29C-24 |
Effectiveness of relaxation in minimizing errors caused by loading normal force during oscillatory rheological measurement |
M. D. PEARCE, Biosystems & Agricultural Engineering Extension, Oklahoma State Univ., 214 Agricultural Hall, Stillwater, OK 74078-6021 and D. D. Bellmer, Oklahoma Food & Agricultural Products Research & Technology Ctr., Oklahoma State Univ., 108 FAPC, Stillwater, OK 74078-6055. Data variability is a commonly reported problem during measurement of viscoelastic properties of semi-solid foods, and has been linked to inconsistency in normal force application during loading. One common method of correction has been to incorporate a relaxation period before testing, although the effectiveness of relaxation protocols has never been quantified. This research evaluated the effectiveness of relaxation time before testing to reverse or minimize data variability caused by inconsistent normal force application during loading of semi-solid food products. Bologna and cheese samples (4-cm discs) were loaded between the parallel plates of a TA-1000N rheometer to a normal force of 5 N or 20N and either tested immediately or allowed to relax to 1 or 10N before testing. Frequency sweeps were conducted at constant stress (20 Pa) and temperature (25„aC), and the storage and loss moduli (G°¦ and G°¨) were determined. Results confirmed that normal force application during sample loading did affect the oscillatory measurements, and that sample relaxation did not prove to minimize these effects. G°¦ and G°¨ values for all samples loaded to 20N, regardless of relaxation time, were greater than samples loaded to 5N. All samples loaded to 20N showed similar G°¦ curves and no reduction in the error generated by loading normal force. Furthermore, the samples allowed to relax to 1N showed an increase in data variability. Sample relaxation before testing does not minimize the effects of inconsistent normal force during loading for bologna or mozzarella samples. These findings contradict previous suggestions that allowing samples of various products to relax for a set time (normally 15 minutes) will eliminate data variability introduced during loading, highlighting the need to evaluate the errors associated with loading normal force and the potential solutions before adopting them as acceptable protocol.
Session 29C, Food Engineering: Rheology and texture
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