Direct determination of methionine sulfoxide in milk proteins by enzyme hydrolysis/high-performance liquid chromatography.

A direct and simultaneous HPLC/UV determination of methionine and methionine sulfoxide in enzyme-hydrolyzed milk proteins is described. Protein hydrolysis is accomplished by a three-enzyme (pronase, leucine aminopeptidase, prolidase) 20-h/37 degrees C digestion. A gradient elution reversed-phase HPLC system with UV detection at 214 nm and 280 nm is then used to determine the quantitative releases of methionine sulfoxide, methionine, tyrosine, and tryptophan. The ease of methionine oxidation by a wide variety of oxidants, coupled with the quantitative release of both methionine and its sulfoxide by the three-enzyme hydrolysis, renders the approach valuable for identifying oxidized milk proteins. The relatively simple method proved accurate and precise in its application to commercial milk products, finding methionine sulfoxide levels as high as 74% of the total methionine.

Growth, tolerance and biochemical measures in healthy infants fed a partially hydrolyzed rice protein-based formula: a randomized, blinded, prospective trial.

OBJECTIVE: To evaluate growth, tolerance and plasma biochemistries in infants fed an experimental rice protein-based infant formula. DESIGN: Randomized, blinded, 16 week parallel feeding trial of 65 healthy infants fed either an experimental partially hydrolyzed rice protein-based infant formula fortified with lysine and threonine (RPF, n = 32), or a standard intact cow's milk protein-based formula (CMF, n = 33) as a control. Assessments occurred at enrollment (average 2 days), 2, 4, 8, and 16 weeks of age. RESULTS: Growth as indicated by weight, length, and head circumference was not different between the 2 formula groups. All plasma biochemistries for both groups were within reference normal range. However, RPF group had lower phosphorus and urea nitrogen, lower essential amino acids except threonine, which was higher, and lower ratio of essential (including semi-essential) to non-essential amino acids. Differences in the concentrations and ratios of amino acids became less as feeding progressed with age. Plasma total protein, albumin, prealbumin, calcium, magnesium, and alkaline phosphatase were not different between groups. CONCLUSION: Healthy infants fed an experimental partially hydrolyzed rice protein-based formula had normal growth, tolerance, and plasma biochemistry comparable to those of infants fed a standard intact milk protein-based formula, despite some differences in amino acid profiles.