Characterization of Vegetable Surface during Drying Using Fractal Analysis Technique Chanthima Phungamngoen, Naphaporn Chiewchan  and Sakamon Devahastin Department of Food Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, 126 Pracha u-tid Road, Tungkru, Bangkok 10140, Thailand Abstract. Combined fractal and image analysis technique was used to quantify the changes of vegetable surface characteristics during drying. Cabbage leaves were used as a test material and were allowed to undergo hot air drying, vacuum drying or low-pressure superheated steam drying (LPSSD) at 60 C. Images of cabbage samples at time intervals during drying were obtained using a scanning electron microscope. An original image was transformed from gray scale to a black and white format. The fractal dimension (FD) of a black and white image was calculated using the box counting method. The changes of surface characteristics were quantified in terms of FD/FD 0 . By comparing among the samples having similar moisture content, samples dried by hot air drying and vacuum drying exhibited more shrinkage (wrinkle) than those dried by LPSSD. The evolution of FD/FD 0 was found to relate well with % volumetric shrinkage of cabbage during drying. Keywords: cabbage, fractal dimension, low-pressure superheated steam drying, vacuum drying 1. Introduction Image analysis has been suggested to be one of the most promising techniques for the evaluation of the microstructural and textural changes of fresh foods and foods being processed [1], [2]. Among several image based analysis techniques, fractal analysis has caught attention of many researchers as it has proved to be adequately capable of characterizing the degree of irregularity of food microstructures or food surfaces [3], [4]. For example, Sansiribhan et al. [5] used the normalized change of fractal dimension to describe the changes of carrot cubes and intercellular spaces of carrot tissues during drying by using different methods, i.e., hot air drying, vacuum drying and low-pressure superheated steam drying (LPSSD). In this study, an image analysis technique was developed and used to characterize the vegetable surface topographical feature during drying. It is important to note that leafy vegetable exhibit non-uniform surfaces and are structured with interconnected networks of veinlets or additional crinkle (or wrinkle) characteristics, making the characterization and, in particular, quantification, of the changes rather difficult. In this study, attempt was made to quantify the changes of the surface topographical features of vegetables as affected by drying methods (i.e., hot air drying, vacuum drying and low-pressure superheated steam drying (LPSSD)) at 60 ºC. Cabbage leaves were selected to represent the non-uniformity of the naturally topographical features of vegetables. 2. Materials and methods 2.1. Sample Preparation White cabbages (Brassica oleracea var. capitata) were obtained from a local market (Pracha u-tid 61 Market, Bangkok, Thailand). Two to three outer leaves were removed; the remaining edible leaves of  Corresponding author. Tel.: +662 470 9243; fax: +662 470 9240. E-mail address: naphaporn.rat@kmutt.ac.th 2014 3 rd International Conference on Nutrition and Food Sciences IPCBEE vol. 71 (2014) © (2014) IACSIT Press, Singapore DOI: 10.7763/IPCBEE. 2014. V71. 8 34