Investigation of Hot Air- and Infrared-Assisted Freeze-Drying of Apple

The dehydration tests were conducted at three drying methods to evaluate the drying curves and the energy uptake. Apple (Malus domesticaL.) cubes were dried under different processing conditions, applying freeze-drying (FD) method, supplemented by hot air (HA) and infrared radiation drying (IR) techniques. The IR heating method produced a higher drying rate than HA drying during the pre-dehydration. The water activity, color, firmness and rehydration ratio (RR) of finished products were measured. The dried material produced with IR-FD resulted the desirable color, moreover higher RR and lower firmness than the other samples dried by HA-FD ones. The quality of single-stage FD samples was close to fresh apple and IR-FD materials. It was observed that the IR-FD method produced a considerable decrease in the energy consumption, compared with FD and HA-FD drying treatments. The thin-layer models were applied, which were used to describe the drying kinetics of food materials. It was found that the applied mathematical models were suited to the requirements in predicting the changes of moisture ratio. Practical ApplicationsApple (Malus domesticaL.) is one of the most widely grown fruit crops in the world. Available in fresh and processed forms, apples are rich source of vitamins, organic acids, polyphenols, anthocyanin and minerals. Currently, dehydration is a frequent practice as apples are components of numerous processed food products, such as snack, integral breakfast foods, etc. Freeze-, hot air- and infrared (IR) drying have been industrially applied in the drying of foodstuffs, and pharmaceutical products. The aim of this article is to examine the effectiveness of freeze-drying (FD) enhanced with two-stage hot air- and IR-FD. The application of the IR-FD produces a fast drying rate and higher drying quality. Our research work confirmed that IR-FD is a good alternative instead of the FD. The development of new drying possibility for apple with good physical and chemical properties may be of interest in the market supply (food supplement, functional food, etc.).