Browsing by Author "Altunkaya, Arzu"

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Effect of Whey Protein Concentrate on Phenolic Profile and Browning of Fresh-Cut Lettuce (Lactuca Sativa)
(Elsevier Sci Ltd, 2011) Altunkaya, Arzu
The in vitro kinetics of lettuce PPO with respect to dissolved oxygen using catechin, chlorogenic acid, caffeic acid and gallic acid has been examined. In-vitro lettuce polyphenol oxidase (PPO) activity was determined by measuring the consumption of oxygen during the oxidation reaction. The effect of whey protein concentrate (WPC) was tested on the inhibition of lettuce PPO comparing with ascorbic acid (AA) and cysteine. A competitive model that considered inhibitors was the most appropriate model to explain reaction kinetics. Browning of lettuce was also monitored during storage for 24 h. Addition of WPC prevented loss of lightness in lettuce. Loss of identified phenolic compounds in lettuce was measured during the enzymatic browning process by high-performance liquid chromatography. Degradation of identified phenolic compounds followed first order kinetics during storage. Combination of WPC with cysteine was proposed for the protection of phenolics compounds against PPO-catalysed oxidation. (C) 2011 Elsevier Ltd. All rights reserved.
Effect of Grape Leaf Extract on Phenolic Profile and Browning of Fresh-Cut Lettuce (Lactuca Sativa)
(Wiley, 2014) Altunkaya, Arzu
This study aimed to investigate the effects of grape leaf extract (GLE) on the inhibition of lettuce polyphenol oxidase (PPO) and on the loss of phenolic compounds in fresh-cut lettuce during storage. The addition of GLE that had been heated at 100C for 15 min exhibited a higher inhibitory effect on the lettuce PPO activity than that of the fresh extract. It was found that heat-treated GLE inhibited the lettuce PPO noncompetitively. The addition of GLE prevented loss of lightness in lettuce monitored during storage. Loss of phenolic compounds was measured during the enzymatic browning process by high-performance liquid chromatography. Protocatechuic acid, chlorogenic acid, ferulic acid, coumaric acid and caffeic acid were identified in lettuce. Degradation of phenolics followed the first-order kinetic pattern during storage. Synergistic effects of GLE, in combination with ascorbic acid or citric acid, were also tested for the protection of phenolics.
Effect of Whey Protein Concentrate on Phenolic Profile and Browning of Fresh-Cut Lettuce (Lactuca Sativa) (Vol 128, Pg 754, 2011)
(Elsevier Sci Ltd, 2014) Altunkaya, Arzu
Partial Purification and Characterization of Polyphenoloxidase From Durum Wheat (Triticum Durum L.)
(Academic Press Ltd- Elsevier Science Ltd, 2012) Altunkaya, Arzu; Gokmen, Vural
A bright yellow color of pasta is an important qualitative trait for the durum wheat industry. Final color is the result of the balance between yellow and brown components in semolina. Polyphenoloxidase (PPO) is implicated as playing a significant role in darkening. This study aimed to characterize PPO activity of durum wheats. PPO was extracted and partially purified by ion-exchange chromatography on a column packed with diethyaminoethyl cellulose (DEAE). This procedure led to 26.33-fold purification with 24.7% recovery. The optimum temperature and pH of PPO were found to be 40 degrees C and 6.5, respectively. Heat stability of durum wheat PPO decreased as the temperatures increased from 30 to 80 degrees C. The z-value was calculated as 23.4 degrees C. It increased to 26.3 and 48.4 degrees C in the presence of 40% sucrose and 1 M NaCl, respectively. Durum wheat PPO was shown to use several phenolic compounds as substrate. Among the substrates used, the greatest substrate specificity was observed with catechol. Durum wheat PPO was sensitive to inhibitors such as ascorbic acid, cysteine, oxalic acid and citric acid. Ascorbic acid was the most effective inhibitor. (C) 2012 Elsevier Ltd. All rights reserved.