Agaricus bisporus browning: a review

Biocatalysis with polyphenol oxidase: a review

A tyrosine-hydroxylating enzyme was partially purified from betacyanin-producing callus cultures of Portulaca grandiflora Hook. by using hydroxyapatite chromatography and gel filtration. It was characterized as a tyrosinase (EC 1.14.18.1 and EC 1.10.3.1) by inhibition experiments with copper-chelating agents and detection of concomitant o-diphenol oxidase activity. The tyrosinase catalysed both the formation of L-(3,4-dihydroxyphenyl)-alanine (Dopa) and cyclo-Dopa which are the pivotal precursors in betalain biosynthesis. The hydroxylating activity with a pH optimum of 5.7 was specific for L-tyrosine and exhibited reaction velocities with L-tyrosine and D-tyrosine in a ratio of 1:0.2. Other monophenolic substrates tested were not accepted. The enzyme appeared to be a monomer with an apparent molecular mass of ca. 53 kDa as estimated by gel filtration and SDS-PAGE. Some other betalain-producing plants and cell cultures were screened for tyrosinase activity; however, activities could only be detected in red callus cultures and plants of P. grandiflora as well as in plants, hairy roots and cell cultures of Beta vulgaris L. subsp. vulgaris (Garden Beet Group), showing a clear correlation between enzyme activity and betacyanin content in young B. vulgaris plants. We propose that this tyrosinase is specifically involved in the betalain biosynthesis of higher plants.

Tyrosinase involved in betalain biosynthesis of higher plants

Treatments to control discoloration of minimally processed mushrooms were investigated. Whole or sliced mushrooms were immersed in browning inhibitor solutions and evaluated for color change during storage. Browning was more intense in first break mushrooms than in second, and in unwashed mushrooms compared to washed. However, washing sometimes induced purple discolorations, associated with bacterial lesions. Other discolorations were induced by hypochlorite, 4-hexylresor-cinol, and acidic dips. The most effective treatment was a combination of sodium erythorbate, cysteine, and EDTA at pH 5.5. Addition of preservatives to browning inhibitor dips did not improve storage life. However, dipping in 5% hydrogen peroxide prior to application of browning inhibitors significantly increased shelf-life.

Enzymatic Browning Control in Minimally Processed Mushrooms

(1998). Biodegradative and Biosynthetic Capacities of Mushrooms: Present and Future Strategies. Critical Reviews in Biotechnology: Vol. 18, No. 2-3, pp. 91-236.

Biodegradative and biosynthetic capacities of mushrooms: present and future strategies

Tyrosinase activities and isoenzymes were monitored in developing mushrooms from small pins to the mature stage. Catechol oxidase activity varied but dihydroxy-o-phenylalanine (dopa) oxidase and tyrosinase activities decreased during development. Latent dopa oxidase activity, detected by including sodium dodecyl sulfate in the assay, increased with development of the mushrooms. The electrophoretic profile of dopa oxidase isoenzymes indicated that three forms were present in each developmental stage and that the amount of these three forms decreased with maturation of the fruiting body. The use of phenolic adsorbents to prevent discoloration of crude extracts resulted in decreased enzyme activities and the loss of specific isoenzyme forms.

Tyrosinase Activity and Isoenzymes in Developing Mushrooms

An inorganic cement binder for a foundry aggregate comprising, in combination, potassium olivine phosphate and as a hardener therefor, water, aqueous sodium silicate, or aqueous phosphoric acid.

Process for preparing olivine sand cores and molds

Affinity and hydrophobic chromatography of mushroom tyrosinase

A hydrogel binder for a foundry aggregate comprising, in combination, a metal silico-phosphate and as a hardener therefor a mixture of aluminum dihydrogen phosphate, water and phosphoric acid and a process for manufacturing molds and cores from same.

Metal silico-phosphate binders and foundry shapes produced therefrom

An improved binder for a foundry aggregate comprising aluminum dihydrogen phosphate in combination with ammonium polyphosphate, potassium polyphosphate, potassium olivine phosphate, volcanic ash, sodium silicate, phosphoric acid or mixtures thereof.

Janis Ingebrigtsen

Papers

Tyrosinase Activity and Isoenzymes in Developing Mushrooms

Process for preparing olivine sand cores and molds

Affinity and hydrophobic chromatography of mushroom tyrosinase

Metal silico-phosphate binders and foundry shapes produced therefrom

Binder for preparing improved cores and molds