36 Chapter 2
animals and among muscles within an animal;
this may relate to initial tenderness
(Novakofski and Brewer 2006 ; Stolowski et
al. 2006 ). A major factor in this variation is
high growth rate that requires a high plane of
nutrition. During growth, rapid protein turn-
over increases proteolytic activity, which
contributes to the aging process (Zgur et al.
2003 ). This increased proteolytic activity
enhances aging because proteolytic cathep-
sins degrade some structural proteins, allow-
ing the sarcomere to relax (Kristensen and
Purslow 2001 ). This allows the infl ow of
water previously expelled during rigor. This
infl ow may be driven by the difference in
protein concentration existing between intra -
and extracellular compartments of the muscle
cell.
Tenderness improvement with aging
varies between animals within a breed, and
between muscles within an animal. It depends
on several factors that may also be related to
initial tenderness (Wicklund et al. 2005 ;
Novakofski and Brewer 2006 ). Wicklund et
al. (2005) reported that changes in tenderness
of strip steaks required 14 days of aging.
Novakofski and Brewer (2006) reported that
the mean improvement in shear with aging
over the fi rst week differed depending on the
shear value starting point (original shear
value); however, no differences occurred
between 7 and 14 days. Rentfrow et al. (2004)
reported that Warner Bratzler shear values
decreased and tenderness increased in beef
from one - and two - year - old heifers during
aging; however, maximum improvement
occurred after only 7 days of aging. Bruce et
al. (2005) indicated that aging for up to 14
days increased tenderness.Aging Effects on Flavor
The effects of aging on fl avor are unclear
(Mottram 1998 ). It can alter the makeup of
the aroma and fl avor precursors, which ulti-
mately affects the characteristics of the
cooked product. Aging can increase carbon-connective tissue component can be affected
by animal age, degree of activity, mechanical
tenderization, and composition (Pearson and
Young 1989 ). Muscle foods have an inherent
set of textural characteristics associated with
them by the nature of the raw material. These
include fi bers, fl uid/fat exudation, and con-
nective tissue. Textural parameters of interest
are those that are affected by these raw mate-
rials characteristics as well as those that are
affected by exogenously induced alterations
(formulation, aging).
Tenderness of the fi nal product depends
on the muscle(s) from which the meat was
derived. Beef Psoas major was more tender
than the Gluteus medius , Infraspinatus , and
Rectus femoris (Stetzer et al. 2007 ). Of the
Complexus , Serratus ventralis , Vastus later-
alis , Vastus medialis , and Longissimus dorsi ,
the Longissimus dorsi was the most tender
and the Vastus lateralis was the least (Stetzer
et al. 2006 ). In general, meat that is the most
tender is derived from muscles that were
least used when the animal was alive, while
meat that is the most tough is derived from
muscles that are used the most (locomotor,
postural). However, both genetics and age
affect tenderness. Meat from two - year - old
Angus/Wagyu heifers was as tender and
juicy as that from yearlings. However, meat
from two - year - old pure Angus lines was less
tender and juicy than that from yearlings or
that from Angus/Wagyu animals (Rentfrow
et al. 2004 ).
Aging
Aging Effects on Tenderness
Sarcomere length, muscle, connective tissue
proteins, and proteolytic degradation account
for most of the variation in tenderness
(Koohmaraie et al. 2002 ). Tenderness
depends, in part, on proteolytic degradation
of structural and myofi brillar proteins
(Koohmaraie et al. 2002 ). Large variation in
aging - induced improvement occurs among