Endogenous Polyphenoloxidase Activity Associated with the “Black Ring” Defect in Canned Beet (Beta vulgaris L.) Root Slices

Abstract

Discoloration of canned beet root slices resulted after 5-10 min exposure of beet roots to live steam, and subsequent incubation of slices in air at least 20 min. The "black ring" of discoloration moved radially toward the center of the slice as time of steam-peeling was increased. Dipping slices (prepared after steam-peeling) in solutions of inhibitors of PPO before incubation in air inhibited or prevented discoloration. Based on these data, thermal stability of PPO and POX, heat penetration profiles, and location of the discoloration zone, a model to explain discoloration was developed.

Characterisation of Latent Polyphenol Oxidase in Table Beet: Effect of Sodium Dodecyl Sulphate

“…These results di †er from the ones obtained from crude beet enzyme extracts (Lee and Smith 1979 ;Im et al 1990) who showed that the PPO activity was maximum at pH 7É0, although in our case the PPO was from the beet leaves. However, when the activating e †ect of SDS with respect to pH was studied ( Fig 1A) the highest value in the activation process was obtained at pH 5É5, although the activity of the enzyme was quite high from 5É0 to 7É0.…”

“…In both cases the enzyme obtained was in its latent state and could be activated by acid pH and by SDS, while the PPO found in chloroplast, mitochondrial and soluble fractions of homogenates prepared from sugar beet leaves by Mayer and Friend (1960) was already active, as was the PPO obtained from table beets (Lee and Smith 1979 ;Im et al 1990).…”

“…These colour alterations are due to either formation or degradation of pigmented compounds usually present in the vegetable and are mediated by endogenous enzymatic activities such as polyphenoloxidase. In canned beet root, the slices show a discoloration or "black ringÏ and it has been demonstrated that polyphenoloxidase (PPO) is responsible for mediating this discoloration (Lee and Smith 1979 ;Im et al 1990).…”

Betalain Stability and Degradation—Structural and Chromatic Aspects

“…Degradation of betaxanthins and betacyanins was observed to be completed after 1 h, and the greatest enzyme activity was found to be close to the highest pigment concentration (Shih and Wiley 1981). Im and others (1990) reported polyphenoloxidase and peroxidase activities in the outside margin of red beet roots. Polyphenoloxidase was stable between pH 5 and 8 with a maximum at pH 7, whereas peroxidase exhibited optimum activity at pH 6, retaining its stability from pH 5 to 7.…”

Inactivation of peroxidase and polyphenol oxidase in red beet (Beta vulgaris L.) extract with high pressure carbon dioxide

“…Like many other natural pigments, betalains are very sensitive to heat, light and oxidation, especially that caused by POD which is one of the major causes of discoloration of the pigment (Lashley & Wiley, 1979;Martinez-Parra & Munoz, 2001;Shih & Wiley, 1981;Wasserman & Guilfoy, 1983). Moreover, enzymatic browning induced by PPO in red beet is another frequently encountered problem in the production of red beet juice (Im, Parkin, & von Elbe, 1990;Lee & Smith, 1979). Although POD and PPO can be effectively inactivated by moist heat, the treatment can lead to the destruction of betalains and loss of nutritional components (Herbach, Stintzing, & Carle, 2004).…”