Abstract:

Three different drying techniques including natural drying, oven drying and hot-air drying was used to dry
fresh seedless purple grapes to explore drying properties and kinetics model. The effects of three drying methods and its
temperatures on the contents of water and total polyphenols in seedless purple grapes were investigated. The results showed
that the hot-air drying method maintained higher contents of total polyphenols in seedless purple grapes. The Henderson-
Pabis model which could be used to describe the relationship of water content and drying time was well fitted and established
based on the experimental data from three different drying techniques. The effective diffusion coefficients of water with
different drying methods were in the range of 1.411 9 × 10–10–4.297 3 × 10–10 m2/s. This study can accurately predict the
changes of water content and water loss rate during the drying process of seedless grapes, and can provide a theoretical basis
for optimizing the drying process and online detecting the water content of seedless grapes.

Key words: seedless purple grapes, oven drying, hot-air drying, drying characteristics, model