Journal of Food Science and Technology

, Volume 56, Issue 11, pp 4911–4924 | Cite as

Effect of ultrasound and chemical pretreatment on drying characteristics and quality attributes of hot air dried pineapple slices

  • Poonam Rani
  • P. P. TripathyEmail author
Original Article


Drying of food materials is a time consuming activity making the process cost and energy intensive and hence, several pretreatments are used to improve the drying rate. The present study aims to study the effect of potassium metabisulphite (KMS solution, 0.25% w/v) and ultrasound (20 and 30 min) pretreatment on hot air drying characteristics and quality of pineapple slices. The results indicated that pretreated samples provided higher drying rate, enhanced moisture diffusivity, brighter color and lower hardness than that of untreated dried sample. It was observed that KMS and ultrasound pretreatment for 20 and 30 min reduced the drying time by 23.8%, 19% and 14.3%, respectively. Further, ten thin layer drying models were applied to the experimental drying data and logarithmic model was best fitted to explain the drying behavior of pretreated and untreated samples. Additionally, the effect of shrinkage on moisture transfer mechanism was also studied. Results highlighted that instantaneous moisture diffusivity was increased during drying while shrinkage was not accounted. However, shrinkage consideration reduced the average moisture diffusivity values by 72–83%. Overall color change (13.95 ± 0.92) and browning index (36.02 ± 2.45) were found to be lowest in ultrasound (30 min) pretreated dried sample, highlighting better color stability. Scanning electron microscopy presented noticeable effects of pretreatment on alterations of microstructure of pineapple slices. It can be interpreted that KMS pretreatment was found to be more effective for improvement of drying characteristics of pineapple slices as compared to ultrasound pretreatment.


Drying Ultrasound Moisture diffusivity Shrinkage Hardness Scanning electron microscopy 

List of symbols

\( {\text{J}}_{\text{o}} ({\text{r}}\upalpha_{\text{n}} ) \)

Bessel function of first kind of the zero order

\( {\text{Y}}_{\text{o}} ({\text{r}}\upalpha_{\text{n}} ) \)

Bessel function of second kind of the zero order


Total color difference


Exposed surface area (m2)


Browning Index


Effective moisture diffusivity (m2/s)


Slope of moisture versus drying time curve


Thickness of slice (m)

Lo*, ao*, bo*

Color parameters corresponding to fresh sample

Ls*, as*, bs*

Color parameters corresponding to dried sample


Moisture content (kg water per kg dry weight)


Equilibrium moisture content (kg water per kg dry weight)


Initial moisture content (kg water per kg dry weight)


Moisture ratio


Experimental dimensionless moisture ratio


Predicted dimensionless moisture ratio


Number of observations


Sample dried without any pretreatment


Drying rate (kg/h.m2)


Coefficient of determination


Inner radius of slice (m)


Outer radius of slice (m)


Solid gain (%)


Time (s)


Ultrasound pretreatment for 20 min


Ultrasound pretreatment for 30 min


Wet basis


Final fruit mass (g)


Initial fruit mass (g)


Water loss (%)


Weight of dry solid (kg)


Final moisture content on wet basis (g water/g)


Initial moisture content on wet basis (g water/g)


Final solid content (g solid/g)


Initial solid content (g solid/g)


Number of constants



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Copyright information

© Association of Food Scientists & Technologists (India) 2019

Authors and Affiliations

  1. 1.Agricultural and Food Engineering DepartmentIndian Institute of Technology KharagpurKharagpurIndia

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