Analysis of volatile flavor compounds in top fermented wheat beer by headspace sampling-gas chromatography

Headspace sampling-gas chromatography(HS-GC)coupled with an internal standard method(ISM)was developed to analyze the volatile flavor compounds in top fermented wheat beer in the laboratory.Eight compounds,i.e.acetaldehyde,N-propanol,ethyl acetate,isobutyl alcohol,isoamyl alcohol,isoamyl acetate,ethyl hexanoate and ethyl octanoate were separated and quantified.This method was validated to ensure the quality of the results:the precision was satisfactory with relative standard deviation(RSD)in the range of 1.51%-4.22%,recoveries for all the analytes ranged from 95.15%to 99.85%,and the limits of detection were in the range of 0.0002-0.024 mg/L.Results of real wheat beer samples analyzed using this method showed that the volatile compound concentrations were in the range of 0.08-99.91 mg/L.Results suggested that this method exhibited good reproducibility,selectivity and high precision,and it can be useful for the analysis of routine beer samples.

Research on Preparation Method of Static Head Space for Volatile Organic Compounds in Drinking Water

[Objective] This research aimed to study the pre-treatment conditions of head space so as to establish a HS-GC determination method, which is suitable for China's conditions, for trace volatile organic compounds in drinking water. [Method]The preparation method of head space was adopted for the volatile organic compounds in drinking water. [Result] The 20 kinds of volatile organic compounds in drinking water all could be detected simultaneously by using HS-GC-FID method,and they all could be separated well. The HS-GC-FID method could analyze the detected substances qualitatively and quantitatively. In addition, this detection method was characterized by larger linear range of concentration, higher precision, higher detection limit and higher recovery rate. [Conclusion] Under certain conditions, HSGC can reduce the loss of volatile organic compound in drinking water and improve the sensitivity of detection. Moreover, the detection results meet the requirements by quality control.

Measurement and prediction of isothermal vapor–liquid equilibrium of a-pinene+camphene/longifolene+abietic acid+palustric acid+neoabietic acid systems

The vapor–liquid equilibrium(VLE)data of a-pinene+camphene+[abietic acid+palustric acid+neoabietic acid]and a-pinene+longifolene+[abietic acid+palustric acid+neoabietic acid]systems at 313.15 K,333.15 K and 358.15 K were measured by headspace gas chromatography(HSGC).These data was compared with the predictions value by conductor-like screening model for realistic solvation(COSMO-RS).Moreover,the calculated data of COSMO-RS and Non-Random Two-Liquids(NRTL)models showed good agreement with the experimental data.It was found that the three resin acids inhibited the volatility of a-pinene,camphene and longifolene and resulted in the decrease of total pressure.Moreover,HE(HB)contributes the most to the excess enthalpy and the hydrogen bonding interaction is the dominant intermolecular force of a-pinene,camphene and longifolene with the three resin acids.In addition,the geometric structures optimization and binding energy were obtained by the DFT to further illustrate the hydrogen bonding interaction and the effects of the addition of the three resin acids on the isothermal VLE.

Effects of different dietary lipid levels on physiological metabolism and odor quality of hepatopancreas in adult female Chinese mitten crab(Eriocheir sinensis)

Objectives:This study aimed to investigate the impact of different dietary lipid levels on the physiological metabolism and odor quality of adult female Eriocheir sinensis during the fattening phase.Materials and Methods:Five dietary schemes,each containing different total lipid levels(4%,7%,10%,13%,and 16%),were administered over a 60-d fattening period for adult female crab(approximately 50 g,n=60).Chromatography and spectroscopy techniques were used for the detection of aroma and key aroma precursors.Results:Dietary lipids had no significant effect on growth performance and hepatopancreas index(P<0.05).The carotenoid content showed an increasing and then decreasing trend,with a significant increase to 1312.51 mg/kg(P<0.05)at 7%lipid content of the diet.In contrast,a diet with a 13%lipid level led to a significant increase in total unsaturated fatty acids(115.3 mg/g,P<0.05),which maximized the contents of major fatty acids(oleic,linoleic,and linolenic,among others),and presented a fluctuating trend.A diet with higher lipid levels(16%)inhibited fatty acid accumulation.Moreover,a 13%dietary lipid level enhanced characteristic aroma compounds(for example,nonanal,octanal,hexanal,3-methylbutanal,and 2-heptanone)in E.sinensis cooked hepatopancreas.Through an orthogonal partial least squares discriminant analysis model,it becomes evident that lipids and carotenoids together promote aroma formation in hepatopancreas.Conclusions:Based on the current findings,the optimal dietary lipid level for enhancing the odor quality of hepatopancreas in adult female E.sinensis during the fattening phase was 13%.This study provides more precise options for the high-quality cultivation of E.sinensis.