30D-11 |
Measurement of solid fat content of chocolate and model systems by ultrasonic reflectance |
R. SAGGIN, Food Science, Penn State University, 103 Borland Lab, University Park, PA 16802 and J. N. Coupland. Tempering is a programmed temperature-time process designed to crystallize chocolate in the correct habit. The key goal is to achieve 2-4% solid fat content (SFC) in the tempering machine at a temperature where only Type V cocoa butter crystals can survive. When this mixture is cooled the pre-existing crystals will act as nuclei for the rest of the solidifying fat. An on-line sensor capable of measuring the SFC in the melt would allow automated control of the tempering process. The goal of this research is to use the ultrasonic reflection coefficient to measure the SFC of various samples and apply it as a temper meter in chocolate manufacture. Confectionery coating fat (5-15 wt%) or cocoa butter (26-36 wt%) was dispersed in corn oil and tempered according to standard protocols. The SFC was measured by NMR, and the ultrasonic reflectance was measured as the proportion of an ultrasonic (2.25 MHz) pulse returning from the interface between the sample and a Plexiglas delay line in contact with it. In the second part of the study, dark chocolate was tempered in a batch kettle and the ultrasonic reflection coefficient was measured on-line throughout the process. The reflection coefficient decreased linearly (r2=0.98) with increasing SFC and could be used to estimate the solids content to within approximately ± 0.2%. When the sensor was applied to tempering chocolate, the reflectance signal decreased with temperature during cooling and remained constant during the subsequent isothermal (29°C) phase until crystallization was initiated, at which point the signal began to decrease once more. The ultrasonic signal was used to select the optimum time for processing and served as the sole criterion for manufacturing well-tempered chocolate. Ultrasonic reflectance can be used to measure SFC on-line to good precision and hence provides a suitable sensor for controlling chocolate tempering.
Session 30D, Food Engineering: Physical and chemical properties
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