocher et al 1990; Siebenmorgen et al 1992). As such, physical properties such as bulk density and milling quality change with harvest moisture content (HMC). The grade of rice typically improved and the bulk density increased as HMC decreased (Morse et al 1967; Fan et al 1998). The number of fissured kernels increased dramatically when the HMC decreased from 19 to 13% and was especially severe when kernel moisture content decreased rapidly in a short time (Jodari and Linscombe 1996). Reports of optimum HMC for maximum head rice yield (HRY) ranges from 18 to 26% based on growing location, harvest date, and cultivar (Kester et al 1963; Huey 1977; Lu et al 1988, 1992; Siebenmorgen et al 1992; Jongkaewwattana et al 1993a; Ntanos et al 1996; Bautista and Siebenmorgen 2000). Limited research has been conducted to determine the effect of the HMC on functional characteristics of rice. Kester et al (1963) reported that the peak viscosity (PV) of short-grain rice first decreased and then increased with maturation. It was explained that amylases were responsible for these changes. Kim et al (2001) also noted differences in PV of medium-grain rice with HMC, however, the trends did not follow consistent patterns. The study reported herein was designed to quantify the effects of rough rice HMC on PV of popular several rice cultivars grown in the midSouth rice producing region of the United States.

Effect of Harvest Moisture Content and Ambient Air Drying on Maize Fiber Oil Yield and its Phytosterol Composition

Effect of harvest moisture content and ambient air drying on maize fiber yield, fiber oil content and the phytosterol composition of maize fiber oil were evaluated. Maize was harvested at approximately five different harvest moisture contents (28.0, 23.0, 20.0, 18.0 and 15.0%). Effect of air drying was studied by ambient drying the maize harvested at 28.0% moisture content to 20.0 and 13.0% moisture content. Effect of both harvest moisture content and ambient air drying were significant on all the dependent variables, however, no clear trends were observed. The results suggest that as harvest moisture content goes down the amount of oil extracted from the maize fiber decreases but the concentration of the phytosterols in the maize fiber oil increases proportionally.

Row Spacing, Plant Density, and Hybrid Effects on Corn Grain Yield and Moisture

Producing corn (Zea mays L.) in narrow row spacings has been attempted over the last several decades with varying degrees of success. The objectives of this study, are to determine: (i) if there is a different optimum plant density or (ii) if hybrids of varying relative maturity respond differently for corn grown in narrow row spacings (38 cm) compared with conventional row widths (76 cm). These studies were conducted at six locations across Iowa over 3 yr. Averaged across years, locations, and plant densities, corn grown in 76‐cm row spacings produced higher yields than that grown in 38‐cm rows (10.5 vs. 10.3 Mg ha−1, respectively). Harvest moisture content of corn grown in 38‐cm row spacings was significantly less than that of corn grown in 76‐cm row spacings (160 vs. 161 g kg−1, respectively). Averaged across years and locations, there was no statistically significant (P < 0.05) yield difference between the two row spacings for four of the six hybrids tested. Hybrid MAX23 yielded significantly more grain in 76‐cm row spacings (9.4 vs. 8.9 Mg ha−1) while ‘MAX454’ yielded more grain in 38‐cm row spacings (10.0 vs. 9.8 Mg ha−1). It is thus concluded that optimum plant densities for narrow‐row corn production are similar to those required to produce maximum yields for conventional wide‐row corn production. In addition, a strong hybrid × row spacing interaction among the six hybrids tested here suggests that certain hybrids may perform better at prescribed row spacings.

A STUDY OF HEAD RICE YIELD REDUCTION OF LONG- AND MEDIUM-GRAIN RICE VARIETIES IN RELATION TO VARIOUS HARVEST AND DRYING CONDITIONS

In this research, the effects of harvest moisture content (HMC), harvest location, variety difference, andheated-air drying conditions on head rice yield reduction (HRYR) of long-grain (Kaybonnet and Cypress) and medium-grain(Bengal) varieties were investigated. The rice was harvested at moisture contents (MCs) of approximately 16 to26% from two locations (Stuttgart and Keiser, Arkansas). The rough rice was dried under three conditions: 43.5C, 38%relative humidity (RH), 9.5% equilibrium moisture content (EMC); 51.7C, 25% RH, 7.3% EMC; and 60C, 17% RH,5.8% EMC. The results indicated that variety, HMC, drying condition, and drying duration had significant interactiveeffects on the HRYR during drying. Medium-grain Bengal rice exhibited more HRYR than did long-grain Cypress orKaybonnet rice under a given drying condition. The results further indicated that a decrease in MC of rice at the earlydrying stages did not substantially affect the HRY until a certain MC level was reached. It appeared in this study that theamount of moisture that could be removed without affecting HRY increased as harvest MC increased.

EFFECTS OF VARIETY AND HARVEST MOISTURE CONTENT ON EQUILIBRIUM MOISTURE CONTENTS OF RICE

Equilibrium moisture contents (EMC) of two long-grain rice varieties (Kaybonnet and Cypress) and one medium-grain variety (Bengal) were measured at temperatures of 4, 21, and 38°C with relative humidities (RHs) ranging from 11 to 96%. In addition to temperature and RH, variety was a significant factor affecting rice EMC. Harvest moisture content (HMC) and harvest location did not significantly affect the EMC of rough rice. Rice harvested at a lower moisture content (MC) had lower EMC values than rice harvested at a higher MC when equilibrated to high RHs; however, these differences were primarily attributed to hysteresis effects. An EMC model including temperature, RH, and variety was developed. At most RHs, the EMCs of Bengal, Kaybonnet, and Cypress rough rice were approximately 0.2 to 0.8 percentage points higher than that calculated from the Chung EMC equation. New coefficients of the Chung equation for rough and milled rice are provided.

Starch Yield Sensitivity of Maize Hybrids to Drying Temperature and Harvest Moisture Content

Nine maize hybrids from the 1994 crop, representing the range of hybrids grown in the U.S. central corn belt, were harvested at high 133-35 %) and low (21-22 %) moisture contents and laboratory dried at either ambient temperature (about 25 °C) or 110 °C. Similarly, nine maize hybrids from the 1995 crop were harvested at two different moisture contents and dried using either ambient temperature or 80 °C. Both sets of samples were wet-milled using a 100g laboratory procedure. Significant differences were observed between hybrids as to the effect of drying air temperature and harvest moisture content on wet-milling yields. Eight of the 9 hybrids dried at 110 °C and harvested at high moisture contents showed significantly lower starch yields (by 7.2-15,1 %) when compared to starch yields of the same hybrids dried at 110°C and harvested at low moisture contents. Results also indicated that there is a hybrid-dependent effect of high-temperature drying and harvest moisture content at 80°C drying air temperature. Starch yields of some hybrids harvested at low moisture contents are negatively affected if dried at 80 °C. However, there were mixed results on starch yields if the hybrids were harvested at high moisture contents and dried at 80 °C.

Bulk Density of Long‐ and Medium‐Grain Rice Varieties as Affected by Harvest and Conditioned Moisture Contents

ABSTRACTThe effect of harvest and conditioned moisture contents (MC) on bulk density (BD) of rough, brown, and white rice was determined for several long‐ and medium‐grain rice varieties harvested from different Arkansas locations. The results indicated that harvest MC (HMC) significantly affected the BD of freshly harvested and conditioned rough rice. Higher HMC levels resulted in lower BD levels for rough rice over the conditioned MC range from 11 to 29% (wb). There was a strong linear relationship between rough rice BD and conditioned MC for a given HMC. The harvest location had a more pronounced effect on rough rice BD of long‐grain varieties than of medium‐grain varieties. The BD of brown and white rice was less dependent on harvest location and conditioned MC than the BD of rough rice. Rice harvested at low MC level (≈13%) gave a higher BD for both brown and white rice than that harvested at higher MC levels. Medium‐grain varieties showed a higher BD for brown and white rice than did long‐grain varieties.

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

ABSTRACTSeveral 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.

Evaluation of the Displacement Value as a Method to Detect Reduced Corn Wet‐Milling Quality

ABSTRACTA procedure based on the resistance and capacitance (RC) properties of corn to calculate a displacement value (DV) was evaluated for detection of corn that had reduced wet‐milling quality. In 1991 and 1992, three hybrids were dried at air temperatures between ambient and 115°C in batch dryers. Additional samples, obtained from commercial elevators in 1992, had been dried with air temperatures ranging from 52 to 136°C. A baseline reference relationship was developed between log10‐resistance and capacitance with data from ambient‐dried samples. A DV was defined as the horizontal distance along the capacitance axis from a sample RC data point to the baseline reference. RC properties of samples dried at air temperatures >50°C were compared to the baseline and the DV determined. Selected drying treatments were wet‐milled by a laboratory‐scale procedure to verify milling quality and correlation with DV. The effects attributed to hybrid and harvest moisture content on the RC properties of ambient‐dried samples were small, allowing the baseline reference to be applied to a wide range of corn samples. In 1992, the baseline shifted upward from the 1991 baseline by 0.5 units on the log10‐resistance axis. DV increased significantly at drying air temperatures >50°C for batchdried samples. While DV correlated with drying temperature in batchdried samples (r = 0.66), it did not correlate with starch yield or recovery of commercial samples (r ≤0.10). Although the specific causes could not be determined, the shift in the baseline indicates the method would be difficult to implement on a practical scale. Although not indicated by DV, starch recovery decreased significantly for samples batch‐dried at air temperatures ≥70°C. All samples dried at 115–136° had significantly lower starch recoveries.

Mechanical seed quality of soyabeans related to drying parameters

Investigations were conducted on the mechanical seed quality of soyabeans after drying from a harvest moisture content of 20% (w.b.) in a 5cm thick bed in an air oven. The drying period and the drying air temperature were varied between 26 and 94 h and 48 and 164 °C, respectively. Response surface contours generated from quadratic functions fitted to the data indicated that low drying air temperature (below 50 °C) and drying periods above 80 h resulted in breakage resistant soyabeans having compressive resistance of 275 N and breakage susceptibility of less than 2%. However a competitive set of drying parameters was found in the air temperature range of 50–80 °C (drying periods less than 10 h) which may be a more economic region.

RELATING DRYING RATE CONSTANT TO HEAD RICE YIELD REDUCTION OF LONG-GRAIN RICE

Long-grain rough rice was dried at various rates and durations and milled to determine head rice yield. The drying data were described by a Newton equation, and the resultant head rice yield reduction data were described by an empirical rate equation. Effects of drying condition, variety, harvest moisture content, and storage time prior to drying were investigated, but only the first two of those variables significantly affected the drying rate constant, and the first three of those variables significantly affected the head rice yield reduction. Head rice yield reduction was directly related to the drying rate constant. At a given drying rate constant, head rice yield reduction increased with drying duration. An empirical model was developed to predict the head rice yield reduction as a function of drying rate constant and drying duration. This model may lead to optimal control of rice dryers in terms of minimizing head rice yield reduction during the drying process.

Effect of Rice Moisture Content at Harvest on Economic Return

Economic analyses were conducted to assess the impact of rice harvest moisture content (MC) on economic return to a producer. The primary factors considered included percent milled rice, percent head rice, field yield, and drying costs. The results showed that rice harvest MC had a dramatic impact on the final gross income to a producer. The optimal harvest MC was influenced by field yield loss rate and, to a lesser degree, drying charge schedule. The relative price of broken to head rice also affected the optimal harvest MC. Significant losses in gross income could be incurred if rice is harvested at MCs lower than 15% or higher than 22%.

Evaluation of Cateto Maize Accessions for Grain Yield and Physical Grain Quality Traits

Because many exotic corn (Zea mays L.) races have different evolutionary histories from those of U.S. races, they may possess unique, favorable alleles for physical grain quality traits. This study explored the effectiveness of using exotic inbreds from Uruguay, Argentina, South Africa, and Taiwan (representing ‘Cateto’‐type, intermediate, and non‐Cateto races) to improve physical grain quality of U.S. Corn Belt hybrids. Eighteen exotic inbreds were crossed to two Corn Belt inbreds, Mo17 and B73, which represent the ‘Lancaster Sure Crop’ and the ‘Iowa Stiff Stalk Synthetic’ backgrounds, respectively. A randomized complete block design was used to evaluate testcrosses (F1s), their F2 and backcross (to the Corn Belt inbreds) generations, and four checks grown at two locations in Iowa and at one location in Missouri. The experiment showed significant differences among races for 1000‐kernel weight, test weight, grain yield, and harvest moisture content. Testcrosses and generations were significantly different for kernel weight, test weight, breakage susceptibility, grain yield, and harvest moisture content. Significant differences were also found between testers for all traits except moisture. Entry × tester interaction, however, was significant only for breakage susceptibility and yield, whereas entry × generation interaction was significant for all the traits except breakage susceptibility. This study showed that Catetotype inbreds have the potential to improve test weight of Corn Belt hybrids. The Cateto race inbreds also contributed favorable alleles for lowering harvest moisture content, which may indirectly help reduce breakage losses.

Evaluation of Cateto Maize Accessions for Grain Yield and Other Agronomic Traits in Temperate and Tropical Environments

The temperate maize (Zea mays L.) race Cateto may have potential for improving grain quality in temperate breeding programs. Temperate germplasm may also be useful in tropical breeding programs for improving yield, agronomic traits, and grain quality. The objective of our study was to assess the yield potential of Cateto race accessions testcrossed with two Corn Belt inbreds for grain yield and other agronomic traits in both temperate and tropical environments. Exotic inbreds representing Cateto, intermediate, and non‐Cateto races were crossed to two U.S. Corn Belt inbreds (Mo17 and B73). Testcrosses (F1s), their F2 and backcross generations, and four checks were evaluated in 1989 through 1991 at three temperate (two in Iowa and one in Missouri) and two tropical (Florida and Zimbabwe) locations. Data were recorded for grain yield, harvest moisture content, days to tassel, ear height, stalk lodging, and root lodging. The testcross‐by‐generation interaction was significant for all traits, except grain yield, whereas the testcross‐by‐tester interaction was significant for ear height, stalk lodging, and root lodging. B73 contributed more favorable alleles for improved standability and grain yield than did Mo17. Although the testcross by location interaction was significant for all traits, the tropical and temperate environments ranked testcrosses similarly. The tropical locations had both the highest and the lowest mean grain yields. The best testcrosses identified in temperate locations may have potential for introgression in the tropics.

A Simulation Model of Wheat Harvesting and Drying in Northern Australia

A simulation model of a conventional wheat harvesting and drying system was developed to examine the effect of many variables on the total cost of wheat production in northern Australia. The effect of grain moisture content at harvest and machinery capacities on the overall system cost was studied in detail. The results show that maximum return is obtained when grain is harvested at moisture contents of 15 to 19% wet basis, then artificially dried. The optimum harvest moisture content depends on crop area and the capacity of harvesting machinery. The effect of maturity date, spread of maturity, grain losses and operational strategies on production costs are discussed. The results of this investigation are specific to wheat, but the general conclusions apply to other cereal and legume crops.