FREE-SPACE MICROWAVE MEASUREMENT of LOW MOISTURE CONTENT IN POWDERED FOODS

Abstract

A free‐space microwave transmission technique has been developed and tested for rapid inline noninvasive measurement of the moisture content of various types of food powders. the basis of this technique is the relation between the attenuation of X‐band microwave radiation through a sample of the food powder to its moisture content by weight. Since food powders generally lose their utility and desirable properties, such as flowability and resistance to spoilage, at lower levels of moisture content, typically 3–7%, special techniques must be developed in order to accurately characterize the moisture content at these low levels. One such technique is to use frequency averaging to enhance the accuracy of the measurements to avoid multiple reflection effects prevalent in low‐loss low‐moisture attenuation measurements. This technique was implemented in the moisture content estimation. Overall accuracies in moisture content estimation are generally less than 1%, although in some cases, accuracies are in the vicinity of 5%.

Measurement Methods and Extraction Techniques to Obtain the Dielectric Properties of Materials

“…In this framework, researches have been carried out on the analysis of many kinds of materials, and the results are shared. Some researches attempted to determine the effects of ambient conditions, which are created for the preservation of foods and preservation of freshness for a long time in food industry, on the material by the change in the permittivity [14,15]. Successful studies have been conducted to examine the effect of changes in humidity on the freshness of the food [16,17].…”

Prediction of moisture content of alfalfa using density-independent functions of microwave dielectric properties

“…The high temperature (103 • C) and the extensive time (24 h) required for determining the moisture content (mc) of vegetation materials in the standard oven method [1] have excluded it from being used in an on-line process. On the other hand, rapid and non-destructive moisture measurement techniques have only been studied for grains such as wheat, barley, corn, rice and oat [2][3][4][5], followed by food products such as coffee, dry milk, salt and sugar [6,7], but not for commercially important plant materials such as alfalfa, a highly nutritious plant. In North America alone, the annual production of forage and processed products for local and international use, particularly alfalfa cubes and pellets, is worth over $15 billion [8].…”

“…Density-independent functions are one of the techniques used to minimize the density effect, keeping both the frequency and the temperature constant. These methods have been studied for powdered foods [6] and grains [9], for wool-water system [10] and for green tea [11], but none of the work has been directed towards vegetation. Hence, the investigation of the effectiveness of these functions for such materials as alfalfa was the prime objective of this work.…”