Classification of longan fruit bruising using visible spectroscopy T. Pholpho a , S. Pathaveerat b , P. Sirisomboon c,⇑ a Post graduate Education and Research Development Project in Post-harvest Technology/Post-harvest Technology Innovation Center, Kasetsart University, Kamphaengsaen Campus, Nakohnpathom, Thailand b Department of Agricultural Engineering, Faculty of Engineering, Kasetsart University, Kamphaengsaen, Nakohnpathom, Thailand c Agricultural Engineering Curriculum, School of Mechanical Engineering, Faculty of Engineering, King Mongkut’s Institute of Technology, Ladkrabang, Bangkok 10520, Thailand article info Article history: Received 27 August 2010 Received in revised form 8 December 2010 Accepted 12 December 2010 Available online 16 December 2010 Keywords: Longan Visible range Spectroscopy Bruise Principal Component Analysis (PCA) Partial Least Square Discriminant Analysis (PLS-DA) Soft Independent Modeling of Class Analogy (SIMCA) abstract This research showed the potential of using visible spectroscopy for classification of non-bruised and bruised longan fruits. The visible spectra of bruised and non-bruised longan fruits were acquired from 400 to 700 nm with 10 nm resolution by the spectrophotometer. The principal component analysis (PCA), Partial Least Square Discriminant Analysis (PLS-DA) and Soft Independent Modeling of Class Anal- ogy (SIMCA) were used to develop classification models. The Partial Least Square Discriminant Analogy (PLS-DA) showed better classification accuracy than SIMCA with 100% correctness. The result was found to be helpful for the application in the industry for on-line and portable application. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Longan fruit (Dimocarpus longan Lour.) is native to south-east Asia, spanning from India to southern China. It is an economically important fruit for Thailand. In the year 2009, Thailand exported fresh, dry and frozen longan to the amount of 409,976 tons with a va- lue of 200 million USD (Office of Agricultural Economics, Ministry of Agriculture and Co-Operatives, 2009). Longan contains a number of important vitamins and minerals, including iron, magnesium, phosphorus and potassium, and large amounts of vitamins A and C. The most popular variety of the fruit is the Edo type. Mature Edo longan fruit is approximately 1.5–2 cm diameter, conical, heart- shaped or spherical in shape and light brown in color (Jiang et al., 2002). Bruising is the most common type of post harvest mechanical injury. Most post harvest pathogens cannot infect healthy tissue, and typical enter through dead or wounded tissue before contam- inating the rest of the fruit and it is likely that minor mechanical injuries were not counted by the market inspectors and were only manifested by their consequent fungal infection, and thus mechan- ical injury could be the most important case of defects and disease (Van Zeebroeck et al., 2007). According to the study of Pholpho et al. (2008), the bruise of longan was 0.5% after transportation in 10 h by 10 wheel trucks and storing in room temperature for 24 h. The longan fruit bruises occur during transportation and stor- age by the impact and compression forces. The result of Pholpho et al. (2009) indicated that the compression and impact energy threshold causing bruise were 0.027 J and 0.034 J, respectively. It means that at these energy levels or higher the longan fruit will be ruptured. The bruised will be occurred under these energy lev- els. Detecting bruises on fruits and vegetables is a challenging, but necessary work required to maximize the value of agricultural crops. For Jonagold apples, bruised areas are usually darker than the green color but lighter than the blush color (Leemans et al., 1999). Spectral analysis offers to the traditional methods in food quality analysis (Geoola and Peiper, 1994; Lammertyn et al., 1998). For example, Gao et al. (2003) conducted bruise identifica- tion studies on apples with Raman spectroscopy. They stated that the spectroscopic technique should not only be used in laboratory but also be added to the array of on-line inspection devices to in- sure the accurate sorting of fruits. In addition, Xing et al. (2005a,b) used visible/near infrared spectroscopy for detecting bruises on Jonagold apples. In this case it was possible to separate pale flesh from red flesh (Xing et al., 2007). They used multivariate data analysis techniques to extract the key features associated with bruised fruit from the wide range of wavelengths assessed. Near-infrared (NIR) and visual (VIS) spectroscopy has also been ap- 0260-8774/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2010.12.011 ⇑ Corresponding author. Tel.: +66 2 329 8000x5120; fax: +66 2 329 8336. E-mail address: kspanman@kmitl.ac.th (P. Sirisomboon). Journal of Food Engineering 104 (2011) 169–172 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng