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YEMENİCİOĞLU, Ahmet; CEMEROĞLU, Bekir
Turkish journal of agriculture and forestry, 1998, Volume: 22, Issue: 3Journal Article
Bu çalısmada "Hale Haven" seftalilerinde polifenol oksidaz (PPO) enziminin nitelikleri arastırılmıstır. Ham, yarı olgun ve tam olgun seftalilerden öncelikle "Aceton powder" hazırlanmıstır. "Aceton Powder"dan hazırlanan enzim çözeltisinde optimum pH, Michaelis konstantı (Km), maksimum hız (Vmax) ve enzim aktivitesinin termal inaktivasyonu incelenmistir. Olgunluk asamasına göre enzimin optimum pH derecesi 6.0-6.5 arasında bulunmustur. Tam olgun seftalilerde elde edilmis enzimin pH 6.2 de Km=14.3 mM katesol ve Vmax=1.25 Abs.da-1. mL-1 oldugu saptanmıstır. Enzimin termal inaktivasyon kinetigi 70oC de arastırılmıstır. Her enzim ekstraktının termal inaktivasyon kurvesi, baslangıçta dik bir dogru, sonra daha yatık bir dogru olmak üzere iki bölümden olustugu belirlenmistir. Bu nedenle seftali PPO enziminin ısıya direnci farklı iki izoenzimden olustugu sonucuna varılmıstır. Baslangıçtaki hat, ısıya duyarlı enzimin inaktivasyonunu, ikinci hat ise ısıya dirençli enzimin inaktivasyonunu temsil etmektedir. Isıya dirençli fraksiyonun 70oC de inaktivasyonu, birinci dereceden reaksiyon kinetigine uymaktadır. Reaksiyon hız konstantları, ham, yarı olgun ve tam olgun seftalilerde sırasıyla, 20.36, 23.17 ve 19.66.10-2.dak-1 olarak hesaplanmıstır. Toplam enzim aktivitesinde ısıya dirençli kısmın oranı, inaktivasyon kurvesinin sıfır zamana kadar ekstrapolasyonu ile hesaplanmıstır. Bu degerlerin, ham, yarı olgun ve tam olgun meyveler için sırasıyla %83, %48 ve %55 oldugu saptanmıstır. The characteristics of polyphenol oxidase (PPO) from "Hale Haven" peaches were investigated. "Aceton Powder" was first prepared from peaches at three different maturity stages, namely unripe, half-ripe and fully ripe. The optimum pH, Michaelis costant (Km), maximum velocity (Vmax) as well as thermal inactivation of enzyme activity were studied with the enzyme solution prepared form "Aceton Powder". According to the degree of maturity, the pH optimum of PPO was between 6.0 and 6.5. The enzyme from fully ripe peaches showed a Km of 14.3 mM for catechol and Wmax of 1.25 OD min-1 mL-1 at pH 6.8. The termal inactivation kinetics of enzyme was studied at 70oC. The heat inactivation curve for each enzyme extract consisted of an inital steep straight line, and a final straight line with a shallow slope. It was therefore concluded that two isoenzymes of PPO with different resistances were present in peaches. The inital line represented inactivation of heat-labile enzyme and second heat-resistant enzyme. The inactivation of the heat-resistant fraction at 70oC followed a first order reaction kinetics. The rate constants were 20.36, 23.17 and 19.66.10-2.min-1 for unripe, half-ripe and fully ripe peaches, respectively. The proportion of heat-resistant portion in total activity was estimated by extrapolating the heat resistant curve to zero time. These values were 83%, 48% and 55% of total enzyme activity for unripe, half-ripe und fully ripe fruit, respectively.
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