Cysteamine-CdTe Quantum Dots Electrochemically Synthesized as Fluorescence Probe for Resveratrol

This work proposes a fluorescent probe based on CdTe quantum dots (QDs) for the determination of resveratrol in wine samples. The synthesis of cysteamine (CA) capped CdTe QD was carried out in a one-pot eco-friendly process, resorting to the electrochemical reduction of metallic tellurium powder in a graphite macroelectrode (cavity cell). The reduced species of tellurium (Te^2? and Te₂^2?) migrated to an intermediate compartment of the electrochemical cell and in the presence of a cadmium salt and organic stabilizing agent (CA), forming the colloidal dispersion of CdTe in a single step. Under optimum synthesis conditions, the fluorescence intensity of the prepared nanoparticles varied linearly with the resveratrol concentration in the range from 3.25 to 75 μg L^?1 (R²?=?0.9984), with a detection limit of 0.97 μg L^?1 and RSD of 3.7% (5.0 μg L^?1 resveratrol, n?=?10). The method was successfully applied to the resveratrol determination in wines, with recoveries from 97.8 to 112.4%. Student’s t test was applied and no statistically significant difference was observed between the two methods (HPLC and proposed), with a confidence level of 95% (t_tabulated?=?2.45 and t_calculated?=?0.38). The resveratrol determination method, by using CdTe-CA QDs as fluorescence probe, was simple, rapid, inexpensive, and sensitive.     

Simultaneous Determination of Phenolic Compounds in Different Matrices using Phenyl-Hexyl Stationary Phase

A novel unique liquid chromatographic method has been developed consisting of diode array and fluorescence detection, using phenyl-hexyl stationary phase of the column, for the determination of over thirty phenolic compounds (anthocyanins, flavonols, flavan-3-ols, hydroxybenzoic acids, hydroxycinammic acids, and stilbenes). The method was validated including the following parameters: linearity, limits of detection and quantification, precision, and reproducibility. Excellent selectivity and sensitivity have been achieved. Detection levels ranging from 1.79?×?10^?5 mg/L to 0.26 mg/L were obtained. New fluorescence wavelengths for detection of flavan-3-ols (λ _ex?=?225 and λ _em?=?320 nm) were more sensitive than previously published. The new optimized method showed good repeatability and reproducibility, and values for relative standard deviations (RSD) were less than 3 %. Applicability of the method was demonstrated for five different matrices, white and red wine from Vitis vinifera cultivars, apple cider, blackberry wine, and grape skin extracts, showing that method is robust and can be applied for routine analysis.     

Determination of benzo[α]pyrene in edible oil using tetraoxocalix[2]arene[2]triazine bonded silica SPE sorbent

Benzo[α]pyrene (BaP) is a well-known carcinogen in edible oil. In this study, a method combined solid-phase extraction (SPE) with fluorescent detection was developed using tetraoxocalix[2]arene[2]triazine sorbent (SiO₂-OCA) for the clean-up and enrichment of BaP. The interaction between SiO₂-OCA and BaP involves a donor–acceptor complex mechanism. The experimental procedure was as follows: BaP was extracted from edible oil with DMF/H₂O (9:1, v/v). Then, the ratio of DMF/H₂O was adjusted to 1:2 prior to SPE. The final concentrate was analysed using a fluorescence detector at excitation and emission wavelengths of 255 and 420 nm. The method was fully validated. The linearity was in the range of 0.1–100 μg kg^?1 with a coefficient of 0.999. The limits of detection and quantification were 0.03 and 0.1 μg kg^?1, respectively. The average recoveries were in the range of 88.0 ? 122.3%. The intraday and interday precisions were 6.8% and 9.2%, respectively. Compared with other methods, the method reported in this article shows a good detection limit, high reproducibility and recovery and linearity over a broad concentration range. This established method was also applied to evaluate real samples. The concentration of six tested samples was below 5 μg kg^?1.     

Fluorescence immunoassay through histone-ds-poly(AT)-templated copper nanoparticles as signal transductors for the sensitive detection of Salmonella choleraesuis in milk

The rapid and sensitive detection of foodborne pathogens is one of the most important issues in food safety control. In this work, we developed a novel fluorescence immunoassay method for the sensitive detection of Salmonella choleraesuis. The method uses the fluorescent signals of histone-ds-poly(AT)-templated copper nanoparticles (His-pAT CuNP) as signal transducers and glucose oxidase as an alternative for horseradish peroxidase for the generation of hydrogen peroxide (H₂O₂) through the catalysis of glucose. The H₂O₂ is then further converted into hydroxyl radical (·OH) by Fenton reagents. Owing to the ultrahigh sensitivity of His-pAT CuNP synthesis toward ·OH, the proposed fluorescence immunoassay method exhibited excellent sensitivity for S. choleraesuis, with a limit of detection of 8.04 × 10¹ cfu/mL, which is 3 orders of magnitude lower than that of the tetramethylbenzidine-based traditional immunoassay. The reliability of the proposed method was evaluated by using spiked milk samples with S. choleraesuis concentration ranging from 8.8 × 10¹ to 8.8 × 10⁴ cfu/mL. The average recoveries for the intra- and inter-assay ranged from 73.52 to 96.59% and from 66.99 to 98.24% with a coefficient of variation from 6.85 to 31.26% and 5.46 to 17.99%, respectively. These results indicated that the proposed fluorescence immunoassay possesses a great potential for ultra-sensitive detection of foodborne pathogens in food safety control.     

Upconversion Nanoparticles Capped with Molecularly Imprinted Polymer as Fluorescence Probe for the Determination of Ractopamine in Water and Pork

A novel fluorescence probe was designed and synthesized to quantify ractopamine in foods using molecularly imprinted polymer (MIP) as a specific recognition element and YF₃:Yb³⁺, Er³⁺ upconversion nanoparticles (UCNPs) as a fluorescence signaling component. The developed UCNP@MIP probe was characterized using X-ray powder diffraction, scanning electron microscopy, and thermogravimetric analysis. The fluorescence of UCNP@MIP probe was quenched specifically by ractopamine, and good linear regression ranging from 1.66 × 10^?8 to 3.3 × 10^?7 mol/L was obtained with the limit of detection of 8.6 × 10^?10 mol/L. This method was further applied to determine ractopamine in water and pork samples. Recoveries between 76.61 and 88.97% were obtained with relative standard deviation ranging from 1.15 to 2.67% (n = 3). This UCNP@MIP probe combined high selectivity of MIP and high sensitivity of upconversion fluorophore and showed potential to determine various food chemical hazards.     

The effect of nitrogen source on yeast metabolism and H2S formation

The impacts of aspartic acid and glutamine used as nitrogen supplements for alcoholic fermentations conducted by Saccharomyces were studied. Synthetic grape juice media and commercially prepared grape juices were supplemented with diammonium phosphate, aspartic acid, or glutamine to increase yeast-assimilable nitrogen concentrations to 250 mg N/L prior to fermentation. Two yeast strains, UCD522 and EC1118, were inoculated at 10⁵ CFU/mL and fermentations were monitored for soluble solids, hydrogen sulfide (H₂S), and residual amino acids. In general, unsupplemented media/juices fermented slower than supplemented ones, produced more H₂S, and contained lower concentrations of amino acids after fermentation. Among the supplemented treatments, fermentation rates, H₂S production, and amino acid utilization varied depending on the nitrogen source and yeast strain. Those fermentations supplemented with aspartic acid were generally slower and sometimes did not achieve dryness. In contrast, glutamine additions yielded fermentation rates and H₂S production equivalent or better than other supplemented treatments. Based on these results, the use of glutamine appears promising as an alternative nitrogen supplement for wine production.     

Loss and formation of malodorous volatile sulfhydryl compounds during wine storage

Volatile sulfur compounds (VSCs), particularly low molecular weight sulfhydryls like hydrogen sulfide (H₂S) and methanethiol (MeSH), are often observed in wines with sulfurous off-aromas. Recent work has shown both H₂S and MeSH can increase up to a few µM (> 40 µg/L) during anoxic storage, but the identity of the latent sources of these sulfhydryls is still disputed. This review critically evaluates the latent precursors and pathways likely to be responsible for the loss and formation of these sulfhydryls during wine storage based on the existing enology literature as well as studies from food chemistry, geochemistry, biochemistry, and synthetic chemistry. We propose that three precursor classes have sufficient concentration and metastability to serve as latent sulfhydryl precursors in wine: 1) transition metal-sulfhydryl complexes, particularly those formed following Cu(II) addition, which are released under anoxic conditions through an unknown mechanism; 2) asymmetric disulfides, polysulfanes, and (di)organopolysulfanes formed through transition-metal mediated oxidation (e.g., Cu(II)) of sulfhydryls or pesticide degradation, and released through sulfitolysis, metal-catalyzed thiol-disulfide exchange or related reactions; 3) S-alkylthioacetates, primarily formed during fermentation, and releasable hydrolytically. Some evidence also exists for S-amino acids serving as precursors. Based on these findings, we propose a “decision tree” approach to choosing appropriate strategies for managing wines with sulfurous off-aromas.     

A sensitive immunochromatographic assay using colloidal gold–antibody probe for rapid detection of fumonisin B1 in corn

A sensitive immunochromatographic assay (ICA) using a colloidal gold–antibody probe for the rapid detection of fumonisin B₁ (FB₁) in corn samples was developed. The colour density of the test line correlated with the concentration of FB₁ in the range 2–40 ng ml^–1 by the assay, and the detection limit for FB₁ was 2 ng ml^–1. The linear range for FB₁ was 50–1000 µg kg^–1, and the visual limit detection of the test was 1000 µg kg^–1 in corn samples. The ICA to detect FB₁ is sensitive, specific and rapid. Specific anti-FB₁ monoclonal antibody (mAb) and FB₁-ovalbumin (FB₁-OVA) conjugate antigen were prepared. FB₁ mAb, labelled with colloidal gold, was used as the probe on the immunochromatographic strip. FB₁-OVA and goat-anti-mouse IgG were coated onto a nitrocellulose (NC) membrane as test lines and control lines, respectively. FB₁ in samples will competitively combines the FB₁ mAb with the FB₁-OVA in an NC membrane and the results are directly observed by the colour of the detection and quality control lines. The concentrations of FB₁ mAb labelled with colloidal gold, detecting antigen and goat anti-mouse IgG, were optimised. The results indicate that the test strip is specific for FB₁, with no cross-reactivity to other toxins. The strip assay for FB₁ was simple, only needing one step without complicated assay performance and expensive equipment, and the total time for visual evaluation was less than 10 min. A survey of 24 corn samples from Hefei, China, was performed with the test strip and HPLC, and the detection results showed that the developed ICA and the HPLC were in excellent agreement. Hence, the developed ICA can be used as a method for rapid detection of FB₁ in corn samples.     

Speciation Determination of Selenium in Seafood by High-Performance Ion-Exchange Chromatography-Hydride Generation-Atomic Fluorescence Spectrometry

A high-performance ion-exchange chromatography coupled with hydride generation-atomic fluorescence spectrometry (HPIEC-HG-AFS) method was developed for simultaneous speciation of selenium in seafood. Three selenium species including of selenocystine (Se-Cys), selenome-thionine (Se-Met), and selenite Se(IV) were separated on an anion-exchange column (PRP-X100) with eluent of 30 mM NH₄H₂PO₄ and methanol (39:1, v/v) in 10 min at the flow rate of 1.0 mL min^?1. Variables affecting the HG-AFS detection of selenium species were optimized. The optimum conditions found were the following: reducing agent, 2.0 % of KBH₄, and 5.0 % of HCl; lamp current, 90 mA; photomultiplier tube voltage, 280 V; flow rate of carrier gas, 300 mL min^?1; and shielding gas, 800 mL min^?1. Under the optimized conditions, the good linearity of calibration curves (R ²?>?0.999) between signal of fluorescence and concentration of selenium species was obtained in the range of detection limits (DLs), 80 μg L^?1, and the DLs of Se-Cys, Se-Met, Se(IV) were 1.66, 0.990, 1.10 μg L^?1, respectively. The repeatability of the method, expressed as relative standard deviation, was less than 5.0 % (n?=?10), and the average recoveries for spiked test were from 87.3 to 103 % for three analytes in real seafood samples. The developed HPIEC-HG-AFS method was successfully applied for the speciation of selenium in seafood samples.     

QuEChERS Method for the Determination of 3‑Alkyl‑2‑Methoxypyrazines in Wines by Gas Chromatography-Mass Spectrometry

A new method for determining 3-isopropyl-2-methoxypyrazine, 3-sec-butyl-2-methoxypyrazine, and 3-isobutyl-2-methoxypyrazine in wines is presented. A modified quick, easy, cheap, effective, rugged, and safe method and gas chromatography-mass spectrometry (GC-MS) were used for sample preparation and compound determination, respectively. The analytes were extracted from wine (30 mL) with 1 mL toluene, in the presence of 12 g anhydrous MgSO₄ and 3 g NaCl. Cleanup of the toluene phase was performed by a miniaturized dispersive solid-phase extraction with a combination of anhydrous CaCl₂ (25 mg), anhydrous MgSO₄ (25 mg), and primary-secondary amine (10 mg), which was effective for minimizing co-extractives and matrix effects. GC-MS parameters were also tuned up to optimize limits of detection between 4.2 and 7.1 ng L^?1. The overall recoveries (trueness) of the method ranged between 71 and 87 % for the white and red wine samples, respectively, spiked at 40 and 100 ng L^?1, with relative standard deviations below 21 %. The method was applied for the determination of target methoxypyrazines in the samples of commercial wines from Argentina.     

Effects of nutrient supplementation on fermentation kinetics, H2S evolution, and aroma profile in Verdicchio DOC wine production

Different yeast nutrient additions were studied for the 2008 and 2009 vintages of Verdicchio grape juice fermentation. Addition of yeast derivatives at the beginning of fermentation and/or different amounts of diammonium phosphate at various times within the first half of fermentation were examined, with initial yeast assimilable nitrogen concentrations set at 200 and 250 mg l^?1. Supplementation with glutathione in combination with this nitrogen addition was also evaluated. Fermentation rates were monitored throughout these fermentations carried out under different nutrient conditions. H₂S production during fermentation and synthesis of volatile compounds in the finished wines were quantified; the wines also underwent sensory evaluation. The fermentation kinetics were almost exclusively influenced by the inorganic nitrogen supplementation with diammonium phosphate. H₂S evolution was more affected by assimilable nitrogen than glutathione. Diammonium phosphate significantly reduced H₂S production, with a further reduction in the presence of yeast derivative. This nitrogen supplementation yielded higher concentrations of acetate esters, and in particular of isoamyl acetate (fruity aromas), which positively influences the analytical and aroma profile of wines and results in a general reduction in 2-phenylethanol production (floral aromas). Overall results (two harvesting times and vintages) indicate that the management with diammonium phosphate and yeast derivative supplementation improves the kinetics of fermentation and provides a good tool to reduce H₂S formation and increase the analytical and sensory quality of Verdicchio wine.     

A Fluorescence‐Based Method for Cyanate Analysis in Ethanol/Water Media: Correlation between Cyanate Presence and Ethyl Carbamate Formation in Sugar Cane Spirit

Based on the fluorescence properties of 2,4‐(1H,3H)‐quinazolinedione, a product of the reaction between cyanate and 2‐aminobenzoic acid, a simple, sensitive, selective, and reproducible method for the cyanate analysis in aqueous ethanolic media is proposed. In this method, λ_exc and λ_em are 310 and 410 nm, respectively, and the limits of detection and quantification are 2.2 × 10^?7 and 6.7 × 10^?7 mol/L, respectively. Under optimal conditions (pH = 4.5, 40% ethanol), a concentration of 5.0 × 10^?6 mol/L cyanate can be determined in a single measurement, at a 95% level of confidence, with an uncertainty of ± 0.13 × 10^?6 mol/L. Cyanide, thiocyanate, chloride, nitrate, and sulfate ions, as well as urea and urethane in concentrations 1 × 10³ higher than that of cyanate do not interfere with the measurement. The methodology was applied to cyanate analyses in the different fractions of the sugarcane distillate and the data strongly suggest a correlation between the presence of urea in wine, and the cyanate and ethyl carbamate concentrations in the spirit.     

Enhanced Chemiluminescence Determination of Hydrogen Peroxide in Milk Sample Using Metal–Organic Framework Fe–MIL–88NH<Subscript>2</Subscript> as Peroxidase Mimetic

The presence of hydrogen peroxide (H₂O₂) in milk is a major concern because it constitutes a public health hazard. Here, a sensitive flow injection chemiluminescence method was established for the detection of H₂O₂. As a peroxidase mimetic, metal–organic framework Fe–MIL–88NH₂ was found to significantly enhance the chemiluminescence of luminol–H₂O₂ reaction. The enhancement mechanism could be attributed to peroxidase-like activity of Fe–MIL–88NH₂, which effectively catalyzed the decomposition of H₂O₂ into hydroxyl radical. The experimental conditions for the chemiluminescence reaction were thoroughly investigated. The chemiluminescence intensity was proportional to the concentration of H₂O₂ in the range of 0.1–10.0 μmol/L. The detection limit was 0.025 μmol/L H₂O₂, and the relative standard deviation was 2.6 % for 11 replicated measurements of 1.0 μmol/L H₂O₂ solution. The practicability of this method was demonstrated by determining H₂O₂ in milk samples.     

Determination of fumonisins B1 and B2 in Chinese rice wine by HPLC using AQC precolumn derivatisation

BACKGROUND: Fumonisins are a group of naturally occurring mycotoxins produced by various Fusarium species that commonly infect maize and other cereals, including sorghum and rice. In this study a sensitive and selective method was developed for the determination of fumonisins B₁ and B₂ (FB₁ and FB₂) in Chinese rice wine. The method is based on high‐performance liquid chromatography and fluorescence detection following precolumn derivatisation with 6‐aminoquinolyl‐N‐hydroxysuccinimidyl carbamate (AQC). RESULTS: FB₁ and FB₂ in Chinese rice wine were extracted and purified using strong anion exchange cartridges and derivatised with AQC at room temperature. The AQC derivatives were stable for 5 days. Optimal fluorescence was obtained at an excitation wavelength of 246 nm and an emission wavelength of 390 nm. Chromatography was performed using a C₁₈ column and gradient elution at 1 mL min^?1 with methanol and 0.05 mol L^?1 phosphate buffer at pH 4. The limit of detection was 6 µg L^?1 for both FB₁ and FB₂. The method was successfully applied to the determination of FB₁ and FB₂ in Chinese rice wine, with recoveries of 87.5–94.5% being obtained. CONCLUSION: The established method was stable and sensitive for the determination of FB₁ and FB₂ in Chinese rice wine. © 2012 Society of Chemical Industry     

Simultaneous Determination of Aflatoxin B1 and Aflatoxin M1 in Food Matrices by Enzyme-Linked Immunosorbent Assay

Aflatoxins are a class of highly toxic chemical contaminants occurring in food. Consumption of aflatoxin-contaminated food can lead to harmful effects on human health. A rapid and reliable analysis of aflatoxins in food is crucial. In this study, we generated a broad–specific monoclonal antibody (MAb) 3 C10 against aflatoxin B₁ (AFB₁). The MAb 3 C10 binds specifically to AFB₁ and AFM₁ and has a IC₅₀ of 0.13 μg L^?1 for AFB₁ and 0.16 μg L^?1 for AFM₁. Furthermore, the MAb showed high cross-reactivity to AFB₂, AFG₁, and AFG₂. To enable simultaneous AFB₁ and AFM₁ detection in different food matrices, an indirect competitive enzyme-linked immunosorbent assay (icELISA) based on MAb 3 C10 has been developed and optimized. In addition, the extraction methods of different food matrices (peanut, corn, soybean, wheat flour, rice, soy sauce, vinegar, wine, raw milk, pure milk, skimmed milk, and yogurt) were established. The average recovery ranged from 73 to 121 %, with relative standard deviation values less than 15 %. The limit of detection was 0.52?+?0.36 μg kg^?1 (mean?+?3SD) for AFB₁ in eight agricultural products and 0.031?+?0.015 μg kg^?1 (mean?+?3SD) for AFM₁ in four dairy products. The sensitivity of icELISA was below the limit set by the European Commission for aflatoxin detection in different food matrices and similar to LC–MS/MS method. We demonstrate a rapid, simple, and reliable method for simultaneous screening of AFB₁ and AFM₁ in different food matrices.     

Similar Reduction of Salmonella enterica Typhimurium on Grape Tomatoes and Its Cross-Contamination in Wash Water by Washing with Natural Antimicrobials as Compared with Chlorine Treatment

Thymol (THY), a generally recognized as safe (GRAS) compound found in thyme oil, has inhibitory effects against foodborne pathogens including Salmonella. Hydrogen peroxide (H₂O₂) is another GRAS agent to effectively inactivate Salmonella. The aim of the current study was to develop a GRAS wash solution containing THY (or H₂O₂) and other GRAS antimicrobials (organic acids and food surfactants) that would effectively reduce Salmonella enterica on grape tomatoes and minimize cross-contamination in washing water. A systematic approach including minimum inhibitory concentration and minimum bactericidal concentration tests, inhibition zone tests, and small-scale and scaled-up tomato washing tests was used to develop such wash solutions. Grape tomatoes surface-inoculated with S. enterica Typhimurium were washed with selected solutions containing combination of 0.2 mg/ml THY, 5 % sodium dodecyl sulfate (SDS) and 2 mg/ml acetic acid (AA), 800 ppm H₂O₂, combination of 200 ppm H₂O₂ with 4 % SDS, or 200 ppm chlorine for 2 min. THY 0.2 mg/ml + SDS 5 % + AA 2 mg/ml, 800 ppm H₂O₂, or 200 ppm chlorine achieved around 7.5 log reductions of Salmonella on the tomatoes as compared to the control in tests involving 10 or 100 g tomatoes. More than 5.0 log reductions in the spent washing solutions (0.2 mg/ml THY + SDS 5 %?+?2 mg/ml AA; 800 ppm H₂O₂) was observed. None of these antimicrobial washes changed the color, pH, texture, sensory quality of the tomatoes during 16-day storage at 4 and 22 °C. These treatments also achieved a 1.3 log reduction of total aerobic bacteria. Thus, washing with 0.2 mg/ml THY + SDS 5 %?+?2 mg/ml AA and 800 ppm H₂O₂ as alternative to chlorine-based washing could be an effective method to inactivate Salmonella on tomatoes and reduce the transmission of pathogens from tomatoes to washing solutions.     

Effects of maltodextrin glycosylation following limited enzymatic hydrolysis on the functional and conformational properties of soybean protein isolate

The soy protein hydrolysate (HSPI) was first prepared using Neutrase and then glycosylated with maltodextrin (Md) at different incubation times (120, 180, 240, 270, and 300 min). The effect of glycosylation following limited enzymatic hydrolysis on the physicochemical properties of HSPI was investigated. The sodium dodecylsulphate polyacrylamide gel electrophoresis was used to confirm the covalent conjugation and determine the changes in the molecular weight of soybean protein isolate (SPI) during the structural modification. Surface hydrophobicity (H ₀) measurements revealed that limited hydrolysis as well as glycosylation at 120 min increased H ₀; however, further glycosylation decreased H ₀ due to the shielding effect of the maltodextrin bound. The increased secondary, tertiary conformation stability was confirmed by the far-UV circular dichroism spectroscopy, the intrinsic fluorescence analysis, and the results of differential scanning calorimetry. Subsequently, the functional properties including solubility, heat stability, emulsifying property, as well as antioxidant activities were evaluated. Results indicated that the emulsifying activity index was improved notably from 86.13 ± 1.31 m²/g for the native SPI to 109.07 ± 4.45 m²/g for HSPI–Md conjugates after 270-min incubation. Additionally, the glycosylation had obviously positive effects on the antioxidant activities of the modified SPI proteins. Therefore, HSPI–Md conjugates might be used as potential emulsifiers or multifunctional wall materials for the microencapsulation of bioactive ingredients.     

Comparison of Six Methylation Methods for Fatty Acid Determination in Yak Bone Using Gas Chromatography

Yak bone is rich in nutrition but not used efficiently. Six methylation methods (M1: acetyl chloride-methanol method, M2: H₂SO₄-methanol method, M3: HCl-methanol method, M4: KOH-methanol method, M5: M2 in combination with M4, and M6: M3 in combination with M4) with (system 1 (S1)) or without (system 2 (S2)) prior acid hydrolysis for fatty acid (FA) determination using gas chromatography in yak bone were comprehensively compared. The contents of total FA determined by using M1 and M2 were significantly higher (p < 0.05) than those by using M3 for both S1 and S2 (119.83 versus 118.34 versus 38.31 mg/g in S1; 104.03 versus 93.73 versus 30.08 mg/g in S2 for M1 versus M2 versus M3, respectively). The result determined by M4, M5, and M6 was less than 5 mg/g. Validation results of M1 and M2 indicate that for most (>90%) of the FA, the intra-day and inter-day CVs were <9%. Recoveries for more than 90% of the FA were within a range of 85–117%. In addition, C18:1n9c, C16:0, C18:0, and conjugated linoleic acid were the major FAs in yak bone, approximately accounted for 50, 20, 10, and 10% of the total FA, respectively. And the ratio of saturated and unsaturated FA in yak bone was about 1:2. The acid hydrolysis/H₂SO₄-methanol esterification method would be more efficient for the accurate determination of FA in yak bone, whereas the direct acetyl chloride-methanol method would be used as an alternative for the fast analysis.     

INTERACTIVE EFFECTS OF SELECTED NUTRIENTS AND FERMENTATION TEMPERATURE ON H2S PRODUCTION BY WINE STRAINS OF SACCHAROMYCES

ABSTRACT

Metabolic interactions between yeast assimilable nitrogen (YAN), biotin, pantothenic acid, and fermentation temperature that affect H₂S production by wine yeast during alcoholic fermentation were examined. Strains of Saccharomyces cerevisiae (UCD 522 and EC1118) were inoculated into a synthetic grape juice medium with H₂S evolution monitored under fermentative conditions. While a number of interactions affected the evolution of H₂S, YAN as a factor by itself was found to be not significant (P > 0.05) for both yeasts examined. Maximal cumulative H₂S production for strain UCD 522 occurred in media fermented at 30C with 60 mg/L YAN, 10 µg/L biotin, and 50 µg/L pantothenic acid while minimum production was observed with 250 mg/L YAN and 250 µg/L pantothenate. Similarly, strain EC1118 produced the most H₂S at 30C, but with 250 mg/L YAN, 0.5 µg/L biotin, and 50 µg/L pantothenic acid and the least in media that contained 250 mg/L YAN and 250 µg/L pantothenic acid.

PRACTICAL APPLICATIONS

“Reduced” off‐odors of wines, primarily associated with sulfur‐containing molecules such as H₂S, continue to be a difficulty facing winemakers worldwide. One strategy for wineries to limit these problems is to add yeast nutrients prior to fermentation, most commonly, nitrogen‐containing compounds such as diammonium phosphate. However, nitrogen deficiency is not always the sole cause for these problems. Rather, the current research suggests the need to consider factors other than nitrogen including availability of biotin and pantothenic acid as well as fermentation temperature in order to minimize these off‐odors.     

Hydrogen sulphide production during cider fermentation is moderated by pre‐fermentation methionine addition

Yeast assimilable nitrogen (YAN) concentration and composition impact hydrogen sulphide (H₂S) production and fermentation kinetics during wine fermentation, but this phenomenon has not been extensively studied in cider fermentation. Our hypothesis was that H₂S production during cider fermentation could be decreased through pre‐fermentation modification of concentrations of individual amino acids. Apple juice (53 mg L⁻¹ YAN) was supplemented with asparagine, arginine, methionine or ammonium and fermented with EC1118 and UCD522 yeast strains. No difference in H₂S production among fermentations was observed with addition of asparagine, arginine or ammonium. Methionine addition of 5 mg L⁻¹ decreased H₂S production by yeast strain EC1118 at 53 mg L⁻¹ YAN. With 153 mg L⁻¹ initial YAN, only methionine addition of 50 mg L⁻¹ decreased H₂S production, and no tested methionine rates decreased H₂S production with 253 mg L⁻¹ initial YAN. Supplementation to 153 mg L⁻¹ YAN resulted in increased H₂S production at all methionine concentrations tested. Sensory differences in aroma were detected in samples supplemented with ammonium and methionine, and these differences were correlated with observed differences in H₂S production. Our results indicate that supplementing cider fermentations with methionine leads to lower H₂S formation, especially in apple juice containing low YAN. © 2017 The Authors Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling