Enzymes pectin methyl esterase

The chromatogram of the serum from juice with poor cloud stability obtained after mash treatment with the enzyme mixture including the pectin depolymerisation enzyme combination of polygalacturonase and pectin methyl esterase is seen to be lacking the A-peak. High molecular pectin is therefore considered to be a prerequisite for a cloud stable juice. 

Enzymes can be used to specifically modify the pectins. Pectin methyl esterase is already widely used to adjust the gelling properties of commercially available pectins. The acetyl esters also strongly affect the gelation [2,3] and removal is important for the upgrading of sugar beet pectin, extractable from a by-product of the sugar industry. 

This enzyme [EC 3.1.1.11] also known as pectin methyl-esterase, pectin demethoxylase, and pectin meth-oxylase, catalyzes the reaction of pectin with n water to produce pectate and n methanol. 

Schols and Voragen, 2002). Other substrates, such as citrus pectin, may be used in some cases, but overall PGase activities will probably be lower on the esterified pectins, and results from assays using the esterified pectins are more likely to be influenced by non-PGase enzymes, particularly pectin lyase and pectin methyl esterase (see Commentary). 

Each enzyme has one—and some enzymes have more—optimum pH values. For most enzymes this is in the range of 4.5 to 8.0. Examples of pH optima are amylase, 4.8 invertase, 5.0 and pancreatic a-amylase, 6.9. The pH optimum is usually quite narrow, although some enzymes have a broader optimum range for example, pectin methyl-esterase has a range of 6.5 to 8.0. Some enzymes have a pH optimum at very high or very low values, such as pepsin at 1.8 and arginase at 10.0. 

Pectinesterase action was first reported in 1840 by Fremy (56). He noted that the addition of carrot juice to a pectin solution caused formation of a gel. This gel was produced by the enzymatic deesterification of pectin followed by precipitation of the resulting polygalacturonic acid as calcium pectate 20), Various names such as pectin meth-oxylase and pectin methyl esterase have been applied to the enzyme, but pectinesterase is the preferred trivial name (57). 

In strawberry puree, pressurization above 250 MPa generated a poly-phenoloxidase activity loss of 60%, while peroxidase activity decreased in 25% with pressures above 230 MPa. A combination of temperature and pressure reduced the activity of pectin methyl esterase in orange juice by up to 50% (Cano et al., 1997). As shovm by Basak and Ramaswamy (1996), the inactivation of pectin methyl esterase in orange juice depends on pressure level, time of treatment, pH, and soluble solids content. In Satsuma mandarin juice, 300-400 MPa for 10 min was required to partially inactivate the pectin methyl esterase, which was reactivated neither after treatment nor during storage. This demonstrated that the greater the concentration of soluble solids in the medium the lower the inactivation of the enzyme (Ogawa et al., 1990). 

Pectin methyl esterase in juices requires processing times of 10 min combined with pressures of 600 and 1000 MPa and temperatures of 57 and 20°C, respectively. These combinations prevent microbial deterioration, but must be combined with a mild blanching, refrigerated storage and addition of inhibitory enzymes to achieve a stable product with respect to pectin methyl esterase (Cheftel, 1992). Guava puree samples were treated with pressures of 400 and 600 MPa looking for pectinesterase and pol)q)henoloxidase inactivation. The residual activity of the former was greater than 76%, while of the latter was above 63% at the lower pressure. 

Aspartic carbohydrate esterases. CE 8 contains only pectin methyl esterases, which demethylate methyl esters of a-(l- 4)-polygalacturonan. Two X-ray crystal structures - from the bacterial plant pathogen Erwinia chry-santhemi and from carrot (Daucus carota), have been solved.The enzyme... 

The structure of the carrot CE 8 pectin methyl esterase was very similar to the bacterial enzyme, although for reasons which are not clear a mechanism involving one of the aspartates as a nucleophile, rather than a general base, was preferred to the aspartate protease mechanism. Such mechanisms have been previously proposed for the aspartic proteinases, but were thoroughly disproved when one of this class of enzymes, the HIV proteinase, was found to... 

Giner-Segui et al. (2006) studied the evolution of polygalacturonase (PG) (EC 3.2.1.15) activity in aqueous solution of commercial enzyme preparation. Up to 76.5% reduction of the PG activity could be achieved at 38 kV cm and 1100 J,s EF intensity and treatment time, respectively. However, an enhancement of PG activity at soft PEF treatment conditions (up to 110.9% at = 15kV cm and 300 J,s) was observed. A maximum of 80% of pectin methyl esterase activity in orange juice was inactivated at 35 kV cm and 1500 J,s EF strength and treatment time, respectively (Elez-Martinez et al., 2007). 

All other polymers are synthesised inside the cell and transported in lipid vesicles that fuse with the plasma membrane and release their contents into the extracellular space. It is likely that this process occurs alongside cellulose deposition, and hence wall assembly is likely to be influenced by the interaction between cellulose and non-cellulosic polymers. After initial deposition, cell walls can be further modified both by integration of further secreted polymers and by the action of modifying enzymes such as pectin methyl esterase, xyloglucan endo-transglycosylase and peroxidase. 

Other enzyme studies (employing species of Pythium) have shown that Terrazole decreases the activity of exocellulase, increases that of endocellu-lase, and is substantially without effect on that of polygalacturonase and pectin methyl esterase.484 It partially inhibits the incorporation of uridine diphosphateacetylglucosamine into chitin in the presence of chitin synthetase, in vitro 485... 

Pectol5 ic activity of pectin lyase, pectin methyl esterase and polygalacturonase enzymes. 

The addition of pectolytic enzymes in crushed grapes can improve juice extraction for certain varieties very rich in pectic substances (Muscat, Sylvaner, etc.). Commercial preparations contain diverse enzymatic activities which are active at a low pH pectin methyl esterases, polygalacturonases, pectin lyases and hemicellulases. At a concentration of 2-4 g/hl, 15% more juice can be obtained during a settling period of 4-10 hours even a shorter settling period (1-2 hours) increases the proportion of free run (Table 11.8). Effectiveness varies according to the nature of the grapes. 

Since the exogenous enzymes used to supplement the spore medium were from sources other than the pathogen> the particular kind of enzyme mixtures that were required to get effective fungal penetration cannot be taken as firm evidence for the Involvement of such enzymes In a natural Infection. For example, the requirement for pectin methylesterase might simply Imply that the exogenous pectlnase used worked more effectively In the presence of this methyl esterase. The nature of the enzymes produced by the pathogen to disrupt the wall barrier can be elucidated only by direct studies on the pathogen Itself. 

Each fruit has specific quantities and ratio of pectin, hemicelluloses and cellulose. These polysaccharides are important concerning enzymes activities required to produce juices and concentrates. Moreover, even if molecular weight and methylation degree of the pectin are specific for each fruit, during the fruit maturation, endogenous pectinases depolymerases and esterase are changing the pectin characteristics This broad variability of raw material makes difficult the standardisation of fruits processing. 

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