H2S在LPG与MDEA水溶液中的溶解度测定

介绍了一种H2S在醇胺水溶液与LPG中分布的测定方法，此方法可分析H2S摩尔分数低至0．0002％的含量(H2S摩尔分数范围0．0002％～5％，MDEA的摩尔浓度为3．0mol／L和4．2mol／L)。实验数据表明在LPG中H2S的摩尔分数低于1％时，其摩尔分数的对数与胺相中H2S负荷的对数近似呈线性关系。因此，可将H2S摩尔分数适当外推到0．0001％，来满足生产和设计的需要。     

固相微萃取和GC/MS分析JOB炸药老化释放气氛

采用3种不同吸附性能萃取头的固相微萃取器对JOB炸药在自然密封存放和加热老化一定时间后所释放出来的微量气氛进行了萃取吸附研究，采用GC／MS测试技术对其进行了定性分析。研究结果表明，固相微萃取装置对该炸药老化过程中释放的微量无机气体和有机挥发性组分具有选择性吸附和萃取浓缩作用，峰强度显示不同老化条件下放出的气体组分和含量具有不同的结果。初步探讨了老化释放气体的机理，JOB炸药老化放出的主要是一些合成溶剂、杂质等。     

超高压处理对桃汁挥发性化学成分的影响

利用超高压装置(400 MPa,25℃,20 min)处理桃汁,采用顶空固相微萃取与毛细管气相色谱-质谱联用技术检测桃汁中的挥发性成分,并用面积归一化法测定了各种成分的相对质量分数。经与超高压处理前桃子原汁的41种主要香气成分分析比较发现,超高压处理后桃汁中主要特征香气成分的质量分数明显增加,其中γ-己内酯、cis-2-己烯醇、γ-癸内酯、叶醇和己醇等物质的质量分数分别增长了41.7%、52.0%、109.5%、288%、313.1%,并且新增加了乙酸己酯(0.29%)、cis-2-己烯醇乙酸酯(0.13%)、cis-3-己烯醇乙酸酯(0.47%)和十八醛(0.41%)等香气成分;感官评定表明,桃汁的青鲜香气更加突出,说明超高压处理增强了桃汁的特征香气。     

Volatile fraction of DOP “Castelo Branco” cheese: Influence of breed

“Castelo Branco” cheese is a Portuguese DOP cheese made from raw ewe’s milk coagulated with Cynara cardunculus, ripened for at least 40 days. “Merino da Beira Baixa” pure race is frequently used to produce milk for this cheese, however, exotic races such as Assaf and crusade of these two races are also used. The aim of this work has been to compare the volatile profile and sensory characteristics of DOP “Castelo Branco” cheeses manufactured during winter season with milk of breeds from Merino, Assaf and crusade of these two races and identify volatile compounds that can distinguish these cheeses.     

Odor Significance of the Volatiles Formed During Deep-Frying With Palm Olein

Palm olein is currently considered to be one of the best options for deep-frying, but as with any other edible oil, during frying, deteriorative reactions produce off-flavor compounds that reduce the oil sensory quality. This study assessed the odor significance of the volatiles formed during 136 h of deep-frying a chicken product in palm olein, aiming to identify potential markers of the oil sensory quality during frying. The volatiles were isolated by solid phase microextraction, and identified by GC–MS. Trained judges assessed the odor intensity and quality of the volatiles formed during frying, evaluating the GC effluents through a GC–olfactometry technique called OSME. Two hundred and eight volatiles were detected by GC/MS in the palm olein after 136 h frying. Of these, heptanal, t-2-heptenal, decanal and t-2-undecenal were identified as potential markers of the sensory quality of palm olein during frying. Hexanal, pentanal and pentane, usually associated with lipid oxidation, showed no odor impact in the GC effluents, and were thus proven not to be good markers of the sensory quality of palm olein when used for a long frying period.     

Colorimetric assay for determination of trimethylamine-nitrogen (TMA-N) in fish by combining headspace-single-drop microextraction and microvolume UV–vis spectrophotometry

In this work, headspace-single-drop microextraction has been used in combination with microvolume UV–vis spectrophotometry to enhance the determination of trimethylamine-nitrogen (TMA-N) in fish samples. TMA-N is often used for monitoring fish freshness, but due to the low analytical sensitivity usually achieved, its determination must be performed after certain time of storage in some fish species. The proposed methodology, based on the extraction and subsequent complexation of volatile TMA-N onto a picric acid-containing xylene microdrop exposed to the headspace, involves an important improvement of sensitivity (detection limit 6 × 10⁻⁴ mg TMA-N per 100 g of fish), a miniaturization of the AOAC Official Method (971.14) and a simple approach for routine labs. This method is well suited to determination of TMA-N in different species of frozen and fresh fish samples from markets and to study the evolution of TMA-N concentration in farmed turbot at the earliest stages of deterioration.     

Profiling volatile compounds from Mucuna beans by solid phase microextraction and gas chromatography-high resolution time of flight mass spectrometry

Four solid phase microextraction (SPME) fibres, polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB), polyacrylate (PA), and carboxen/polydimethylsiloxane (CAR/PDMS), were evaluated for profiling of volatile compounds during cooking of Mucuna pruriens beans. A gas chromatograph coupled to a high resolution time of flight mass spectrometer system was employed for separation, detection and identification of the volatile compounds. For the first time we report a total of 26 compounds, mostly alkyl benzenes and polycyclic compounds, identified in black, white, black–white, and yellow green Mucuna beans during head space sampling employing a CAR/PDMS fibre with subsequent detection with high resolution mass spectrometry. The number of volatile compounds sampled, most notably alkylbenzenes, decreased with each hour of boiling and discarding of water extracts. As the beans approached being fully cooked, benzoic acid 2-hydroxy methyl ester was the most dominant compound in all the four types of beans. These results are a first step towards addressing some of the occupational exposure associated with cooking Mucuna beans by rural communities.     

Effect of cooking or handling conditions on the furan levels of processed foods

The aim of this study was to investigate the possible effects of cooking or handling conditions on the concentration of furan in processed foods. The analytical method used to analyse furan levels in foods was optimized based on solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). In baby soups, the concentration of furan decreased by up to 22% after opening a lid for 10 min. In the baby food in retort packaging, the level of furan was reduced by 15–33% after heating the foods at 50°C without a lid. Furan in rice seasonings was evaporated completely after heating the foods at 60°C. Regarding powered milk, the levels of furan were too low to be compared under various conditions. The levels of furan decreased to 58% in beverage products for babies, after storing them at 4°C for 1 day without a lid. The levels of furan in canned foods such as cereal and vegetable were reduced by zero to 52% when they were stored without stirring in a refrigerator at 4°C for 1 day. When we boiled canned fish, the furan present was almost completely evaporated. It is recommended that canned meats be heated up to 50–70°C for the reduction (26–46%) of furan levels. The levels of furan in instant and brewed coffee samples were significantly reduced after storing for 11 to 20 min at room temperature without a lid (p < 0.05).