A comparative study of raspberry dehydration by lyophilisation or conventional drying

Dehydration is a food preservation process that allows to increase the availability of products on the market, as well as the introduction of new products. The objective of this work was to perform a comparative study of processes of dehydration of raspberry by freeze-drying (lyophilisation) or conventional drying. Raspberry is a perishable fruit, with about 85% (w/w) water content, and there is a need for preservation processes that generate new products with long term availability. Raw materials were subjected, or not, to blanching pre-treatments. It was analysed the effect of these treatments on physical parameters, such as water activity, colour and moisture content as well in the drying kinetics. It was found that conventional drying allowed to reduce water content to 20.7 to 35.8% while lyophilisation permitted to achieve values from 11.6 to 14%. It was also observed that lyophilisation process correspond to higher colour difference indexes, ranging from 5.30 to 11.8 values.