The potential use of acylglycerols on the thermal inactivation of lactic acid bacteria for the manufacture of long-life fermented products

The effect of acylglycerols on the thermal inactivation of lactic acid bacteria used in the production of fermented products was studied. The starting point was the observation of an increase in thermal sensitivity in the presence of an emulsifier based on mono- and diacylglycerols in the culture medium. Analysis of the emulsifier showed that monoacylglycerols were the compounds responsible for this effect, with monopalmitin being the main contributor. Monostearin, on the other hand, showed significantly less potentiating effect. Interestingly, monoacylglycerols showed a greater bactericidal effect when used individually than when used in combination. On the other hand, the rate of thermal inactivation observed in reconstituted skim milk emulsions was lower than in peptone water emulsions, showing that the presence of proteins and colloidal particles increased the resistance of bacteria to heat treatment. With respect to pH values, a reduction in pH from 6.6 to 5.5 promoted an increase in the rate of thermal death. However, at pH = 5.5, the enhancing bactericidal effect was only detectable when the heat treatment was performed at low temperatures but not at high temperatures. This finding is of interest, since it will allow the design of moderate heat treatments, combining the use of temperature with the addition of acylglycerols, to prolong the shelf life of products fermented with lactic acid bacteria, and minimizing the destruction of desirable compounds that were obtained by the fermentation process.

Thermo-oxidative stability of asymmetric distigmasterol-modified acylglycerols as novel derivatives of plant sterols

The study investigated the thermo-oxidative stability of distigmasterol-modified acylglycerols as a new structured acylglycerols. Samples were heated at 60 and 180 °C for 8 h. Their percentage degradation and products formed during heating were compared with free stigmasterol and stigmasteryl esters. The remaining of stigmasterol and fatty acid parts, the formation of stigmasterol oxidation products and the composition of polar and non-polar fractions were analysed using chromatographic methods. The cytotoxicity and genotoxicity were determined with the use of an MTT test and a comet assay, respectively. The highest stability during heating was observed for 2,3-distigmasterylsuccinoyl-1-oleoyl-sn-glycerol (dStigS-OA) and the lowest for 2,3-distigmasterylcarbonoyl-1-oleoyl-sn-glycerol (dStigC-OA). Data showed that the formation of thermo-oxidative degradation products is affected by the temperature and chemical structure of lipids present in the molecule. The dStigMAs bonded by a succinate linker and products formed during their thermo-oxidation showed no cytotoxic or genotoxic activity to normal human cells.

Simultaneous high-temperature gas chromatography with flame ionization and mass spectrometric analysis of monocarboxylic acids and acylglycerols in biofuels and biofuel intermediate products

Triacyl-, diacyl- and monoacylglycerols (TAGs, DAGs, MAGs) along with monocarboxylic acids (MCAs) are intermediate products in many triacylglycerol oil-to-biofuel conversion pathways. Accumulation of these compounds leads to poor biofuel characteristics and may result in fuel system damage. We developed a method for simultaneous identification and quantification of a wide range of MCAs (C₄-C₁₈), MAGs, DAGs, and TAGs. The method is based on trimethylsilylation followed by high temperature GC with programmed temperature vaporizer (PTV) injection coupled to parallel FID and MS detectors (HTGC-FID/MS). To minimize the discrimination of both low and high molecular weight species typically occurring on the injector, we optimized injection conditions using a central composite design. The critical variables were the time at initial temperature (40 °C), splitless time, and the interaction between these two parameters. Among three tested electron ionization source/quadrupole analyzer temperatures, a 350/200 °C setting provided the highest response and signal-to-noise ratio for TAGs and did not have an effect on MAGs and DAGs. Similar results were obtained when quantifying target analytes in intermediate products of soybean oil cracking with FID and MS (using specific acylglycerol fragmentation ions). The instrumental FID limits of detection (LODs) were 0.07-0.27 ng for most of the target analytes. Selected ion monitoring (SIM) LODs were 0.01-0.05 ng for MCAs and 0.03-0.14 ng for acylglycerols. For the total ion current (TIC), LODs observed increased with acyl chain length and degree of unsaturation, resulting in an increase from 0.05 to 0.18 ng for MCAs (C₅ to C₁₈) and from 0.03 to 1.8 ng for acylglycerols (TAGs C₈ to C₂₂). Deviations in the repeatability of sample preparation, intra- and inter-day analyses, including sample stability over an eight-day time period, did not exceed 10% variance. These results demonstrate that the developed method is accurate and robust for the determination of acylglycerols and MCAs produced during the processing of TAGs into biofuels.

Comparison of High-Pressure Behavior of Physicochemical Properties of the Di- and Triacylglycerols Established by Ultrasonic Methods

Two samples of triacylglycerols i.e., olive oil and triolein, and one sample of diacylglycerol were investigated. In the course of compression, the density of the samples was determined by measurements of the change of piston position in a pressure chamber and volume correction due to chamber expansion under pressure. The speed of sound was evaluated from the time of flight of an ultrasonic impulse between emitting and receiving transducers placed in the high pressure chamber. The adiabatic compressibility, the intermolecular free length, the molar volume, the van der Waals' constant b and the surface tension were evaluated from the density, the speed of sound and the average molecular mass. All tested liquids undergo a high-pressure phase transition. Discontinuities in the measured isotherms of the physicochemical parameters of the investigated oils indicate the presence of high-pressure phase transitions. Moreover the time dependent change of pressure at constant volume during the phase transition was measured. The fundamental difference in the molecular structure of these acylglycerols influences their behavior significantly under high pressure.