IN-VITRO DIGESTION OF PROTEINS IN HUMAN-MILK FORTIFIERS AND IN PRETERM FORMULA

Background: Knowledge about the digestibility of the proteins in new p roducts designed for feeding preterm infants is limited. The purpose o f this study was to observe in vitro the hydrolysis of the bovine and human whey proteins in such products. Methods: Proteins in human milk, in human milk fortifiers (Presemp [Semper AB, Stockholm, Sweden] and Enfamil [Mead Johnson, Evansville, LN, U.S.A.] human milk fortifiers), in preterm formulas (Similac Special Care [Ross, Columbus, OH, U.S.A. ] and Enfalac [Mead Johnson]), and whey protein concentrates with vary ing degrees of denaturation were digested by duodenal juice from healt hy preterm infants, from a S-year-old child, and from adults. Digestio n was studied in vitro using polyacrylamide gradient gel electrophores is, electroimmunoassay, and nonprotein nitrogen analysis. Results: Cas ein was the protein most rapidly degraded in all products. Human and b ovine whey proteins were more slowly digested; as much as 68% of human lactoferrin was still immunoreactive after 40 minutes of digestion. T he corresponding figure for bovine serum albumin was 24-69%; for B-lac toglobulin, 20-40%; for bovine alpha-lactalbumin, 20-51%; and for huma n alpha-lactalbumin, 41%. Contrary to common belief, digestibility of bovine whey proteins decreased with a high degree of denaturation of t he proteins. Conclusions: Bovine whey proteins in human milk fortifier s and in preterm formulas are relatively slowly digested in vitro by n ormal duodenal juice. The results may have implications for the design of products for feeding preterm infants. (C) 1998 Lippincott-Raven Pu blishers.