Abstract:Soybean milk is a traditional plant protein beverage in China. Total solids content is an important indicator of soybean milk. However, the usually used total solids content determination methods, i.e., oven drying method, empirical method and refractometry method, had some shortcomings such as long time consuming, low precision or inconvenience. Developing a portable, quick and precise detector for measuring total solids content of soybean milk is helpful to guarantee the quality of soybean milk and soybean products. Therefore, the influence of total solids content over the range of 2.13~6.50g/(100mL) and temperature from 20℃ to 70℃ on the conductivity was investigated firstly. The results indicated that the conductivity was increased with the increase of total solids content and temperature. A binary quadratic model with determination coefficient of 0994 could be used to describe the relationship between conductivity and total solids content and temperature over the investigated ranges. Furthermore, the hardware system of a portable total solids content detector for soybean milk was developed by using the singlechip microcomputer of STC12C5A16S2 as controller, DJS—1 conductivity pole as conductivity sensor, DS18B20 as temperature sensor, and lithium cell as battery. C51 language was used to develop the software of the detector to realize data collection, treatment and display. Another batch of soybean milk samples were prepared to investigate the performance of the detector. The results indicated that when the total solids content was within the range of 2.00~8.00g/(100mL) and the temperature was within the range of 20~70℃, the measurement error of the detector was within the range of -0.52~0.37g/(100mL), the mean absolute error was 0.17g/(100mL), and the response time was less than 5s. Future research will focus on improving the accuracy of the detector.
