Rapid Gas Chromatographic Technique for Quantifying 2‐Acetyl‐1‐Pyrroline and Hexanal in Rice (Oryza sativa,L.)

The aroma of rice plays a role in its consumer acceptability. The popcorn‐like smell of aromatic rice stemming primarily from its 2‐ acetyl‐1‐pyrroline (2‐AP) content is considered desirable by many consumers. Conversely, hexanal has been correlated with off odors in rice that develop from lipid oxidation. A rapid method for 2‐AP and hexanal quantification suitable for use in breeding programs, large‐scale research efforts, and quality assurance programs is needed. While developing such a method, sample preparation (degree of milling, particle size), solvent extraction time and temperature, and gas chromatographic parameters were studied. Particle size had no influence on 2‐AP or hexanal recovered. One extraction solubilized ≈80% of the 2‐AP and 56% of the hexanal present in milled rice. The optimum extraction method was assessed to require 0.3 g of ground brown or milled rice in methylene chloride held at 85°C for 2.5 hr. The complete gas chromatographic run requires ≈25 min, and 50 samples can be analyzed per day. The optimized method's linear response (R² = 0.99) and reproducibility was demonstrated. The stability of 2‐AP and hexanal in frozen milled rice and in refrigerated methylene chloride extracts was excellent for at least six months. Milled and unmilled commercial and breeders' aromatic rice samples contained 10–1,104 ng/g of 2‐AP and 148–2,541 ng/g of hexanal. Genotype had the greatest effect on the 2‐AP and hexanal content of two lines grown over four years and in four states.     

Identification and quantitation of the rice aroma compound, 2-acetyl-1-pyrroline,in bread flowers (Vallaris glabra Ktze)

The aroma impact compound, 2-acetyl-1-pyrroline (2AP), has been identified for the first time in headspace of fresh bread flowers (Vallaris glabra Ktze) in which volatile components were extracted by solid-phase microextraction (SPME) at room temperature prior to analysis by gas chromatography-mass spectrometry. A total of 50 volatiles were detected. Among these, 23 volatiles were identified, predominantly in a group of terpenes. More volatiles were found in the extract of fresh bread flowers obtained by continuous steam distillation and solvent extraction (SDS). Of the 40 volatiles identified, the additional components were mainly straight-chain saturated hydrocarbons. 2AP was found in the extracts obtained by both SPME (0.37%) and SDS (2.71% relative proportion). Quantitative analyses of 2AP in bread flowers and other plant materials were performed by solvent extraction employing acidic solutions and capillary GC with flame ionization detection. The highest concentration of 2AP was found in dried flowers of V. glabra at 26.1 mg/kg. By comparison with other plant sources, fresh leaves of Pandanus amaryllifolius Roxb contain 2AP at 10.3 mg/kg and Thai fragrant rice, Khao Dawk Mali 105, at 3.0 mg/kg.     

氮锌肥配施对南方香粳稻产量和品质的影响

【目的】研究氮锌肥配施对南方香粳稻产量和外观加工品质、蒸煮食味品质、香气的影响,为南方香粳稻的调优栽培提供科学依据。【方法】田间试验于2020和2021年在扬州大学试验基地进行,供试粳稻品种为宁香粳9号和南粳46。在施锌(+Zn)和不施锌(Zn0)条件下,分别设3个施氮水平：0 (N0)、180 kg/hm²(N180)、270 kg/hm²(N270),共6个处理。于收获期,测定产量和产量构成因素,分析籽粒加工外观、食味和香气品质。【结果】提高氮肥用量可显著增加香粳稻产量,而施用锌肥对香粳稻产量无显著影响,+ZnN270处理宁香粳9号和南粳46产量均最高,分别达10.48 t/hm²和10.40 t/hm²;相同氮肥用量下,增施锌肥对产量没有显著影响。宁香粳9号和南粳46的最佳稻米加工和外观品质均以+ZnN270处理最优。在相同氮肥用量下,施用锌肥改善了香粳稻的加工和外观品质。与N0处理相比,在N180和N270处理下两品种的直链淀粉含量下降了8.44%～13.16%,蛋白质含量增加了9.79%～...     

Analysis of 2‐Acetyl‐1‐Pyrroline in Rice by HSSE/GC/MS

An extremely sensitive method for the analysis of 2‐acetyl‐1‐pyrroline (2AP) in rice, employing stir bar sorptive extraction (Twister) was studied. The Twister stir bar is placed in the headspace of a 20‐mL vial containing 1 g of rice kernels, 7.5 mL of 0.1M KOH, and 2.2 g of NaCl, along with a second Teflon‐coated stir bar for mixing. Analytes are adsorbed onto the Twister for 4 hr at 40°C and then desorbed at 270°C into a GC column while cryofocusing at –80°C. The headspace sorptive extraction (HSSE) method was able to detect <0.1 ppb of 2AP in rice. The precision of the HSSE method (>10%) was not as good as the GC/FID method (≈6%). Using HSSE, 2AP was observed in all samples generally considered to be aromatic and was not observed in any nonaromatic samples. Additionally, a modified method for the synthesis of 2‐acetyl‐1‐pyrroline was studied and the presence of a tautomer of 2‐acetyl‐1‐pyrroline was confirmed.     

Screening for 2-acetyl-1-pyrroline in the headspace of rice using SPME/GC-MS

Solid phase microextraction (SPME) is used to collect and concentrate the compounds in the headspace of rice. This research describes optimization parameters of temperature, moisture, and sampling time. Optimization was based upon the recovered levels of 2-acetyl-1-pyrroline (2-AP), the popcorn aroma in aromatic rice. The method uses a sampling temperature of 80 degrees C and adds 100 microL of water to a 0.75 g sample of rice. The rice was preheated for 25 min, a carboxen/DVB/PDMS SPME fiber was exposed to the headspace for 15 min, and a subsequent GC-MS analysis took 35 min. Samples of rice can be analyzed as the flour, milled kernels, or brown rice. Twenty-one experimental rice varieties were analyzed by the SPME method and compared to a wet technique. Recoveries of several nanograms of 2-AP from 0.75 g samples of aromatic rice were observed, whereas only trace amounts of 2-AP were recovered from nonaromatic rice. Recovery from a single SPME headspace analysis is calculated to be 0.3% of the total 2-AP in the sample.     

Determination of aflatoxins in high-pigment content samples by matrix solid-phase dispersion and high-performance liquid chromatography

A fast, efficient, and cost-effective method was developed for the analysis of aflatoxins in farm commodities with high-pigment content, such as chili powder, green bean, and black sesame. The proposed method involved matrix solid-phase dispersion (MSPD) and high-performance liquid chromatography (HPLC)-fluorescence detection (FLD) with postcolumn electrochemical derivatization in a Kobra cell. The MSPD procedure combined the extraction with neutral alumina and pigment cleanup with graphitic carbon black (GCB) in a single step. The recoveries of aflatoxins ranged from 88% to 95% with the relative standard deviations (RSD) less than 6% (n = 6). The limits of detection (LODs) were 0.25 ng/g aflatoxin B1, G1, and 0.10 ng/g aflatoxin B2, G2, respectively. The analytical results obtained by MSPD were compared to those of the immunoaffinity column (IAC) cleanup method. No significant differences were found between the two methods by t-test at the 95% confidence level.     

Quantification of the rice aroma compound, 2-acetyl-1-pyrroline, in uncooked Khao Dawk Mali 105 brown rice

Volatile components of uncooked Khao Dawk Mali 105 brown rice were extracted using indirect steam distillation under reduced pressure and controlled temperature in order to prevent cooking. Analysis of the fresh extract by capillary gas chromatography-mass spectrometry revealed that there were >140 volatile constituents. Among these, 70 volatiles were identified, including 2-acetyl-1-pyrroline (2AP), a key aroma compound of cooked rice. Further study concentrated on an improved method for the quantification of 2AP in uncooked brown rice. The method was simplified by utilizing a solvent extraction procedure. Quantitative analysis was performed using a capillary gas chromatographic system employing a flame ionization detector with the aid of a more selective column, CP-Wax 51, for amines. This improved chromatographic system had remarkable detection sensitivity for 2AP in the rice extracts so that 2AP in an extract of only 0.5 g of uncooked Khao Dawk Mali 105 brown rice could be detected.     

Effect of timing and duration of salt treatment during growth of a fragrant rice variety on yield and 2-acetyl-1-pyrroline, proline, and GABA Levels

In greenhouse experiments, Aychade, a fragrant rice variety, was grown under one level of salt solution (EC of 3800 ± 400 μS·cm(-1)) sufficient to induce salt stress in rice. Timing and duration of salt solution application varied according to the growth stages. 2-Acetyl-1-pyrroline (2AP), a characteristic flavor compound of fragrant rice as well as biogenetically related compounds, proline, and γ-aminobutyric acid (GABA) were quantified. Salt treatments induced 2AP synthesis in the leaves, but the increase was often higher in the vegetative phase. This increase was correlated with proline level but not with that of GABA. Interestingly the grains from all the salt treated plants contained significantly higher levels of 2AP (733-998 μg·kg(-1)) than those from the control (592 μg·kg(-1)). The highest 2AP synthesis occurred when the plants were subjected to salt treatment during whole vegetative or reproductive phases. However in the latter case crop yield decreased significantly.     

Determination of 2-methylisoborneol and geosmin produced by Streptomyces sp. and Anabaena PCC7120

A new sample preparation and enrichment technique, headspace liquid-phase microextraction (HS-LPME) linked to gas chromatography-mass spectrometry (GC-MS), was developed for the determination of the off-flavor odorants, 2-methylisoborneol and geosmin, produced by Streptomyces sp. and Anabaena PCC7120. Some of the factors that influence the extraction efficiency of HS-LPME, such as the type of extraction solvent, ionic strength of sample solution, and sample agitation rate, were studied and optimized by a single factor test. Other factors, including extraction temperature, extraction time, microdrop volume, and headspace volume were optimized by orthogonal array design. Extraction of 2-methylisoborneol and geosmin was conducted by exposing 2.5 microL of 1-hexanol for 9 min at 50 degrees C in the headspace of a 20 mL vial with a 10 mL of sample solution saturated by NaCl and stirred at 800 rpm. The developed protocol demonstrated good repeatability (relative standard deviations (RSDs) < 5%), wide linear ranges (10-5000 ng/L, r2 > 0.999), and low limits of detection (LODs) for 2-methylisoborneol and geosmin (0.05 ng/L for both analytes). Subsequently, the method was successfully applied to extract the analytes in bacterial cultures with high recoveries (from 94% to 98%). Compared with headspace solid-phase microextraction (HS-SPME), HS-LPME demonstrates better linearity, precision, and recovery. Importantly, the sensitivity is about 1 order of magnitude higher than that of most HS-SPME. The results showed that HS-LPME coupled with GC-MS is a simple, convenient, rapid, sensitive, and effective method for the qualitative and quantitative analysis of 2-methylisoborneol and geosmin.     

香稻产量和品质对化肥施用及气候因素的响应

  【目的】  香稻因其独特的香味深受消费者喜爱,明确香稻产量和品质对化肥施用的响应及其与气候条件的关系,对综合提升香稻产量和品质具有重要意义。  【方法】  在中国知网、谷歌学术等数据库以关键词“水稻”、“香气”、“香味”以及“香稻”和“香米”及其组合进行文献检索,共获得501组试验数据对。将施肥与对照分为两组,采用整合分析方法(meta-analysis),分析了施用氮磷钾肥对香稻产量和品质的影响,以及在不同生育期累积降水量、积温和日照时数条件下的变化率。  【结果】  施用氮、磷、钾肥,香稻的平均增产率分别为23.7%、25.8%、18.0%。与不施用氮肥相比,施用氮肥对粳稻和籼稻增产率分别为27.6%和20.2%;与不施用钾肥相比,施用钾肥对粳稻和籼稻的增产率分别为29.9%和7.3%。施用氮肥可显著增加香稻碾磨品质(整精米率)和蒸煮品质(粗蛋白含量,胶稠度),施用钾肥可显著增加香稻碾磨品质(整精米率)、蒸煮品质(粗蛋白含量,胶稠度)、外观品质(垩白度)和香味品质(2-乙酰-1-吡咯啉含量,以下简称2-AP)。施用氮肥对籼型常规香稻的品质提升效果显著,而施用钾肥则对籼型杂交香稻的品质提升更显著。此外,施用氮肥下香稻整精米率的变化率随生育期内有效积温升高呈持续增加趋势,而随累积降水量和日照时数的增加呈先升后降趋势;胶稠度的变化率随气候变化(有效积温、降水量和日照时数等的增加)呈现先降后增趋势。施用钾肥下香稻整精米率的变化率随生育期内有效积温和日照时数升高呈现先降后增趋势,而随累积降水量的变化呈先升后降趋势;垩白粒率的变化率随气候变化均呈先降后增的趋势;胶稠度的变化率随气候变化(有效积温、降水量和日照时数等的增加)均呈降低的趋势。  【结论】  施用氮肥或钾肥均有助于香稻产量和品质的协同提升,且对籼型香稻增产提质效果更显著。同时生育期内累积降水量、有效积温、日照时数影响着氮肥和钾肥的产量和品质效应,分别达到800～1100 mm、2900～3400 ℃·d和800～1000 h时,结合氮肥调控可协同提高香稻产量、加工品质和蒸煮品质;分别达到500～800 mm、2900～3400 ℃·d和400～600 h时,结合钾肥调控可协同提高香稻产量、加工品质、蒸煮品质和外观品质。     

Comparison of isolation methods for the determination of important aroma compounds in black currant (Ribes nigrum L.) juice, using nasal impact frequency profiling

The influence of isolation method on the determination of important aroma compounds in black currant juice was investigated by surface of nasal impact frequency (SNIF) gas chromatography-olfactometry (GC-O). The applied methods were solvent extraction, static headspace, and purge and trap using 15 and 60 min of purge time. By the four methods, a total of 59 odors were observed, and, of these, 44 corresponded to compounds that could be identified. For the headspace methods increasing purge volumes resulted in recoveries of additional, less volatile compounds. The main compound groups recovered by the headspace methods were esters and terpenes, whereas compounds recovered by solvent extraction were not as dominated by fruity odors. For most compounds there was agreement between the size of the SNIF value obtained by GC-O and the amount of the measurable compound found by gas chromatography-mass spectrometry.     

Characterization of pyrazines in some Chinese liquors and their approximate concentrations

Pyrazines are very important impact aroma compounds in Chinese liquors. The identification of pyrazine derivatives was carried out by liquid-liquid extraction (LLE). The liquor sample was adjusted to the H(+) concentration of 1 N with 12 N HCl and then concentrated by rotatory evaporator under vacuum condition. The concentrated liquor was extracted by diethyl ether, and the residual aqueous phase was adjusted to pH 10. The basic compounds were detected and identified by gas chromatography (GC)-mass spectrometry (MS). A total of 27 pyrazines were identified in Chinese liquors, mainly alkyl- and acetylpyrazines. A method for determining pyrazines in Chinese liquors was developed. It involves extraction by headspace (HS) solid phase microextraction (SPME) and determination using GC-flame thermionic detector (FTD). The optimum method was that the sample alcohol concentration was diluted to 12% vol by freshly redistilled-deionized water, and the diluted samples were saturated with NaCl and equilibrated at 50 degrees C for 15 min and extracted for 30 min at the same temperature. The developed method enabled detection limits of <200 ng/L. Linearity (R(2) > 0.99) and recovery rate were satisfied in all cases. Pyrazines of 12 commercial typical Chinese liquors were quantified by HS-SPME followed by GC-FTD and had a wide range of concentration.     

Ultratrace analysis of nine macrolides, including tulathromycin A (Draxxin), in edible animal tissues with minicolumn liquid chromatography tandem mass spectrometry

The analysis of nine macrolides is presented, including tulathromycin A (Draxxin), in beef, poultry, and pork muscle with a simple multiresidue extraction and analysis method using high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The sample preparation method involves extraction with acetonitrile and defatting with hexane followed by dilution of the extracts for analysis. Separation of the nine macrolides was performed using an Atlantis dC 18, 3 mum, 3.9 mm x 20 mm minicolumn (guard column). Detection was carried out with two multiple reaction monitoring experiments per macrolide. The method detection limits (MDLs) were based on three times standard deviation of eight repeat spikes at 3.0 ng/g of a mix of the nine macrolides in the various tissues. The MDLs and retention times for the macrolides were as follows: lincomycin, 0.19 ng/g (t R = 5.00 min); tulathromycin, 0.46 ng/g (t R = 5.63 min); spiramycin, 0.21 ng/g (t R = 6.06 min); pirlimycin, 0.10 ng/g (t R = 6.04 min); clindamycin, 0.16 ng/g (t R = 6.20 min); tilmicosin, 0.29 ng/g (t R = 6.38 min); erythromycin, 0.19 ng/g (t R = 6.62 min); tylosin, 0.10 ng/g (t R = 6.72 min); and josamycin, 0.09 ng/g (t R = 6.98 min). Precision at 25 ng/g (n = 4) ranged from 2.3 to 9.4% for the compounds from beef muscle. Of interest is the detection of incurred residues of tulathromycin A in edible calf tissue at 0.10-7 mug/g, which is presented here for the first time.     

Development of an improved liquid phase microextraction technique and its application in the analysis of flumetsulam and its two analogous herbicides in soil

An improved liquid phase microextraction (LPME) technique has been developed. As part of this technique, analytes were extracted into an extractant microdrop which was laid on the cone-shaped bottom of a PCR tube (polychloroprene rubber tube) but not at the needle tip of a microsyringe, and the sample vial and PCR tube were horizontally placed so that the extractant was not affected by the force of vertical orientation (gravity and floating force). The stability of the extractant microdrop increased greatly, and the selection of extractant was extended. In this work, flumetsulam and its two analogous herbicides were chosen as model analytes in investigating the feasibility of the new pretreatment method by coupling it to high-performance liquid chromatography (HPLC). Under the optimized experimental conditions, the linear range and the limits of detection (S/N = 3) were 0.01-5 microg/mL (r = 0.9997) and 0.8 ng/mL for flumetsulam, 0.002-5 microg/mL (r = 0.9994) and 0.5 ng/mL for analogue 1, and 0.002-1 microg/mL (r = 0.9993) and 0.5 ng/mL for analog 2, respectively. The inter- and intraday reproducibilities (RSD) were below 5.3 and 4.5%, respectively. Good recoveries that ranged from 79.4 to 115.0% were obtained in the analysis of real soil samples. The extraction efficiency of the improved method was 4-8 times higher than that of the conventional liquid phase microextraction method. The novel, simple, rapid, sensitive technique is very suitable for extraction of apolar and medium polar analyte in complex environmental samples.     

Development of a single fluorescence-based optosensor for rapid simultaneous determination of fungicides benomyl and thiabendazole in waters and commercial formulations

A novel, sensitive, and straightforward spectrofluorimetric flow injection method is proposed in this work for the resolution of a binary mixture of two widely used fungicides (thiabendazole and benomyl). The continuous flow methodology is based on the implementation of on-line solid phase extraction (SPE), preconcentration, and separation of both analytes on a surface of C(18) silica gel beads placed just in the flow cell, with solid surface fluorescence detection. A 45- and 25-fold sensitivity enhancement was obtained for benomyl and thiabendazole, respectively (in relation to the liquid phase measurements in the absence of solid support). The separation of the pesticides was performed because of the different retention-desorption kinetics in their interaction with the solid support, in the zone where the stream impinges the solid material. No previous separation of the analytes before they reach the flow cell is needed, simplifying extraordinarily both the procedure and the manifold. Using a sample volume of 3200 microL, the system was calibrated in the range of 0.4-20 and 20-400 ng x mL(-)(1) with detection limits of 0.06 and 3.6 ng x mL(-)(1) for thiabendazole and benomyl, respectively, and RSD values (n = 10) smaller than 0.8% for both analytes. The RSD values obtained replacing the solid support in each measurement were lower than 3%, and the day-to-day reproducibility RSD value was also lower than 5%. Sampling frequencies of 10 and 18 h(-)(1) were obtained with 600 and 3200 microL of sample volume. Recovery studies carried out on natural water samples spiked with known amounts of both analytes at concentration levels in the range of 1-10 and 25-200 ng x mL(-)(1) provided mean recovery percentages ranging from 98.8 to 102% and from 98 to 103% for thiabendazole and benomyl, respectively. The proposed methodology was also applied to pesticide formulations.     

Flavor release and rheology behavior of strawberry fatfree stirred yogurt during storage

The influence of storage on the aroma release in headspace and rheological properties in strawberry-flavored fatfree stirred yogurts was determined. Three periods of storage at 10 degrees C were chosen for analysis: 7, 14, and 28 days. The headspace composition was assessed in a flask in static mode. The SPME fiber was carefully chosen, and results are presented in detail (choice and degradation). The flow properties of the final product were measured in order to follow n (flow behavior index) and K (consistency index), and the apparent viscosity was determined (eta in Pa.s). The quantity of flavors in the headspace of products at the 28 days of aging was significantly weaker for methyl 2-methyl butanoate, ethyl hexanoate, and hexyl acetate. The decrease was half of that in comparison with the seventh day. It was supposed that modification in rheological parameters can partly explain these results. Indeed, the apparent viscosity of the products significantly increased during the three times of storage. The composition of the flavored yogurt, proteins, exopolysaccharides, and fruit preparation, seemed to have a great impact on the release of aroma compounds. The aroma compound amount in the headspace decreased when the matrix changed from water to yogurt. With the fruit preparation, the headspace amounts for esters were significantly lower than in water alone, respectively, 23, 27, 29, and 17% less for methyl 2-methylbutanoate, ethyl hexanoate, hexyl acetate, and benzyl acetate. In flavored yogurt, the amount of aroma compounds in the headspace decreased again in comparison with the result obtained with the fruit preparation. Ethyl hexanoate and hexyl acetate presented the higher decreases of 48 and 53%, respectively.     

Co-occurrence of ochratoxin A and citrinin in cereals from Bulgarian villages with a history of Balkan endemic nephropathy

Cereal samples were collected in 1998 from Bulgarian villages without [control village (C), n = 20] or with [endemic villages (E); E1, n = 21; E2, n = 30; E3, n = 23] a history of Balkan endemic nephropathy (BEN). Sampling included foods (wheat, corn) and feeds (barley, oats, wheat bran). Analysis of ochratoxin A and citrinin was done by enzyme immunoassays (EIA), with detection limits of 0.5 and 5 ng/g, respectively. Ochratoxin A-positive results were confirmed by HPLC after immunoaffinity chromatography. Highest toxin levels were found in wheat, wheat bran, and oats. For ochratoxin A, the percentages of positives were 35% (C), 29% (E1), 30% (E2), and 47% (E3), the mean/median values of positives were 1.5/1.3 ng/g (C), 11/1.6 ng/g (E1), 18/1.6 ng/g (E2), and 3.5/1.5 ng/g (E3). For citrinin, 5.0% (C), 14% (E1), 3.3% (E2), and 13% (E3) were positive, and the mean/median values were 6.1/6.1 ng/g (C), 180/83 ng/g (E1), 10/10 ng/g (E2), and 84/20 ng/g (E3). Highest concentrations of ochratoxin (maximum = 140 ng/g) and citrinin (maximum = 420 ng/g) were found in samples from endemic villages. Co-contamination with ochratoxin A and citrinin was found for one sample (14% of positives) from village C and for six samples (22% of positives) from villages E1-E3. Citrinin levels in these samples were 2-200 times higher than those of ochratoxin A.     

Comparison of odor-active compounds from six distinctly different rice flavor types

Using a dynamic headspace system with Tenax trap, GC-MS, GC-olfactometry (GC-O), and multivariate analysis, the aroma chemistry of six distinctly different rice flavor types (basmati, jasmine, two Korean japonica cultivars, black rice, and a nonaromatic rice) was analyzed. A total of 36 odorants from cooked samples were characterized by trained assessors. Twenty-five odorants had an intermediate or greater intensity (odor intensity >or= 3) and were considered to be major odor-active compounds. Their odor thresholds in air were determined using GC-O. 2-Acetyl-1-pyrroline (2-AP) had the lowest odor threshold (0.02 ng/L) followed by 11 aldehydes (ranging from 0.09 to 3.1 ng/L), guaiacol (1.5 ng/L), and 1-octen-3-ol (2.7 ng/L). On the basis of odor thresholds and odor activity values (OAVs), the importance of each major odor-active compound was assessed. OAVs for 2-AP, hexanal, ( E)-2-nonenal, octanal, heptanal, and nonanal comprised >97% of the relative proportion of OAVs from each rice flavor type, even though the relative proportion varied among samples. Thirteen odor-active compounds [2-AP, hexanal, ( E)-2-nonenal, octanal, heptanal, nonanal, 1-octen-3-ol, ( E)-2-octenal, ( E, E)-2,4-nonadienal, 2-heptanone, ( E, E)-2,4-decadienal, decanal, and guaiacol] among the six flavor types were the primary compounds explaining the differences in aroma. Multivariate analysis demonstrated that the individual rice flavor types could be separated and characterized using these compounds, which may be of potential use in rice-breeding programs focusing on flavor.     

Direct and combined methods for the determination of chromium, copper, and nickel in honey by electrothermal atomic absorption spectroscopy

In the present work, direct methods for the determination of chromium, copper, and nickel in honey by electrothermal atomic absorption spectroscopy were developed using experimental design as an optimization tool. Once the optimum conditions for the individual methods were established, a direct method for the combined determination of the three elements was optimized using the response surface tool. Palladium was used as chemical modifier in all cases. Honey was diluted in water, hydrogen peroxide, and nitric acid. Triton X-100 was added to minimize the matrix effect and the viscosity of the sample. The RSD (better than 10%) and the analytical recovery (98-103%) were acceptable for all of the developed methods. Calibration graphs were used in the four methods to determine the concentration of the analytes in the sample. The detection limits of the combined method (0.21, 0.35, and 0.37 microg L(-)(1) for Cr, Cu, and Ni, respectively) were similar to those obtained for the individual methods (LOD = 0.17, 0.21, 0.33 microg L(-)(1) for Cr, Cu, and Ni, respectively). The direct-combined proposed method has been applied to the determination of chromium, copper, and nickel content in representative honey samples from Galicia (northwestern Spain). The concentrations found in the analyzed samples were in the range of (5.75 +/- 0.64)-(26.4 +/- 0.38) ng g(-)(1) of Cr, (79 +/- 7.8)-(2049 +/- 80) ng g(-)(1) of Cu, and (12.6 +/- 1.36)-(172 +/- 6.88) ng g(-)(1) of Ni.     

Model studies on the influence of coffee melanoidins on flavor volatiles of coffee beverages

Addition of the total melanoidin fraction isolated by water extraction from medium-roasted coffee powder to a model solution containing a set of 25 aroma compounds mimicking the aroma of a coffee brew reduced, in particular, the intensity of the roasty, sulfury aroma quality. Model studies performed by static headspace analysis revealed that especially three well-known coffee odorants, that is, 2-furfurylthiol (FFT), 3-methyl-2-butene-1-thiol, and 3-mercapto-3-methylbutyl formate, were significantly reduced in the headspace above an aqueous model solution when melanoidins were added. In particular, the low molecular weight melanoidins (1500-3000 Da) led to the most significant decrease in FFT. In contrast, for example, aldehydes remained unaffected by melanoidin addition.