Wicker

Department of Food Science and Technology, Food Process Research and Development Laboratory, University of Georgia, Athens, GA 30602, USA 

The effect of pH and cation concentration on pectinesterase (PE) activation and permeation on 30 kD MWCO ultrafiltration (UF) membrane was evaluated. In order of increasing effectiveness, PE activity was stimulated by monovalent and divalent cations, poly amines and trivalent cations. A similar trend was observed for permeation on UF membranes. Cation addition and higher pH releases PE from an inactive complex, increases activity, and increases permeation. Higher cation concentration decreases activity and permeation. These results suggest a common mechanism is involved in PE activation and permeation. 

Thermostable pectinesterases (TSPE), operationally defined as activity that survives 5 min at 70°C, contribute most to cloud loss in juices at low temperatures and juice pH (26). The percentage of total activity that is thermostable is highly variable and differs in kinetic properties, (22, 26), ease of solubilization (28, 29), stability to low pH (25) and stability to freeze-thaw cycles (23). Some of the variability in reported total PE and TSPE may be related to limitations of current methods to quantify activity. Any processing treatment or assay condition that increases cell wall breakdown or release PE from a pectin complex would enhance detection of total and TS-PE activity. Commercially, PE is inactivated by pasteurization in a plate heat exchanger or during concentration in the TASTE evaporator. 

Other methods to inactivate or inhibit PE have been identified, but violate standards of identity for 100% citrus juice (1,6), are highly variable (1), and change flavor (2). 

Marsh grapefhiit (MGF) pulp was homogenized in 5 volumes of extraction buffer at 4 C and maintained at pH 8.0 (28). The homogenate was stirred for one hour, centrifuged and the supernatant used as the PE extract. Activity was measured by titration with a Brinkman (Westbury, NY) pH stat titrator at pH 7.5 and 30°C in 25 mL of 1 % high methoxyl pectin (Citrus Colloids Limited, Hereford, UK) with O.IM NaCl. PE units are expressed as the microequivalents of ester hydrolysed per minute. Uronic acid analyses were conducted based on the m-phenyl phenol (4) as modified for microplate reading (30). 

---

Professor James A. Moore for reading the manuscript. Special thanks are also due to Halina and Piotr Starewicz for drawing the structures, and to Kim Chen, Ruth Emery, Janice Smith, and Ann Wicker for typing the manuscript. 

Wicker GW, Williams WA, Guthrie FE. 1979. Exposure of field workers to organophosphoms insecticides Sweet com and peaches. Arch Environ Contam Toxicol 8 175-182. 

ESPIN J c, soLER-RivAS c and WICKERS H J (2000) Characterization of total free radical scavenger capacity of vegetable oils and oil fractions using 2,2-diphenyl-1 -picryUiydrazyl radical, JAgric Food Chem, 48, 648-56. 

Seymour, T.A. Preston, J.F. Wicker, L. Lindsay, J.A. Marshall, M.R. 1991a. Purification and properties of pectinesterases of Marsh white grapefruit pulp. J. Agric. Food Chem. 39 1080-1085. 

Snir, R. Koehler, P.E. Sims, K.A. Wicker, L. 1995. pH and Cations Influence Permeability of Marsh Grapefruit Pectinesterase on Polysulfone Ultrafiltration Membrane. J. Agric. Food Chem. 43 1157-1162. 

Wicker, L. Vassallo, M. Echeverria, E. 1988. Solubilization of cell-wall-bound, thermostable pectinesterase from Valencia oranges. J. Food Sci. 53 1171-1174 and 1180. 

Wicker, L. Leiting, V.A. 1995. Microscale Galacturonic Acid Assay. Anal. Biochem. 157 L14-N. 

Nirode WF, Luis JM, Wicker JF, Wachter NM (2006) Bioorg Med Chem Lett 16 ... 

Farrell, H. M., Jr., Qi, P. X., and Uversky, V. N. (2006b). New views of protein structure Implication for potential new protein structure-function relationships. In "Advances in Biopolymers Molecules, Clusters, Networks and Interactions", (M. L. Fishman, P. X. Qi, and L. Wicker, Eds), pp. 1-18. American Chemical Society, Washington, DC. 

Jallon J-M, Wicker-Thomas C (2003) In Blomquist GJ.Vogt RG (eds) Insect sex pheromone biochemistry and molecular biology. Academic Press... 

Wicker-Thomas C, Henriet C, Dallerac R (1997) Insect Biochem Mol Biol 27 963... 

Solerrivias C, Espin JC and Wickers HJ. 2000. An easy and fast test to compare total free-radical scavenger capacity of foodstuffs. Phytochem Anal 11 330—338. 

Weber CJ, Zabinski S, Koschitzky T, Wicker L, Rajotte R, D Agati V, Peterson L, Norton J, Reemtsma K (1990) Transplantation 49 396... 

Moore, L. D., Rule, M. and Wicker, H., Process for preparing high molecular weight polyesters, US Patent 4 446 303, 1984. 

This two-point measurement technique is used in the system reported by Wicker-sheim and Sun,(27) where a lamp phosphor, tetravalent manganese-activated magnesium fluorogermanate, mentioned above, is used as fluorescent sensor. The excitation... 

---