Studies on the Inductive Methodology for Evaluating the Soluble Solid Content of Watermelon
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Abstract:
Current rapid detection methods based on electrical properties usually use electromagnetic waves or external electrical fields to stimulate food materials. However, the electrical property of fruit juice containing diverse electrolytes, based on transformers, has not been reported. It was suggested that the measurements of the terminal voltage of juices, which acts as the secondary winding (constrained by thin, non-conductive tubing) in alternating magnetic flux, may be a novel method to assess qualitative changes. In the present research, a measurement system based on the principle of electromagnetic induction has been established to simulate the basic structure of the step-down transformer, which is able to assess the electrical properties of watermelons with different soluble solid contents (SSC). All measurements were conducted at a temperature of 22 ℃, and the test conditions were as follows: the applied voltage on the primary coil was 5~20 V; the operating frequency range was 50~400 Hz. The results showed that the values of terminal voltage and λ were maintaining at a stable level as the frequency increased, but the increasing SSC of watermelon triggered a decrease in the terminal voltage or an increase in λvalue. Simultaneously, the values of terminal voltage were observed to increase along with increasing values of excitation voltage. The effects of eight different combinations of operating frequencies (50, 120, 200, and 400 Hz) and excitation voltage levels (10 and 20 V) on the estimation of the soluble solid content was also analyzed, resulting in a significant level (a ≤ 0.01). The highest linear correlation between the terminal voltage and the SSC values was obtained at 50 Hz and 10 V (R2 = 0.969). The validation models for the SSC of 60 samples had a bias of -0.238 Brix%, and those for the SEP had a bias of 0.893 Brix%. These results encourage the industrial application of this technique for the rapid assessment of the quality parameters in liquid food products.
