Coating crystalline methionine with tripalmitin-polyvinyl alcohol slows its absorption in the intestine of Nile tilapia, Oreochromis niloticus

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Supplemental free amino acids (FAA) can be used to satisfy dietary amino acid requirements when plant products replace fish meal and other animal byproducts in formulated diets. Use of coated FAA in diets could provide benefits by slowing the rate of FAA absorption and perhaps by increasing utilization efficiency. A laboratory feeding trial was conducted to determine the effect of two coatings—tripalmitin-polyvinyl alcohol (TPA) and cellulose-acetate-phthalate (CAP)—on absorption of supplemental methionine by Nile tilapia. Forty-five adult fish (mean weight, 185 g) were stocked individually in 5-l aquaria and fed one of three, semipurified diets containing uncoated l-[ 35S]methionine (UM) or TPA- or CAP-coated methionine as 50% of the dietary sulfur amino acid requirement. Three fish were taken from each treatment 0.5, 1, 3, 6, and 12 h after force-feeding to measure relative rates of 35S uptake and the amount of 35S-activity in intestinal tissues, liver, spleen, muscle, and blood plasma. Methionine uptake was highest in the foregut area, but absorption appeared to occur throughout the length of the intestine, including the hindgut. TPA-coated methionine was absorbed more slowly than uncoated methionine and fish fed with TPA-coated methionine had significantly lower levels of 35S-activity in tissues than fish fed with UM. Activity of labeled methionine in tissues of fish fed with CAP-coated methionine usually was not significantly different from 35S-activity in fish fed with UM. The TPA coating appeared to effectively slow the absorption of free methionine in the gut of Nile tilapia, but additional work is needed to determine if TPA-coated methionine is utilized more efficiently than the uncoated amino acid.