Effect of microwave-vacuum, ultrasonication, and freezing on mass transfer kinetics and diffusivity during osmotic dehydration of cranberries

ABSTRACT

The objectives of this study were (i) to evaluate moisture loss (ML), solids gain (SG), moisture loss rate (d(ML)/dt), solids gain rate (d(SG)/dt), effective moisture diffusivity (D_eM), and effective solids diffusivity (D_eS) during osmotic dehydration (OD), ultrasound-assisted osmotic dehydration (UA-OD), and osmotic dehydration of whole cranberries, preceded by microwave-vacuum pretreatment (MV + OD) or freezing/thawing treatment (F + OD ) and (ii) to use a mathematical model to predict moisture content ML_∞ and solids content SG_∞ in equilibrium state and the distribution of moisture and sucrose in whole cranberries during dehydration. Microwave-vacuum and OD treatments produced cranberries with the highest values of ML and SG (39.7 and 8.4 g 100 g fresh fruit⁻¹, respectively), d(ML)/dt and d(SG)/dt (76.9 and 8.5 h⁻¹, respectively), D_eM and D_eS (6.1 and 3.7 × 10⁻¹⁰ m² s⁻¹, respectively). Azuara’s and Peleg’s models adequately described the OD kinetics of whole cranberries in terms of ML and SG. The results indicate that the equilibrium values of ML_∞ and SG_∞ were not reached under the conditions specified in the present study.

KEYWORDS:

• Freezing
• mathematical modeling
• microwave-vacuum pretreatment
• osmotic dehydration
• ultrasound

Additional information

Funding

The authors would like to thank the National Science Center in Poland for funding project No. 2015/17/B/NZ9/03601 entitled: “The effect of unconventional pretreatment methods on the kinetic of hybrid dehydration and physical and chemical properties of cranberries (Vaccinum macrocarpon)”. This study was also partially financed by the University of Warmia and Mazury in Olsztyn. The authors are also grateful to Waldemar Brandt of the University of Warmia and Mazury in Olsztyn for technical support and providing microstructural images of cranberries for the needs of this study.