Application of ultrasonic techniques to evaluate the viscoelastic changes in masa /
Knowledge of the viscoelastic properties of masa is important to quantify the effects of formulation on processing, to provide information on textural and organoleptic properties, and to improve product design. As the food industry becomes more automated, conducting rheological tests online becomes...
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| Format: | Thesis eBook |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Summary: | Knowledge of the viscoelastic properties of masa is important to quantify the effects of formulation on processing, to provide information on textural and organoleptic properties, and to improve product design. As the food industry becomes more automated, conducting rheological tests online becomes essential. Ultrasonic sensors can nondestructively provide the same measurements as some fundamental rheological tests. At present though, there is a lack of experimental studies that explore the correlation of ultrasonic measurements to the viscoelastic measurements of masa. Therefore, the goals of this research were to evaluate the influence of particle size distribution and moisture content on masa rheological behavior and to show if results obtained from ultrasonic techniques could be correlated with results obtained from fundamental rheological measurements. Commercial nixtamalized corn flour (NCF) was sieved into three different particle size distributions (PSD). Each NCF fraction was then rehydrated into masa with three different moisture contents: 51%, 54.5%, and 58%. Stress relaxation tests were conducted using a TA.XT2 texture analyzer. Measurements were conducted in triplicate and their averages were computed to give a force-time relationship. Stress as a function of time was calculated. Then the stress relaxation time was predicted. To determine equilibrium stress values, the experimental data were fit using nonlinear regression. Absorption of acoustic power was determined by reflection of a longitudinal wave at three different frequencies (500 kHz, 1 MHz, and 2 MHz). Acoustic power was calculated from the reflected ultrasonic wave. Results indicated that stress relaxation time increased significantly with decreasing PSD from coarse to intermediate. But when PSD decreased from intermediate to fine, stress relaxation time decreased. Equilibrium modulus varied inversely with PSD. Both equilibrium modulus and stress relaxation time decreased as moisture content increased. Acoustic power absorbed by samples versus rheological results indicated a non-linear relationship. However, as the frequency increased the amount of power transmitted became relatively constant. The 2.25 MHz data are analogous to strain values above 2% in that the acoustic behavior is in the non-linear region and should not be considered. |
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| Item Description: | "Major subject: Agricultural Engineering". Vita. |
| Physical Description: | xi, 90 leaves : illustrations ; 28 cm. Also available online. Issued also on microfiche from Lange Micrographics. |
| Bibliography: | Includes bibliographical references (leaves 61-68). |