Solubilisation des protéines de poisson, supplémentation en tryptophane et valeur alimentaire pour le porcelet

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Abstract
Water-soluble fish protein concentrates (SFPC) can be obtained by enzyme hydrolysis of white fish byproducts. A solubility of 75% was obtained for the 1st SFPC (E1) with a hydrolysis length T, and an enzyme concentration E. Solubility increased to 86% when the hydrolysis lasted 8 T with an enzyme concentration of 1.5 E. A similar solubility (87%) was observed with the combination 2 T + 1.25 E when an important part of the unsolubilized fraction was centrifuged off. An increase in the threonine content together with a decrease in the histidine and tryptophan contents were found in E2 and E3 compared to E1. This last amino-acid appeared to be the 1st limiting factor of the SFPC. The 3 products (E1, E2 and E3) supplied 85% of the crude protein in the experimental diets (number 2, 3 and 5) of a trial involving 120 piglets weaned at 10 days and raised up to 63 days of age. The feeding schedule included 2 feeds, a prestarter containing 22% protein and fed from 10-42 days of age, a starter containing 18% protein and fed from 28-63 days of age. The rest of the protein (15%) came from refattened skim-milk (prestarter) and from barley (starter). Two diets (number 4 and 6) including the most soluble SFPC (E2 and E3) were supplemented with 0.05% L-tryptophan. In the control diet, 67% of the protein was supplied by SFPC E1 and 33% either by skim-milk in the prestarter feed or by a mixture of barley and soybean oilmeal in the starter feed. Performances, gain and feed efficiency were significantly higher with SFPC E1 than with E2 and E3 in the unsupplemented diets. Feed intake was enhanced by the supplemental L-tryptophan. In the same way, weight gain and feed efficiency were both improved. Digestibility of N was slightly but significantly increased from 21-28 days of age in the groups fed SFPC E2 and E3 compared to the experimental group fed SFPC E1. A tendency to more scouring and unsatisfactory adaptation to the starter feed was noted in some of those groups. Tryptophan was finally confirmed to be the 1st limiting amino-acid of SFPC.