Characterization and Role of Polyphenol Oxidase and Peroxidase in Browning of Fresh-Cut Melon

Abstract

Polyphenol oxidase (PPO) and peroxidase (POD) were extracted from two different varieties of melon ( Cucumis melo L. cantalupensis cv. Charentais and C. melo L. inodorus cv. Amarillo) and characterized using reliable spectrophotometric methods. In both cases the enzymes followed Michaelis-Menten kinetics, showing different values of kinetics parameters between the two cultivars: K m = 7.18 +/- 0.70 mM ('Charentais') and 6.66 +/- 0.20 mM ('Amarillo') mM; V max = 7.93 +/- 0.35 units/min ('Charentais') and 13.82 +/- 0.37 units/min ('Amarillo'), relative to PPO; K m = 24.0 +/- 2.10 mM ('Charentais') and 5.05 +/- 0.19 mM ('Amarillo') mM; V max = 344.83 +/- 10.32 units/min ('Charentais') and 80.64 +/- 2.01 units/min ('Amarillo'), relative to POD. Optimum pH for PPO was 7.0 for 'Charentais' and 7.5 for 'Amarillo, whereas it was 4.5 for both cultivars relative to POD. Melon PPO had maximum activity at 60 degrees C in both 'Charentais' and 'Amarillo' cultivars, whereas POD maximum activity was found at 45 degrees C in 'Charentais' and at 25 degrees C in 'Amarillo'. POD from both cultivars showed higher thermolability compared with PPO, losing >90% of relative activity after only 5 min of incubation at 70 degrees C. POD's activation energy was much higher than that of PPO (Delta E (#) = 86.3 and 160.6 kJ mol (-1) for 'Charentais' and 'Amarillo', respectively). PPO and POD activities from both cultivars showed a decreasing pattern as sugar concentration in the assay medium increased, except in POD extract from 'Charentais', which maintained its activity in the presence of high d-glucose concentration (up to 5 M). Changes in L*, a*, b*, chroma, and hue angle values were chosen to describe the browning development in the samples during storage at 5 degrees C. A slight decrease in L* value and a more marked reduction of a* value were noted in both cultivars above all at the end of storage period. POD activity during storage at 5 degrees C was highly correlated with changes of parameters a*, b*, chroma, and hue angle ( r (2) from 0.82 to 0.97) for cultivar 'Charentais'. According to these results, only POD activity seemed to be involved in browning of minimally processed melon.

Kinetic characterisation and thermal inactivation study of red alga (Mastocarpus stellatus) peroxidase

“…In the case of M. stellatus seaweed POD, the value obtained for E a (121.6 kJ/mol) was about half that obtained for grape POD (271.9 kJ/mol; Fortea et al, 2009), four times lower than those obtained for potato (478 kJ/mol) or carrot (480 kJ/mol) PODs (Anthon & Barrett, 2002), but was similar to that obtained for ''Amarillo'' melon (160 kJ/mol; Chisari et al, 2008), ''Charantais'' melon (86 kJ/mol; Chisari et al, 2008), pepper PODs (151 kJ/mol; Serrano-Martínez et al, 2008), ''Elsanta'' and ''Madame Moutot'' strawberry PODs (96 and 74 kJ/mol, respectively; Chisari et al, 2007). The range of temperatures required for the inactivation of M. stellatus seaweed POD was 30-50°C, similar to that required for pepper POD (30-60°C; Serrano-Martínez et al, 2008), but lower than that required for Crimson Seedless grape (60-80°C; Fortea et al, 2009), potato (67-85°C) and carrot (70-84°C) (Anthon & Barrett, 2002), strawberry (50-80°C; Chisari et al, 2007), and melon PODs (40-70°C; Chisari et al, 2008). These results indicated that M. stellatus seaweed POD is less thermostable than crimson seedless grape, strawberry, melon, potato and carrot PODs, but similar to pepper POD.…”

Characterisation of polyphenol oxidase and peroxidase and the role in browning of loquat fruit

“…The temperature dependence of k was evaluated using the Arrhenius equation: Figure 3. Other activation parameters, namely, ΔG # (Gibbs free energy for enzyme inactivation), ΔH # (enthalpy change, a measure of the number of non-covalent bonds broken), and ΔS # (entropy change, a measure of net enzyme and solvent disorder), were calculated using the relationships given below as described previously (Forsyth et al 1999 (Chisari et al 2007a), but different from those for strawberries (Chisari et al 2007b).…”

“…Food Sci., 33, 2015(2): 109-117 doi: 10.17221/384/2014 upon any cell-damaging treatment, the enzyme may become exposed to substrates, leading to rapid oxidation of phenols (Chazarra et al 2001). There have been numerous studies on PPO from various sources, such as olives (Ünal et al 2011), bananas (Ünal 2007), melon (Chisari et al 2007a), and strawberries (Chisari et al 2007b). However, there are few studies regarding the role of loquat PPO (Ding et al 1998a;SellesMarchart et al 2006;Şener et al 2011ab), and no specific studies regarding the loquat cv.…”

Thiol-Cyclodextrin: A New Agent For Controlling The Catalytic Activity Of Polyphenol Oxidase From Red Delicious Apple

“…PPO extraction from Red Delicious apple [4,[15][16][17][18] Organic Apples (Red Delicious) were purchased from a green store with the purpose of avoiding the mixture of chemical substances present in conventional grown apples. In order to optimize the extraction process different conditions were assessed involving changes in: Triton X-100 concentration, pH, ionic strength and buffer composition.…”

“…This enzymatic process lowers fruit quality, changing aspect, taste and nutritional characteristics [1].The major enzyme responsible for this damage is polyphenol oxidase (PPO), a metalloprotein with two Cu (II) in its active site, which are essential for its activity. In the presence of oxygen PPO oxidizes o-diphenols to quinones and leads to brown pigments ( Figure 1) [2][3][4][5].…”