ACTA ALIMENTARIA VOL. 12 (A QUARTERLY OF THE COMMITTEE ON FOOD SCIENCE OF THE HUNGARIAN ACADEMY OF SCIENCES, 1983)

1983 / 1. sz. - VÁMOS-VIGYÁZÓ, L.-NÁDUDVARI-MÁRKUS, V.: Inactivation of polyphenol oxidase and depletion of o-dihydroxy phenol content during the enzymatic browning reaction of fruit tissues

2 VÁMOS-VIGYÁZÓ & NÁDUDVARI-MÁRKUS: ENZYMATIC BROWNING REACTION concentration in which the browning reaction was accelerated by aeration and enzyme activity as well as substrate concentration were determined at intervals during the reaction. 1. Materials and methods 1.1. The fruits All the fruits were picked in the years 1977 and 1978. The apples of the cultivars Jonathan and Starking were purchased from the Research Station of the University of Horticulture, Ujfehértó, the apricots of the cultivars Bibor (Purple) and Mandula (Almond) were supplied by courtesy of the Research Station of the Research Institute for Fruits and Ornamental Plants, Cegléd. 1.2. The analytical methods Enzyme activity was determined in appropriately diluted fruit homoge­nates by a kinetic spectrophotometric method developed at the Central Food Research Institute (MIHÁLYI & VÁMOS-VIGYÁZÓ, 1976), using chlorogenic acid (Fluka, Switzerland), as substrate. A change in optical density (OD) of 10_4 per min was adopted as unit enzyme activity and related to fruit mass (fresh mass basis). Ortho-dihydroxy phenol (ODP) content was assessed in the methanol ex­tracts of the fruits by a modified version of the method of ALMÁSI and MOLNÁR (1961) based on the Hoepfner reaction. ODP content was expressed as mg chlorogenic acid in 1 g of fruit flesh (fresh mass basis) (VÁMOS-VIGYÁZÓ et ah, 1981). 1.3. Aeration of the fruit homogenates Fruit homogenates were prepared from (7:2), later from (6:1) tap water dilutions of fruit flesh comminuted with a stainless steel knife. Homogeniza­tion was carried out in an Atomix blendor equally equipped with stainless steel knives. In the 1977 experiments 3 sain pies of homogenate of 140 g each were stirred in beakers at 22 ±2 °C and 180 rpm with vertical stainless steel blades mounted on a vertical stainless steel shaft. In 1978 this equipment was replaced by a 12 cm 0 sintered glass funnel (G 1), holding 750 g of homog­enate. Aeration was performed by an upward flow of air and simultaneous stirring. Aeration and stirring were carried on for several hours at r.t. and samples were taken for the determinations of PPO activity and ODP content before aeration and, subsequently, every 30 and 60 min, resp. Ada AUmentaria 12, 1983

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