Effect of protein thermo aggregation on the binding of BSA to gelatin type A.

We study the effect of limited heat-induced aggregation of BSA on structure development in the water-gelatin-thermally aggregated BSA (BSA(TA)) system. The pH is set at 5.4 and the temperature is higher than the conformation transition temperature of gelatin, but lower than the denaturation temperature of BSA. Dynamic light scattering, circular dichroism, and fluorescence measurements are used to monitor structure changes. Interaction of gelatin with BSA(TA) leads to formation of large complex particles with an average radius ∼1500 nm. BSA-gelatin complex formation accompanies partial destabilization of the secondary and tertiary structures of BSA and an additional exposure of hydrophobic tryptophan residues on the surface of the globule. It is shown that electrostatic interaction of the oppositely charged groups of BSA(TA) and gelatin is responsible for formation of such complex particles, whereas the secondary forces (hydrophobic interaction and hydrogen bonds) play an important role in stabilization of the complex particles. The zeta potentials of the native and the thermally aggregated BSA samples were determined, and the solvent quality has been quantified by determining the activity of the protein samples in their saturated solutions. It was shown that steric reasons (large size of the thermally aggregated BSA(TA) particles), and uncomplete charge compensation of the positively charged gelatin molecules by the negatively charged BSA(TA) particles are the main factors in determining structure formation, while the levels of the activity of the native BSA and BSA(TA) have a smaller effect on the structure of complex.

[A study of diluted aqueous solutions of humic acids by scanning microcalorimetry].

It has been found by reversed-phase chromatography that humic acids obtained from vermicomposts of different duration of vermicomposting consist of a hydrophilic and a hydrophobic fractions, the hydrophobic fraction having a substantially lower content of charged, probably carboxylic, groups. A change in the sign of the temperature dependence of the heat capacity of diluted aqueous solutions of humic acids at approximately 58 degrees C has been found by differential scanning microcalorimetry, which indicates an increase in the hydration of hydrophobic groups. A jumpwise increase in heat capacity in the temperature range from 86 to 90 degrees C was also found, which is due likely to the hydration of hydrophobic groups in the interior of "micelles", due to the "devitrification" of the hydrophobic nucleus of micelle-like structures. It was shown that increasing the duration of vermicomposting leads to an increase in the relative content of the hydrophobic fraction of humic acids and in the cooperativity of the thermodynamic transition, which manifests itself in a jump of heat capacity, which probably results from the increase in the "micelle" size.

Interactions of flavor compounds with pectic substances.

Investigation has been conducted using equilibrium dialysis on the sorption of flavor compounds (FC) in solutions of low- and high-esterified pectinates (LEP and HEP, respectively). The compounds include 2-acetyl pyridine, 2,3-diethyl pyrazine, 2-acetyl thiophene and some normal 2-ketones. A method of direct gas chromatographic analysis has been developed for the determination of the FC in aqueous solutions at concentrations as low as 10(-3)% v/v. Additional information was obtained by the analysis of circular dichroism (CD) and apparent molar heat capacity. The results indicate: (1) In LEP solutions, sorption of normal aliphatic 2-ketones with chain length greater than C6 presumably proceeds via van der Waals interactions between alkyl groups of the 2-ketone and hydrophobic regions of the pectinate. The sorption increases with increased alkyl chain length. The Gibbs energy of the methylene group transferring from the solvent to the LEP solution is found to be 1.8 kJ/mol for 2-ketones at C7-C9. (2) In acidic media, binding of heterocyclic FC with pectinates mostly proceeds via hydrogen bonding involving the hydrogen atoms in undissociated carboxyl groups in the pectinate macromolecules. It can also be affected by the self-association of the pectinate macromolecules, depending on pH and pectinate concentration. (3) Under neutral conditions, the presence of Mg2+, Ca2 and Zn2+ ions or the formation of the calcium-pectinate gel network has little effect on the sorption of 2-ketones with the LEP. However, in acidic media, metal ions inhibit the sorption of FC through hydrogen bonding. The sorption of 2-octanone in acidic media depends extremely on Ca++ concentration by the correlationship with changes in the structure of LEP solutions in terms of apparent molar heat capacity.

Gas chromatographic investigation of volatile nitrogen containing bases of Antarctic krill Euphausia superba Dana.

The composition of the volatile nitrogen-containing bases of fresh-caught Antarctic krill E. superba has been investigated by gas chromatography. The analysis was carried out on three packed columns with Apiezon L, Triton X-305, PEG-1000 and one glass capillary column with Triton X-305. The components were identified by standardless gas chromatographic method with a special computer program. No less than 63 compounds have been found and 54 compounds have been identified, among these primary, secondary and tertiary aliphatic amines as well as heterocyclic bases. The presence of 5 compounds has been confirmed by GC/MS technique. Analysis with the help of a specific flame-photometric detector has shown the presence of 9 bi-functional nitrogen- and sulfur-containing compounds.

Amines in soil as possible precursors of N-nitroso compounds.

Volatile nitrogen bases in soil have been analysed by gas chromatography. Two samples of soils taken from different regions have been investigated. The first sample was loam. The second was a mixed sample with a predominance of chernozem. At least 48 amines have been found in the samples and 34 of them have been identified. Among the compounds identified are primary, secondary and tertiary amines and heterocyclic bases. The most numerous group is that of the secondary amines (14 compounds), which can be directly nitrosated to give carcinogenic N-nitrosamines. In the chernozem soil, the qualitative amine analysis is practically identical to that of the loam, but the total amount of amines is approximately 10 times higher. For the first time, a wide variety of amines capable of undergoing nitrosation has been found in soils not cultivated by man.

[Gas chromatographic analysis of volatile nitrogen bases in boiled beef; possible N-nitrosamine precursors]. / Gazokhromatograficheskii analiz letuchikh azotistykh osnovanii varenoi goviadiny, bozmozhnykh predshestvennikov N-nitrozaminov.

The composition of nitrogen-containing organic bases in the volatile substances of boiled beef has been studied. For the first time 30 compounds have been identified, including primary, secondary, and tertiary aliphatic amines, pyrazines, pyridine, piperidine and their alkyl substituted derivatives. The content of trimethyl-, diethyl-, diisopropyl-amines, and piperidine, possible precursors of N-nitrosamines, has been quantitated.