Esterases pectinesterase

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... 

To maintain cloud stability in fruit juices, high-temperature-short-time (HTST) pasteurization is used to deactivate pectolytic enzymes. Pectin is a protective colloid that helps to keep insoluble particles in suspension. Cloudiness is required in commercial products to provide a desirable appearance. The destruction of the high levels of pectin-esterase during the production of tomato juice and puree is of vital importance. The pectinesterase will act quite rapidly once the tomato is broken. In the so-called hot-break method, the tomatoes are broken up at high temperature so that the pectic enzymes are destroyed instantaneously. 

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). 

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. 

---