High methyl pectins

However the addition of exogeneous pectic substrate increased the incorporation of radioactivity up to twelve-fold. At neutral pH, the stimulation was larger in the presence of highly methylated pectin than in the presence of polygalacturonic acid. At pH 5.5, on the other... 

The main part (80%) of pectins were in the edible apple zones but no change in galacturonic acid concentration was observed between the different tissue zones. So, carpels and epidermis zones are potentiel sources of highly methylated pectins. 

In mild alkaline conditions, highly methylated pectin was demethylated following a (pseudo)-first order kinetics with respect to the concentration of methoxylated galacturonate moieties. Investigation in this pH range, where the initial concentration of methylesters was higher than the initial concentration of OH ions, was complicated by the necessity to use a buffer. This led to deviations from the theoretical behavior as the concentration of OH ions still varied in proportions which could not be neglected in the equations of the kinetics. However these deviations could be accounted for be the pH variation, and the pH variation itself predicted from the amount of liberated methanol. The constant we found was similar to previously reported data (Scamparini Bobbio, 1982). 

Cmde microsomes I High-methylated pectins Low-methylated pectins... 

A third group of hydrolytic enzymes specific for highly methylated pectins (polymethylgalacturonase, EC 3.2.1.41) has been described particularly in the older literature prior to the discovery of the pectin lyase by Albersheim et al. (21). We have never been able to find either exo-PL nor endo- and exo-PMG in our extensive screening of commercial preparations and micro-organisms. Many authors now agree that enzymes described as endo-or exo-PMG may very well have been a combined PE-PG activity, or a PL activity or even PG activity alone in cases where only initial velocities were measured. Extensive reviews of pectic enzymes have been published (22-26). 

PME activity is almost not affected in the usual pressure range up to 600 MPa [7]. In the intact cell, PME is bound to the cell wall, upon HP-application PME is liberated and gets into contact with its substrate the highly methylated pectin. This causes a de-esterification not only during the HP-application, but a continuous further deesterification can be observed after release of the pressure [8]. Therefore, the tissue hardening and poor cooking behaviour is even more pronounced after a storage of 3 - 4 days (fig. 5, 6). 

The pectinic acids can be subdivided into two types LM-pectins (low methyl pectins) are those that contain less than 50% methyl esters, and HM-pectins (high methyl pectins) are those that contain greater than 50% methyl esters. 

A pectinolytic bacterium isolated from a mixed microbial population by means of a chemostat enrichment procedure was identified as Erwinia carotoyora, It grew only on highly methylated pectin and produced a pectin lysase which released unsaturated monomer and dimer from 71% esterified citrus pectin. The pectin lyase was inducible only by pectins having a high methyl ester content. 

Pectins are divided into two categories (1) pectinic acids which are poly-galacturonic acids that are partly esterified with methanol, and (2) pectic acids which are polygalacturonic acids with no or only a negligible amount of methyl ester. The pectinic acids can be subdivided into two types LM-pectins (low methyl pectins) are those that contain less than 50% methyl esters, and HM-pectins (high methyl pectins) are those that contain greater than 50% methyl esters. 

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