Figure 5 - uploaded by Sanjeev .......
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Schematic representation of enzymatic and subsequent non-enzymatic condensation processes for browning.
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Context 1
... the case of diphenolase activity ( Fig. 5.), BH 2 is not required because the existing o-diphenols are sufficient for the reaction (Whitaker, 1995). Two molecules of o-diphenol are oxidized to two molecules of o-quinone. Since both atoms of the oxygen molecule are reduced to water, diphenolase activity is referred to as a four-electron transfer oxidase (Mason, 1957). Evidence concerning the appearance of a lag period dependent on pH in the expression of catecholase activity from grape PPO put forward the hysteretic nature of the enzyme (Valero & Garcia-Carmona, 1992;). The lag period was shown to be independent of enzyme concentration but dependent on substrate concentration, suggesting the ionization of a group located outside the active site in a domain of the protein that undergoes a slow pH induced conformational transition during assay and/or perhaps in vivo (Valero & Garcia-Carmona, ...
Context 2
... of SO 2 were determined in the range 6 to 19 µgm -3 and annual average at commercial site (SI) and residential site (SII) is recorded 11 and 9 µgm -3 respectively. The concentration of SO 2 at both sites was reported below in comparison to National Ambient Air Quality Standard 50µgm -3 ( Fig ...
Context 3
... two general reactions, where phenols and oxygen are the substrates and BH 2 stands for an o-diphenolic compound acting as the electron donor are shown in Fig. 5. In the absence of an o-diphenol (BH 2 , there is a characteristic lag or induction period in the monophenolase reaction prior to attaining a steady state rate (Kahn & Pomerantz, 1980;Sanchez-Ferrer et al., 1993). When the ...
