Aqua feed manufacture requires flexible formulations and effective methods to screen suitable feed ingredients.
In vitro digestionmay assist in the characterization and quality control of protein in feedstuffs for fish species once
standardized species-specific digestive enzyme extracts are available. This study aimed to develop a species-specific
in vitro enzymaticmethod to assess protein digestion in fish under the pH-stat concept. Two carnivorous (rainbow
trout, Oncorhynchus mykiss, and cobia, Rachycentron canadum) and one omnivorous (Nile tilapia, Oreochromis
niloticus) fish specieswere used asmodels. Crude digestive enzyme extractswere recovered from stomach and pyloric
caeca or intestine of individuals of differentweight groups, feeding status, and farming systems. The hydrolytic
capacity of the species-specific enzyme extracts was standardized on purified protein substrates and measured as
degree of protein hydrolysis (DH) in the pH-stat assay. A group of twenty-four feed ingredients, including fish
meals and by-products of plant and animal origin, was assessed for DH using the recovered enzymes
from stomach and pyloric caeca/intestine. Ingredients were hydrolyzed with fish (i) stomach extract, (ii) pyloric
caeca/intestine extract or (iii) stomach enzymes followed by pyloric caeca/intestine extract. Among plant
by-products, cotton seedmeal presented the highestDHwith stomach plus pyloric caeca/intestine enzymes, followed
by soy protein concentrate and soybean meals. Blood meals were the land animal by-product with higher DH
outputs compared to poultry by-product meals and feather meals. No significant difference was observed among
the DHs of fish meals. The significance of measuring the DH with stomach enzyme extract is still not well understood
but, overall, the pre-hydrolysis of feedstuffs with stomach enzymes increased pyloric caeca/intestine DH
value. For cage and pond farmed Nile tilapia, ingredient DHs followed the same trend, describing a significant
correlation and a high determination coefficient regression. Routine use of the method may yet depend on the
prompt availability of more practical sources of enzymes. The determination of the degree of protein hydrolysis
by the in vitro pH-stat with species-specific enzymes has shown to be a precise method that may be a useful tool
to rank feed ingredients, and also an accessory method in the quality control of feedstuffs.
Aqua feed manufacture requires flexible formulations and effective methods to screen suitable feed ingredients.
In vitro digestionmay assist in the characterization and quality control of protein in feedstuffs for fish species once
standardized species-specific digestive enzyme extracts are available. This study aimed to develop a species-specific
in vitro enzymaticmethod to assess protein digestion in fish under the pH-stat concept. Two carnivorous (rainbow
trout, Oncorhynchus mykiss, and cobia, Rachycentron canadum) and one omnivorous (Nile tilapia, Oreochromis
niloticus) fish specieswere used asmodels. Crude digestive enzyme extractswere recovered from stomach and pyloric
caeca or intestine of individuals of differentweight groups, feeding status, and farming systems. The hydrolytic
capacity of the species-specific enzyme extracts was standardized on purified protein substrates and measured as
degree of protein hydrolysis (DH) in the pH-stat assay. A group of twenty-four feed ingredients, including fish
meals and by-products of plant and animal origin, was assessed for DH using the recovered enzymes
from stomach and pyloric caeca/intestine. Ingredients were hydrolyzed with fish (i) stomach extract, (ii) pyloric
caeca/intestine extract or (iii) stomach enzymes followed by pyloric caeca/intestine extract. Among plant
by-products, cotton seedmeal presented the highestDHwith stomach plus pyloric caeca/intestine enzymes, followed
by soy protein concentrate and soybean meals. Blood meals were the land animal by-product with higher DH
outputs compared to poultry by-product meals and feather meals. No significant difference was observed among
the DHs of fish meals. The significance of measuring the DH with stomach enzyme extract is still not well understood
but, overall, the pre-hydrolysis of feedstuffs with stomach enzymes increased pyloric caeca/intestine DH
value. For cage and pond farmed Nile tilapia, ingredient DHs followed the same trend, describing a significant
correlation and a high determination coefficient regression. Routine use of the method may yet depend on the
prompt availability of more practical sources of enzymes. The determination of the degree of protein hydrolysis
by the in vitro pH-stat with species-specific enzymes has shown to be a precise method that may be a useful tool
to rank feed ingredients, and also an accessory method in the quality control of feedstuffs.
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