Effects of hot-air and hybrid hot air-microwave drying on drying kinetics and textural quality of nectarine slices

• Published in: Heat and mass transfer 2018-04, Vol.54 (4), p.915-927
• Main Authors: Miraei Ashtiani, Seyed-Hassan, Sturm, Barbara, Nasirahmadi, Abozar
• Format: Article
• Language: English
• Subjects: Air drying; Air temperature; Chi-square test; Color; Engineering; Engineering Thermodynamics; Fitness; Heat and Mass Transfer; Industrial Chemistry/Chemical Engineering; Mathematical models; Original; Root-mean-square errors; Shrinkage; Surface roughness; Thermodynamics; Water hardness
• ISSN: 0947-7411; 1432-1181
• DOI: 10.1007/s00231-017-2187-0

Drying and physicochemical characteristics of nectarine slices were investigated using hot-air and hybrid hot air-microwave drying methods under fixed air temperature and air speed (50 °C and 0.5 m/s, respectively). Microwave power levels for the combined hot air-microwave method were 80, 160, 240, and 320 W. Drying kinetics were analyzed and compared using six mathematical models. For both drying methods the model with the best fitness in explaining the drying behavior was the Midilli–Kucuk model. The coefficient of determination ( R 2 ), root mean square error (RMSE) and reduced chi square ( χ 2 ) for this model have been obtained greater than 0.999 and less than 0.006 and 0.0001 for hybrid hot air-microwave drying while those values for hot-air drying were more than 0.999 and less than 0.003 and 0.0001, respectively. Results showed that the hybrid method reduced the drying time considerably and produced products with higher quality. The range of effective moisture diffusivity ( D eff ) of hybrid and hot-air drying was between 8.15 × 10 −8 and 2.83 × 10 −7  m 2 /s and 1.27 × 10 −8  m 2 /s, respectively. The total color difference (ΔE) has also been obtained from 36.68 to 44.27 for hybrid method; however this value for hot-air drying was found 49.64. Although reduced microwave power output led to a lower drying rate, it reduced changes in product parameters i.e. total color change, surface roughness, shrinkage and microstructural change and increased hardness and water uptake.