Comparison of Three Extraction Systems for Determining Surface Lipid Content of Thickness‐Fractionated Milled Rice

The surface lipid content (SLC) of rice is often used to objectively measure the degree to which bran has been removed from rice kernels, commonly known as degree of milling (DOM). This study was conducted to evaluate new, rapid extraction technology for potential timesaving measurements of SLC of milled rice. The SLC of two long‐grain rice cultivars, Cypress and Drew, were determined using three extraction systems: Soxtec, accelerated solvent extraction (ASE), and supercritical fluid extraction (SFE). Before milling, rough rice was separated into three thickness fractions (<1.84, 1.84–1.98, and >1.98 mm) and samples from each thickness fraction were milled for durations of 10, 20, and 30 sec. Head rice collected from each milling duration was extracted using each of the three methods. Results showed that regardless of the extraction method, thinner kernels had lower SLC measurements than thicker fractions. In most cases, both the ASE and Soxtec produced SLC greater than that of the SFE. The ASE also showed SLC measurements at least as great as those from Soxtec extraction, suggesting that the ASE is as thorough in extracting lipids as commonly used methods.     

Quantifying Surface Lipid Content of Milled Rice via Visible/Near-Infrared Spectroscopy

Visible/near-infrared calibrations were developed and tested for surface lipid content (SLC) of milled long-grain rice. Three rice varieties were divided into two sample sets, with one containing two variables (degree of milling and variety) and another containing three variables (degree of milling, variety, and kernel thickness). The reflectance calibration equation from the set with three variables was much more accurate in predicting SLC than was the calibration from the two-variable set. Optimal calibration and prediction were obtained by combining both visible and near-infrared wavelength ranges and using the modified partial least squares technique on spectra pretreated by standard normal variate and first derivative methods. The best calibration yielded a coefficient of determination (R²) of 0.99 and a standard error of prediction of 0.04% SLC, which was approximately 1.5 times the standard error of calibration and also 1.5 times the SLC measurement error.     

Rapid Methods for Milled Rice Surface Total Lipid and Free Fatty Acid Determination

Total lipids and free fatty acid (FFA) determination is widely used in the food industry to assess the quality of milled rice. An improved rapid ambient temperature isopropanol (IPA) extraction method to determine milled rice surface lipid was more effective than Soxhlet solvent extraction. The improved method was probably due to better extraction of polar lipids and antioxidants by IPA. A colorimetric method to determine FFA requiring only 30 μL of sample is also described. The new technique provides results similar to those obtained using the slower, conventional acid‐base titration method. The colorimetric FFA method requires a smaller sample size, has greater precision, and is more objective. The new methods are particularly suitable for industrial use in providing rapid results for large numbers of samples.     

Correcting Head Rice Yield for Surface Lipid Content (Degree of Milling) Variation

Head rice yield (HRY) is the primary parameter used to quantify rice milling quality. However, HRY is affected by the degree of milling (DOM) and thus HRY may not be comparable between different lots if the DOM is different. The objective of this study was to develop a method by which HRY values can be adjusted for varying DOM values when measured by surface lipid content (SLC). Seventeen rough rice lots including long‐grain and medium‐grain cultivars and hybrids were harvested from two 2003 and five 2004 locations. Duplicate subsamples of each lot were milled in a McGill No. 2 laboratory mill for 10, 15, 20, or 40 sec after zero, one, two, three, and six months of storage. HRY and SLC were measured. The average HRY versus SLC slope across all milling duration data sets was 9.4. As such, it is suggested that, when milling with a McGill No. 2 laboratory mill, the HRY of a rice lot can be adjusted by a factor of 9.4 percentage points for every percentage point difference between the rice lot SLC and a specified SLC.     

Development and Validation of Prediction Models for Rice Surface Lipid Content and Color Parameters Using Near‐Infrared Spectroscopy: A Basis for Predicting Rice Degree of Milling

Degree of milling (DOM) of rice plays a key role in determining rice quality and value. Therefore, accurate, nondestructive, quick, and automated surface lipid content (SLC) measurement would be useful in a commercial milling environment. This study was undertaken to provide calibration models for commercial use to provide quick and accurate evaluation of milled rice SLC and Hunterlab color parameters (L,a,b) as indications of rice DOM. In all, 960 samples, including seven cultivars from seven southern United States locations, stored for 0, 1, 2, 3, and 6 months, were milled for four durations to obtain samples of varying DOM. The samples were used to develop calibration models of milled rice SLC and L,a,b values. Another sample set (n = 58) was commercially milled and used to validate the developed models. A DA 7200 diode array analyzer was used to scan milled rice samples in wavelength spectra of 950–1,650 nm. SLC and color parameters were measured using a Soxtec system and a HunterLab colorimeter, respectively. The partial least squares regression (PLS) method using the full near‐infrared spectra was used to develop prediction models for rice SLC and color parameters. Milled rice SLC was well fitted with a correlation of determination of predicted and measured values of (R² = 0.934). Color parameters were also successfully fitted for L (R² = 0.943), a (R² = 0.870), and b (R² = 0.855). Performance of the developed models to predict rice DOM was superior in predicting SLC and L,a,b values with R² predicted and measured values of 0.958, 0.836, 0.924, and 0.661, respectively.     

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.     

Evaluation of Operating Conditions for Surface Lipid Extraction from Rice Using a Soxtec System

The degree of milling (DOM) of rice is a measure of how well the germ and bran layers are removed from the surface of rice kernels during milling. Because the majority of rice kernel lipids are found on the surface, measuring the surface lipid content (SLC) of rice after milling may be one way to quantify the DOM of rice. While there are several methods to measure the lipid content (LC) of rice, there is not an established standard method for determining the SLC of milled rice. The objective of this study was to evaluate the primary operating variables of a Soxtec apparatus in measuring the SLC of milled rice. This was accomplished by varying the preextraction drying, boiling, rinsing, and postextraction drying durations, as well as the solvent used for extraction, to achieve the maximum extraction of lipids from rice. Experiments were performed on stored Oryza sativa L. ‘Cypress’ and ‘Bengal’ rice milled for 10, 30, and 60 sec. Results showed that durations of 1 hr of preextraction, 20 min of boiling, 30 min of rinsing, and 30 min of postextraction drying provided the maximum lipid extraction from milled head rice with petroleum ether. Of the three solvents tested, petroleum ether, and ethyl ether yielded similar extraction results.     

Surface Lipid and Free Fatty Acids (FFA) Content of Head and Broken Rice Produced by Milling After Different Drying Treatments

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.     

An Improved Procedure for Determining Magnesium Fertilizer Dissolution in Field Soils

Abstract

The sequential extraction procedure currently used to measure magnesium (Mg) fertilizer dissolution in soils consists of removing dissolved Mg (step 1), and partially dissolved Mg (step 2), followed by an 18‐h extraction with 2 M HCl at room temperature to determine undissolved Mg (step 3). This procedure is satisfactory for soluble and moderately soluble Mg fertilizers but is not an accurate procedure for slightly soluble fertilizers, such as serpentine. When step 3 is replaced by a digestion procedure using 2 M HCl for 4 h at 90–95°C (improved step 3), the total serpentine Mg recovery (dissolved and undissolved Mg) from soil samples, either immediately after serpentine was added to soil or after a 21‐day incubation with moist soil, was about 100% compared to 40–50% by the original procedure. The improved procedure also increased the recovery of serpentine Mg applied to field soils. Therefore, this study recommends that the third step of the sequential extraction procedure be replaced by a 4 h digestion using 2 M HCl (90–95°C).     

Postcolumn Fluorimetric HPLC Procedure for Determination of Niacin Content of Cereals

Analytical procedures for determining niacin or vitamin B3 content of foods are tedious, require large quantities of toxic chemicals, and are timeconsuming. In addition, food matrices are difficult as samples because of their complex nature. A selective, sensitive HPLC technique was developed with postcolumn derivatization as well as fluorescence and spectroscopic detection systems. Niacin was separated and retained for 6.5 min on a polymeric column with an aqueous mobile phase containing sodium acetate buffer. A postcolumn system consisting of a stainless-steel pump and reaction coil allowed detection and quantitation of niacin. An acid-enzyme sample-extraction method was most compatible with HPLC and postcolumn derivatization with 5% each of acidified p-aminophenol and cyanogen bromide. Lower detection limit and mean recovery were 3.6 ng and 99.43%, respectively. Fluorescence response for nicotinamide was half that of nicotinic acid. A lower response for nicotinamide was also noted with conventional spectroscopy. However, the new method yielded comparable values for six of eight ready-to-eat commercial cereal samples. No significant difference was observed between the AACC reference and HPLC fluorimetric methods. Chemical derivatization was done within a reaction coil with reagents at half strength, limiting exposure to hazards and minimizing waste-disposal problems.     

灌溉定额分月趋势确定法及其在旱作水稻上的应用

为了探索旱作水稻灌溉定额确定方法,通过对长系列(1992-2014年)单季稻生长季(6-10月份)及旱季(7-9月份)降雨量进行排频,并参考蒸发量确定不同灌溉保证率代表年;通过计算多年日均有效降雨量和水稻需水量,按月绘制成不同保证率的水稻需水量与有效降雨量变化趋势线图;通过积分法计算曲线方程差,即为月灌水额,合计后为灌溉定额,或通过测算曲线间的图形面积快速获得月灌水额。结果表明,当地单季水稻90%、75%和50%的年份能够满足的灌溉定额分别为416.9、338.7和216.1 mm,旱作水稻取其50%~60%的灌溉量值。应用试验表明,干旱年(2013年)按90%、平水年(2014年)按50%的年份能够满足的定额减半灌溉,粳稻旱作产量分别为5 924.3 kg·hm-2和6 511.8kg·hm-2,是淹灌栽培的84.1%和91.2%。该方法不仅能计算灌溉总量,还能体现灌溉量在作物生长过程中的分配趋势,对于提高旱作水稻的水分管理水平具有重要意义。     

有机肥料总氮含量的测定方法研究

氮作为有机肥料养分的重要来源,其含量是评价有机肥料质量的一项重要指标。为了给有机肥料总氮含量的测定提供快速且精确的测定方法。选择了6个有机肥料样品,用H2SO4-H2O₂消煮,分别用连续流动注射分析仪和半自动凯氏定氮仪测定消煮液中的全氮含量,以探讨不同方法快速而精确地测定有机肥料总氮含量的可行性。结果表明,利用连续流动注射分析仪和半自动凯氏定氮仪测定方法的结果间没有显著性差异,相对标准偏差均在5%以下,且连续流动注射分析仪加标回收率为97.5%～102.0%。同时由于连续流动注射分析仪测定有机肥料总氮具有快速准确、试剂用量少的优点,适合大批量有机肥料总氮的测定分析。     

Evaluation of Air Oven Moisture Content Determination Methods for Rough Rice

The effects of air oven drying temperature and drying duration on moisture content determination of medium grain rough rice were studied for moisture content levels from 10·2 to 32·5% (w.b.). Six different methods were compared in this study. A moisture content determination model for an air oven was developed to describe the effect of drying temperature, drying time, and sample grinding on moisture content determination. Drying whole kernels for 72 h at 105°C had the smallest standard deviation. Regression equations obtained from the measured data were used to validate the model developed in this study. This model could be employed to evaluate the moisture determination methods for other varieties of rough rice and other crops obtained from previous literature.     

Establishing Soil Silicon Test Procedure and Critical Silicon Level for Rice in Louisiana Soils

Calibration of crop responses to applied silicon (Si) serves as a basis for developing Si fertilizer recommendation guidelines. A greenhouse experiment was set up in a randomized complete block design with five replications, two sources of Si (wollastonite and slag) and four Si rates (0, 170, 340 and 680 kg ha^?1) to calibrate plant-available Si for growing rice in Louisiana soils. Silicon concentrations were determined in soils using seven different extraction procedures. Based on a quadratic model (p < 0.05), the estimated soil Si critical level using 0.01 M calcium chloride (CaCl₂) for Sharkey clay soil was 110 mg kg^?1 while for Crowley silt loam and Commerce silt loam, levels were 37 and 43 mg kg^?1, respectively. These results suggest that suitability of an extractant that gives the best estimate of plant-available Si could considerably depend on soil type and it is unlikely that there is a universal extractant for all soils.     

A Program for Determining Cocompost Blending Ratios

? A program is presented that computes blending ratios for two ingredients of a co-compost. The program is written in the RPN language, requires 61 lines of memory, and will support hand-held programmable calculators, making it suitable for use in the field. Use of this program allows the composter to determine blending ratios quickly and with increased precision and accuracy.     

Solventless Microextraction Techniques for Determination of Trihalomethanes by Gas Chromatography in Drinking Water

Three different solventless sample preparation techniques based on microextraction, membrane extraction, and headspace extraction have been developed and optimized for determination of trihalomethanes in drinking water by gas chromatography electron capture detector and mass spectrometry detection. The techniques employed were headspace (HS) solid-phase microextraction, hollow fiber liquid-phase microextraction (HFLPME) and HS extraction. All techniques used were optimized with different experimental designs in order to select the most relevant variables which significantly affect the different processes. The different analytical figures of merit such as limit of detection (LOD), limit of quantification, reproducibility, accuracy, and linear dynamic range were obtained. The new HFLPME method applied used a hollow fiber membrane of polypropylene and the optimized variables were extraction time, extraction temperature, and salting-out effect. The software MODDE 6.0 was used and its design was one central composite on face with a total of 17 runs. The best conditions for the HFLPME were 20 min, 40°C, and 10% NaCl, respectively. The LODs ranged from 0.018 μg·L⁻¹ (for CHClBr₂) to 0.049 μg·L⁻¹ (for CHBr₃), being this technique the most sensitive one among those studied. Finally, after having optimized the sample preparation techniques and chromatographic conditions, several water samples were taken in two different water treatment plants in Spain (Zaragoza) and Colombia (Viterbo, Caldas). The results obtained are shown and discussed.     

控灌条件下稻田田面水含氮量、土壤肥力及水氮互作效应试验研究

通过田间试验,研究了不同控制灌溉模式下不同氮素用量稻田田面水铵态氮、硝态氮的变化特征,综合评价了试验区稻田土壤肥力等级,并分析了水分与氮素用量对水稻产量和产量构成因素的互作效应。结果表明:在水稻整个生长过程中,过量施肥对土壤最后残留的氮含量影响较大;土壤肥力等级的高低、每次施氮后所取水样铵态氮与硝态氮浓度的均值同相应的施氮水平有较高的因果效应。施返青肥后田面水铵态氮浓度最高值在施氮后第3天出现,施穗肥后田面水铵态氮浓度最高值在施氮后第2天出现,田面水硝态氮浓度出现最高值的时间要滞后于铵态氮1天。氮肥对水稻产量及其构成因子均表现为正效应,且高施氮量的正效应大于中施氮量的。控水效应和土壤水分胁迫与氮素互作效应对产量及其构成因素的影响多数为负效应,表明进行水分胁迫会影响产量构成因素进而降低水稻的产量。