43-2 |
The use of ultrasound, rheology, and microscopy as tools for measuring bubbles in an agar gel-microstructural and macrostructural considerations |
K. A. ROSS, Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009, L. J. Pyrak-Nolte, Physics Dept., Purdue Univ., 525 Northwestern Ave., West Lafayette, IN 47907-2036, and O. H. Campanella, Dept. of Agricultural & Biological Engineering, Purdue Univ., 1146 Agricultural & Biological Engineering Bldg., West Lafayette, IN 47907-1146. Formation of bubbles in food systems can be affected by preparation conditions and product characteristics. Mixing is a commonly used preparation step and may affect the size and number of bubbles in the food, which will affect material properties and utility of the food system. Agar gels are simple systems that have laboratory and industrial applications, in essence a model system. Ultrasound and rheology are suitable methods for sizing bubbles as they are sensitive to parameters affected by bubbles. The research objective was to develop a method using ultrasound and rheology to size bubbles in an agar gel and to validate this method using microscopy. Agar gels in 1 and 3% concentrations were prepared. The gels were subjected to different mixing conditions: no mix, slow (400rpm), fast (900rpm). A pulse-echo ultrasound technique was utilized to obtain ultrasound velocity and attenuation. A rheometer to perform rheological tests and differential scanning calorimetry (DSC) to measure thermal transitions were used. Microscopy was also performed. An analysis based on ultrasound attenuation was used to determine the size of bubbles. Values obtained agreed with those obtained from microscopy. A relationship between rheological properties and ultrasound velocity was observed. Mixing speed had an effect on the size of bubbles induced in the system and the rheology of the system. Mixed gels were stronger than the no mix gels even though the no mix gels exhibited negligible bubbles. DSC indicated that gels mixed at different conditions underwent key thermal transitions at different temperatures. Ultrasound measurements may be used to size bubbles and deduce a system's rheology. Ultrasound has potential as an in-line quality control technique. Rheological measurements may be more sensitive to the microstructure of the system versus the macrostructure of the system. This highlights the relationship between preparation conditions, analytical methods, and a food system's utility.
Session 43, Food Engineering: Rheology and texture
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