A Novel Device to Prevent Global Fruit Wastage
by Ashwat Subbaraman
In a late-2016 Scientific Reports paper, Anshuman Das, a postdoctoral researcher at MIT’s Media Lab, introduced his handheld spectrometer device that can evaluate how ripe an apple is by measuring the glow of chlorophyll in the fruit’s skin under ultraviolet light.
In order to understand the implications of Das’ device, it is first crucial to understand the current process of assessing ripeness in fruits. The food industry currently employs two primary methods for evaluating apple ripeness. One is to measure firmness using a device called a penetrometer. This device is pushed into the fruit, and the measure of the resistance of the pulp to the spectrometer is correlated to the ripeness of the fruit. The second technique, called Brix, involves measuring the sugar content of the fruit juice using light refraction. “Both methods are destructive,” added Das.
In an increasingly technology-dependent society with machine learning methods often operating beyond human-level performance, it seems strange to hear of a widespread lack of tools in the market for non-invasively measuring fruit ripeness. However, Das explains, “Most spectrometers are expensive and the compact versions are USB-based which require a laptop to operate. This makes it unattractive for use in the field.” Das and his colleagues, who are comprised of Sant’Anna School of Advanced Studies Biorobotics researcher Akshat Wahi, MIT Media Lab Associate Professor Ramesh Raskar, and MIT Camera Culture Group intern Ishan Kothari, sought to make a user-friendly and noninvasive handheld spectrometer that could be just as accurate as the expensive, bulky spectrometers and also simple enough for anybody to build at home.
In his work, which was partly funded by the Tata Center for Technology and Design, Das began by elaborating on how measuring fruit ripeness could greatly help apple distributors decide when to sell their products. At a time without noninvasive and quantitative methods to easily determine fruit ripeness, the primary method to determine shipping location relied on the highly fallible method of visual inspection. Resultantly, even though the ripest apples would ideally go to the location where they were expected to sell out rapidly, there were many instances where they just didn’t get sold because they decayed earlier than expected. “There is a tremendous amount of wastage,” Das said, referring to the tons of perfectly ripe fruit that were not dispersed to consumers in time.
The seemingly Herculean task of assessing apples in a novel, nondestructive manner was ultimately accomplished by Das and his colleagues, who took advantage of a common but tremendously handy tool.
“Most of us already carry around a very powerful computing device — the smartphone — so we began exploring how we could build a device that works with a smartphone,” explained Das.
Das’s device operates using a technique called chlorophyll fluorescence. Ultraviolet light is first shined onto the fruit, which the spectrometer then measures using fluorescence emissions from the UV-excited chlorophyll in the apple’s skin. “Because chlorophyll determines photosynthetic activity, it is a good indicator of growth as well as nutrient and color compounds in the fruit. The strength of fluorescence drops as the fruit ripens,” explained Das.
After the light is shined on to the apple, the device uses a smartphone app interface in order to plot and store the fluorescence data. After rigorous testing of the gadget on three different varieties of apples over 11 days, Das and his colleagues obtained results that correlated with ripeness as measured by a penetrometer. Acquiring comparable ripeness data between the device and a penetrometer objectively showed that the device could in fact output accurate ripeness data while keeping the fruit completely unharmed in the process. What was originally a process involving bulky and expensive equipment was now reduced to a 48-gram device that could fit in the palm of a hand.
Apples aren’t the only items that the device can assess. They were simply the easiest fruits to begin testing the device with due to the availability of extensive research and literature. “This technique can easily be expanded to other fruits and vegetables. There is already work done on a variety of them including guava, broccoli and avocado among others,” Das added.
When asked about other possible applications for his device, Das mentioned that it could be used for a variety of purposes ranging from studies of minerals and rocks to biological compounds. “Several biological compounds and structures like porphyrins, collagen and certain types of bacteria also have fluorescent properties so the device could be used to study these materials,” Das expanded.
Das’ hope is to make a large database to collect all of his instrument’s ripeness readings in order to more accurately assess its performance. With a larger database of ripeness values, there also comes the opportunity to detect relationships between different variables and get progressively better accuracy in future readings through machine learning. This in turn can bring significant impacts on pressing problems like world hunger and global food wastage if a sufficient collaborative effort is attained. Simple, preventable problems like throwing away an apple just because of a funny texture or odd coloration will be removed by using this device, which can assure the consumer that the apple is in fact ripe and perfectly edible. In addition, the large amounts of fruit wastage from penetrometers and Brix can also be prevented by adopting Das’ less invasive model. Now that the technology is developed, the next step is for consumers to understand the importance of the device and build one of their own to integrate into their own lives.