New Zealand Journal of Agricultural Research abstracts
Conservation of conjugated linoleic, trans-vaccenic and long chain
omega-3 fatty acid content in raw and cooked lamb from two cross-breeds
T. W. Knight
S. O. Knowles
A. F. Death
AgResearch Ltd Grasslands
Private Bag 11 008
Palmerston North, New Zealand
email: terry.knight@agresearch.co.nz
T. L. Cummings
AgResearch Ltd Ruakura
Private Bag 3123
Hamilton, New Zealand
P. D. Muir
On-Farm Research Ltd
P.O. Box 1142
Hastings, New Zealand
Abstract Available literature mainly describes the fatty
acid (FA) content of raw meat, with only limited data explaining the effect
of different preparation and cooking temperatures on health-promoting FA
such as conjugated linoleic acid (CLA), its metabolic precursor trans-vaccenic
acid (TVA), and long chain omega-3 FA (LC omega-3 FA). We collected m.
longissimus thoracis (LT) from rib chops of Poll Dorset x East Friesian
(EF) and Poll Dorset x Romney (R) lambs raised together. The FA composition
of raw LT was compared with LT prepared with bone and all fat trimmed away
or bone and fat left intact before cooking under a fan-grill. The LT from
EF lambs had less cooking loss, lower lipid and total fatty acid (TFA) contents,
and a lower proportion of saturated fatty acids (SATFA) than the LT from
R lambs. Raising cooking temperature from medium to well-done increased cooking
losses and dry matter (DM) yield but did not affect FA content or composition.
Compared with raw LT, cooking of the trimmed LT resulted in more TFA and
lipids in the DM, and these were greater still in the intact LT. Similar
increases occurred in the DM content of most individual and groups of FA,
except for CLA and LC omega-3 FA which increased with cooking of trimmed
LT without further significant increase with cooking intact LT. The proportions
of SATFA and TVA in the TFA increased after cooking trimmed LT and increased
further after cooking intact LT. In contrast, proportion of polyunsaturated
fatty acid (PUFA) was reduced at each step, while the proportion of CLA was
not affected by cooking. Thus, the FA content of raw lamb underestimates
that of cooked meat, especially if the lamb is cooked with bone and fat left
intact allowing infiltration of FA from the surrounding intermuscular and
subcutaneous fat. This influx of lipids from the surrounding adipose tissue
dilutes the proportions of PUFA and LC omega-3 FA in the TFA.
Abbreviations East Friesian (EF); Romney (R); m. longissimus
thoracis (LT); trans-vaccenic acid (TVA); conjugated linoleic
acid (CLA); long chain omega-3 fatty acids (LC omega-3 FA); fatty acids (FA);
total fatty acids (TFA); saturated fatty acids (SATFA); mono-unsaturated
fatty acids (MUFA); polyunsaturated fatty acids (PUFA).
Keywords lamb; breeds; cooking methods; conjugated linoleic
acid; omega-3 fatty acids
A03041; Received 30 June 2003; accepted 11 February 2004; Online publication
date 27 May 2004
New Zealand Journal of Agricultural Research, 2004, Vol. 47: 129-135
0028-8233/04/4702-0129 © The Royal Society of New Zealand 2004
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