Apple Qualitys More Than Skin Deep
Each fall for the past 3 years, Renfu Lu has gone into Michigan orchards,
picked fruit off the trees, and tasted hundreds of apples and peacheswithout
taking a single bite. How did he do it? With a futuristic technology called imaging
spectroscopy, or multispectral imaging, that uses laser beams to detect the sweetness
and firmness of fruit.
Using a multispectral imaging system to collect light
scattering from the fruit, visiting assistant professor Yankun Peng (from
Michigan State University) estimates apple firmness.
Michigan has a $100 million farmgate apple industry, the third largest in the
country. It ranks first in production of tart cherries and fifth in peach production.
Nationally, the tree fruit industry is worth about $2 billion a year.
Lu, an agricultural engineer with USDAs Agricultural
Research Service, partners with Michigan State Universitys (MSU) Agricultural
Engineering Department to address priority needs of the fruit industry in the
state and the nation.
Nondestructive technologies for grading and sorting fruit by internal
qualitysuch as firmness and sugar and acid contentare a top priority,
says Lu. Such technologies would ensure a consistent premium quality product,
increase consumer satisfaction, and enhance the U.S. fruit industrys competitiveness
Laser Tastebuds Leave Fruit Intact
Engineering technician Benjamin Bailey (front) and agricultural
engineer Renfu Lu take near-infrared spectra from an apple to measure
its sugar content.
Currently, thick steel probes are used to test fruit samples by punching a
hole in the fruit, making it unmarketable. We have to presume that by
destructively testing a few fruits that way, well learn about the condition
of the thousands of other fruits in a particular batch, says Lu. But
our system tests every single fruit, and it can all be sold.
Lu and colleagues in the ARS Sugarbeet and Bean Research Unit, located on MSUs
East Lansing campus, sample apples with a prototype optical detector. The detector
fuses four laser beams, each at a different waveband of light, into one. Light
photons momentarily scatter all the way to a fruits core.
An imaging spectrograph, a digital camera, and a computer analyze the amount
of laser light absorbed by the apples, which indicates sweetness. The amount
of light bounced back after interacting with fruit tissue reflects fruit firmness.
Sweet and sour tastes are a factor for apples, cherries, peaches, and other
fruitbut firmness analysis is often more important to consumers and technologically
Multispectral imaging combines spectroscopywhich analyzes light wavelengthswith
machine vision, which enables a computer to see. Its emerged
in recent years as a powerful sensing technique for quality evaluation and safety
inspection of food and agricultural products as well as for precision farming.
It is also used in a wide range of scientific, military, and industrial fields,
including space exploration and remote sensing of Earth from space, medical
diagnostics, biological research, and military target detection. This is the
first time its been tried for remote tasting of fruit for
sweetness and firmness.
When commercialized, Lus optical sensor would be used by the fruit industry
to sort fruit just after its been picked. Hes built a larger version
fitted into a mini-packing line for lab use. Its a prototype for a machine
that would be used on fruit-processing lines to make a second quality check
after some time had passed and the fruit had been handled.
Agricultural engineer Renfu Lu (front) and visiting assistant
professor Yankun Peng (from Michigan State University) test a laser-based
multispectral imaging prototype for real-time detection of apple firmness
and sugar content.
Lu and his team developed and tested the computer model and accompanying software
as well as the prototypes.
Our sensor can sort peaches and apples into two or three firmness grades.
The technologys comparableor superiorto the accuracy of other
nondestructive mechanical techniques, as reported in the scientific literature.
But its relatively easy to implement for rapid online sorting and has
potential for measuring multiple quality attributes simultaneously, Lu
The sensors work better on peaches than on apples in terms of firmness
measurements, says Lu. Apples are challenging because they are more
variable in firmness and have a narrower firmness range from apple to apple.
But our sugar-content predictions for apples compared well with actual sugar-content
measurements, he says.
His goal is to sign a cooperative research and development agreement with one
or more companies to commercialize the prototypes for use in fruit quality labs,
packinghouses, and orchards. We will continue to improve and refine the
system so it can meet online sorting needs, Lu says. He is currently working
to speed up scanning speed to match that of commercial apple conveyors: 10 fruits
per second. The ability of a spectrograph to capture images from four light
bands at once makes this speed possible.
You Cant Judge a Fruit by Its Appearance
Lu is researching other factors that might affect firmness predictions, such
as variety, orchard, geographic location, and season.
His equipment would be merged with existing industry sensors that nondestructively
assess superficial visual traits, including size, color, and bruising. Skin-deep
appearance gives us the first impression about fruit quality, but its
internal qualitiesmainly flavor and texturethat ultimately deliver
consumer satisfaction, Lu says. Together those two qualities make
up taste. Its vital that each fruit variety consistently taste the way
it should to develop and retain loyal customers, Lu says. Poor,
inconsistent fruit quality has turned some consumers away to other food products,
causing the industry to lose market share and competitiveness.
Eventually Lus system will also sense acidityanother aspect of
flavorand it will measure those qualities simultaneously. His laser system
would sort out the best-tasting fruit during harvesting and again during packaging
so that, for example, soft or sour red apples would be redirected for use in
the packing plants applesauce and juice facilities.
Lasers are giving Lu the high-quality light beam needed for accurate firmness
prediction. This should bring us closer to the day when you can shop for
fresh produce in a grocery store and be sure youll get just the amount
of crunchiness and sweetness or sourness you expect, justifying your first impression
based on the fruits attractive appearance, says Lu.By Don
Comis, Agricultural Research Service Information Staff.
This research is part of Quality and Utilization of Agricultural Products,
an ARS National Program (#306) described on the World Wide Web at www.nps.ars.usda.gov.
Renfu Lu is in the USDA-ARS Sugarbeet
and Bean Research Unit, 224 Farrall Hall, Michigan State University, East
Lansing, MI 48824-1325; phone (517) 432-8062, fax (517) 337-6782.
"Apple Qualitys More Than Skin Deep" was published in
the May 2005
issue of Agricultural Research magazine.