Discussion and conclusions
It was not possible to obtain an equal distribution of samples
covering all the variables of season and origin for Pangasius.
However, sufficient samples were obtained to look at trends in
the overall mean and uncertainty and show that where significant differences were found, these were not of practical significance.
The recommended nitrogen factors for whole and
commercial Pangasius fillets for both the Dumas and Kjeldahl
methods are given in Table 6. These values have been rounded
up or down to the nearest 0.05. The values take into account the
low fat contents of the fish, with the standard uncertainty (2
SEM) for means of duplicate analyses. Whole Pangasius is not
widely sold on the UK market, therefore, its nitrogen factor is
used as a comparison with the processed product, commercial
Pangasius fillets. The nitrogen content of the fish ingredient
produced by good manufacturing practice for commercial
Pangasius fillets is 5% less than for the whole fish. This figure
compares favourably with the interim factors in the UK Code of
Practice,10 which indicated a 7% difference in nitrogen factor
between whole fish and commercial fillets.
The recommended nitrogen factor for Pangasius commercial
fillets of 2.69 (Kjeldahl 2.65) compares favourably to a previous
German study,4 which found that organically produced Pangasius
fillets had a Kjeldahl nitrogen content of 2.72 g per 100 g.
Non-organic commercial Pangasius fillets had a Kjeldahl
nitrogen content of 2.13–2.52 g per 100 g and were deemed to
have been previously soaked in either polyphosphate or citrate
before freezing. The nitrogen factor values obtained in this
study also compare favourably with historic data from 2007–
2013 provided by Young's Seafood11 for 31 samples of
commercial fillets with an average nitrogen content of 2.82 g per
100 g (SD 0.208).
Table 4 Summary of chemical analyses
Variable No. Mean SD SEM
Nitrogen % 75 2.69 0.21 0.024
Fat % 75 1.23 0.46 0.052
Moisture % 75 81.4 1.28 0.15
Ash % 75 0.89 0.10 0.012
Table 6 Recommended nitrogen factors for Pangasius
Product Nitrogen factor (Kjeldahl)
Whole Pangasius 2.85 (2.80) 0.04
Commercial Pangasius fillets 2.70 (2.65) 0.05
Table 5 One way ANOVA analysis of results from 3 labs, origin and
season
N % Fat % Moisture % Ash %
Lab *
A 2.60 1.28 81.6 0.86
B 2.74 1.14 81.2 0.90
C 2.75 1.28 81.5 0.91
Season * *
D 2.65 1.20 81.7 0.89
W 2.76 1.29 80.9 0.88
Fillet plant * *
Agish 2.57 1.15 82.4 0.91
DL147 2.76 1.28 80.8 0.89
DL355 2.70 1.25 81.4 0.84
* ¼ Difference(s) significant at 95% confidence.