30E-12 |
Rheological models and properties of catfish oils as affected by extraction and purification process |
S. SATHIVEL1, W. Prinyawiwatkul1, and I. I. Negulescu2. (1) Department of Food Science, Louisiana State University Agricultural Center, Baton Rouge, LA 70803-4200, (2) School of Human Ecology, Louisiana State University Agricultural Center, Baton Rouge, LA 70803-4200 The purification process of fish oils includes degumming, neutralization, bleaching, and deodorization. Impurities (e.g., free fatty acids, protein, moisture, pigments, etc.) are removed from the oils after each processing step. Removal of impurities alters the oil flow behavior. There is no satisfactory model for predicting flow behavior and viscosity changes of fish oils at each purification step. The objectives were to investigate effects of purification steps on rheological properties of catfish oil and to derive a predictive model for describing rheological behavior of catfish oils. Rheological properties of crude and processed (degummed, neutralized, bleached, and deodorized) catfish oils were determined using a rheometer at 25°C. The Herschel-Bulkley, Bingham, Casson and Newtonian models were used to fit to the experimental data. Effects of free fatty acids (FFA), water activity, and minerals (Ca, Fe, Mg) on oil rheological properties were determined. Triplicate experiments were conducted. Yield stress and consistency coefficient of oils decreased after each purification step. The highest shear rate index (0.904) was observed in deodorized oil. Crude oils exhibited the shear-thinning nature. Removal of impurities (e.g., FFA, Ca, Fe, Mg, and water) shifted the flow behavior of oils from non-Newtonian closer to Newtonian. The regression coefficients (R2) for the 4 models were above 0.95 for oils from all processing steps. Both Herschel-Bulkley and Casson models adequately described the flow behavior of all oils. However, the Casson model was selected as it works well at both lower or higher shear rates. Prediction and mathematical representation of flow behaviors of catfish oils from each purification step will be useful for an optimum design of unit operations in the processing plant and for better control of the final oil quality. The knowledge of rheological properties of catfish oils also helps solve problems related to transfer or movement of bulk quantities of the oils.
Session 30E, Food Engineering: Rheology and texture
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