Protein nutrition during infancy. An update

Bioactives in bovine milk: chemistry, technology, and applications

The significance of dairy in human health and nutrition is gaining significant momentum as consumers continue to desire wholesome, nutritious foods to fulfill their health and wellness needs. Bovine milk not only consists of all the essential nutrients required for growth and development, it also provides a broad range of bioactive components that play an important role in managing human homeostasis and immune function. In recent years, milk bioactives, including α-lactalbumin, lactoferrin, glycomacropeptide, milk fat globule membrane, and milk oligosaccharides, have been intensively studied because of their unique bioactivity and functionality. Challenges for the application of these bioactive components in food and pharmaceutical formulations are associated with their isolation and purification on an industrial scale and also with their physical and chemical instability during processing, storage, and digestion. These challenges can be overcome by advanced separation techniques and sophisticated nano- or micro-encapsulation technologies. Current knowledge about the chemistry, separation, and encapsulation technology of major bioactives derived from bovine milk and their application in the food industry is reviewed here.

Applications for α-lactalbumin in human nutrition

α-Lactalbumin is a whey protein that constitutes approximately 22% of the proteins in human milk and approximately 3.5% of those in bovine milk. Within the mammary gland, α-lactalbumin plays a central role in milk production as part of the lactose synthase complex required for lactose formation, which drives milk volume. It is an important source of bioactive peptides and essential amino acids, including tryptophan, lysine, branched-chain amino acids, and sulfur-containing amino acids, all of which are crucial for infant nutrition. α-Lactalbumin contributes to infant development, and the commercial availability of α-lactalbumin allows infant formulas to be reformulated to have a reduced protein content. Likewise, because of its physical characteristics, which include water solubility and heat stability, α-lactalbumin has the potential to be added to food products as a supplemental protein. It also has potential as a nutritional supplement to support neurological function and sleep in adults, owing to its unique tryptophan content. Other components of α-lactalbumin that may have usefulness in nutritional supplements include the branched-chain amino acid leucine, which promotes protein accretion in skeletal muscle, and bioactive peptides, which possess prebiotic and antibacterial properties. This review describes the characteristics of α-lactalbumin and examines the potential applications of α-lactalbumin for human health.

Growth, Nutrition, and Cytokine Response of Breast-fed Infants and Infants Fed Formula With Added Bovine Osteopontin

OBJECTIVES

Breast milk contains a high concentration of osteopontin (OPN), a protein having multiple functions. In contrast, infant formula is low in OPN. A randomized clinical trial was performed to evaluate effects of adding a highly enriched bovine OPN fraction to formula, and infants whose mothers had already decided not to breast-feed were recruited. They were fed regular formula (F0) or the same formula with bovine OPN at 65 (F65) or 130 (F130) mg/L (50% and 100% of human milk level, respectively) from 1 to 6 months of age and were compared with a reference group of breast-fed (BF) infants.

METHODS

Morbidity was recorded daily and 3-day dietary records collected monthly. Anthropometry was assessed monthly, and blood samples were taken at 1, 4, and 6 months of age. Hematology and iron status, serum cytokines, plasma amino acids, and blood urea nitrogen were analyzed.

RESULTS

Formulas were well tolerated and there were no significant differences in formula intake or growth among the formula-fed groups. The F130 group had significantly lower plasma threonine than the F0 and F65 groups, and significantly lower plasma branched-chain amino acids (BCAAs) than the F0 group and, thus, was closer to BF infants. Plasma TNF-α was higher in formula-fed infants than in BF infants. Among the formula-fed groups, the proinflammatory cytokine TNF-α was significantly lower in the F65 and F130 groups than in the F0 group, suggesting that OPN downregulates inflammatory cytokines and thus affects immune function.

CONCLUSIONS

Addition of OPN to infant formula changes amino acid metabolism and cytokine responses of FF infants and makes them more similar to BF infants. The lower prevalence of pyrexia in the F130 infants than in F0 infants suggests that adding OPN may confer health benefits.

Infant formula and infant nutrition: bioactive proteins of human milk and implications for composition of infant formulas

Human milk contains an abundance of biologically active components that are highly likely to contribute to the short- and long-term benefits of breastfeeding. Many of these components are proteins; this article describes some of these proteins, such as α-lactalbumin, lactoferrin, osteopontin, and milk fat globule membrane proteins. The possibility of adding their bovine counterparts to infant formula is discussed as well as the implications for infant health and development. An important consideration when adding bioactive proteins to infant formula is that the total protein content of formula needs to be reduced, because formula-fed infants have significantly higher concentrations of serum amino acids, insulin, and blood urea nitrogen than do breastfed infants. When reducing the protein content of formula, the amino acid composition of the formula protein becomes important because serum concentrations of the essential amino acids should not be lower than those in breastfed infants. Both the supply of essential amino acids and the bioactivities of milk proteins are dependent on their digestibility: some proteins act only in intact form, others act in the form of larger or small peptides formed during digestion, and some are completely digested and serve as a source of amino acids. The purity of the proteins or protein fractions, potential contaminants of the proteins (such as lipopolysaccharide), as well as the degree of heat processing used during their isolation also need to be considered. It is likely that there will be more bioactive components added to infant formulas in the near future, but guidelines on how to assess their bioactivities in vitro, in animal models, and in clinical studies need to be established. The extent of testing needed is likely going to depend on the degree of complexity of the components and their bioequivalence with the human compounds whose effects they are intended to mimic.

Human milk fatty acid composition from nine countries varies most in DHA

Many published studies of breast milk FA composition are limited to populations from one or two countries. We aimed to examine the degree to which FA compositions vary across a number of diverse populations. Because diet and maternal adipose stores influence breast milk FA composition, differences in FA composition between groups most likely reflect habitual dietary differences. Approximately 50 breast milk samples (full breast expression) were collected from women in Australia, Canada, Chile, China, Japan, Mexico, Philippines, the United Kingdom, and the United States. The proportion of saturated FA was relatively constant among countries, with the exception of the Philippines, where levels of lauric and myristic acids were elevated (means greater than two times the mean of most other countries). Monounsaturated FA also varied little, with the exception of low levels of oleic acid in the Philippines and high levels of erucic acid in China. Although arachidonic acid (C20:4n-6) levels were similar among all countries (means ranging from 0.36 wt % to 0.49 wt %), mean DHA (C22:6n-3) levels ranged from 0.17 to 0.99 wt %, with the highest levels in Japanese milk and the lowest levels in Canadian and U.S. samples. The results of this study demonstrate that the proportion of saturated and monounsaturated FA are relatively constant across a large number of countries, whereas the level of some of the PUFA, especially DHA, are highly variable.

Characterisation of proteins in the milk of fur seals

Milk protein composition was investigated throughout the lactation periods of the Australian fur seal (Arctocephalus pusillus doriferus) and Antarctic fur seal (Arctocephalus gazella). The mean protein content of the milk was found to be 10.9% and 10.6% respectively. The concentration of total protein did not change during lactation, although a decline in casein content of the milk in late lactation was apparent. Milk protein concentration during a foraging/suckling cycle of the Antarctic fur seal analysed at the time of arrival on shore, and 24 h and 72 h after arrival was 12.8%, 11.4% and 12.5% respectively. Re-feeding animals at 72 h resulted in a significant increase in milk protein content to 14.9%. Characterisation of milk protein by SDS-PAGE analysis revealed 5 casein and 10 major whey protein bands. Amino-terminal sequencing indicated that the majority of the whey fraction of the milk is beta-lactoglobulin (beta-LG). The limited amino acid sequence indicated 3 different beta-LGs were secreted in the milk. Subsequently, RT-PCR was used to extend the sequence of one of the beta-LGs and translation of the 464 bp fragment indicated that it shared 79% sequence identity with feline beta-LG II.

A multinational study of alpha-lactalbumin concentrations in human milk

Alpha-lactalbumin, a 14-kD protein, plays a central biochemical role in the mammary gland as the regulatory subunit of lactose synthase, and also plays a nutritional role for the rapidly growing neonate as the protein in highest concentration in human milk. The current study was undertaken to better characterize alpha-lactalbumin concentrations in human milk from a variety of countries. Mature human milk (lactation duration > or =1 month) was collected from at least 50 women from nine different countries on five continents. Alpha-lactalbumin concentration was determined by HPLC. The mean +/- SD for 452 samples was 2.44 +/- 0.64 g/L. The mean value of the samples from the United States was significantly higher than that from any other country, and the mean in Mexico was significantly lower than that from every country except China and Canada. Alpha-lactalbumin concentration decreased with increasing duration of lactation and was positively correlated with total nitrogen. On average, alpha-lactalbumin contributed 16% of the total nitrogen content of human milk and consequently an important part of the amino acid content.