Multiple Forms of Pectinmethylesterase from Citrus Peel and Their Effects on Juice Cloud Stability

Abstract

Heparin chromatography of a dialysis supernatant fraction from total salt extractable proteins of Citrus sinensis (L.) Osb. var. Valencia fruit peel (flavedo plus albedo) resolved four peaks of pectinmethylesterase activity (PME 1–4). One of these was thermally tolerant (PME 3). Binding to concanavalin A suggested PME 3 was a glycoprotein. At 30°C and 5 U ‐ mL1 PME 1, 2 and 3 destabilized the cloud of pasteurized FCOJ within 10 days. PME 1 caused the most rapid cloud loss (3d), followed by PME 3 and PME 2. PME 4 had no effect on juice cloud during this time period. At 4°C PME 3 caused the most rapid cloud loss (3d), followed by PME 1 (14d) and PME 2 (>14d). PME 4 had no effect on juice cloud stability after 10 days at 30°C or 14 days at 4°C.

Pectin methylesterase and its proteinaceous inhibitor: a review

“…Section 2.1.3), molar mass, degree of glycosylation, thermostability and/or catalytic properties. 15,16,31,32 For instance, different pH optima, salt dependences (cf. Section 2.3.2), substrate specificities and demethoxylation action patterns (cf.…”

“…148,149 Orange juice, in particular, has been the subject of in-depth research already for decades. 32,[150][151][152][153][154][155] Although cloud or turbidity loss is a rather complex phenomenon of which the mechanism is not yet fully understood, 152 the exact features differing for different plant sources, 156 the role played by PME is clear. By its action, blocks of free carboxylic acids on adjacent pectin molecules are formed, which can be cross-linked by endogenous divalent cations (mostly calcium), leading to precipitation of the pectins.…”

“…In the presence of juice cloud and adequate serum calcium ions, this precipitation entrains and removes the pulp particulates ('co-precipitation'). 32,142,157 Cloud loss is considered a serious quality defect of juices, determining consumer acceptance, not only because of the appearance (i.e., phase separation) but also since sensory properties such as colour, flavour and texture (i.e., mouthfeel), associated with the cloud particles, are reduced. 153,154,157,158 Cloud stabilisation is traditionally accomplished by heating the juice to inactivate PME (cf.…”

“…186 However, thermostable forms occur as well and often cause technological problems (e.g., cloud loss). 32,143,187 Additionally, thermal stability is dependent on environmental factors, such as pH, ionic strength, additives (e.g., sugars and/or polyols), and degree of purity (e.g., PME in real food systems is less vulnerable to thermal inactivation as compared to the purified form). 186,188,189 On the other hand, increasing the temperature also enhances pectin demethoxylation by PME, like other enzymecatalysed reactions, until the point is reached where protein denaturation prevails.…”

Calcium and pH influence on orange juice cloud stability

“…The thermostable isozyme, however, rapidly clarified the juice. Cameron et al 10 isolated four PME isozymes from Valencia orange, three of which were thermolabile. Two of the thermolabile isozymes showed juice clarification.…”