Page 23 - Aquauclature Research and Studies (01)

AQUAUCLATURE
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Research and Studies 1 (1): 15-01, 2026 page of 193

4. Discussion
Autoclaving and soaking only marginally changed the proximate com-
position of CSGM. However, ANFs were significantly decreased with pre-
treatment and autoclaving was more efficient than soaking. The higher effi-
ciency of autoclaving in decreasing ANFs was a direct result of the known
effects of heat processing on heat-labile nature of ANFs and their structures.
These results were in agreement with those reported in several earlier studies
(Alonso et al., 2000; Bhatt et al., 2011; Garg et al., 2002; Hossain et al., 2001;
Siddhuraju and Becker, 2003).
Several factors are known to affect the digestibility of feed ingredients.
Some factors are related to the ingredients while others are related to the feed
preparation processes (Francis et al., 2001). ANFs such as glucosinolates,
saponins, phytic acids, trypsin inhibitors, tannins and soluble non-starch pol-
ysaccharides are known to affect the digestibility of the feed ingredients
(Cheng and Hardy, 2003; Drew et al., 2007; Francis et al., 2001). Tannin, the
main ANF in carob seeds, can form complexes with proteins that bind to hy-
drophobic regions via hydrogen and ionic bonds, resulting in deficiencies and
imbalances of amino acids that are detrimental to fish growth (Alexis, 1990;
Nachtomi and Alumot, 1963). Nevertheless, the full effects of tannins on fish
are still unclear (Francis et al., 2001). Collins et al. (2013) demonstrated that
tannins have a positive and significant effect on feed intake in rainbow trout
unlike other ANFs (e.g. phytic acid, saponins, and glucosinolates), which
have been shown to have considerable negatives effect on food utilization. A
dietary level of up to 2% tannins does not have any negative effect on the
growth performance of common carp but the fish rejects hydrolysable tannins
(Makkar and Becker, 1999). Furthermore, Alexis (1990) and Martínez-
Llorens et al. (2012) found that tannins suppress the protein digestibility of
feed in both the rainbow trout and gilthead sea bream. In this study, pre-treat-
ment significantly reduced tannin level in CSGM by almost 72% and im-
proved the protein digestibility by 31-40%.
Phytate is the stored form of phosphorus in numerous plant tissues such
as bran and seeds and it restricts the availability of plant phosphorus for fish
and reduces the digestibility of other divalent mineral ions (Cain and Garling