Biosystems Engineering (2006) 95 (1), 43–49 doi:10.1016/j.biosystemseng.2006.05.001 PH—Postharvest Technology Thin-layer Drying Kinetics of Raw Mango Slices R.K. Goyal 1 ; A.R.P. Kingsly 2 ; M.R. Manikantan 1 ; S.M. Ilyas 1 1 Central Institute of Post Harvest Engineering and Technology, P.O. : PAU campus, Ludhiana 141004, India; e-mail of corresponding author: rkgoyal63@yahoo.co.in 2 Central Institute of Post Harvest Engineering and Technology, Malout-Hanumangarh Byepass, Abohar 152116, Punjab, India; e-mail: arpkingsly@rediffmail.com (Received 12 September 2005; accepted in revised form 2 May 2006; published online 12 July 2006) Thin-layer drying behaviour of raw mango slices was studied in a laboratory model tunnel dryer. The samples were dried at 55, 60 and 65 1C air temperature with control, blanching and blanching in 1% potassium metabisulphide (KMS) solution as pre-treatments. Six thin-layer drying models (Newton, Page, Modified Page, Henderson and Pabis, logarithmic and Wang & Singh) were fitted to the moisture ratio data. Among the drying models investigated, the Page model satisfactorily described the drying behaviour of raw mango slices. The effective moisture diffusivity varied from 262  10 10 to 439  10 10 m 2 s 1 . r 2006 IAgrE. All rights reserved Published by Elsevier Ltd 1. Introduction Drying of fruits and vegetables is one of the oldest methods of preservation. Drying prevents occurrence of undesirable changes due to microbial activity. Although preservation is the primary reason for drying, it also lowers the product mass and volume. The reduction in mass and volume improves the efficiency of packaging, storing and transportation. Mango (Mangifera indica L.) is a good source of carbohydrates, vitamin C and a very rich source of pro- vitamin A (Bhatnagar & Subramanyam, 1973). In India, raw mango has been dried historically to produce ‘amchur’, a dried powder for use in culinary prepara- tion. Commercially, amchur is used for the manufacture of pickles, chutneys and sauces (Kesarwani et al., 2000). It is used to give a slightly sour and tangy taste to dishes. Usually the dropped immature mangoes are dried in direct sunlight for preparation of amchur. Sun drying takes 16–18 h for complete drying (Teaotia & Pruthi, 1987). During drying, exposure to the open environment for a long time may cause contamination and spoilage of the product (Vagenas & Marinos-Kouris, 1991). Industrial dryers enable a uniform, hygienic dried product to be produced in within a shorter timescale (Abdelhaq & Labuza, 1987; Karathanos & Belessiotis, 1997; Doymaz & Pala, 2002). The drying rate can also be enhanced by pre-treatments like blanching and sulphitation (Dabhade & Khedkar, 1980; Doymaz, 2004). Also, pre-treatments prevent fruits from darken- ing. Dehydration of raw mango slices after sulphitation in potassium metabisulphide solution (KMS) (1–4%, w/ w) has helped in better retention of sulphur dioxide during storage (Mehta & Tomar, 1982). The drying kinetics of food is a complex phenomenon and requires simple representations to predict the drying behaviour, and for optimising the drying parameters. Recently, studies have been done on drying kinetics of fruits and vegetables (Sabarez & Price, 1999; Togrul & Pehlivan, 2002; Soysal, 2004; Doymaz, 2004; Cao et al., 2004; Jain & Pathare, 2004). However, no detailed studies were found in literature on drying kinetics of raw mango. The objectives of this study were: (a) to study the effect of temperature and pre-treatments on drying behaviour of raw mango; and (b) to evaluate a suitable thin-layer drying model. 2. Materials and methods 2.1. Experimental material Raw mango (cv: Dasehari) used for the drying experiments were purchased from local market, Ludhi- ARTICLE IN PRESS 1537-5110/$32.00 43 r 2006 IAgrE. All rights reserved Published by Elsevier Ltd