STUDY ON FOOD PROCESS MONITORING BY SOLENOID SENSOR

Abstract

ABSTRACT Electric impedance spectroscopy (EIS) is able to find the material properties of organic materials, such as phase change, ion concentration, water transfer and water content. The relationships between important process properties of foods and their impedance to 1V‐AC input from 100 kHz to 5 MHz were determined experimentally by the use of an EIS system with two noncontact sensors (solenoids winded by ϕ0.5‐mm nichrome wire on polyvinyl chloride tubes; one is 86.3‐mm length, the other is 247‐mm length). The model foods, which were aqueous glucose solution (0–50%) and sucrose solution (0–50%), showed a negative linear function between the concentration and the inductance obtained from the impedance values. However, sodium chloride solution (0–40%) presented a form of an exponential function. For agar gel (2–10%), the relationship between the hardness and the inductance was a positive linear function, which means that the inductance increases with the increase of gel hardness. These relationships were confirmed in yogurt processing. The system can be applied to yogurt processing as a technique for monitoring both fermentation and coagulation. In pudding processing, through this system, it can be found that the change of temperature affected the efficacy of the used system.PRACTICAL APPLICATIONSIn this work, an electric impedance spectroscopy (EIS) system with a noncontact sensor was used to monitor some food processing, for example, to monitor the fermentation and coagulation processing of producing yogurt. The results show that the EIS system with a noncontact sensor has the feasibility to be applied to monitoring food processing or nondestructive testing.