The formation of cholesterol oxidation products (COPs) during heating of cholesterol at 150 °C for up to 30 min was kinetically studied using nonlinear regression models. The various COPs were analyzed by TLC and HPLC. Results showed that the COPs concentration increased with increasing heating time, and the cholesterol loss reached 64.8% after 30 min of heating. In the early stage of oxidation, the highest rate constant (h-1) was observed for 7-hydroperoxycholesterol (7-OOH) formation, followed by epoxidation, dehydration, reduction, and dehydrogenation. The reactions for formation of 7-OOH (7α-OOH and 7β-OOH) and 5,6-epoxycholesterol (5,6α-EP and 5,6β-EP) fit the second-order, while the other reactions fit the first-order. The correlation coefficients (r 2) for the reactions ranged from 0.79 to 0.99. The kinetic model developed in this study can be used to predict the concentration changes of COPs during the heating of cholesterol. Keywords: Cholesterol oxidation; heating; kinetic model; HPLC analysis

The effects of various processing methods, steaming, roasting, smoking, charcoal grilling, and liquid smoke flavoring (LSF), on the formation of polycyclic aromatic hydrocarbons (PAHs) in duck breast steak were studied. The various PAHs in the duck samples were analyzed by gas chromatography with ion-trap detection. Results showed that with processing time from 0.5 to 1.5 h, charcoal grilling of duck samples with skin contained the highest amount of total PAHs, followed by charcoal grilling of duck samples without skin, smoking, roasting, steaming, and LSF. For carcinogenic PAHs, smoking contained the highest amount, followed by charcoal grilling and roasting. No carcinogenic PAHs were observed for steaming and LSF-treated duck samples. Also, the highest amounts of both total and carcinogenic PAHs were found after smoking duck samples for 3 h.

An edible biopolymer poly(gamma-glutamic acid) (gamma-PGA) was evaluated for possible use as an chelating/binding agent in the treatment of metal intoxication in humans. In vitro binding of the toxic heavy metals lead and cadmium as affected by pH, contact time, metal concentration, gamma-PGA dose, and essential metals was carried out in a batch mode. A maximum binding occurred in the pH range 5-7, corresponding to the gastrointestinal pH values except for the stomach. Binding isotherms at pH 5.5 were well described by the heterogeneous models (Freundlich and Toth), while the lead isotherm at pH 2.5 showed a S-type curve, which was fitted as multiple curves with the Langmuir model and a shifted-squared Langmuir model. However, no adsorption occurred for cadmium at pH 2.5. The maximum binding capacities of lead and cadmium at pH 5.5 were 213.58 and 41.85 mg/g, respectively. A curvilinear biphasic Scatchard plot signified a multisite interaction of metals. Binding was extremely rapid with 70-100% of total adsorption being attained in 2 min. Kinetics at low and high metal concentrations obeyed pseudo-first-order and pseudo-second-order models, respectively. The gamma-PGA dose-activity relationship revealed a low dose of gamma-PGA to be more efficient in binding a large amount of metals. Incorporation of Cu, Zn, Fe, Mg, Ca, and K showed only a minor influence on lead binding but significantly reduced the binding of cadmium.

SummaryLycopene is an important biological compound that is widely distributed in fruits and vegetables. Epidemiological study has shown that the dietary intake of lycopene may reduce the risk of certain types of cancers such as prostate cancer. However, the formation of c/s-isomers of lycopene during food processing and storage may decrease its biological activity Thus, it is important to learn about the content of lycopene and its cis isomers in foods. In this studywe compared I',,vo types of columns (C18 and C30) and various solvent systems for the separation of lycopene and its cis isomers by HPLC. Results showed that all-trans-lycopene and its nine cis isomers could be resolved by employing a C30 column with a mobile phase of n-butanol-acetonitrile-methylene chloride (30:70:10, v/v/v) and detection at 476 nm within 35 min. A C30 column was found to provide more powerful resolution of lycopene and its cis isomers, but the retention time was drastically increased compared to that of a C18 column. The c/s-isomers of lycopene were tentatively identified as 5-cis, 9-cis, 13-cis, 15-cis-lycopene, and possibly as four lycopene di-cis isomers, based on spectral characteristics and Q ratios as reported in the literature. The method developed in this study could be applied to determine the lycopene content in tomatoes.