Color Development Time Research Articles

Kinetics of color changes of popped rice during microwave popping: Effect of salt and moisture content

AbstractPaddy, coated with a dielectric salt was popped using microwave energy. The kinetics of color changes of the popped rice with the variation of heating time (0–60 s), sample moisture content (12–18% wb), and level of salt coating (0–5% w/w) were studied. The parameters, estimating the change in color of the popped rice, were measured in terms of L*, a*, b* color coordinate system using a Chroma‐meter. The total color change (ΔE*), chroma (C*), hue angle (H*), and browning index (BI*) were estimated from these measured parameters. The shift in color change with microwave popped paddy was found darker side with the increase in heating time and salt content. These color changes showed that, ΔE* was fitted well to zero‐order kinetic model, while BI* followed a first‐order kinetic model. All these color parameters were fitted to a quadratic equation as a function of salt and moisture content. Both ΔE* and BI* increased with the increase in salt:moisture ratio.Practical applicationsThe color development in the product during microwave popping of paddy is an important sensory quality attribute concerning consumer acceptability. The popping characteristics of paddy and simultaneously kinetics of its color changes are closely associated with the factors like moisture content, level of salt (dielectric) coating and heating time adopted in domestic MW oven. Modeling of the kinetics of color changes could be a useful practical tool in predicting the final and acceptable color of the product. Estimation of heating time for desirable color development of the product could be arrived with certain ratio of salt to moisture contents of the paddy.

Phosphorus Analysis in Wastewater: Best Practices White Paper

Phosphorus (P) monitoring at wastewater treatment plants is essential as phosphorus (as total phosphorus) is an important main constituent regulated in treatment plant effluents. Recent trends are towards increasingly lower phosphorus limits, requiring reliable lower and lower phosphorus measurements. There is a long history of P analysis in dilute matrices; i.e., river and lake water and best practices have been developed. These best practices for surface waters are reported herein. Potential issues in wastewater P analysis by colorimetry include pH, proton to molybdenum ratio, color development time, and digestion method. Of equal importance are the QA/QC measurement protocols implemented by wastewater analysis labs; demonstrably well performing examples from Coeur d'Alene, Spokane, and the City of Las Vegas are presented. Total reactive phosphorus is an ambiguous analytical measurement because the quantitative results depend strongly on color development time. For low level analysis, long path lengths have advantages in more precisely resolving low concentrations. Replicate measurements are essential, especially for low level P samples, in order to capture the true value of the sample within variability. When dealing with low concentrations, even a small absolute error is a large relative error; thus, replicate measurements are essential to estimate true concentrations for dilute phosphorus samples. This title belongs to WERF Research Report Series ISBN: 9781780407807 (eBook)

Graduated characterization method using a multi-well microplate for reducing reactivity of nanoscale zero valent iron materials

Even though nanoscale zero valent iron (nZVI) has been intensively studied for the treatment of a plethora of pollutants through reductive reaction, quantification of nZVI reactivity has not yet been standardized. Here, we adapted colorimetric assays for determining reductive activity of nZVI and its composites with other metals. The assay quantifies reduction products to avoid interfering reactions, such as sorption and volatilization. Three different reaction products, ammonium, phenol, and aniline, generated as the result of reduction of nitrate, p-halophenols, and nitrobenzene, respectively, could be quantified using the same reagent for all reactions. The colorimetric assays were further adapted to the 96-well microplate format, thus minimizing sample and reagent use, as well as lowering color development time to 2h. The substrates showed graduated reactivity, and thus, reduction potency and kinetics of different materials and reaction mechanism was distinguished. The applicability was successfully proven by determining the reactivity of a commercial nZVI sample, and investigating the effect of nickel content on dehalogenation. Therefore, the suggested reactivity test with different compounds, combined with the use of a multi-well microplate based color assay, promises to be a useful and simple tool in various nZVI related research topics.

Development of multivariate calibration method for simultaneous determination of nickel, lead and zinc in tap water

Conventional spectrophotometric methods for simultaneous determination of nickel, lead and zinc in forms of complexes with a reagent is not feasible due to the overlap of their absorption spectra. A multivariate calibration method was used to overcome this problem. In this study, the calibration model was constructed based on absorption spectra of 30 mixture standards in the range from 490 to 600 nm. Factors influencing experimental results such as amount of reagents, pH, and color development time were optimized. The standard calibration ranges for determination of nickel, lead and zinc were found at 0.5-5 ppm. The method was applied for determination of these ions in tap water samples at ppm level, with recoveries (and RSD) of nickel, lead and zinc were 103.3 % (3.0 %), 74.9 % (11.5 %) and 104.6 % (4.6 %), respectively.

A simple, rapid one-step ELISA using antibody-antibody complex.

The enzyme-linked immunosorbent assay (ELISA) is one of the most frequently employed assays for clinical diagnostic testing and biological research. However, its time-consuming operation is a major drawback. The present work aims to establish a one-step ELISA method through the preparation of a primary antibody (Ab)-secondary Ab complex (Ab-Ab complex) in hopes of realizing more sensitive and faster detection of the trace amount of antigen (Ag). By controlling the mole ratio of the primary Ab to the secondary Ab, one-step ELISA can be successfully achieved. Compared with the traditional ELISA, the one-step ELISA could not only improve the detection sensitivity to 1ngmL(-1) , but also reduce the operating time by 30%. Moreover, the signal intensity can be controlled by adjusting the ratio of the secondary Ab in the complex or by changing the color development time. This technique is further optimized to detect trace amounts of proteins adsorbed onto poly(N-vinylpyrrolidone) (PVP)-modified silicon surfaces (Si-PVP), and the results are close to the radiolabeling method. It is concluded that the simple one-step ELISA can be used for the rapid detection of trace amount of protein. The method holds promise for the clinical detection of trace Ag in solution and on low-adsorption material surfaces.

Baking of muffins: Kinetics of crust color development and optimal baking time

Baking is a decisive stage in the production of bakery products, in general—muffins, in particular—for most of the quality attributes of the final products depend on it. The aim of this work is to model the kinetics of muffin crust color development during baking and to evaluate the feasibility of this kinetic model to predict the baking times. Surface color is represented by the Browning Index, and the effect of baking temperature (from 140 to 220 °C) and process convective characteristics (natural convection, forced convection, and steam-assisted forced convection) are analyzed. Minimal bak- ing times are calculated from experimental core temperature measurements. The modeling of browning kinetics, which incorporates the optimal crust color determined by sensory analysis,allowstheestimationofoptimalbakingtimes.Forall the tested conditions top>tmin, assuring a product whose inner structure wasalready totallybaked.Finally, minimal,half,and optimal baking times present an exponential dependence with the oven temperature. Besides, there are no significant differ- ences between both forced convection modes.

Effects of relay intercropping maize on rhizosphere soil microbial ecological characteristics in capsicum fields

采用常规稀释平板法、氯仿熏蒸法、BIOLOG GN微平板反应系统及种间根系分隔技术, 以线辣椒单作(SC)为试验对照, 研究了间套作处理[玉米/线辣椒套作+根部塑料膜分隔(ICP)、玉米/线辣椒套作+根部尼龙网分隔(ICM)、玉米/线辣椒套作根部无分隔(ICN)]对线辣椒根际土壤微生物生态特征的影响。结果表明: 整个线辣椒生育期内, 各套作处理线辣椒根际土壤微生物总数与细菌总数具有相同的变化趋势, ICN和ICM处理的真菌、细菌、放线菌数量和细菌/真菌(B/F)、放线菌/真菌(A/F)比值均大于ICP与SC处理。盛果期, ICN处理根际土壤微生物量碳和微生物量氮比同处理其他生育期增加14.2%~54.0%和10.6%~54.7%。各处理土壤微生物群落<i>AWCD</i>的变化随培养时间呈现明显的"S"型曲线。间套作玉米显著提高了线辣椒根际土壤微生物群落的Shannon-Wiener指数(<i>P</i><0.05)、Simpson指数、种间相遇几率和McIntosh指数(<i>P</i><0.05), 并改变了土壤微生物对单一碳源的利用能力。线辣椒根际土壤微生物的不同多样性指数分别与其生物学产量之间存在显著或极显著正相关。说明间套作改善了土壤微生态环境。

Developing a novel sensitive visual screening card for rapid detection of pesticide residues in food

A novel sensitive visual screening card for rapid detection of pesticide residues was developed based on the blue-green color intensity changes, which were generated as a result of indoxyl acetate hydrolysis catalyzed by acetylcholinesterase (AChE) and the inhibition of AChE activity by pesticides. The procedure for preparing the test card was optimized. The AChE was immobilized onto the Hybond N+ nylon membrane using physical adsorption method. The immobilization temperature was set at 4 °C and the immobilization time was set to 30 min. The immobilized enzyme was freeze dried under vacuum conditions for 2 min. The indoxyl acetate was dissolved in methanol and diluted to 10 mM by phosphate buffer solution (pH7.5). The inhibition time and the color development time were set to 15 min and 10 min respectively. The final experimental results on determining various pesticides showed that the limit of detection (LOD) of this assay system was 1 μg/mL for omethoate, 0.1 μg/mL for dichlorvos, 2 μg/mL for methamidophos, 0.05 μg/mL for chlorpyrifos, 1.5 μg/mL for carbaryl, and 0.8 μg/mL for pirimicarb. Detection results of pesticide residues in real food samples of fruit juices and vegetable showed this visual screening card had high sensitivity, good reproducibility and stable-storage property, suggesting its great potential for practical application in rapid determination of pesticide residues.

Periodic acid–Schiff’s reagent assay for carbohydrates in a microtiter plate format

Microtiter plate colorimetric assays are widely used for analysis of carbohydrates and glycoconjugates. However, mucins are often not easily detected, as they have low neutral sugar content. We have adapted and optimised the periodic acid–Schiff’s reagent (PAS) staining for microtiter plate assay by examining five factors: concentration and volume of periodic acid, oxidation time, volume of Schiff’s reagent, and color development time. This assay requires just 25 μl of sample, utilises standardised Schiff’s reagent, and has decreased assay time (140 min to completion). Seventeen monosaccharides (acidic, neutral, basic, phosphorylated, and deoxy) and four disaccharides were assessed. PAS-positive carbohydrates (amino, N-acetylamino, deoxy, and certain neutral monosaccharides, and sialic acids) responded linearly within a 10–100 nmol range approximately, which varied for each carbohydrate. The assay response for fetuin and porcine gastric mucin (PGM) was linear up to 150 μg (highest concentration tested), with no response from nonglycosylated protein. A lower response for asialofetuin was observed, but desialylated PGM preparations were similar or higher in response than their sialylated counterparts. The simplicity and low sample consumption of this method make it an excellent choice for screening or quantitation of chromatographic fractions containing carbohydrates and glycoconjugates, especially in the case of mucins.

Ferulic Acid Enhances IgE Binding to Peanut Allergens in Western Blots

RATIONALE: Because phenolic compounds can precipitate or complex with proteins, we postulated that interactions of phenolics with IgE antibodies help enhance IgE binding to peanut allergens in Western blots. METHODS: Three different phenolics such as ferulic, caffeic and chlorogenic acids were examined. Each was mixed with a diluted pooled plasma from peanut-allergic patients, and incubated with a PVDF membrane containing major peanut allergens transferred from SDS-PAGE. The membrane was probed with a goat anti-human IgE peroxidase and o-phenylenediamine. A control without phenolics was also performed. RESULTS: Of the phree phenolics tested, only ferulic acid was able to enhance the density of allergen bands on the membrane and reduce the color development time. In this case, the ferulic acid protocol was approximately 6 times faster than the control. CONCLUSIONS: Feulic acid in complexation with IgE antibodies enhanced IgE binding to peanut allergens in Western blots. The improved ferulic protocol was approximately 6 times faster than the control.

Color development time of the Lowry protein assay

Color development of the Lowry protein assay was tracked over time for bovine serum albumin (BSA) concentrations ranging from 40 to 600 μg/ml. The time interval between 2 and 4 h produced the most stable readings. This time frame also improved linearity of the standard curve.

Detection of factors influencing nitrite determination in meat

A critical assessment was made of the official Spanish method for determining nitrite content in meat, using a 2 (k-p) fold-over Plackett–Burman experiment to identify influencing factors (IF) affecting the analytical method; these factors were drawn from seven apparent critical factors (ACF): sample weight ( W S), extraction temperature ( T E), stirring extraction time ( S ET), addition of Carrez I reagent ( C I-R), addition of Carrez II reagent ( C II-R), addition of borax reagent ( B R) and color development time ( D CT). In the experimental conditions assayed, the analytical method does not require protein precipitation. In addition, a negative effect of the Carrez reagent on nitrite determination was detected; it is thus proposed that this reagent be eliminated, in accordance with AOAC method 973.31. The use of borate improved nitrite extraction, but the W S/ B R ratio must be adjusted to determine the best ratio and to eliminate any negative effect when the ratio increases.

For Consistent Detection of Tissue mRNA in Human Surgical Material by Non-Radioactive In Situ Hybridization Technique.

Detection of tissue mRNA in human surgical materials by non-radioactive in situ hybridization technique may be difficult owing to inconsistent retention of tissue mRNA. This inconsistency is generally ascribed to different timing of ligation of feeding arteries during surgical operation. To improve this inconsistency, we adopted fixation in 4% paraformaldehyde/0.5% glutaraldehyde for 12-16hr with paraffin embedding. This method resulted in improved retention of tissue mRNA: higher in sensitivity and more consistent with cases. Furthermore, this procedure has shortened the color development time of the labeled enzyme, alkaline phosphatase. This helps to reduce nonspecific reactivity because prolonged color development time (up to 24) is one of the major causes of non-specific reactions. Cut sections can be stored at 4°C for more than a year, not resulting in detectable reduction of sensitivity. These are major advantages of this method particularly as human surgical specimens are concerned, because accumulation of cases is important for clinicopathologic analyses. Therefore, this fixation method is, at least, recommendable to improve in situ hybridization technique.

Determination of phosphate in solution at different ionic composition using malachite green1

The malachite green method was sometimes used to determine low concentrations of inorganic phosphate due to its high sensitivity. The aim of this work was to test the suitability of this method for the determination of phosphorus (P) extracted by various reagents, e.g., KCl 0.01–1.20M, CaCl2 0.01–0.1M, Na2SO4 0.01–0.40M, NaHCO3 0.1M at pH 8.5, and NaOH 0.1M+NaCl 1M. The malachite green method was also compared with the traditional molybdenum blue method on 35 soil extracts. Color development reached stability within 2 hrs and was stable for up to 24 hrs for dilute solutions. For concentrated solutions the stability was inversely proportional to the concentration of the reagent. Salt concentration appeared to have no effect on absorbance in KCl extracts of up to 1.2M and in Na2SO4 extracts of up to 0.05M. Higher concentrations of sodium sulfate induced flocculation and precipitation of the dye complex, as did CaCl2 above 0.04 M. A strong correlation was found between the malachite green and the molybdenum blue method. The malachite green method can be used for P determination in soil extracts when appropriate time of color development is provided and salt concentration is taken into account.

Detection of ricin by colorimetric and chemiluminescence ELISA

M. A. Poli, V. R. Rivera, J. F. Hewetson and G. A. Merrill. Detection of ricin by colorimetric and chemiluminescence ELISA. Toxicon 32, 1371–1377, 1994.—A highly sensitive and specific ELISA was developed to detect ricin in biological fluids. The assay utilizes an affinity-purified goat polyclonal antibody to adsorb ricin from solution. The same antibody (biotinylated) is then used to form a sandwich, and avidin-linked alkaline phosphatase allows color development and measurement of optical density at 405 nm. Our routine assay uses a standard curve over the range of 0–10 ng/ml ricin, with accurate quantitation below 1 ng/ml (100 pg/well) in assay buffer as well as in a 1:10 dilution of human urine or 1:50 dilution of human serum spiked with ricin. Ricin measured in spiked samples demonstrated accuracy typically within 5% of the expected value in all matrices. The coefficient of variation ranged from 3–10% at 10 ng/ml to 8–25% at 2.5 ng/ml. Two variations on the routine assay were also investigated. First, lengthened incubation times and additional time for color development allowed accurate quantitation in serum dilutions as low as 1:2. Second, increased concentrations of biotinylated antibody and avidin-linked enzyme from 1:250 to 1:70 enhanced the sensitivity of the assay 10-fold, achieving a detection limit of at least 100 pg/ml (10 pg/well). The assay was also configured to a format based upon chemiluminescence, which allowed quantitation in the 0.1–1 ng/ml range, but was subject to slightly greater variability than the colorimetric assay.

A malachite green procedure for orthophosphate determination and its use in alkaline phosphatase-based enzyme immunoassay

An improved procedure for phosphate determination based on a highly colored complex of phosphomolybdate and malachite green is described. All necessary reagents are combined in one concentrated solution, making the assay sensitive and convenient. The procedure is based on the finding that the dye is easily soluble and stable in the presence of 6 n acid. The addition of Tween 20 is required to stabilize the dye-phosphomolybdate complex at phosphate concentrations above 10 μ m. The time of color development at 25°C is about 3 min. The procedure was adopted to measure alkaline phosphatase activity in heterogeneous enzyme immunoassay with p-nitrophenyl phosphate and pyrophosphate as substrates. In both cases, a 4-fold increase in sensitivity in terms of absorbance readings was obtained compared to the standard method based on p-nitrophenol measurement. In visual analysis, the gain in sensitivity was as high as 20-fold, due to contrast color change (yellow to greenish blue).

Simplex Optimization of the Blue Tetrazolium Assay Procedure for α-Ketol Steroids

Two independent, simplex procedures were employed to optimize the official blue tetrazolium reaction. The net absorbance for a fixed amount of hydrocortisone was maximized by the simultaneous variation of five factors of the pharmacopeial method, i.e.: concentrations of tetramethylammonium hydroxide, blue tetrazolium, and water, as well as temperature and time for color development. An initial simplex was used to determine an optimum response, while a second was performed to minimize the blank absorbance obtained at the optimum. A series of pharmaceutically important steroids: prednisone, prednisolone, hydrocortisone acetate, and cortisone acetate were also analyzed by the optimized method. The results indicated improvements in sensitivity ranging from 9.27 to 22.95% for the corticosteroids studied. The optimized method also decreased the assay time in relation to the official procedure by one-sixth.

Indican interference with six commercial procedures for measuring total bilirubin.

We have studied the effect of indican on six commercial procedures for the measurement of total bilirubin in serum. Total bilirubin measured by the Bilirubin A-Gent (Abbott) 2,4-dichlorophenyl diazonium procedure increased by 50 mg/L for each 1 mmol/L of added indican. Similarly, total bilirubin measured by the Bilirubin C-System (Boehringer Mannheim) 2,5-dichlorophenyl diazonium procedure increased by 33 mg/L per mmol/L of indican. Indican also interfered with the Micro Bilirubin Reagent Set (Harleco) Malloy-Evelyn procedure, but to a much lesser extent. The Jendrassik Bilirubin Reagent System (American Monitor) and a modified Jendrassik-Grof procedure (Hoffmann-LaRoche) adapted to the Cobas Bio analyzer were unaffected by the presence of indican. The amount of interference with the 2,5-dichlorophenyl diazonium procedure increased significantly with color development time and was twice the initial amount after 30 min. Concentrations of indican as high as 0.38 mmol/L have been found in sera of patients with renal failure, which would increase total bilirubin values measured by the first two procedures above by 19 and 12 mg/L, respectively. Users of these procedures should therefore be suspicious of unexpectedly high bilirubin values obtained with sera from patients with chronic renal disease.

Spectrophotometric determination of nitrite

A new reagent for the absorptiometric determination of nitrite ion is used. Nitrite is reacted with 1-amino-4-naphthalenesulfonic acid to form a diazonium ion, which gives an orange color at pH 1.5 with maximum absorption at 310 nm, or an orange-red color at pH 4 with maximum absorption at 485 nm. Diazotation is fast at pH 1.5 but is stable only for 30 min after which the color fades continuously. However, at pH 4, the color develops after 1 hr and remains stable for >40 hr. The time of color development at pH 4 can be reduced to 30 min when heated to 60–70 °C for 5 min, but is followed by reduction of its intensity to half. The described method is found suitable for the determination of 0.1–5.0 ppm of the titled ion.

Determination of ammonium in KCl extracts of soils by the salicylate method

Abstract A method is described for the direct estimation of NH+ 4‐N in 2M KCl extracts of soils based on the emerald green color formed when NH3 and salicylate react in the presence of NaOCl at high pH.‐The reagent concentration, solution pH, and time and temperature of color development specified are those giving maximum molar asorptivity. Precipitate formation observed when KCl extracts containing divalent cations were treated with color developing reagents was eliminated by addition of 1 mL of 6% EDTA to complex Ca2+ and Mg2+. Free EDTA or complexed Ca2+ or Mg2+ did not markedly affect color development or molar absorptivity. The proposed method efficiently recovered NH+ 4‐N added to 2M KCl extracts of soils and studies showed that the proposed method and two other procedures differing in principle gave similar values for NH+ 4‐N in extracts of 5 soils. The proposed method is a simple, rapid, accurate, and precise technique for the colorimetric determination of NH+ 4‐N in KCl extracts of soils.