There are several destructive and nondestructive methods for quality evaluation of agricultural products. Most of the employed traditional techniques are time-consuming and involve considerable degree of manual works. Destructive methods provide reasonable success rate of quality determination of fruits; however, they practically have many concerns about effectiveness, time, and cost. Therefore, developing portable, fast, and cost-effective techniques without harming fruits are desired for fruit quality evaluation. This work aims to develop a complete nondestructive quality evaluation system with (a) ultrasonic testing and (b) volume estimation by automatic machine vision techniques. The ultrasonic system consisted of a programmable bipolar remote pulser unit, a couple of piezoelectric probes for ultrasonic signal acquisitions as a transmitter and a receiver, an oscilloscope, and a computer. Visual appearance (size/volume) was determined using a machine vision system based on image processing techniques. Five different images of a fruit from different angles were captured by high-resolution digital cameras. Volume of the fruit was computed after horizontal and vertical distance of the fruit’s images captured. The calculated volume values by the computer vision system are validated with the theoretical values. Although nondestructive ultrasonic estimation and volume estimation by image processing methods are cheap, fast, and practical, the results obtained in our experiments concluded that these methods are not as reliable as claimed in the literature.
The quality (texture, color, shape, size, sugar content, and nutritional value) of agricultural products is highly important in terms of consumers, determining market acceptance, and thus, directly or indirectly affects storage and postharvest processing operations (such as transportation and conditions for storage) [
Destructive methods and professionally trained panels are widely used to determine the quality of fruits and vegetables. These methods are obviously more reliable; however, they are time-consuming and cost intensive and require specialized sample preparation. Therefore, the methods in this class are not suitable for industries such as packaging industry as it ruptures the fruit tissue and evaluation of whole lot cannot be done [
The raising awareness of consumers in high quality of foods directs the producers to a reliable, rapid, nondestructive, and noninvasive technique for maturity determination, especially during harvesting and packaging processes. Therefore, in recent years, the application of nondestructive, noninvasive, and noncontact methods and designing new instruments for food quality determination have been the focus of interest by researchers. These techniques are becoming more favored and practical compared to destructive techniques as nondestructive methods allow the measurement and analysis of individual fruit, reduce waste, and permit repeated measurements on the same item [
Nondestructive ultrasonic method itself is not enough to determine the fruit quality using internal parameters. It is essential to use a proper method to obtain the physical characteristics of fruits in terms of size, shape, and volume as well. Nondestructive custom-designed ultrasonic system combined with a noncontact physical measurement unit can provide superior quality assessment of fruits.
Intensive researches have been conducted to design and build computer-aided machine vision system for a variety of fruit samples, and promising results of machine vision system for fruit quality have been shown [
The aim of this study is to introduce a nondestructive system integrated with ultrasonic and machine vision methods for fruit quality evaluation. This system is eligible to monitor the maturity of tomato, peach, apple, and apricots and evaluate volumes. Although the ultrasonic system integrated with automatic machine vision could provide more accurate fruit quality assessment, our results showed that quality assessment of fruits using ultrasonic methods using through transmission (TT mode) technique has drawback in terms of reliability. Experimental results of this study conflict with the results in the literatures. Therefore, we concluded that more studies are required to confirm the reliability of the ultrasonic system for fruit quality assessment.
In this study, two methods, including ultrasonic measurement and image processing-based machine vision measurement, were used to evaluate the fruit quality based on external and internal parameters of fruits. These methods are explained in the following sections.
Developed ultrasonic system performance was tested before measurements. Experimental setup as shown in Figure
Experimental setup to show ultrasonic system reliability.
The 167
Transmission and reception performance of the ultrasonic system that received signal (a) 10.7
Figure
The schematic view of the ultrasonic measurement experimental setup.
The components of the machine vision system are five high-resolution cameras, a 50 W LED light source, and a sample holder. Connections of cameras to PC were achieved over the USB communication port. Cube-shaped white box (40 × 40 × 40 cm) made of wood was fabricated in the laboratory to cover the experimental system and eliminate unwanted light sources from outside as shown in Figure
The proposed machine vision system for fruit volume calculation [
Two different schemes have been designed for TT mode ultrasonic experimentation. Fruits with and without shell have been exposed to the ultrasonic signal. According to the experimental results, the ultrasonic signal is strongly reduced due to absorption while the signal passes through the fruit. As it can be seen in Figures
Ultrasonic testing of fruits: no signal was observed in (a) a tomato with skin and (b) an apricot without skin. Receiving probe can collect transmitted signals when the shell of (c) a tomato and (d) an apricot was used for experimentation, respectively.
The porous-uneven surface and pericarp of the fruit result in scattering of ultrasound, and this thereby prevents the transmission of the ultrasonic signal. Because after the fruits were peeled and ultrasound applied to the peel, the receiver probe could have measured the attenuated signal (Figures
To do that, ultrasonic horns made of aluminum are designed and manufactured. The inside portions of these horns are empty; therefore, they are filled with ultrasonic gel during the application to reduce signal loss. Measurements were repeated with the horns mounted at the ends of the receiver/transmitter probes. After assembly, the probes were tested by contacting each other, and the received signal was observed on the oscilloscope. However, when the measurements were repeated on the fruits, the same result was not observed as shown in Figure
(a) Fabricated ultrasonic horns to focus ultrasonic signals; (b) no signal passed through the whole fruit when the transmitted signal was focused using the horn.
In the literature [
In this study, the machine vision system developed in our previous study was used, and successful results were obtained in determining the size of the fruit [
However, in contrary to the literature, the TT mode ultrasonic system is not a reliable method in determining the quality of fruit due to the aforementioned reasons. In the future studies, the PE mode ultrasonic method will be used as an alternative to TT mode ultrasonic measurement. Ultrasonic waves reflected from the fruit shell will be measured, and the quality of the fruit will be obtained by designing a
The TT mode ultrasonic system has been developed for fruit quality determination. In addition to the ultrasonic system, image processing based on the machine vision system was used to determine the quality of the fruit.
First of all, the outer characteristics (size and volume) of the fruits were determined by the machine vision system. This technique consists of multiple cameras which is much more practical, unlike the conventional method in which images are captured from a single camera and fruits have to be rotated by the hand. More accurate results may be obtained by reducing unwanted noise (shadows) in the images.
Secondly, expected results could not be obtained with the ultrasonic system developed to determine the fruit quality using the correlation between ultrasound parameters and the properties of the fruit. According to our results, TT mode ultrasonic measurement is not possible, although it is mentioned in the literature that the quality of fruits can be determined with the same method. Therefore, both PE mode ultrasonic system and machine vision system can be more efficient tool in determining the fruit quality. Therefore, this study may lead to more intensive study and development of PE mode applications of ultrasonic systems in order to determine the fruit quality.
Previously reported results of our image vision system were used to support this study and are available at doi:
The authors declare that there are no conflicts of interest.
Fikret Yildiz, Ahmet Turan Özdemir, and Selman Uluışık proposed the research topic, supervised the study, and prepared the initial draft of the manuscript together. Fikret Yildiz contributed significantly to the writing and organization of the manuscript. Ahmet Turan Özdemir mostly coordinated the experimental work and analyzed the experimental data in Ultrasonar Defense and Aviation Technologies Inc.
We would like to thank Ultrasonar Company (