308 Part III: Muscle Foods
food deprivation may result in an induced lipoly-
sis that can be rapidly detected (in just 72 hours)
through a higher content of free fatty acids and
monoacylglycerols, especially in glycolytic muscles
(Fernández et al. 1995). Fasting within 12–15 hours
preslaughter is usual to reduce the risk of microbial
cross-contamination during slaughter.
CARCASS CLASSIFICATION
CURRENTGRADINGSYSTEMS
Meat grading constitutes a valuable tool for the clas-
sification of a large number of carcasses into classes
and grades with similar characteristics such as qual-
ity and yield. The final purpose is to evaluate specif-
ic characteristics to determine carcass retail value.
In addition, the weight and category of the carcass
are useful for establishing the final price to be paid
to the farmer. Carcasses are usually evaluated for
conformation, carcass length, and backfat thickness.
The carcass yields vary depending on the degree of
fatness and the degree of muscling. The grade is de-
termined based on both degrees. The grading system
is thus giving information on quality traits of the
carcass that help producers, processors, retailers,
and consumers.
Official grading systems are based on conforma-
tion, quality, and yield. Yield grades indicate the
quantity of edible meat in a carcass. In the United
States, beef carcasses receive a grade for quality
(prime, choice, good, standard, commercial, utility,
and cutter) and a grade for predicted yield of edible
meat (1 to 5). There are four grades for pork carcasses
(U.S. No. 1 to U.S. No. 4) based on backfat thick-
ness and expected lean yield. The lean yield is pre-
dicted by a combination of backfat thickness mea-
sured at the last rib and the subjective estimation of
the muscling degree. In the case of poultry, there are
three grades (A to C) based on the bilateral symme-
try of the sternum, the lateral convexity and distal
extension of the pectoral muscles, and the fat cover
on the pectoral muscles (Swatland 1994).
In Europe, beef, pork, and lamb carcasses are clas-
sified according to the EUROP scheme (Council re-Table 13.7.Effect of Type of Feed on Total Fatty Acid Composition (Expressed as Percent of
Total Fatty Acids) of Pork Muscle LipidsFatty Acid\ Barley Soya Safflower Tallow High Oleic
Feed Enriched in Bean Meala Oilb Dietc Sunflower Oild Canola Oile
Myristic acid (C 14:0) — — 1.37 0.05 1.6
Palmitic acid (C 16:0) 23.86 27.82 24.15 6.35 20.6
Estearic acid (C 18:0) 10.16 12.53 11.73 4.53 9.8
Palmitoleic acid (C 16:1) 3.00 3.56 3.63 0.45 3.6
Oleic acid (C 18:1) 39.06 37.81 46.22 71.70 45.9
C 20:1 — 0.01 0.29 0.26
Linoleic acid (C 18:2) 17.15 14.60 8.95 15.96 12.3
C 20:2 — 0.01 0.44 — 0.4
Linolenic acid (C 18:3) 0.91 0.01 0.26 0.71 3.0
C 20:3 0.21 0.01 0.25 — 0.1
Arachidonic acid (C 20:4) 4.26 2.14 2.13 — 0.74
Eicosapentanoic acid (C 22:5) 0.64 0.01 — — —
Hexadecanoic acid (C 22:6) 0.75 0.01 — — —
Total SFA 34.02 40.35 37.83 10.93 33.6
Total MUFA 42.06 42.38 50.26 72.41 49.5
Total PUFA 23.92 16.79 11.91 16.67 16.6Ratio M/S 1.24 1.05 1.33 6.62 1.47
Ratio P/S 0.70 0.42 0.32 1.53 0.49
Sources:aFrom Morgan et al. 1992, bLarick et al. 1992, cLeszczynski et al. 1992, dRhee et al. 1988, eMiller et al. 1990.