Polyphenoloxidase (PPO) of Amasya apple was partially purified by (NH&SO, precipitation and dialysis. The sample was used for characterization of the PPO. Optimum pH were 7.0, 9.0, 8.6 and 6.6 on substrates catechol, 4-methyl catechol, pyrogallol and L-dopa respectively. Catechol was the most suitable for Amasya apple PPO. The optimum temperature for maximum PPO activity was 18°C with catechol. Of seven inhibitors tested, the strongest was L-cysteine. Effectiveness of inhibitors increased in the order: thiourea, glutathione, P-mercaptoethanol, sodium cyanide, ascorbic acid, sodium metabisulfide, and L-cysteine. The KM was 34 mM of catechol. The activation energy with catechol was 107 cal/mol. In electrophoretic separation, three isoenzymes were detected with both catechol and L-dopa substrates.

Catechol and pyrogallol are allelochemicals which belong to phenolic compounds synthesized in plants. Their antimicrobial activities were investigated on three bacteria (Pseudomonas putida, Pseudomonas pyocyanea, Corynebacterium xerosis) and two fungi (Fusarium oxysporum, Penicillium italicum) phytopathogenic species as test organisms using the disc diffusion method. Both catechol and pyrogallol were found to have antibacterial effects on all the bacteria used in the study at 5 and 10 mm concentrations. Catechol has also been found to have an antifungal effect on the fungi used in the study, whereas no antifungal effects of pyrogallol were observed. The most sensitive species among the bacteria was P. putida which was inhibited by the allelochemicals even at 1 mm concentration.

This study aimed to synthesize and characterize juglone-entrapped poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles and compare the antifungal properties of free juglone with its PLGA nanoparticle formulation for the first time. The juglone-loaded nanoparticles prepared using the oil-in-water (o/w) single-emulsion solvent evaporation method were characterized by the reaction yield (RY), encapsulation efficiency (EE), polydispersity index (PDI), particle size, zeta potential (ZP), FT-IR, and in vitro release properties and evaluated for their morphological features using SEM. The nanoparticle formulation had size, RY, ZP, EE, and PDI values of 212 nm, 66.91 ± 2.4%, -16.3 ± 0.7 mV, 70.66 ± 3.1%, and 0.083 ± 0.024, respectively. In vitro release showed a triphasic pattern with initial burst followed by sustained release and dormant phase over the study period, releasing about 72.8% in total after 42 days. The antifungal studies against Aspergillus flavus, Candida albicans, and Fusarium spp. using agar dilution and top agar dilution methods indicated that the juglone-encapsulated nanoparticle was more effective than free juglone. This study showed that the top agar method, which was applied for the first time on antifungal activity, is more suitable for the nanoparticular system based on sustained release. Therefore, PLGA nanoparticle formulations may be an important tool for application in many areas for the effective and beneficial use of hydrophobic compounds such as juglone.

The use of nanoparticle formulations of juglone in biological systems and applications could be more beneficial than its free form due to its toxicity.

Polyphenol oxidase (PPO) of dog-rose fruit was extracted and purified through (NH 4 ) 2 SO 4 precipitation, dialysis, gel filtration, and DEAE-Sephacel ion-exchange chromatography. The sample obtained from ammonium sulfate precipitation and dialysis was used for characterization of the PPO. For this aim, optimum conditions, i.e., pH, temperature, and ionic strength, were determined with eight substrates. The best substrate of the PPO was found to be 4-methylcatechol. Optimum pH and temperature were found at pH 8.5 and 20°C, and K M and V max values were 8.64 mM and 431.96 with 4-methylcatechol, respectively. Eleven inhibitors were tested in the study and the most effective was found to be sodium metabisulfide as competitive inhibitor. The PPO has showed renaturation property after it denatured, as well. Therefore, heat inactivation process for preventing enzymatic browning of dog-rose fruit products is not recommendable. Two isoenzymes of the PPO were detected by polyacrylamide slab gel electrophoresis.