Instrument texture profiles of many foodstuffs have been made
using General Foods texturometers or Instron universal testing
instruments (7); however, systematic comparisons of instrument
texture profile variables with sensory attributes of apples have
not been published. The mechanically measured properties most
often used to define textural characteristics are force, deformation,
and elasticity. Apparent elasticity is the rate of change
of force with respect to deformation, often calculated as slope
from the initial straight portion of a compression force/deformation
curve. The point at which to determine slope and the
method of measuring slope are subject to many interpretations
(14). Finney (11 ) has recommended that "firmness" of fruits
and vegetables be defined as elasticity measured under smalldeformation
conditions (not to exceed 1% and where no yielding
occurs). Bourne (5) defines small-deformation for foods as less
than 25% absolute deformation or less than 50% of the rupture
deformation, whichever is less. Bourne (4) characterized "crispness"
as resistance to deformation under load up to the point of
sudden fracture and suggested that this characteristic can be
measured by elasticity. In the General Foods texture profile,
crispness is associated with fracturability, the force at failure or
rupture. The yield point is a point on the force/deformation curve
prior to the point of maximum force at which there is an increase
in deformation with a decrease or no change in force (13). The
yield point in apples is often a sharp drop in the curve and is
an indication of initial cell rupture. Szczesniak and Smith (17)
interpreted the yield point on General Foods texture profile curves
as crispness in their study of strawberries. Brennan et al. (9)
reported high correlations between sensory crispness scores of
apples and shear press maximum force (r = 0.91), General
Foods Texturometer hardness (r = 0.87), and Instron texture
profile fracturability (r = 0.86).
This study was undertaken to compare, on the same apples,
measurements of sensory textural attributes, Magness-Taylor
firmness, and texture profile variables, including experimental
variables and variations of the customary variables.