New Zealand Journal of Agricultural Research abstracts
Variability in marbling in Angus steers and an evaluation of subjective
marbling assessment
P. D. MUIR
D. R. SMITH
N. B. SMITH
G. J. WALLACE
AgResearch Poukawa
P. O. Box 8144
Havelock North, New Zealand
Abstract Currently there are no marbling grades within the
New Zealand beef classification system, yet within some of our major markets
(e.g., the United States and Japan) marbling is an important component of the
grading system. This paper aims to examine the extent of marbling within Angus
steers in New Zealand and relate these data to US and Japanese marbling grades.
The amount of intramuscular fat (marbling) in the M. longissimus
thoracis at the 12th rib site was estimated for samples from 259 Angus
steers using NIRS. Carcass weight ranged from 220 to 540 kg and explained 66%
of the variability in chemical fat. For carcasses in the 300 to 400 kg range,
intramuscular fat content increased at average rate of 3.5 g kg-1
fresh weight of muscle for each 10 kg increase in carcass weight.
Marbling was assessed in 118 ribeye steaks by 11 novice panellists using both
the Japanese (JMGA) and United States (USDA) marbling grading standards and the
scores obtained were compared against the predicted chemical fat content for
each sample as estimated by NIR spectroscopy. Panellists assessed 8 to 13
steaks per session to determine between-grader variability. Immediately after
each session, steaks were re-randomised and reassessed to determine
within-grader variability. There was sufficient between-operator variability to
indicate that graders should be trained or screened if carcasses are to be
graded on the basis of marbling scores.
The regression equations of mean panel scores on chemical fat content
accounted for approximately 87% of the variation in panel means. Each unit
increase in Japanese marbling score was equivalent to an increase in
intramuscular fat content of 27 (+/-1.0) g kg-1. Each unit increase
in USDA marbling score was associated with an increase in intramuscular fat of
30 (+/-1.1) g kg-1. Our results using novice graders differed
substantially from earlier calibrations of intramuscular fat on marbling score
using trained graders.
The longissimus thoracis muscle of heavyweight Angus steers was
estimated to contain intramuscular fat contents equivalent to JMGA marbling
scores of up to 8 and USDA scores of 6, suggesting that New Zealand has cattle
genotypes capable of producing well marbled beef.
Keywords Angus steers; marbling; intramuscular fat;
subcutaneous fat; subjective measurement
New Zealand Journal of Agricultural Research, 1998, Vol. 41: 335-346
0028-8233/98/4103-0335 $7.00/0 (c) The Royal Society of New Zealand
1998
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