An alternative method for the industrial monitoring of osmotic solution during dehydration of fruit and vegetables: A test-case for tomatoes

In this paper, an alternative procedure for in situ and continuous monitoring of the status of the hypertonic solutions used in industrial osmotic dehydration (OD) process of fruit and vegetables is presented and validated. The proposed method, which is based on microwave reflectometry technique, circumvents the limitation of traditional control methods, since it discovers the relation between the characteristic parameters of osmotic solutions and the corresponding measured reflection coefficients. In fact, as the OD proceeds, the dielectric characteristics of the solution, associated to the reflectometry measurements, can be directly related to the variation of the water activity (a_w), which is the parameter that is typically considered to assess the dewatering capacity of the solution. As a result, through the method presented herein, a continuous monitoring of the dewatering capacity of the osmotic solution, associated to its qualitative status, is possible, which, in turn, is useful also for optimizing the OD industrial process. The proposed method was preliminarily validated on reference aqueous solutions of sucrose. Successively, the method was tested also in a typical industrial application, involving the OD process of tomatoes.