Gel electrophoresis of polyphenol oxidase with instant identification by in situ blotting

Biochemical characterization and thermal inactivation of polyphenol oxidase from elephant foot yam (Amorphophallus paeoniifolius)

Polyphenol oxidase from Amorphophallus corm was purified (5.54 fold) by acetone precipitation and ion exchange chromatography. Electrophoretic-blot analysis revealed that the molecular weight of enzyme is 40 kDa. Enzyme preferred catechol as substrate and showed optimum activity at pH 6 and 35 °C with Km of 17.56 mM and Vmax 0.023 U/ml/min. Thermal inactivation kinetics study showed that 5.68% inactivation was achieved at 75 °C within 40 min. The half-life time of PPO is between 126.00 and 32.54 min. The activation energy (Ea) and Z values are 64.22 kJ/mol and 34.01 °C, respectively. The inhibitory action of L-ascorbic acid, sodium azide, NaCl, CaCl₂, ZnSO₄ and EDTA were studied. Thermodynamic studies indicated a non-spontaneous (ΔG > 0) and endothermic reaction process. Other thermodynamic activation parameters, such as Ea, ΔH^#, ΔG^# and ΔS^#, were also studied. Amorphophallus paeoniifolius polyphenol oxidase can find application in baking industry.

Polyphenol Oxidase Containing Sidestreams as Emulsifiers of Rumen Bypass Linseed Oil Emulsions: Interfacial Characterization and Efficacy of Protection against in Vitro Ruminal Biohydrogenation

The low transfer in ruminants of dietary polyunsaturated fatty acids to the milk or peripheral tissues is largely due to ruminal biohydrogenation. Lipids emulsified by a polyphenol oxidase (PPO) rich protein extract of red clover were shown before to be protected against this breakdown after cross-linking with 4-methylcatechol. Protein extracts of 13 other vegetal resources were tested. Surprisingly, the effectiveness to protect emulsified lipids against in vitro ruminal biohydrogenation largely depended on the origin of the extract and its protein concentration but was not related to PPO activity. Moreover, PPO isoforms in vegetal sources, effectively protecting emulsified lipids, were diverse and their presence at the emulsion interface did not seem essential. Potato tuber peels were identified as an interesting biological source of emulsifying proteins and PPO, particularly since protein extracts of industrial potato sidestreams proved to be suitable for the current application.

Browning in Annona cherimola fruit: role of polyphenol oxidase and characterization of a coding sequence of the enzyme

Cherimoya (Annona cherimola Mill.) fruit is an attractive candidate for food processing applications as fresh cut. However, along with its desirable delicate taste, cherimoya shows a marked susceptibility to browning. This condition is mainly attributed to polyphenol oxidase activity (PPO). A general lack of knowledge regarding PPO and its role in the oxidative loss of quality in processed cherimoya fruit requires a better understanding of the mechanisms involved. The work carried out included the cloning of a full-length cDNA, an analysis of its properties in the deduced amino sequence, and linkage of its mRNA levels with enzyme activity in mature and ripe fruits after wounding. The results showed one gene different at the nucleotide level when compared with previously reported genes, but a well-conserved protein, either in functional and in structural terms. Cherimoya PPO gene (Ac-ppo, GenBank DQ990911) showed to be present apparently in one copy of the genome, and its transcripts could be significantly detected in leaves and less abundantly in flowers and fruits. Analysis of wounded matured and ripened fruits revealed an inductive behavior for mRNA levels in the flesh of mature cherimoya after 16 h. Although the highest enzymatic activity was observed on rind, a consistent PPO activity was detected on flesh samples. A lack of correlation between PPO mRNA level and PPO activity was observed, especially in flesh tissue. This is probably due to the presence of monophenolic substrates inducing a lag period, enzyme inhibitors and/or diphenolic substrates causing suicide inactivation, and proenzyme or latent isoforms of PPO. To our knowledge this is the first report of a complete PPO sequence in cherimoya. Furthermore, the gene is highly divergent from known nucleotide sequences but shows a well conserved protein in terms of its function, deduced structure, and physiological role.