Postprandial changes in the content and composition of nonprotein nitrogen in human milk.
The effect of a meal on human milk (HM) total nitrogen (TN) and nonprotein nitrogen (NPN) content and composition was examined. Two studies were performed in which milk and blood samples were collected 2-3 h after subjects consumed either a test breakfast or lunch. To monitor the rate of transfer of plasma urea into milk, two women were given [15N]2-urea with the meal. Milk TN concentrations were not significantly different from premeal values. However, concentrations of milk NPN, urea nitrogen, and alanine were increased by greater than or equal to 20% over premeal values. [15N]2-Urea appeared in plasma and milk within 15 min and reached maximum enrichments of 10% and 5.5% in plasma and milk, respectively. Several HM NPN components increase in concentration postprandially; however, these concentrations were not always correlated with changes in plasma concentrations, suggesting that milk NPN may also reflect metabolic activities within the mammary gland.
Nonprotein nitrogen and protein-derived peptides in human milk
Abstract Beyond proteins, milk contains an array of smaller nitrogen (N)-containing components generally referred to as nonprotein nitrogen (NPN). These include milk protein–derived peptides, peptide hormones, amino acids (AAs), N-containing oligosaccharides, N-containing monosaccharides, nucleic acids (DNA and RNA), free nucleotides, and small molecules, including urea, uric acid, ammonia, creatine, creatinine, carnitine, and polyamines. Human milk (HM) is unique in that NPN comprises up to 25% of the total N, compared to 5% in cow milk. Many of these milk components have functions in infants; for example, urea N can be used to synthesize nonessential AAs or converted by the gut microbiota as an N source. In addition, some milk protein–derived peptides have antimicrobial, antihypertensive, and other activities. This chapter reviews components of the NPN fraction of HM, their physiological relevance, typical amounts in milk, factors that affect their concentrations, the analytical techniques used to determine their concentrations, and areas for future research.
Evaluation of Lapping Grains based on Shape Characteristics.
The shape and size of abrasive grains during lapping varies complicately and irregularly. In this study, the aspect ratio of grain size and the fractal dimension of the grain external form were used as shape characteristics of grain in order to evaluate grains with lapping time. The results obtained are summarized as follows : (1)The fractal dimension increases due to microscopic fracture and decreases due to macroscopic fracture or attritious wear. (2)The aspect ratio and the fractal dimension, which are grain shape characteristicsis of the macroscopic shape and the microscopic surface complication of grain respectively, can be used for evaluating grain shape variation during lapping.