Osmotic dehydration under low agitation laminar flow condition: Effect on dielectric properties of broccoli stalk slices at 2.45 GHz

Abstract The variation in dielectric constant, ε ′ and the loss factor, ε ″ of broccoli stalk slices after osmotic dehydration process conducted under continuous solution circulation with low agitation laminar flow condition was studied using open‐ended coaxial probe technique at 2.45 GHz. The results showed that both ε ′ and ε ″ were significantly influenced by all the osmotic dehydration operating variables. The relationship of osmotic dehydration operating variables on the dielectric properties of the broccoli stalk slices could be established by second‐order polynomial model, with the coefficient of determination higher than .9. Compared to fresh sample, the ε ′ decreases and ε ″ increases when broccoli stalk is subjected to the osmotic dehydration pretreatment under its optimum conditions of mass transfer exchange process. Higher dissipation factor with shorter penetration depth was obtained after osmotic pretreatment, which could facilitate absorption of energy during microwave drying of broccoli stalk slices. Practical Applications Dielectric properties are key factors to understand the interaction of microwaves with food materials. In recent years, there has been an increasing interest in osmotic dehydration used as pretreatment prior to microwave drying to achieve faster drying time and improves the final product quality. As osmotic dehydration process will cause a change in the dielectric properties of the food material and its ability to absorb microwaves energy, this work investigated the effects of osmotic dehydration on the dielectric properties of broccoli stalk slices at 2.45 GHz. The osmo‐pretreated sample improved the dielectric properties which result in rapid heating and therefore lead to fast drying process. The information provided in this study is helpful in the development of dried broccoli stalk slices using microwave drying.