The "melon inspector" is on fire! What is the scientific basis for "distinguishing melons by listening to sounds"? There is another method that is more efficient, melons master | watermelon | method
With the arrival of summer, the "cooling tool" watermelon has received more and more attention, and a profession related to melons - "melon inspector" has also entered the public eye. Recently, related topics have also attracted enthusiastic discussions from netizens. Because one of the key actions in the work of a "melon inspector" is to pat the watermelon, and some people have given them an interesting nickname: "melon inspector".
A melon with a low voice is a good melon
According to media reports, these professional "watermelon quality inspectors" can determine whether the melon is raw, ripe, good or bad by simply taking a look, patting, and bouncing it, and a series of operations only take a few seconds. During the peak season of melon production, "melon inspectors" need to "take" at most tens of thousands of melons per day to select qualified individuals.
After reading the operation of the "melon inspector", a netizen said, "Every time I buy a watermelon, I take a photo, but I really don't know what I did." In fact, it's not only this netizen who doesn't understand the mystery of "taking a photo", many "foreigners" also don't understand. A few years ago, there was a media report that an Italian supermarket deliberately put up a warning sign asking customers not to take a photo of watermelons when picking them - "because these watermelons really don't respond to you."
However, in fact, according to relevant research results, "listening to sounds to distinguish melons" is actually a quite scientific way of selecting melons.
The data shows that selecting watermelons based on the sound of tapping is based on the principle that the propagation of sound waves in a medium is influenced by the density and texture of the medium. Therefore, there is a connection between the sound waves obtained by tapping watermelons and their quality.
Specifically, the structure of watermelon is divided into skin and pulp. During the ripening process of watermelons, the hardness and elastic modulus of the skin will change, which means that the skin with ripe flesh has greater elasticity and will have a slight rebound when tapped. In addition, under the action of cellulase, the internal cellulose of the melon pulp is degraded, and the sugar content and structure of the watermelon also change, resulting in different tapping sounds.
So what kind of sound is a good melon? A study by the team from Hebei Agricultural University provides the answer. In the experiment, researchers first collected tapping audio signals from the central equatorial position of the watermelon, and then conducted destructive maturity detection on the watermelon. The monitored watermelons were divided into four levels: raw, ripe, mature, and over ripe.
In the level set by the researchers, the center of the "raw" watermelon pulp is light pink, with thicker white pulp on the edges, and the taste is meaty but not sweet; The ripe watermelon flesh is all pink, with a sweet taste and a crispy texture; The ripe watermelon flesh is bright red, fluffy, and can be seen with small particles, with a soft, crispy, sweet or sandy taste; Overripe watermelon has a fluffy, dark red flesh with filamentous fibers or voids, and a noticeable spoiled taste.
The final research results showed that the processed audio related frequencies between 133-160 Hz were ripe melons, those with frequencies greater than 189 Hz were raw melons, those with frequencies between 160-189 Hz were suitable ripe melons, and those with frequencies less than 133 Hz were over ripe melons.
In terms of auditory perception, the higher the Hertz, the sharper and thinner the sound, and vice versa, the lower and deeper the sound. From this, it can be inferred that melons with a relatively low tapping sound belong to mature and palatable melons, while those with a crisp tapping sound are raw melons.
Using "Light" to Test Watermelon More Efficiently
In addition to manual tapping, some non-destructive testing technologies that can be used for large-scale and rapid watermelon inspection have gradually emerged in recent years, helping China's watermelon industry further move towards mechanization and intelligence.
At the 12th Spectral Network Conference held in mid June, Researcher Huang Wenqian from the Agricultural Intelligent Equipment Research Center of Beijing Academy of Agriculture and Forestry introduced an efficient watermelon detection technology based on full transmission near-infrared spectroscopy technology. With a series of technical assistance, watermelon can quickly complete quality testing such as sugar content, maturity, and hollowing during the process of passing through the equipment.
In the display video, it can be seen that watermelons are placed in the base of the conveyor belt, and the speed of the detection equipment is fast and smooth, almost completing the quality inspection of a melon in just a few seconds.
According to Huang Wenqian, light can enter the interior of the object being measured and carry useful information. They have independently developed a fully transmissive multi-point visible/near-infrared spectroscopy system, OnlineNIR, based on this physical foundation. The system can obtain relevant information about hydrogen groups in samples by illuminating them with a special type of incandescent lamp. With the support of this information, a chemometric model can be established to achieve non-destructive testing of sample sugar content, acidity, and internal defects.
In fact, watermelon, a common fruit, has many difficulties in non-destructive testing, including thick skin and uneven sugar distribution; The spectral signal is weak and unstable under high-speed dynamic conditions; The model is susceptible to factors such as fruit size, posture, and texture.
In order to address these difficulties, Huang Wenqian's team focused on optimizing the optical path structure and improving the signal-to-noise ratio of the spectral signal in the development process of this new spectral detection system, ensuring stable spectral signals can be obtained under low-power illumination and short integration time conditions. Moreover, the information obtained by the team using precision positioning technology can achieve comprehensive analysis of the entire watermelon, as well as selective analysis for specific areas.
Regarding why continuous research and development of non-destructive testing technology for watermelon quality is necessary, Huang Wenqian stated at a spectral network conference that quality and intensification are the future development directions of the watermelon industry. Developing standards for watermelons and classifying them for sale according to these standards can achieve the transformation from agricultural products to commodities, increase the added value of watermelons, increase farmers' income, optimize production management, and have significant economic and social benefits. However, currently, there are few non-destructive testing technologies for the internal quality of watermelons in China, and related equipment abroad is expensive.
In addition, data shows that China is the world's largest watermelon producing country, with a watermelon production of 60.2469 million tons in 2020, accounting for 59.29% of the world's total watermelon production. Faced with such a large number of melons, relying solely on manual inspection and sorting during the peak period of watermelon market often makes it difficult for "melon inspectors" and farmers to bear it. The emergence of new technologies for non-destructive testing of watermelon quality in recent years may help alleviate their work pressure.
