Furthermore, human inspection is a time-consuming method. These factors often lead to considerable profit losses [3,4]. Therefore, an automated fruit grading system is highly required. An automated fruit grading system must be rapid, accurate and reliable. Apart from that, any oil palm grading system should not destroy the palm oil FFB during the analysis [5,6].In the past few years, a number of different automated fruit grading systems were proposed and tested. The most popular is the use of the color vision system that requires an advanced digital camera to capture pictures of oil palm FFBs and a computer for analysis [7�C10]. An artificial intelligence system is sometimes used together with the color vision system to classify the oil palm FFBs [11�C15].

Overall, this method requires complicated algorithms and precise image collection for the recognition stages and it produced an average success rate of 73.3% [11,16�C18].Another method used by researchers is the assessment using the RGB space. This oil palm grading method uses spectral analysis based on the different wavelengths of red, green and blue color of the image [19,20]. In this method, the color quality of the image is relatively important. Classifications of the ripe category within the bunch for the average value of red component were successfully carried out. However, the red components for unripe and under ripe categories cannot be differentiated and the average success rate for this method is reported as 49% [21]. Other disadvantages of this method are that this type of classification has to be performed indoors [22,23].

Analyzing the moisture content of oil palm fruits is another grading method. The moisture content of the mesocarp in the fruit affects the surface color and the weight of the oil palm fruit. Microwave moisture sensors are used to investigate the moisture content of oil palm fruits [24�C28]. However, the measurement procedure is quite complicated and time-consuming.Aside from these, Magnetic Resonance Imaging (MRI) and bulk Nuclear Magnetic Resonance (NMR) are other methods used by researchers to monitor the development and ripeness of oil palm FFBs [29]. FFB samples are harvested at different Week After Anthesis (WAA). Then, both equipments are used to measure the continuous change in spin-spin relaxation times of protons of the water and lipids for the development of a ripening tracking process for FFBs.

The changes between oil and moisture content in the oil palm FFBs are observed based on the differences in their spin-spin relaxation times and significant results are obtained. This method requires the usage of complicated and expensive equipment. In addition to that, skilled personnel are needed to Entinostat operate it, limiting the testing to be done indoors.Another type of imaging method involves Non-destructive near Infra Red (NIR) spectroscopy.