Search

A first report of an active and stable polyphenol oxidase system in tubers of Jerusalem artichoke (Helianthus tuberosus L.) is presented. The crude enzyme, extracted in 0.1M phosphate buffer, pH 6.5, showed optimum activity using dihydroxyphenol substrates. In this respect, chlorogenic acid followed by catechol showed the best reactivity. The enzyme exhibited an optimum pH of 6.0 using 0.01M catechol as a substrate. The specific activity of the enzyme was approximately 13 and 3 times the level found in potatoes and sugar beets, respectively. Thermal inactivation data indicated an apparent activation energy of 54 KJ/mole. Over 84% of the total soluble enzyme was located in the tuber peels.

A bacteriocin-like agent, thermocin, produced by the rough variant (Rh) of Bacillus stearothermophilus var. calidolactis was shown to inhibit acid production in Delvotest® P ampoules. The minimum concentration of thermocin resulting in a positive test was 0.9 arbitrary units(Au) per mL. Thermocin concentrations of 0.8-0.6 and 0.5 Au/mL resulted in doubtful and negative results, respectively. Preincubation of the ampoules for one hour at 63°C slightly decreased the sensitivity of the Delvotest® to thermocin. It is suggested that assay tests yielding false positive results should be analyzed for the presence of Rh (thermocinogenic) variants, as a possible source for these type of results.