Control of polyphenol oxidase in whole potatoes by low temperature blanching

Abstract

Russet Burbank potatoes can be blanched up to 60 min at 50°C without any loss in firmness and without appearance of browning on their peels, eyes or infected areas. Low temperature blanching (LTB) for 45 min did not cause a significant reduction in crude polyphenol oxidase (PPO) activity (12%). However, when heating time was extended to 60 min, the activity and specific activity of the enzyme were reduced by 27-45% and 22-43% respectively. The remaining enzyme extracted from heated potatoes was partially purified 3.3-3.75-fold by 0-95% ammonium sulphate precipitation and dialysis, and its kinetic parameters were determined. The comparison of the kinetic parameters of PPO in control (K m =10.3 mM and V max /K m =0.15) and in 60 min heated potatoes (K m =13 mM and V max /K m =0.054) indicated the reduced affinity of the remaining enzyme to its substrate. Thus, LTB at 50°C for 60 min not only inactivated part of the PPO activity but also reduced the kinetic capacity of remaining enzyme. Extending heating time to 75 min caused the appearance of slight browning on the peels and eyes of potatoes and reduced their firmness. The observed browning was due to the sharp drop in the K m that caused the activation of the PPO. Heating at 50°C did not affect lipoxygenase activity, but the K m of the enzyme dropped from 0.4 to 0.15 mM and the enzyme became kinetically more reactive at low substrate concentrations. Covalently bound pectin methylesterase considerably activated (38%) by heating and this caused the drop of pH in potato tissues.

Physiological and biochemical responses of grapefruit seed extract dip on ‘Redglobe’ grape

“…Determination of PPO activity and total phenolics content PPO (EC.1.10.3.1) activity was determined by measuring the increase in absorbance at 412 nm for catechol. This method has been reported to determine PPO activity in various kinds of horticulture products (Rocha & Morais, 2001;Yemenicioglu, 2002). The reaction mixture contained 2.9 ml substrate solution and 0.1 ml enzyme.…”

Effects of aqueous chlorine dioxide treatment on polyphenol oxidases from Golden Delicious apple

“…This method has been reported to determine PPO activity in apples (Podsedek, Wilska-Jeszka, Anders, & Markowski, 2000;Rocha & Morais, 2001) and other products (Arslan, Erzengin, Sinan, & Ozensoy, 2004;Pilar Cano, Begona de Ancos, & Gloria Lobo Mariana Santos, 1997;Yemenicioglu, 2002). The reaction mixture contained 2.8 ml substrate solution and 0.2 ml enzyme.…”

“…In recent years, some new techniques (low temperature blanching, gamma irradiation, and high-pressure treatment) and anti-browning agents (dipeptides and 2,3-diaminopropionic) have also been reported for the control of PPO activities (Arslan & Dogan, 2005;Gautam, Sharma, & Thomas, 1998;Girelli et al, 2004;Sun et al, 2002;Yemenicioglu, 2002).…”

Pectin Methylesterases: A Review

“…The free carboxyl groups produced then were cross-linked with divalent ions in the medium or CaCl 2 added to form a stable network. Firming by this method is suitable to apply for whole or sliced potatoes to be processed to French fries [76].…”