Review The application of internal grading system technologies for agricultural products – Review Meftah Salem M. Alfatni a,⇑ , Abdul Rashid Mohamed Shariff a , Mohd Zaid Abdullah b , Mohammad Hamiruce B. Marhaban a , Osama M. Ben Saaed a a Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia b School of Electrical and Electronic of Engineering, Universiti Sains Malaysia Engineering Campus, 14300 Seri Ampangan, Penang, Malaysia article info Article history: Received 4 April 2012 Received in revised form 21 December 2012 Accepted 2 January 2013 Available online 16 January 2013 Keywords: Internal grading system Agriculture crop Quality inspection Signal processing abstract Quality assessment of agricultural products has been the subject of numerous reviews; however, not many papers address internal visualization as a means of quality grading. This paper reviews established as well as emerging visualization techniques utilized in the quality assessment of food products. In this discourse, the authors set out to underscore some of the most novel signal processing techniques employed in the non-destructive grading of agricultural products by way of an automated quality veri- fication system. Such systems utilize advanced engineering principles with imaging, signal processing as well as color differentiation to accomplish the grading task. The materials presented will be useful to agricultural engineers, manufacturing engineers, food engineers and any other researchers in the food and agriculture industries. Ó 2013 Elsevier Ltd. All rights reserved. Contents 1. Introduction ......................................................................................................... 703 2. Internal grading system ................................................................................................ 704 2.1. System design .................................................................................................. 705 2.2. Signal processing steps ........................................................................................... 705 3. Methods and techniques ............................................................................................... 705 3.1. Fruit moisture measurements ..................................................................................... 706 3.2. Fruit sugar measurements ........................................................................................ 708 3.3. Fruit acid measurements ......................................................................................... 710 3.4. Fruit ripeness measurements ...................................................................................... 712 3.5. Fruit damage measurements ...................................................................................... 714 4. Discussion and conclusion .............................................................................................. 718 Acknowledgments .................................................................................................... 721 References .......................................................................................................... 721 1. Introduction Agricultural product quality grading is based on two inspection types namely; agricultural external grading systems which have been reviewed previously by Alfatni et al. (2011) and agricultural product grading based on internal quality assessment which has gained untold prominence in the recent past. Although traditional techniques have been employed since long before, they are greatly tedious, costly and time consuming. The previously used systems are also thought to suffer severely from subjective inferences lead- ing to inconsistencies (García-Ramos et al., 2005). Even where this system is regarded as unbiased, the system fails to support the large-scale production requirements of our current time. It is against this background that high-technology solutions are being sought to make use of machine vision for quality, timely assess- 0260-8774/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jfoodeng.2013.01.001 ⇑ Corresponding author. Tel.: +60 389467543 (O), mobile: +60 147343616; fax: +60 389466425. E-mail addresses: mefth2000@yahoo.com, Mefth1083@gmail.com (M.S.M. Alfatni). Journal of Food Engineering 116 (2013) 703–725 Contents lists available at SciVerse ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng