Orange, pectin-methylesterases

However, since pectins can be methylesterified and/or acetylesterified, sections were treated on grid with an orange peel methylesterase to remove the methyl groups or with NaOH to remove both methyl and acetyl groups. After the enzymatic treatment, all the primary walls of most of the samples bind the... 

Castaldo, D., Lovoi, A., Quagliuolo, L., Servillo, L., Balestrieri, C. and Giovane, A. 1991. Orange juices and concentrates stabilization by a proteic inhibitor of pectin methylesterase. J. Food Sci. 56 1632-1634. 

Christensen TMIE, Nielsen JE, Kreiberg JD, Rasmussen P, Mikkelsen JD. Pectin methylesterase from orange fruits characterization and localization by in situ hybridization and immunohistochemistry. Planta 1998 206 493-503. 

When freshly squeezed orange juice is allowed to stand, the suspended pectic compounds ("cloud") separate and settle from the juice. This phenomenon can be prevented by heating the freshly squeezed juice to inactivate the pectin methylesterase, producing a "cooked flavor." Alternatively, additional polygalacturonase can be added to the juice (53). Cloud precipitation is caused by Ca + chelating the pectic acid produced by pectin methylesterase. 

Lacroix, N., Fliss, I., and Makhlouf, J. 2005. Inactivation of pectin methylesterase and stabilization of opalescence in orange juice by dynamic high pressure. Food Res. Int. 38, 569-576. 

Polydera, A.C., Galanou, E., Stoforos, N.G., and Taoukis, P.S. 2004. Inactivation kinetics of pectin methylesterase of Greek Navel orange juice as a function of high hydrostatic pressure and temperature process conditions. J. Food Eng. 62, 291-298. 

Pectin methylesterase (EC 3.1.1.11) causes the flocculation of pectic acid (cf. 2.7.2.2.13) in orange juices and reduces the consistency of tomato products. In orange juice, irreversible enzyme inactivation reaches 90% at a pressure of 600 MPa. Even though the enzyme in tomatoes is more stable, increasing the temperature to 59-60 °C causes inactivation at 400 MPa and at 100 MPa after the removal of Ca + ions. 

Pectolytic enzymes are described in section 4.4.5.2. Pectic acid which is liberated by pectin methylesterases flocculates in the presence of Ca + ions. This reaction is responsible for the undesired cloud flocculation in citrus juices. After thermal inactivation of the enzyme at about 90 °C, this reaction is not observable. However, such treatment brings about deterioration of the aroma of the juice. Investigations of the pectin esterase of orange peel have shown that the enzyme activity is affected by competitive inhibitors oligogalacturonic acid and pectic acid (cf. Fig. 2.51). Thus, the increase in turbidity of citrus juice can be prevented by the addition of such cort5)ounds. 

For bUayer formation in emulsions in a first set of experiment, commercially available pectin samples were used [51 ]. To get a deeper understanding of the impact of molecular structure of the pectin on the functionality of the bilayer-stabilised emulsions, pectin samples with well-defined degree of methoxylation and distribution of these groups were produced on the lab scale. Enzymatic demethoxylation was performed in a similar way using either a commercially available fungal pectin methyl esterase or plant-derived pectin methylesterase, which was isolated from orange peel as described in Stoll et al. [52]. Commercially available high... 

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