Page 52 - New additives and ingredients in the formulation of aquafeeds

The degrees of hydrolysis obtained in both cases by the sequential
hydrolytic process using Alcalase and Flavourzyme as proteases is more
than 40%, which implies a change in the protein molecular profile of protein
hydrolysates, presenting mainly low molecular weight peptides (Figure
1). Thus, some studies on the proteolytic capabilities of fish larvae have
suggested that the incorporation of small peptides or protein hydrolysates
in diets for larvae improve development processes in the digestive tract of
the larvae (Kotzamanis et al., 2007; Kolkovski, 2008; Hermannsdottir et
al., 2009). However, the majority of these trials have been made from fish
or animal origin hydrolysates and never from plant protein hydrolysates.
Therefore, and although the fish or animal protein source has been the
most used in the development of aquaculture diets, due to the above
mentioned reasons, there is currently a great demand for the production
of food formulations from vegetable protein sources to replace the animal.
This new molecular profile observed in plant protein hydrolysates also affects
the solubility of proteins according to the pH of the medium compared
to the intact native protein in the protein isolates (Figure 2). As shown,
while the starting protein presents maximum solubility at basic pHs and
minimum (isoelectric point) at acid pHs, the protein hydrolysate has a high
and greater solubility in the whole pH range studied (pH 2 to 12) as a result
of the decreasing in the size of the peptides and the increased presence of
ionic groups (COO-and NH3+) that promote greater interaction with water
molecules. It has been observed that the use of native casein as the only
source of nitrogen in food supplements in the larval stages of common carp
is not enough to survive and grow satisfactorily, contrary to the juvenile
stages that seem to use effectively this protein (Sen et al., 1978). However,
the partial substitution of the native casein by casein hydrolizate (Szlaminska
et al., 1993) or sodium caseinate, a soluble form no hydrolyzated of casein,
improves the larval performance (Radünz-Neto et al., 1993). As both products
are soluble in water, unlike native casein, these results suggest that the
solubility may be an important criterium of using protein by fish larvae. In this
way, studies by Carvalho et al., (2004) have shown that the total or partial
50 Plant protein isolates and hydrolysates as alternative to the animal protein in aquaculture diets
Figure 1. Molecular profile by gel filtration chromatography f chickpea and
lupin hydrolysates and isolates obtained in trial facilities.
Figure 1: Molecular
profile by gel filtration
chromatography of
chickpea and lupin
hydrolysates and
isolates obtained in
trial facilities