Date Palm Fruit Quality Inspection | Automatic Fruit Seeds & Foreign Bodies Detection
Date palm fruits are nowadays called superfood due to their high content of nutrients, fiber and antioxidants. Dates are consumed in various shapes: fresh, under various levels of dehydration, as a sweetener, in a syrup form, or as an added ingredient in other food products.
DATE PALM FRUITS PROCESSING STEPS
Processing date fruits has different steps, and right after harvesting, the sorting of dates commences. At this point, the procedures start to vary depending on the desired finish-product. However, caps and pits are removed from the fruits out of marketing considerations, and for reducing transfer costs.
An interesting article in Food Reviews International describes in detail the processing of dates, and starts by explaining that the pitting process can be done by crushing the fruits, while other methods are more developed and imply the removal of the seed through a piercing-resembling procedure. Next, pest control is assured through fumigation and sterilization of fruits. Even though irradiation could ensure a insect-free fruit batch, apparently this type of pest control method is not that popular yet, compared to fumigation and cold storage.
DATE PALM FRUITS QUALITY INSPECTION
Fig. 0 Low-energy X-ray image of date fruits, one of them without seed or foreign object inside, and the other fruit with an inserted foreign object.
After multiple processing steps, dates are finally ran through a metal detector and packed. The problem is that the numerous processing steps the fruits go through, as well as the pitting phase that lacks a method of quality checking, all increase the risks of foreign body contamination and product irregularities (some dates might have slipped through the pitting process and still have the seed inside). Particularly in the case of pitted dates, customers pay an extra price and therefore have higher expectations regarding product quality.
Also, as previously mentioned, the more steps there are between processing and packaging, the more risk points of contamination are present as well. Given the natural sticking texture dates have, this risk increases even more. That is why it is necessary to have a quality inspection system able to detect much more than just metal – for instance, glass, rubber, plastic etc. and also a method of verifying whether all seeds have been removed from the fruits. All these features should, however, not over-complicate the processing of palm dates.
X-RAY INSPECTION OF DATES
When ran through the X-ray system, the seed itself does not attenuate the X-rays more than the other parts of the date. This makes the simplest approaches for automatic detection impossible. However, the seed is definitely visible in the X-ray image due to the fact that it’s presence adds to the total attenuation. Using more advanced image analysis it is possible to determine if the date contains the seed or not.
Fig. 1 Low-energy X-ray image of date fruits, some of them with the seed inside, and some of them without seed inside.
The X-ray analysis software individually identifies the dates by shape, size and X-ray absorbance. Then, the system determines the date’s orientation and center of mass. Based on gathered data (analysis of the edges of the fruit, density of the fruit’s inside vs. density of the fruit’s outside) the system is able to conclude whether a specific date contains the seed or not. In addition to this, our X-ray system also detect the presence of physical contamination with different types of foreign objects.
The low X-ray energy results in a high contrast for even small product irregularities, which cannot be detected using ordinary X-ray systems that use shorter wavelengths and therefore lose the contrast from small, thin or light material differences. Image acquisition is at a very high frame rate, which entails a high inspection speed – up to 30 m/min, in standard applications.
Fig. 2 Dates with one remaining stone, one with a foreign object embedded in the pit, along with various foreign objects.
The image resolution used by InnospeXion is 0.1 mm × 0.1 mm compared to 0.4 mm × 0.4 mm used in standard X-ray systems. Because of the high resolution, it is possible to detect small details in the image. The high imaging resolution implies that a defect is represented by many pixels, which highly improves the software ability to recognize a defect as such and reduces false rejects due to lower noise.