18A-16

C.-S. CHEN, Dept. Food Science and Technology, Oregon State Univ., 100 Wiegand Hall, Corvallis, OR 97331-6602 and M. H. Penner, Dept. of Food Science & Technology, Oregon State Univ., 100 Wiegand Hall, Corvallis, OR 97331-6602.

Polygalacturonic acid (PGA) is a functional macromolecular component of many food and beverage systems. The solution behavior of PGA is dependent its chemical composition (degree of polymerization, degree of methylation, etc.) and environment. This behavior is particularly important with respect to the clarity of beverage products. In this study we have systematically analyzed the effect of temperature and salt (NaCl) on the solution behavior of low-methoxy PGA preparations. Our objective was to generate profiles correlating salt and temperature environments with the solubility and turbidity of aqueous low-methoxy PGA solutions/suspensions; thus leading to a better understanding of how these common factors impact the solution behavior of PGA. Commercial PGA and polygalacturonase preparations were used as starting materials for fractionation and analysis and for PGA processing, respectively. Experiments investigated the affect of salt concentrations to 2.5 M, PGA concentrations to 0.2%, and temperatures from 0 to 100^oC. Solubility was determined by colorimetric analyses, reducing sugar and total uronic acids, following centrifugation and turbidity via percent transmittance at 400 nm. Interrelationships between experimental parameters were complex. Precipitates yielding maximum turbidities were favored at salt concentrations in the 0.5 to 1.0 M range and temperatures ³ 60^o C. Mixtures outside these parameters yielded solutions and/or translucent gels. Solution phase polygalacturonic acid was not a consistent predictor of relative turbidity. Polygalacturonase treatments prior to salt-induced precipitation demonstrated a non-linear relationship between degree of polymerization and relative turbidity. These results may be rationalized, in part, in terms of ion shielding. These results will be helpful in predicting the behavior of low-methoxy PGA-containing beverages, particularly with respect to precipitate, cloud, and haze formation. The results also provide useful insight with respect to the use of defined, aqueous, PGA systems for the analysis of pectin depolymerase enzymes.

Session 18A, Carbohydrate: General
2:00 PM - 5:30 PM, Sunday PM Room Hall I-2

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana