Food Biochemistry and Food Processing (2 edition)

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298 Part 3: Meat, Poultry and Seafoods

Table 15.7.Effect of Type of Feed on Total Fatty Acid Composition (Expressed as Percentage of Total Fatty Acids)

of Pork muscle Lipids

Fatty Acid\Feed Enriched

Barley+

Soybean Meala

Safflower

Oilb

Tallow

Dietc

High Oleic

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

Stearic acid (C 18:0) 10.16 12.53 11.73 4.53 9.8

Palmitoleic acid (C 16:1) 3 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

Eicosapentaenoic acid (C 22:5) 0.64 0.01 −− −

Hexadecanoic acid (C22:6) 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 16.6

Ratio MUFA/SFA 1.24 1.05 1.33 6.62 1.47

Ratio PUFA/SFA 0.70 0.42 0.32 1.53 0.49

Sources:aMorgan et al. (1992),bLarick et al. (1992),cLeszczynski et al. (1992),dRhee et al. (1988),eMiller et al. (1990).

SFA, saturated fatty acids; MUFA, monosaturated fatty acids; PUFA, polysaturated fatty acid.

The fatty acid profile in ruminants is more saturated than in

pigs, and thus the fat is firmer (Wood et al. 2003). The ma-

nipulation of fatty acids in beef is more difficult due to the

rumen biohydrogenation. More than 90% of the PUFA are hy-

drogenated, leaving a low margin for action to increase the

PUFA:SFA ratio above 0.1. However, meats from ruminants are

rich in conjugated linoleic acid (CLA), mainly 9-cis,11-trans-

octadecadienoic acid, which exerts important health-promoting

biological activity (Belury 2002).

In general, a good level of nutrition increases the amount of

intramuscular fat. On the other hand, food deprivation may result

in an induced lipolysis that can be rapidly detected (in just 72

hours) through a higher content of free fatty acids and monoa-

cylglycerols, especially in glycolytic muscles (Fernandez et al.

1995). Fasting within 12–15 hours preslaughter is usual to re-

duce the risk of microbial cross-contamination during slaughter.

CARCASS CLASSIFICATION

Current Grading Systems

Meat grading constitutes a valuable tool for the classification of

a large number of carcasses into classes and grades with similar

characteristics such as quality and yield. The final purpose is

to evaluate specific 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 back-fat thickness. The carcass yields vary depending on

the degree of fatness and the degree of muscling. The grade

is determined 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 conformation, 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 (1–5). There

are four grades for pork carcasses (US No. 1 to US No. 4) based

on back-fat thickness and expected lean yield. The lean yield is

predicted by a combination of back-fat thickness measured at

the last rib and the subjective estimation of the muscling degree.

In the case of poultry, there are three grades (A–C) based on

the bilateral symmetry of the sternum, the lateral convexity and

distal extension of the pectoral muscles, and fat cover on the

pectoral muscles (Swatland 1994).

In Europe, beef, pork, and lamb carcasses are classified ac-

cording to the EUROP scheme (Council regulation 1208/81,

Commission directives 2930/81, 2137/92, and 461/93). These

European Union Directives are compulsory for all the mem-

ber states. Carcass classification is based on the conformation

according to profiles, muscle development, and fat level. Each

carcass is classified by visual inspection, based on photos cor-

responding to each grade (see Fig. 15.9). The six conformation

classification ratings are S (superior), E (excellent), U (very

good), R (good), O (fair), and P (poor). S represents the highest

quality level and must not present any defect in the main pieces.

The five classification ratings for fat level are 1 (low), 2 (slight),

3 (average), 4 (high), and 5 (very high). The grading system for

each carcass consists in a letter for conformation, which is given