The kinetics and thermodynamics of the thermal inactivation of polyphenol oxidase (PPO) in an aqueous extract from mushroom Agaricus bisporus (J.E. Lange) Imbach was studied, using pyrocatechol as a substrate. Optimal conditions for enzymatic studies were determined to be pH 7.0 and 35-40 °C. The kinetics of PPO-catalyzed oxidation of pyrocatechol followed the Haldane model with an optimum substrate concentration of 20 mM. Thermal inactivation of PPO was examined in more detail between 50 and 73 °C and in relation to exposure time. Obtained monophasic kinetics were adequately described by a first-order model, with significant inactivation occurring with increasing temperature (less than 10% preserved activity after 6 min at 65 °C). Arrhenius plot determination and calculated thermodynamic parameters suggest that the PPO in aqueous extract from Agaricus bisporus mushroom is a structurally robust yet temperature-sensitive biocatalyst whose inactivation process is mainly entropy-driven.

Polyphenol oxidase (PPO) from mushrooms (Agaricus bisporus (J.E.Lange) Imbach) was partially purified and characterized. The enzyme exhibited both monophenolase and diphenolase activities that were measured spectrophotometrically using L-tyrosine and pyrogallol as substrates. A two-fold purification in both activities was achieved by ammonium sulfate fractionation. The monophenolase activity was 3.35 EU/ml, and the diphenolase activity was 189.3 EU/ml. PPO was relatively stable at -15°C for 44 days. The enzyme was not very heat stable, and its activity decreased when incubated at the temperatures higher than 35°C. PPO activity showed two pH optima, at 5.3 and 7.0 at 25°C when pyrogallol was used as the substrate.Mono-, di- and triphenols were substrates for PPO. Using Vmax/Km as a specificity constant, pyrocatechol was the better substrate followed by pyrogallol. The kinetic parameters of the enzyme were: Vmax = 78 EU/min/ml, Km = 1.4 mM and KS = 250 mM for pyrogallol and Vmax = 168 EU/min/ml, Km = 0.40 mM and KS = 270 mM for the pyrocatechol. Of the inhibitors tested, competitive-type inhibition was observed with benzoic acid and sodium azide. A mixed-type inhibition was observed with L-cysteine and sodium fluoride.

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Wild edible truffles (namely, Terfezia leonis, Tirmania pinoyi, and T. nivea) were commercially obtained from Southern Algeria and methanolic extracts were prepared from these truffles. Their antioxidant and antiradical properties were studied by using five analytical methods: scavenging capacity on 1,1-diphenyl-2-picrylhydrazyl (DPPH·), 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS·+), superoxide anion (O2·-) radicals, ferric reducing antioxidant power (FRAP), and ferricyanide/Prussian blue assay. Chemical constituents contributing to these activities were also investigated. T. leonis had the highest total phenolics, total carotenoids, and anthocyanin contents. At 2.6 mg/mL, scavenging effects on the DPPH· radical were 92.47%, 53.06%, and 41.34% for T. leonis, T. pinoyi, and T. nivea, respectively. T. leonis showed the most potent radical scavenging activities on DPPH·, ABTS·+, and O2·- radicals, with EC50 values of 1.08, 1.35, and 7.27 mg/mL, respectively. On the other hand, T. leonis exhibited the highest reductive capabilities. On the basis of the EC50 values, T. leonis had good antioxidant and antiradical properties. These results showed that methanolic extracts from these three truffles species had effective antioxidant and antiradical properties. Therefore, wild edible desert truffles could serve as an easily accessible item of food rich in natural antioxidants, as a possible food supplement, or even as a pharmaceutical agent.

The aim of this study is to evaluate the in vitro effects of aqueous extracts of three species of Algerian desert truffles (Terfezia claveryi, T. leonis, and Tirmania nivea) on the growth of Pseudomonas aeruginosa and Staphylococcus aureus. The antimicrobial activity of the three aqueous extracts was tested using the agar well diffusion and kinetic bacterial growth curves methods. The aqueous extracts of Terfezia claveryi and Tirmania nivea were found to possess a very powerful antibacterial activity against both S. aureus and P. aeruginosa using agar well diffusion. Using 4% and 11% of the aqueous extracts of T. claveryi and T. nivea in the growth medium of S. aureus caused a significant inhibition of S. aureus growth by 86.48% and 99.09%, respectively. The aqueous extracts of T. claveryi and T. nivea were found to cause a significant inhibition of the growth of P. aeruginosa by 71.11% and 100%, respectively. However, the aqueous extract of Terfecia leonis did not show any antibacterial activity. Therefore, T. claveryi and Tirmania nivea can be considered a source of natural therapeutic agents that can be used to treat eye infections caused by resistant bacteria such as P. aeruginosa and S. aureus.

optical catechol biosensor based on a desert truffle tyrosinase extract immobilized into a sol-gel silica layered matrix. AbstractAn optical biosensor for the determination of catechol, a widely used yet toxic and carcinogenic molecule, is proposed using a crude extract of desert truffle (Terfezia leonis Tul.)as an enzymatic source of tyrosinase. The biosensor is constructed by the immobilization of tyrosinase crude extract in a bi-layered silica gel film prepared by dip-coating of an alkoxide/colloidal silica solution containing the enzyme on glass slide. Encapsulation has a moderate effect of the enzyme optimal pH stability but largely increases its thermal stability.Immobilized enzymes have a higher substrate affinity towards catechol but smaller maximum conversion velocity. The optical biosensor provides a linear response for catechol in the concentration range of 50-400 µM and a limit of detection was 52 µM. AFM studies show that the enzymes impact on the silica gel structure, preventing further deposition of additional layers. Comparison with similar dopamine biosensors points out that the impact of encapsulation on enzymatic activity may depend on the considered substrate.

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