Influence of High-Pressure Blanching on Polyphenoloxidase Activity of Peach Fruits and its Drying Behavior

Application of novel pretreatment technologies for intensification of drying performance and quality attributes of food commodities: a review

Drying is an energy-intensive process that can be reduced by the application of pretreatment prior to drying to enhance mass transfer and minimize energy consumption. This review summarizes the mechanistic aspects and applications of emerging pretreatment approaches, namely ohmic heating (OH), ultrasound (US), high pressure processing (HPP), and pulsed electric field (PEF), with emphasis on the enhancement of mass transfer and quality attributes of foods. Novel pretreatments significantly improved the drying efficiency by increasing mass transfer, cavitation, and microchannel formation within the cell structure. Various processing parameters have great influence on the drying performance and quality attributes of foods. Several studies have shown that novel pretreatments (individual and combined) can significantly save energy while improving the overall drying performance and retaining the quality attributes. This work would be useful for understanding the mechanisms of novel pretreatment technologies and their applications for future commercial research and development activities.

Evaluation of Mass Transfer Properties in Convective Drying of Kiwi and Eggplant

The present work aimed at studying the mass transfer properties of two plant foods, kiwi (a fruit) and eggplant (a vegetable). For this convective drying experiments were conducted at different temperatures (from 50 to 80 ºC) and an air flow rate of 0.5 m/s, using slices with 6 mm thickness for both products. For the mathematical modelling two different methods were used, one based on the thin layer model and the other based on the Fick’s second law of diffusion. The results obtained allowed concluding that different methodologies allowed to obtain different values of the mass transfer properties, so care must be taken when choosing an appropriate calculation method. Regarding the values of diffusivity and mass transfer coefficient, in all cases they were found to increase with increasing operating temperature. Both the activation energy and the activation energy for convective mass transfer were similar for kiwi and for eggplant, indicating that both foods behave in a very similar way when exposed to the drying conditions tested.

Drying Kinetics and Quality Attributes of Peach Cylinders as Affected by Osmotic Pretreatments and Infrared Radiation Drying

The effect of osmotic dehydration (OD) and ultrasound-assisted osmotic dehydration (ULOD) on drying kinetics and quality of peach cylinders by infrared radiation drying were investigated. The moisture state and redistribution after osmotic pretreatments and subsequent drying process were also studied by low field nuclear magnetic resonance. The water loss and solute gain increased with osmotic time, and ULOD could promote water transfer. The signal amplitude of free water and immobile water diminished and shifted to the left for samples pretreated by both ULOD and OD. The brightness in T2-weighted images appeared a declining trend with increasing osmotic time of ULOD and OD, indicating the moisture content reduced gradually. During dying process, the free water of all samples was removed completely after drying for 120 min. ULOD and OD could increase water activity and decrease shrinkage of samples. Long pretreatment of ULOD and OD improved the color of dried peach cylinders.

Influence of Citric Acid Pretreatment on Drying of Peach Slices

The effect of citric acid pretreatment on the drying characteristics of peach slices was investigated in a cabinet dryer. The experiments were conducted on peach slices with a thickness of 5 mm at temperatures of 45, 55, 65 and 75°C with an air velocity of 2.0 m/s. The drying time of peach slices pretreated with citric acid solution was shorter than the control ones. The drying data were fitted to five thin-layer drying models. The results show that the Midilli et al. model was the most appropriate model for drying of peach slices. The values of effective moisture diffusivity were found to range between 1.94 × 10−10 and 8.49 × 10−10 m2/s over the temperature range studied. The values of activation energy were calculated as 36.82 and 37.12 kJ/mol for control and pretreated samples, respectively. Superior rehydration was noticed for citric acid pretreated slices dried at 65°C.