food and bioproducts processing 9 0 ( 2 0 1 2 ) 155–164 Contents lists available at ScienceDirect Food and Bioproducts Processing j our nal ho mepage: www.elsevier.com/locate/fbp Modeling of combined far-infrared radiation and air drying of a ring shaped-pineapple with/without shrinkage Kamon Ponkham a , Naret Meeso a,∗ , Somchart Soponronnarit b , Sirithon Siriamornpun c a Research Unit of Drying Technology for Agricultural Products, Faculty of Engineering, Mahasarakham University, Kuntarawichai, Mahasarakham 44150, Thailand b School of Energy, Environment and Materials, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand c Department of Food Technology and Nutrition, Faculty of Technology, Mahasarakham University, Muang, Mahasarakham 44000, Thailand a b s t r a c t A ring shape is commonly used for industrial process of pineapple. Unfortunately, there has been no study on modeling of pineapple rings. Therefore we developed the mathematical model of pineapple rings during combined far-infrared radiation and air convection drying to investigate the evolutions of moisture content and qualities. The drying model based on the solution of Fick’s law was used to estimate moisture diffusion coefficient (D). The D val- ues with and without taking into account shrinkage phenomenon of dried products were compared. The kinetics of dried pineapple qualities such as color, shear force ratio and shrinkage during drying also were studied. Pineapples were pretreated, cut into rings and dried at far-infrared intensities of 1–5 kW/m 2 combined with air temperatures of 40–60 ◦ C and air velocities of 0.5–1.5 m/s. The D values were found to increase with increasing intensity and air tem- perature. The D values with shrinkage consideration were lower than the D values without shrinkage consideration for all drying conditions. The quartic model gave a better fit over the other three polynomial models for describing the color kinetics. The thin layer drying models such as Page, Henderson and Pabis, Logarithmic and Midilli–Kucuk were modified in order to describe shear force ratio (SFR) of dried pineapple. The statistically analyses from this present study indicated that modification of drying models can be used to describe the kinetics of SFR and Midilli–Kucuk’s form gave a better fit over the other form. The quadratic model was better than the linear model to predict shrinkage kinetics for all four dimensions (outer radius, inner radius, thickness and volume) of pineapple rings. Crown Copyright © 2011 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers. All rights reserved. Keywords: Far-infrared drying; Finite hollow cylinder; Diffusion coefficient; Color; Shear force ratio; Shrinkage 1. Introduction Pineapple (Ananas comosus L. Merr.) is an important tropi- cal fruit in terms of production and consumption. It is the third most important tropical fruit after bananas and man- goes in the world (Moyle et al., 2005). Thailand is one of the leading countries in the world producing pineapple with 13.5% of the global output in 2007. Other important producers include Brazil, Philippines, China, India, Costa Rica, Indonesia, Nigeria, Mexico and Kenya (FAOSTAT, 2009). Pineapple has been claimed to have health benefits, being rich in vitamin C and fiber. It can be prepared in many different ways to make ∗ Corresponding author. Tel.: +66 2 470 8663; fax: +66 2 470 8663. E-mail address: n meeso@yahoo.com (N. Meeso). Received 3 September 2010; Received in revised form 3 February 2011; Accepted 9 February 2011 full use of its flavor. Drying is one way to increase the value of pineapples. It might also help to keep the price of pineap- ple on suitable values. Especially in a good production season, successful production gives a surplus over the market demand resulting in a low price of pineapples. There are many ways to dry pineapples. For example, Bala et al. (2003) used a solar tunnel drier but Silveira et al. (1996) used a cabinet dryer and a vacuum shelf dryer. However, one of the increasingly popular methods for drying is infrared radiation. Infrared radiative drying has many advantages over the most common techniques called hot air convective dry- ing. The main advantages of this drying are the reduction 0960-3085/$ – see front matter Crown Copyright © 2011 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers. All rights reserved. doi:10.1016/j.fbp.2011.02.008