S159 TMA induced Fishy flavour- the major reason behind Off-odour of duck eggs
S.K.Mishra, Rajashree Rath, B.Panigrahy, A. Maity, A.Mishra and C.R.Pradhan
Central Avian Research Institute, Regional Centre
&
College of Veterinary Science
Bhubaneswar, INDIA-751003
ABSTRACT
Acceptance of Duck eggs as a popular table egg variety is at par with chickens, in
whole World and India alike except for its perceptible but uncharacterized off-odour.
An investigation was conducted to analyse causative basis of off-flavour in duck eggs
aimed at detecting trimethylamine (TMA) in egg yolk which is already implicated for
fishy-taint, reported in some stains of layer chickens when fed with higher TMA
precursors. The study was on adult layers @ 30 each of 3 ducks breeds: Khaki
Campbell, Desi and White Pekin in deep litre system. 30 adult commercial WLH
layers, were used as negative control. All experimental birds were fed with 4 TMA
precursors: fish meal (5% and 10% level), choline (0.3% and 0.6% level) and a controldiet devoid of any TMA precursors, for 90 days continuously. The resultant eggs were
analysed for yolk TMA-N following a TCA based spectrophotometric procedure. Few
eggs were also analyzed for other tainting elements by GCMS. The results revealed a
significant difference (P<0.001) between breeds, dietary treatments and breed × dietary
treatments. In general, all duck breeds revealed an enhanced yolk-TMA level (~3times
higher) than WLH, on control diets. There existed an inherent species difference (ducks
vs chicken) possibly due to variant host-TMA metabolism. The study concluded:
Duck’s Yolk TMA levels (more than other components) under a deep litre system, was
significantly higher than chickens, and was a major factor contributing to off-odour.
Key words: TMA, off-flavour, fishy-taint, choline, Duck breeds and WLH chickens.
Introduction
Commercial poultry has gained massive popularity, in past few decades, for its
contribution to table-egg production. Consequently the global per-capita consumption
of eggs has gone up multifold during this period. However, consumers in Indian and
many other Asian countries remain largely engrossed with chickens, as the most
favoured table egg producers, while focus on other poultry species remains at
minimum. For example, the Duck (Anas platyrhynchos) which constitute ~ 6% of
total domesticated poultry in India (Animal Husbandry Statistics, 2012) having
presence in most coastal states, are hardly accepted as a table-egg type poultry, mainly
due to lack of popularity in urban markets. Digging into this popularity-constraint of
duck eggs reveals that: a section of consumers tend to equate smell and aroma of duck
eggs to a fishy smell which is implicated in the brown-shelled chicken eggs upon
feeding of high levels of fish-meal, rape-seed meals/canola meals, as an inherent
component of duck eggs, which is debatable and eludes a consensus.
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It was therefore, surmised that: some sort of off-flavour was present in duck eggs, as
has been cited in meat of wild ducks (McAtee, 1918). The literature is nevertheless
hollow, on exact characterization of this off-flavour and has hardly been elaborated.
Besides, no work has ever been conducted on flavour of eggs from ducks reared on
floor. In view of above, this study was undertaken to study influence of genetic and
nutritional factors on off-odour in duck eggs and if fishy taint reported in chickens was
ever a cause behind the perceived off-flavour of duck eggs.
Materials and Methods
Thee breeds of Ducks maintained in the Regional Centre, Central Avian Research
Institute, Bhubaneswar i.e Khaki Campbell, White Pekins and desi breeds , were used
for this study where in White Leghorn chickens (BV-300 hens) procured from a
commercial source were maintained as control. The study was therefore, on adult layers
@ 30 each of 3 ducks breeds: Khaki Campbell, Desi and White Pekin in deep litre
system. 30 adult commercial WLH layers, were used as negative control. All
experimental birds were fed with 4 TMA precursors: fish meal (5% and 10% level),
choline (0.3% and 0.6% level) and a control-diet devoid of any TMA precursors, for 90
days continuously. On completion the feeding trial, the resultant eggs from different
treatment were analysed for yolk Trimethyl Amine (TMA-N) following a TCA based
spectrophotometric procedure as per Kretzschmar et al. (2007) with slight
modifications. The TMA-N values were obtained from different genetic-dietary
subgroups were then subjected to statistical analysis using SAS 9.2 software and where
Analysis of Variance (ANOVA) and comparison of means were carried following
General linear model analyses.
Results and discussion
Comparison of means of TMA values for different dietary treatments and breeds in
deep litter system are presented in table 1. Within Khaki ducks, the control group
depicted significantly lower level of yolk-TMA as compared to other treatments. The
varying levels of dietary choline did not show any significant difference within them,
for TMA values. However, increase in fishmeal level in diet led to significant increase
in Yolk-TMA level, which nevertheless remained significantly lower than TMA
recorded for both choline-diets. Within Desi group, the variation in yolk-TMA level
was not significantly affected by levels of either TMA precursors in diet. As regards to
dietary effect, the control's TMA values remained significantly lower than the fish-meal
and choline-fed groups. For Pekin ducks, the yolk TMA level was affected significantly
by both the choline levels and higher fish-meal level in diet, as compared to control. As
such, 5% level of fishmeal in the diet appeared to be falling short of the threshold to
increase yolk-TMA level to any significance. However, the trend showed a numerical
rise in yolk TMA upon rise in either fishmeal or choline levels in Pekin diets within
respective dietary treatments.
Table 1. Breed wise Yolk-TMA means realized from varying Dietary-TMA precursors
TREATMENTS KHAKI
DESI
Mean±SE
Control
2.64±2.05
PEKIN
Mean±SE
def
Mean±SE
2.26±2.14
g
2.34±1.98fg
2
FM 5%
3.03±1.96c
3.04±2.07c
2.57±2.35efg
FM 10%
CHCL 0.3%
3.91±1.89a
3.55±0.07b
3.07±1.73c
3.09±1.94c
2.75±1.87cde
2.99±1.82cd
CHCL 0.6%
Overall
3.69±0.82ab
3.36±0.77
2.86±1.88cde 3.08±1.77c
2.87±0.78
2.75±0.77
N.B: Means bearing
dissimilar
superscripts
are
significantly different (P<0.01).
Analysis of variance showed significantly different TMA values realized for all the
duck breads. Both Khaki and Desi ducks produced higher levels of TMA in egg yolk
than the control, which could be attributed to both fish meal and choline in the diet.
Varying levels of fish meal and choline was not consistently able to impact the yolkTMA in Desi and Pekin ducks. Recording of differential but uneven yolk-TMA level
between duck groups in this study finds support from report of Cartar (1968) who
interpreted that surrounding atmosphere were able to impact off flavours in chicken
eggs, which indicates probable contribution of TMA from faecal samples present in
litter materials, than from dietary treatments, per se. TMA being conspicuously present
in faecal materials of birds, this assumption of faeces-contaminated eggs (floor-laying
often being feature of ducks in deep litter) resulting in higher (and yet slightly uneven)
yolk-TMA levels appeared resonable.
The order of yolk TMA levels breed-wise, remained as: Khaki > Desi > Pekin. The
Khaki ducks were significantly different (P<0.01) than the Desi followed by Pekin
ducks. Similarly, in terms of dietary precursors, the TMA values realised was in the
decreasing order: FM10%→ CHCL 0.6% → CHCL 0.3% →FM5%. Results of
significant spurt in yolk-TMA levels getting impacted by dietary choline levels as
realized in this study are supported by findings of Honkatukia et al. (2005),
Kretzschmar et al. (2007) and Ward et al. (2009) in chickens. However, non-significant
impact of differing dietary choline on yolk TMA visible from our result is at variance
from findings of above authors, which hints that threshold of choline level in feed could
be different in ducks than that of chickens. Nonetheless, Significant effect of geneticnutrition interaction level for supplementary choline as detected in this study is in
agreement with the reports (breed × diet interaction) by Vondell (1932) and Wakeling
(1982) in chickens.
Based on findings of this study, it was clear that: the off-odour of duck eggs, already
contributing to a degree of consumer- dislike owing to suspected presence of fishy taint
at a higher level than chicken-eggs was proven to be a fact. Truly, it was, the higher
level of yolk-TMA, that contributed to this difference. It was also proven that speciesdifference existed between ducks and chickens leading to moderately-elevated TMA
levels in Duck eggs that impacted its undefined strong aroma, in general. Genetic
variation between duck breeds effecting resultant yolk-TMA levels, however, warrants
further studies to characterize inheritance of off-odour in duck eggs.
Acknowledgments
The authors gratefully acknowledge the facility and permission provided by Director,
CARI and OUAT authorities for conducting this study.
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