Purdue News

June 5, 1992 Purdue Device Helps Consumers Avoid Sour Grapes WEST LAFAYETTE, IND. – A Purdue University invention could reduce the cost and insure the quality of fruits and vegetables by measuring the ripeness of produce. "The machine uses magnetic fields to detect the amounts of sugar and water in produce," says Gary Krutz, professor of agricultural engineering. "From that we can tell how ripe the individual pieces of produce are in less than a second." With the device, consumers may be able to purchase produce that has a date of maximum ripeness marked on the individual pieces, supermarkets will be able to reduce waste, and growers will be able to harvest produce at the proper time. The ripeness of many fruits and vegetables is related to the amount of sugar they contain. Sweet corn, for example, is tasty when it contains five percent sugar, but is less flavorful when it has just one or two percent sugar. "Some fruits – such as apples and bananas – continue to ripen after they are picked," Krutz says. "Others, such as grapes and strawberries, stop ripening when removed from the plant." Sugar levels in vegetables typically range from 1 to 10 percent; the sugar levels in fruit are higher, ranging from 4 to 25 percent. The Purdue device will help consumers tell which fruits are ready to eat. "Right now we can measure the sugar levels within 2 percent accuracy, which would allow us to grade fruit into three levels," Krutz says. "But our goal is to get the machine accurate to within 1 percent. If we can do that, we could put stickers on fruit that would tell the date of optimum ripeness. "We're hoping to test the device in an Indiana supermarket within a year," Krutz says. "We'll start with a small fruit, nectarines or cherries, and move up from there." Although most consumers want fruit or vegetables with a maximum amount of sweetness, Krutz says that many diabetics are interested in the technology because it would allow them to eat more fruits without increasing their sugar intake by selecting lower-sugar fruit. Supermarkets and producers could use the device to reduce waste. Krutz says about 20 percent of the fruits and vegetables harvested are thrown away before they make it to the consumer because of over-ripening. "You know, if the grocers have one rotten apple in a crate, the other apples will be rotten within a day," Krutz says. Producers could use the device in the field to determine when to harvest the produce, and supermarkets could use it to decide which produce to store and which to sell immediately. French wine makers are even interested in using the device to add more science to the art of selecting grapes for wine. Purdue researchers are working with a scientist from France to develop this application. Eventually, Krutz says, more than just produce will be examined with magnetic waves. "We hope to be able to check the fat or sodium levels in foods," Krutz says. "We will be able to find the fat levels in meat within one-half of 1 percent, which will be precise enough that certain meats can be guaranteed as low-fat on the label. We also plan to use the device to detect bone chips in ground meat." The testing device is now about the size of a microwave, but Krutz expects the final machine to be much smaller and more adaptable to various uses. Richard Stroshine, associate professor of agricultural engineering, says that the fruit-ripeness sensor uses technology similar to that of MRI (magnetic resonance imaging) machines used by hospitals to create images of bones and tissues. "MRI devices create a two- or even a three-dimensional image," says Stroshine, "but our fruit-ripeness sensor doesn't create an image. Instead it gives a single signal that represents an average for the whole fruit, which is much simpler." The fruit-ripeness sensor works by taking advantage of a phenomenon known as magnetic resonance. As molecules spin they can be aligned by a magnetic field. If a second, perpendicular burst of magnetic energy is applied, the molecules will realign to the new field. When this second burst ends the molecules return to their previous alignment, although different molecules realign at different rates. As the molecules realign they produce an electrical signal in a receiving coil. The nature of the signal given off tells researchers what types of molecules are in the sample. Although the fruit-ripeness device uses the same technology used by MRI machines in hospitals, it is much cheaper to test an apple than an ankle. Medical MRI machines cost more than one million dollars, but the Purdue researchers expect their device to sell for less than $20,000. "Advances in digital electronics over the past four years have enabled us to use much lower magnetic fields that before," Krutz explains. "Also, fruit provides a large sampling area, so the device doesn't have to be as precise." Krutz says that most supermarkets should be able to afford the device. "If they can reduce their losses just 5 percent they could pay for the machine in six months," he says. Magnetic Instrumentation Inc., of Indianapolis, plans to manufacture the device for the commercial market. The research on the non-invasive fruit-ripeness sensor was funded by the U.S. Department of Energy. Purdue News Service: (765) 494-2096; purduenews@purdue.edu