Inhibition of lipid autoxidation by vegetable waxes.

This study aims to evaluate the effect of vegetable waxes on the kinetics of lipid oxidation of linseed oil. Apple and orange waxes were obtained using supercritical carbon dioxide. The capacity of waxes to inhibit or retard the oxidation of linseed oil was determined by isothermal calorimetry at 298 K. The results show that waxes were able to slow down linseed oil autoxidation, with apple waxes being more active than orange waxes. However, such activity was visible only at relatively high concentrations (>1% of waxes), greatly higher than the concentration used with radical chain breakers like BHT (0.2%). The inhibition activity was explained by considering three different mechanisms: (1) residual polyphenol content in the wax, (2) high termination rate of the radical chain process, and (3) physical hindrance of the oxidation process by change in viscosity. All these mechanisms were possible, although the latter seemed to be the most important. Finally, the importance of waxes in the inhibition of lipid autoxidation was determined by testing their inhibition activity in combination with primary antioxidants. A mixture of waxes with BHA, ethoxyquin and α-tocopherol showed a higher rate of inhibition than when present individually. This suggested a strong cooperative radical scavenging activity, whose beneficial effect might pave the way to the formulation of novel functional ingredients.

Antimicrobial Effect of Picea abies Extracts on E. coli Growth.

This study aims to investigate the effect of essential oils extracted from wood residues of Picea abies on the growth of Escherichia coli. The essential oils were extracted by supercritical carbon dioxide, leading to a yield of 3.4 ± 0.5% (w/w) in 120 min. The antimicrobial effect was tested at 37 °C by isothermal calorimetry. The heat-flow (dq/dt vs. time) was integrated to give a fractional reaction curve (α vs. time). Such curves were fitted by a modified Gompertz function to give the lag-time (λ) and the maximum growth rate (µmax) parameters. The results showed that λ was linearly correlated with E. coli concentration (λ = 1.4 h/log (CFU/mL), R2 = 0.997), whereas µmax was invariant. Moreover, the overall heat was nearly constant to all the dilutions of E. coli. Instead, when the essential oil was added (with concentrations ranging from 1 to 5 mg/L) to a culture of E. coli (104 CFU/mL), the lag-time increased from 14.1 to 33.7 h, and the overall heat decreased from 2120 to 2.37 J. The results obtained by the plate count technique were linear with the lag-time (λ), where (λ = -7.3 × log (CFU/mL) + 38.3, R2 = 0.9878). This suggested a lower capacity of E. coli to metabolize the substrate in the presence of the essential oils. The results obtained in this study promote the use of essential oils from wood residues and their use as antimicrobial products.