Shimin Wu

Effect of frying and aluminium on the levels and migration of parent and oxygenated PAHs in a popular Chinese fried bread youtiao.

This study investigated the effects of frying conditions on the change, migration and correlation of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (oxy-PAHs) in youtiao, a typical Chinese fried bread. PAH migration was evaluated using an isotope tracer method. High concentrations of oxy-PAHs, especially 9-fluorenone (1.75μg/kg) and anthracene-9,10-dione (6.41μg/kg), were detected. The results revealed that 1) prolonged continuous frying decreased parent PAH and oxy-PAH concentrations, 2) frying temperature and aluminium content did not have significant effects on parent PAH concentrations, 3) PAH migration rates (2.02-18.48%) varied significantly based on the frying oil type, and 4) the sum of five oxy-PAH concentrations was significantly correlated with the sum of 16 parent PAH concentrations in soybean oil-fried youtiao. Three oxy-PAHs (9-fluorenone, anthracene-9,10-dione, and 9,10-dihydrobenzo[a]pyren-7(8h)-one) were significantly correlated with their respective parent PAHs. The results might be helpful for further study and evaluation on oxy-PAHs and PAHs in fried foods.

Chemical compositions of the volatile extracts from seeds of Dendranthema nankingense and Borago officinalis

Volatile extracts from the seeds of Dendranthema nankingense Hand.-Mazz. and Borago officinalis L. were prepared using simultaneous distillation and extraction, and analyzed with gas chromatography-mass spectrometry on two capillary gas chromatography columns of different polarity. Ninety-five volatile compounds were identified in D. nankingense seeds, with hexanal, benzeneacetaldehyde, borneol, (-)-camphor, and 3-methyl-1-butanol being the predominant species. Sixty-five volatile compounds were identified in B. officinalis seeds, with 2-pentanone, 2,3-dihydro-benzofuran, 3-methyl butanal, and hexanal being the most abundant species. Thirty-three compounds, including short-chain aliphatic aldehydes, alcohols, and ketones, were common to both seeds. The volatile composition of both seeds varied significantly depending on their respective origins. The volatile terpenoids borneol and (-)-camphor could be key bioactive contributors to the characteristic flavor and cooling effects of D. nankingense. For the first time, coumaran was identified as an abundant species in plant seeds.

Effect of roasting on the volatile constituents of Trichosanthes kirilowii seeds

Roasted Trichosanthes kirilowii seeds have much more intense flavor than the raw seeds, and are commonly used as food and in the preparations of many medicinal formulations. Volatile constituents in the raw and roasted T. kirilowii seeds were separated by simultaneous distillation and extraction, and analyzed by gas chromatography-mass spectrometry on two capillary gas chromatography columns of different polarities (DB-WAX and HP-1). A total of 40 volatile compounds were identified in the raw seeds, with pentanal, 2-pentanol, styrene, (Z)-2-heptenal, (+)-calarene, and α-muurolene being the predominant compounds; 40 volatile compounds were also identified in the roasted seeds, with 3-methylbutanal, ethanol, 2-butanol, 2,3-butanediol, (E,E)-2,4-nonadienal, and 2-isopropyl-5-methyl-9-methylene-bicyclo[4.4.0]dec-1-ene being the most abundant compounds. A total of 15 compounds, mostly aldehydes, were common in both seeds. Roasting of T. kirilowii seeds resulted in a significant decrease in the levels of sesquiterpenes and short-chain aliphatic aldehydes. By contrast, high concentrations of 3-methylbutanal, ethanol, 2-butanol, and alkyl pyrazines were generated, which was responsible for the unique flavor of the roasted seeds. The study results may be useful for optimizing the roasting process and oil processing of T. kirilowii seeds.

Physicochemical Properties and Volatile Profiles of Cold-Pressed Trichosanthes kirilowii Maxim Seed Oils

The physicochemical properties and volatile profiles of cold-pressed Trichosanthes kirilowii Maxim (T. kirilowii) seed oils from four regions in China were determined in this study. The total oil content and cold-pressed oil yield of the four different sourced seeds were 38.06–44.33% and 15.17–30.97%, respectively. All the cold-pressed oil samples were found to be rich in polyunsaturated fatty acids, with content ranging from 45.41 to 75.32% of the total fatty acids. Punicic, α-eleostearic and catalpic acids were the main conjugated linolenic acid isomers in the cold-pressed T. kirilowii seed oils. The results of melting and crystallization profiles indicated that each oil sample exhibited different transitions steps due to its triacylglycerol composition, crystal structure and total unsaturation. Analysis of volatile profiles showed that 2,4-nonadienal was one of the most important aldehydes in the cold-pressed T. kirilowii seed oils, and less short chain acids (0.20%) but more esters (5.48%) were found in the sample with high content of punicic acid (Hebei sample). Results of oil quality indices indicated that cold-pressed T. kirilowii seed oils were liable to be oxidized, and their stabilities reduced with the increase of acid values. In general, more attention should be paid to improve the oxidative stability of cold-pressed T. kirilowii seed oils in their further application in food industry.

Effect of storage time and temperature on parent and oxygenated polycyclic aromatic hydrocarbons in crude and refined vegetable oils

Changes in polycyclic (PAH) and oxygenated (OPAH) aromatic hydrocarbon concentrations in vegetable oils during storage for 270days at 25°C or 4°C were investigated. The concentrations of OPAHs and PAHs increased with storage time. The increase in PAH concentration was mainly caused by light PAHs. Total PAH concentrations increased from 33.11-36.77μg/kg to 45.12-58.04μg/kg in 26 crude oil samples, while those in 26 refined oil samples increased from 16.52-20.02μg/kg to 25.73-40.01μg/kg. Acid value (AV) and peroxide value (POV) also showed an increase during the storage process from 0.08-0.92mg/kg to 0.33-2.98mg/kg, and from 0.08-0.12mmol/kg to 0.33-3.45mmol/kg in 52 tested oils, respectively. AV and POV were within the regulatory limits of China after storage for 270days. However, concentrations of 16 PAHs in all tested oils exceeded 25μg/kg. The results indicated PAHs and OPAHs formation was better inhibited in oils stored at lower temperature.

Validation and comparable analysis of aluminum in the popular Chinese fried bread youtiao by wavelength dispersive XRF

Aluminum (Al) is an element in alum commonly used as a raising agent for Chinese flour products, especially for a typical fried food youtiao. In the present study, the feasibility of wavelength dispersive X-ray fluorescence spectrometry (WDXRF) for analysis of aluminum levels in youtiao was examined. Youtiao samples spiked with known amounts of aluminum were used for calibration. Linearity, accuracy, precision, and detection and quantification limits were tested, based on three calibration curves. For further validation, test youtiao samples were analyzed by both WDXRF and inductively coupled plasma optical emission spectrometry (ICP-OES). Comparison of the two methods showed that measurement performance was not significantly different. Taken together, these results indicate that WDXRF can form the basis of a rapid and simple methodology for measuring the aluminum content of youtiao, and that it is a good candidate for replacing ICP-OES for analyzing Al-containing flour products.

Correlations between 1 H NMR and conventional methods for evaluating soybean oil deterioration during deep frying

Abstract1H NMR was applied as a fast method to determine soybean oil deterioration during deep frying and its correlations with conventional analytical methods were evaluated. Very high correlations (R = 0.925–0.968) were observed between the secondary oxidation products (n-alkanals, aldehyde, (E,E)-2,4-alkadienals) determined by 1H NMR and the total polar compounds (TPCs) determined by conventional silica gel column method. Strong correlations were found between 1H NMR and conventional gas chromatography method for analyzing linoleic (correlation coefficient R = 0.988), inolenic (R = 0.946) and oleic acids (R = 0.869). Moderate correlations (R = 0.664–0.742) were presented between the secondary oxidation products (n-alkanals, aldehyde, (E,E)-2,4-alkadienals) determined by 1H NMR and p-anisidine value (AnV) determined by conventional spectrophotometer method. The very high correlations between the formation of aldehydes and TPCs found in this study makes 1H NMR a potential tool to predict the maximum number of times that oil can be re-used during frying.

Influences of Light Intensity and β-Carotene on Polycyclic Aromatic Hydrocarbons and Aldehydes in Vegetable Oil: A Case Study Using Palm Oil

This study investigated the effects of three light intensities on four types of palm oils during consecutive storage for 12 months at 4 °C. The concentrations of 4-hydroxy-2- trans-hexenal (4-HHE), 4-hydroxy-2- trans-nonenal (4-HNE), polycyclic aromatic hydrocarbon (PAH)4, and PAH8 in the oils significantly increased with the increasing light intensity after storage. The red palm oil had the lowest rate of increase of 4-HNE, while 5° palm oil had the highest rate of increase of the PAH, OPAH, 4-HNE, and peroxide values during storage. For the same type of oil, OPAHs increased significantly under a light intensity of 6000 lx (lx) after storage. The increasing concentrations of 9FO, ATQ, and BaPO in the oils stored at 6000 lx showed a positive relation to their corresponding parent PAHs, indicating that PAH oxidation occurred at 6000 lx. The results suggest that light intensity and β-carotene may control PAHs, OPAHs, and 4-hydroxy-trans- alkenals for vegetable oil storage, transportation, and retail.

Dietary exposure to aluminium in the popular Chinese fried bread youtiao

ABSTRACT Youtiao is a typical, traditional and widely consumed fried food in China. Fermentation of youtiao involves the use of aluminium potassium sulphate (alum). There are health concerns related to the levels of aluminium in food; therefore, we aimed to determine the aluminium concentrations of youtiao from various locations, and to estimate the dietary exposure by different age groups in southern and northern China. The aluminium content of youtiao samples varied considerably (range = 4.46–852.69 mg kg−1). Both the mean and median aluminium contents of youtiao exceeded 100 mg kg−1, which is the China National Standard (GB) 2760-2014 National Food Safety for Standards for food additives. However, the median and 97.5th percentile of weekly dietary exposure to aluminium from youtiao, estimated using Monte Carlo simulation, did not exceed the provisional tolerable weekly intake (PTWI) set by the joint FAO/WHO Expert Committee on Food Additives (JECFA) for children, adolescents, adults and seniors. The weekly dietary exposure to aluminium would exceed the PTWI if children, adolescents, adults and seniors consumed 134.47, 260.98, 327.10 or 320.41 g of youtiao per week, respectively. GRAPHICAL ABSTRACT