It Takes a Tough Scientist To Make a Tender (and Juicy) Chicken
Sensory panelists Jim Griffin
and Judy Davis evaluate chicken
texture in separate test
booths equipped with special
lighting so visual clues won't
influence their decisions.
Scientists and poultry growers strive to provide the best bird possible
in a cost-efficient manner by breeding, disease control, and changing
the chickens' diet. But do those actions affect the texture and taste
of the meat? What goes into ensuring a product that has consistent characteristics
consumers can count on?
ARS food scientist Brenda G.
Lyon, with the Quality Assessment Research Unit at the Richard B. Russell
Research Center in Athens, Georgia, has researched the characteristics
of poultry meat for over 20 years. And, boy, are there a lot of characteristics.
We all expect a piece of baked chicken to be moist and tender, but there
are many components to those qualities.
Lyon's studies focus on determining how sensory attributes such as
size of the bolus (mass of chewed food) or meat fibrousness are related
to changes and improvements in the production process. These flavor
and texture characteristics give clues to changes in product composition
that ultimately influence consumer acceptance. "This information
leads to more efficient, economical production methods for the poultry
industry and helps processors and product developers provide better,
more consistent items to the consumer," Lyon says.
While genetic selection has helped to supply poultry producers with specific birds for their operations, other poultry production and processing practices may alter characteristics of poultry meat.
The Way We Were
"During my years of research, the biggest change in poultry processing
has been the increase in options to consumerscut-up pieces, deboned
breast meat, ready-to-eat products," asserts Lyon. For many years,
chickens were sold whole, with the giblet pouch inside. In recent years,
producers found that consumers were willing to pay a premium price for
the convenience of precut broiler pieces. Consumers also showed preferences
for particular portions of the bird, so it is now commonplace to see
separate packages containing just thighs, breasts, or drumsticks. Boneless,
marinated, seasoned, ready-to-cook chicken parts are now readily available
in most supermarkets.
But these modifications come at a price. Lyon and other researchers
have found, for instance, that the amount of time the breast muscles
remain on the bone after processing affects meat texture. "The
timing for acceptable tenderness seems to be 4 to 6 hours postmortem,"
says Lyon. This aging process allows time for the muscle fibers to go
through rigor mortis, the natural biochemical process of converting
muscle to meat. But this is an expensive 4 to 6 hours due to the costs
of refrigeration and labor.
To accommodate the added step of cutting and deboning the chicken,
poultry producers shortened the costly chilling time. But there was
a drawback: "Reduced chilling time interfered with rigor mortis,
making cooked breast meat tough," says Lyon.
During rigor mortis, unused energy in the form of glycogen causes muscles
to contract. Glycogen is stored in muscle fibers for 8 to 24 hours after
the bird is killed. As the stored energy dissipates, the muscle relaxes
and should then be removed from the bone. However, sensory panels found
that meat left on the bone for less than 4 hours was tougher than meat
left on the bone longer.
New methods of releasing stored glycogen are being investigated. "Applying pulsed electrical currenttermed electrical stimulationis being explored as a way to force the muscles to use the stored glycogen more rapidly than traditional aging does," says Lyon. The Poultry Processing and Meat Quality Research Unit, also at the Russell Center, is investigating some of these processing methods.
The Senses Tell All
Instruments can measure characteristics that are directly related to
the physical or chemical components of the product, like how much force
it takes to cut through a piece of meat (shear value). However, human
subjects are needed to decipher a wide range of factors involved in
eating satisfaction, such as juiciness, appearance, aroma, taste, and
texture. These are all quality characteristics measured by use of the
senses. Sensory and instrumental measurements are used together to draw
conclusions and make assumptions about quality.
Sensory evaluation is analysis of product attributes perceived by the
human senses of smell, taste, touch, sight, and hearing. Setting up
such a sensory panel test is no small feat.
Characteristics such as mouthfeel, springiness, chewiness, compaction
of the meat after chewing, and ease of swallowing all play a part in
sensory texture profiles. However, it takes training to be able to identify
these characteristics and assign intensity values to them. So human
panelists are given intensive instruction in flavor and texture profiling.
Initial orientation and practice sessions are held to define specific
attributes in each stage of evaluation and to monitor panel performance
for repeatability, consistency, and discriminating ability.
In Lyon's lab, sensory evaluations are conducted at workstations equipped
with special lights so visual clues do not influence panelists' perception
of flavor or texture. The air is filtered so outside odors don't intrude
on the aroma of the sample. Low-pressure sodium vapor lights mask colors,
making everything appear in shades of gray or brown. At each workstation
is a computer equipped with a mouse used to mark the attribute scales
presented on the computer monitor. Filtered water and unsalted crackers
are often given to panelists for mouth cleansing between samples.
Panelists must then complete an evaluation of the samples and mark
the line scale for the intensity of each attribute. Intensity values
range from 0 to 15. As many as 20 flavor and texture attributes may
be developed for a sensory profile. Data analyses usually involve sophisticated
There are several other types of sensory test formats, depending on
the test objective. In difference/discriminative tests, the panelist
evaluates a set of samples and determines whether any samples differ
from others. If a significant number of panelists detect a difference,
then a true difference is assumed to exist. In ranking tests, panelists
are asked to rank samples in a specified order, such as most tender
to least tender.
Informal sensory testing has been used by humans since we began assessing
our environment. Formal sensory testing and analysis have been used
by researchers for a much shorter period, but the desire to eat palatable
food remains the same.
The ultimate goal of food technology research is to assist producers
in bringing to the marketplace a product consumers will purchaseby
providing a consistently performing commodity. The sensory techniques
and trained panelists help make that happen. "Sensory panels are
ultimately the deciding factor in whether a processand productis
successful," Lyon says.By Sharon
Durham, 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 http://www.nps.ars.usda.gov.
"It Takes a Tough Scientist To Make a Tender (and Juicy) Chicken" was published in the February 2002 issue of Agricultural Research magazine.