Pectin methylesterase (PME) from carrots (Daucus carrota L.) was extracted and purified by affinity chromatography on a CNBr-Sepharose 4B-PME inhibitor column. A single protein and PME activity peak was obtained. A biochemical characterization in terms of molar mass (MM), isoelectric points (pI), and kinetic parameters of carrot PME was performed. In a second step, the thermal and high-pressure stability of the enzyme was studied. Isothermal and combined isothermal-isobaric inactivation of purified carrot PME could be described by a fractional-conversion model.

The kinetics of lipoxygenase (LOX) inactivation in green beans due to high-pressure treatment were studied in the pressure-temperature area of 0.1 up to 650 MPa and -10 up to 70 degrees C for systems with different levels of food complexity, i.e., in green bean juice and intact green beans (in situ study). For both systems, LOX was irreversibly inactivated by high-pressure treatment combined with subzero and elevated temperatures and the inactivation could be described as a first-order reaction. At ambient pressure, in situ LOX was less thermostable than in the juice at temperatures below 68 degrees C whereas the stability ranking was reverse at temperatures above 68 degrees C. At temperatures below 63 degrees C, sensitivity of the inactivation rate constants to temperature changes was on the same order of magnitude in the juice and in situ, while at higher temperature it was lower in situ. The pressure needed to obtain the same rate of LOX inactivation at a given temperature was lower in situ than in the juice. Application of high-pressure treatment at low/subzero temperature resulted in an antagonistic effect on LOX inactivation for both systems, whereas no such effect was found above room temperature. The pressure-temperature dependence of the LOX inactivation rate constants in green beans was successfully modeled.

Soybean lipoxygenase (LOX) inactivation [0.4 mg/mL in Tris-HCl buffer (0.01 M, pH 9)] was studied quantitatively under constant pressure (up to 650 MPa) and temperature (-15 to 68 degrees C) conditions and kinetically characterized by rate constants, activation energies, and activation volumes. The irreversible LOX inactivation followed a first-order reaction at all pressure-temperature combinations tested. In the entire pressure-temperature area studied, LOX inactivation rate constants increased with increasing pressure at constant temperature. On the contrary, at constant pressure, the inactivation rate constants showed a minimum around 30 degrees C and could be increased by either a temperature increase or decrease. On the basis of the calculated rate constants at 102 pressure-temperature combinations, an iso-rate contour diagram was constructed as a function of pressure and temperature. The pressure-temperature dependence of the LOX inactivation rate constants was described successfully using a modified kinetic model of Hawley.

No abstract

Abstract. Indrawati I, Miranti M, Mayfi IR. 2017. Antibacterial activity of rhizome extracts of three ginger varieties against acneisolated bacteria. Nusantara Bioscience 9: xxxx. Antibacterial activity of rhizome extracts of three ginger (Zingiber officinale Rosc.) varieties against bacteria isolated from acne was done. Three ginger varieties, namely emprit, gajah and red ginger, were tested to obtain the best concentration of ethanolic extracts among them in inhibiting the growth of the acne-isolated bacteria. This research used experimental approach by Completely Randomized Factorial Design with two factors of treatment, A x B. The first factor (A) were bacteria strain isolated from acne that consists of 3 levels. The second factor (B) was a varied concentration of rhizome ethanolic extract of three ginger varieties which consist of 7.5, 10, 12.5, 15, 17.5 and 20% for emprit and gajah, while for the concentration used for red were 2, 2.5, 5, 7.5, 10 and 12.5%. Moreover, a synthetic antibiotic clindamycin 30 mg mL -1 was used as a comparison. The obtained data were statistically analyzed using ANOVA with 95% of confidence and then followed by Tukey test when the significance was detected. The results showed that the acne-isolated bacteria were identified as Propionibacterium sp 1 and 2 and Staphylococcus. The rhizome ethanolic extract of red ginger had the highest antibacterial activity against the tested bacteria. This finding was supported by the fact that the red ginger variety had a small value of Minimum Inhibitory Concentration (MIC). Additionally, the measurement of clear zone revealed that the interaction between ethanolic extract of red ginger with a concentration of 12.5% producing a clear zone of 13.5, 25.0 and 17.5 mm against Propionibacterium sp.1, Staphylococcus sp and Propionibacterium sp.2, respectively.