利用感应方法检测西瓜可溶性固形物的研究

Studies on the Inductive Methodology for Evaluating the Soluble Solid Content of Watermelon

摘要:

本研究模拟了降压变压器的基本结构并利用电磁感应原理探索了具有不同可溶性固形物含量西瓜的电学参数，于室温22 ℃的环境下进行测试，采用频率范围50~400 Hz以及激励电压5~20 V作为初级线圈的激励条件。结果表明：西瓜汁样品的终端电压和λ值随频率的改变而维持在稳定的范围，但随可溶性固形物的含量的增加而降低，激励电压提高则终端电压也呈现提升的趋势。常用极低频50、120、200和400 Hz及激励电压10和20 V下的电学参数与西瓜可溶性固形物含量呈现较显著的线性关系(a≤0.01)，其中相关系数最高为R2=0.969（50 Hz、10 V）。采用该模型对60个验证样本进行预测，其预测标准差(SEP)为0.893 Brix%，偏差(Bias)为-0.238 Brix%。该研究可将液态食品原料作为变压器的次级线圈并通过检测其基于变压器特性的电学参数来量化其可溶性固形物含量，为食品理化指标检测手段提供了新的参考。

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.