Citrus pectinesterase

For example, holding raw juice for a short time will allow destabilization of the cloud by citrus pectinesterase. This process is not reversible by mechanical homogenization or other treatment. 

Matsuura, Y. (1987). Limit to the de-esterification of citrus pectin by citrus pectinesterase. Agricultural and Biological Chemistry 51, 1675-1677. 

Macdonald, H.M. Evans, R. Spenser, W.J. 1993. Purification and properties of the major pectinesterases in lemon fruits (Citrus limon). J. Sci. Food Agric. 62 163-168. 

Rouse, A.H. 1953. Distribution of pectinesterase and pectin in component parts of citrus fruits. Food Technol. 7 360-362. 

Rouse, A.H. Atkins, C.D. 1955. Pectinesterase and pectin in commercial orange juice as determined by methods used at the Citrus Experiment Station. Florida Agric. Exper. Station Bull. 570 1-19. 

The specificity of pectinesterase is not so marked with respect to the alcohol moiety of the ester, as it hydrolyzes ethyl esters of D-galacturonans at a rate 6-16% that of de-esterification of the methyl esters.36 Citrus natsudaidai pectinesterase de-esterifies the ethyl esters of pectic acid at a rate l/5th to l/7th of that for the methyl esters the propyl and allyl esters are attacked at l/20th to l/80th of the rate.38 The tomato, citrus, alfalfa, and papaya pectinesterases do not hydrolyze the glycol and glycerol esters of pectin.39... 

In the purification of pectinesterase from the fruits of Citrus nat-sudaidai,61 fractional salting-out with ammonium sulfate was followed by chromatography on a column of DEAE-cellulose and by separation of the active fraction on Sephadex G-100. A preparation (purified solution) having a specific activity 460-fold greater than that of the original extract was obtained. Its homogeneity was checked by disc electrophoresis, and its amino acid content was determined and fundamental, kinetic data were obtained. 

Lineweaver and Ballou49 have proposed a pectinesterase unit ( PE. u. ) for expressing PM activity. One such unit is equivalent to 1/930 PMU under the same experimental conditions or the quantity of enzyme that, at 30° and optimum pH, will catalyze the hydrolysis of pectin at an initial rate of one milliequivalent ester bonds per minute in a standard substrate (0.5% citrus pectin containing 8-11% methoxyl) and 0.15 M sodium chloride. The use of the latter unit is unfortunate since the values obtained for the activity in ordinary plant materials are obtained in the third decimal place and because the experimental conditions are so... 

Versteeg (8) speculated on the function of PE in vivo. He noted the high activity of PE in citrus fruit compared to the amount of available pectin. The fruit contain sufficient activity to deesterify the pectin to low methoxy pectin in 10 min at optimum pH. He suggested that the methyl transferase found by Kauss and Hassid (39) to esterify pectic acid to pectin in mung bean shoots and to be located in a lipid-membrane complex (31) functioned as pectinesterase after the lipid membranes were destroyed and the environment changed. However, no definitive experiments to establish the role of PE in fruits were reported. 

Pectinesterase and limonin D-ring lactonase are the only enzymes known to catalyze reactions that adversely affect the quality of citrus juices. Bruemmer et al. (64) listed other enzymes that have been detected in citrus juices and described some of the reactions that can occur in the juices. None of the reactions appear to noticeably affect the quality of commercial juices. Freshly extracted citrus juices contain esterase (EC 3.1.1.1) (65, 66) and phosphatase (EC 3.1.32) (66, 67) activities. Native substrates in orange juice for peroxidase... 

Manabe, M. Purification and properties of Citrus natsudaidai pectinesterase. Agric. Biol. Chem., 1973, 37, 1487-1491. ... 

Rouse, A. H. Atkins, C. D. Further results from a study on heat inactivation of pectinesterase in citrus juices. Food Technol., 1953, 7, 221-223. 

Citrus juices that are pasteurized at the lower temperatures, 65-66°C, can undergo clarification, i.e., a process of separation that results in a lower layer of liquid and sediment and an upper layer of clear liquid. This process is brought about by the natural enzyme, pectinesterase, that occurs in citrus fruits. Studies have shown that processing of the juice at temperatures of 170-210°F (76.7-99°C) for a fraction of a second to 40 seconds will destroy the pectinesterase activity in citrus juices (7-10). The temperature necessary to stabilize the juice is pH dependent. Juices at higher pH require higher temperatures for stabilization. With the new high-temperature short-time techniques and equipment, stabilization can usually be effected in a fraction of a second. Flash pasteurization can be accomplished in either a plate-type or a tube-type heat exchanger. 

The calcium pectate coagulation phenomenon as a result of pectinesterase action improves the pressing characteristics of ground citrus peel and lowers costs when the peel has to be dried for cattle feed. When the pomace has to be dried for pectin manufacture pectin de-esterification must be prevented since otherwise calcium sensitive pectin is obtained. This is achieved by immediate blanching (8). 

Mixtures of the polygalacturonases or of the pectinesterases were also ineffectual. Only the combined action of at least one of the polygalacturonase fractions with one of the pectinesterase fractions was effective in clarification. Purified endopolygalacturonase alone could decrease the viscosity of a solution of citrus pectin (64% esterification), but it was completely ineffectual when apple pectin was used [90% esterified (iS6)]. 

Okada et at 189) reported an unknown enzyme from Aspergillus niger which was not a polygalacturonase nor a pectinesterase but which was a potent clarifier of citrus juices. This factor had no effect by itself, but it strongly accelerated juice clarification when added with polygalacturonase. In subsequent papers 190, 191) the enzyme was reported purified and found to be a hemicellulase. 

Collet et al. (2005) stated that the study of pectinesterase inactivation behavior is important because pectinesterase is responsible for juice cloud stability loss, is composed of several isoenzymes, and occurs naturally in orange. Freshly squeezed juice of Pera orange (Citrus sinensis) was pasteurized at temperatures of 82.5, 85.0, and 87.5°C. At least five runs with different holding times were performed for each temperature. As the isothermal curves obtained showed deviations from the expected first-order kinetics, the data was statistically treated by applying a nonlinear regression, and the estimated best fit was a three-parameter-multicomponent-flrst-order model. At 82.5°C, the isothermal curves showed a nonzero asymptote of inactivation, indicating that at this temperature the most heat-resistant... 

Pectinesterase has been attached covalently to porous-glass particles by reaction of the native protein with pendant benzoyl acide groups on the carrier. The immobilized enzyme, unlike the native enzyme, displayed a five-fold increase in the apparent for a high-molecular-weight fraction of citrus pectin relative to that for a low-molecular-weight fraction. A striking difference exists in the low-pH profile of immobilized pectinesterase relative to that of the native enzyme interactions between the carrier matrix and the polyelectrolyte substrate were invoked to explain this difference. 

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