title: Effects of argon enriched low-oxygen atmospheres and of high-oxygen atmospheres on the kinetics of polyphenoloxidase (PPO).
abstract: The reported benefits of enrichment of air atmospheres with argon or oxygen for control of enzymatic browning were investigated by determining the effects of these atmospheres on PPO kinetics. Kinetics of purified apple PPO and a commercially available mushroom PPO were studied in an in vitro model system. Enrichment with argon produced greater inhibitory effects than the current industry practice of enrichment with nitrogen. Km(app) values (mM) for apple PPO in 3%O(2)/97%Ar, 3%O(2)/97%N(2), and air, were 133, 87, and 48, respectively. The data indicate that inhibition by both gases is competitive, and also support the hypothesis that the greater inhibitory effect of argon was proportional to the size of the Van der Waals radius of argon against nitrogen (1.91 Å against 1.54 Å). Much smaller inhibitory effects were observed in the presence of 80% O(2) (Km(app) 57 mM), and the nature of this inhibition was less clear. The results suggest that the benefits of argon enrichment may be relatively small, and may require critical enzyme, substrate, and gas levels to be successful. However, these benefits may be exploitable commercially in some fresh-cut products, and may allow less anoxic atmospheres to be used. Practical Application: Control of enzymatic browning without sulfites continues to be a challenge in some fresh-cut products. While sporadic benefits of these atmospheres in control of enzymatic browning have been reported, results have been inconsistent in commercial practice. The results suggest that the benefits of argon enrichment may be relatively small, and may require critical enzyme, substrate, and gas levels to be successful. However, these benefits may be exploitable commercially in some fresh-cut products, and allow less anoxic atmospheres to be used.
authors.affiliation: Food Science Research Centre, Dept. of Life Sciences, Univ. of Limerick, Ireland. david.obeirne@ul.ie
authors.forename: David
authors.initials: D
authors.lastname: O'Beirne
authors.forename: Eileen
authors.initials: E
authors.lastname: Murphy
authors.forename: Deirdre
authors.initials: D
authors.lastname: Ni Eidhin
mesh_terms: D000363:Agaricales / Q000201:enzymology; D001128:Argon / Q000494:pharmacology*; D004156:Catechol Oxidase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002396:Catechols / Q000378:metabolism; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D057140:Fast Foods; D018857:Food Packaging; D005519:Food Preservation / Q000379:methods*; D005638:Fruit / Q000201:enzymology; D005656:Fungal Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D007700:Kinetics; D027845:Malus / Q000201:enzymology; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009994:Osmolar Concentration; D010100:Oxygen / Q000378:metabolism*; D010940:Plant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D002396:Catechols; D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D010940:Plant Proteins; D004295:Dihydroxyphenylalanine; D001128:Argon; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; C034221:catechol; D010100:Oxygen