Activity Of Human Milk Research Articles

Premature delivery impacts the concentration of plasminogen activators and a plasminogen activator inhibitor and the plasmin activity in human milk.

Background and aimsPlasmin in human milk partially hydrolyzes milk proteins within the mammary gland and may enhance the hydrolysis of milk proteins within the infant’s stomach. This study examined the effects of extremely preterm (EP)-, very preterm (VP)-, and term-delivery on plasmin activity and the concentrations of plasminogen activators [urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA)], plasminogen activator inhibitor type 1 (PAI-1) and the complexes of PAI-1/uPA and PAI-1/tPA in human milk.Materials and methodsHuman milk samples were collected from mothers who delivered extremely preterm infants [24–27 weeks gestational age (GA), n = 20], very preterm infants (28–32 weeks GA, n = 12), and term infants (38–39 weeks GA, n = 8) during 2–72 days postnatally. Plasmin activity was determined using fluorometric substrate assay, whereas concentrations of uPA, tPA, PAI-1, the PAI-1/uPA complex and the PAI-1/tPA complex were quantified by ELISA.ResultsPlasmin activity, uPA and tPA were detected in all human milk samples, PAI-1 and the PAI-1/uPA complex were present in 42.5 and 32.5% of milk samples, respectively, and the PAI-1/tPA complex was not detected. Plasmin activity was correlated negatively with postnatal age and postmenstrual age (PMA) in the VP group and positively with postnatal age in the term group. uPA and tPA concentrations decreased with increasing postnatal age in both EP and VP groups but did not correlate in the term group. uPA concentration was correlated positively with GA in the VP group and tended to be elevated with increasing GA in the combined three groups. In contrast, tPA concentrations were correlated negatively with GA and PMA in the combined three groups (P < 0.008) and with PMA in the EP and VP groups. PAI-1 concentration tended to be correlated positively with postnatal age in the combined three groups. No correlation was detected with the PAI-1/uPA complex.ConclusionPremature delivery impacted the plasmin activity and the concentrations of uPA, tPA, and PAI-1 in human milk. Whether these changes in milk plasminogen activators and inhibitors have a role in balancing the proteolytic digestion of premature infants remains to be investigated.

Effects of the thawing rate and heating temperature on immunoglobulin A and lysozyme activity in human milk

BackgroundThe percentage of infants receiving frozen human milk (HM) is increasing. The effects of thawing and warming on the secretory immunoglobulin A (SIgA) level and lysozyme activity in frozen HM should be investigated to identify optimal methods for preserving immune factors in frozen HM.MethodsMilk samples were collected from 40 mothers with healthy full-term infants who had been lactating for one to six months. The baseline samples were analyzed within 24 h after collection, and the other samples were frozen at -18 °C before analyses. We compared two methods: placing the container overnight in a refrigerator at 4 °C before warming (slow thawing) and immediately thawing in warm water after removing the sample from the freezer (rapid thawing). Additionally, we investigated the effects of the warming temperature by comparing room temperature (25 °C) and physiological temperature (37 °C). The SIgA concentrations and lysozyme activities in the milk samples were determined using ELISA kits and fluorometric lysozyme activity assay kits, respectively.ResultsThe SIgA concentrations and lysozyme activity in frozen HM were 16.5–52.1% and 16.8–39.3% lower than those in fresh HM, respectively. The SIgA concentrations in frozen HM were stable during slow thawing at 37 °C (p = 0.072) compared with those in fresh HM. The SIgA concentrations and lysozyme activity were maintained at significantly higher levels during slow thawing than during rapid thawing at 25 °C (p = 0.002 and p < 0.001, respectively). Slow thawing preserved higher SIgA concentrations and lysozyme activity than rapid thawing at 37 °C, but the difference was not significant.ConclusionsThe SIgA level in HM frozen at -18 °C for two months was stable after overnight thawing in the refrigerator (4 °C for 12 h) before warming to 37 °C compared with that in fresh milk. The thawing of HM in the refrigerator overnight (and then warming to 25 °C or 37 °C for 30 min) has the potential to preserve the SIgA concentration and lysozyme activity to a greater extent than heating immediately after removal from the freezer. Broader temperature ranges should be analyzed to determine the temperature that minimizes the losses in SIgA concentration and lysozyme activity in HM.

Preservation of Anti-cytomegalovirus Activity in Human Milk Following High-Pressure Processing Compared to Holder Pasteurization.

Pasteurized donor human milk is recommended for hospitalized preterm infants when mother’s own milk is unavailable. Our aim was to compare the antiviral activity of human milk processed by Holder pasteurization (HoP) or high-pressure processing (HPP) against representative enveloped and non-enveloped viruses including cytomegalovirus and hepatitis A virus. Expressed milk from 20 donors collected from the Ontario Milk Bank was combined into 10 pools, each from two unique donors. Each pool was processed by HoP (62.5°C, 30 min) or HPP (500 MPa, 8 min, 4°C) and subsequently inoculated with cytomegalovirus or hepatitis A virus to achieve a final concentration of 5-log plaque-forming units/mL. Plaque reduction assays were used to quantify detectable virus after 30 min incubation (room temperature). Post hoc experiments using a 4 h incubation time were conducted if reductions were detected at 30 min. Irrespective of processing, cytomegalovirus concentrations declined in all pools after 30 min incubation (P < 0.0001). Milk processed by HoP exhibited significantly less reduction compared to raw milk (P = 0.0069). In post hoc experiments, anti-cytomegalovirus activity was maintained at 4 h, with high inter-pool variability. Hepatitis A virus concentration remained unchanged after 30 min incubation in raw and processed milk. Anti-cytomegalovirus activity in human milk is preserved following HoP and HPP, persisting up to 4 h post-inoculation; anti-hepatitis A virus activity was not observed in raw or processed milk. Further research is needed to understand how HoP or promising alternative processing methods affect the antiviral activity of donated milk, given its potential importance to recipient infants.

In Vitro Stimulation of Whole Milk Specimens: A Field-Friendly Method to Assess Milk Immune Activity.

The immune system of milk protects against infections and guides immune system development. A system-level understanding of milk immune activity is critical for research into infant infectious disease risk and lifelong health. To describe a protocol to characterize immune activity in human milk via in vitro stimulation for use in population-based (rather than clinical) research. This study proceeded in two phases, each with a cross-sectional design. Human milk specimens were incubated for 24 hr at 37 °C in mammalian cell culture medium with stimuli (e.g., Salmonella enterica) in a CO2-enriched environment. Immune responses to stimuli were characterized as the change in cytokine: [stimulated]/[baseline]. Predictors of cytokine responses were evaluated with generalized linear models. Patterns were detectable across mother-child dyads: Interleukin-6 responses to stimuli were generally positively associated with child age and with maternal autoimmune disease. Our method allows characterization of pro-inflammatory milk immune activity in vitro in population-based (rather than clinical) research settings. In vitro activity has a system-level interpretation and is likely to be of broad utility in global health research in settings with high infectious disease risk, where understanding the immune system of milk is critical to understanding maternal and child health.

Immunological components and antioxidant activity in human milk processed by different high pressure-thermal treatments at low initial temperature and flash holding times

The effect of high pressure thermal (HPT) processing on the immunoglobulin (IgM, IgA and IgG), and cytokine content (IL-6, IL-8, IL-10, and TNF-α), and antioxidant activity of human milk was analyzed after the application of different treatments between 200, and 800 MPa at low initial temperatures (between −15, and 50 °C) and for 1 s (flash treatments). Low pressures intensities did not induce changes in Igs while at 800 MPa, all combinations reduced the control levels. IL-6 and IL-10 were not affected by any of the treatments applied while IL-8 and TNF-α were reduced at treatments which combined temperatures at 50 °C. In general antioxidant activity was not affected at the processing conditions chosen. The flash HPT treatment applied at 600 MPa and at 0 °C could be the best choice to preserve immunological parameters and the antioxidant activity of human milk.

Antagonistic activity towards the androgen receptor independent from natural sex hormones in human milk samples from the Norwegian HUMIS cohort

In this paper, we investigated the possible presence of endocrine disrupting chemicals (EDCs) based on measuring the total estrogenic and androgenic activity in human milk samples. We used specific bioassays for analysis of the endocrine activity of estrogens and estrogen-like EDCs and androgens and androgen-like EDCs and developed a separation method to evaluate the contribution from natural hormones in comparison to that of EDCs to total endocrine activities. We extracted ten random samples originating from the Norwegian HUMIS biobank of human milk and analyzed their agonistic or antagonistic activity using the ERα- and AR CALUX® bioassays. The study showed antagonistic activity towards the androgen receptor in 8 out of 10 of the assessed human milk samples, while 2 out of 10 samples showed agonistic activity for the ERα. Further investigations demonstrated anti-androgenic activity in the polar fraction of 9 out of 10 samples while no apolar extracts scored positive. The culprit chemicals causing the measured antagonistic activity in AR CALUX was investigated through liquid chromatography fractionation coupled to bioanalysis and non-target screening involving UHPLC-Q-TOF-MS/MS, using a pooled polar extract. The analysis revealed that the measured anti-androgenic biological activity could not be explained by the presence of endogenous hormones nor their metabolites. We have demonstrated that human milk of Norwegian mothers contained anti-androgenic activity which is most likely associated with the presence of anthropogenic polar EDCs without direct interferences from natural sex hormones. These findings warrant a larger scale investigation into endocrine biological activity in human milk, as well as exploring the chemical sources of the activity and their potential effects on health of the developing infant.

Anti-Cytomegalovirus Activity in Human Milk and Colostrum From Mothers of Preterm Infants.

This study aimed to investigate the anti-human cytomegalovirus (CMV) activity of milk from seropositive and seronegative mothers of preterm infants and to analyze its changes throughout the different stages of lactation and after Holder pasteurization, a procedure adopted by donor human milk banks. Eighteen mothers of preterm infants were enrolled in the study. Colostrum, transitional milk, and mature milk samples were collected and tested for anti-CMV activity. Depletion of immunoglobulins A from milk samples was carried out by jacalin resin. Pools of milk samples were pasteurized according to Holder technique. All samples were endowed with anti-CMV activity, although to a different extent. In CMV IgG-positive mothers, colostra were significantly more active than the transitional milk and mature milk samples. Moreover, they were more potent than colostra from seronegative mothers. Immunoglobulins A depletion in colostra from IgG-positive mothers resulted in a partial loss of anti-CMV activity. Holder pasteurization significantly reduced the antiviral activity. Human milk is endowed with anti-CMV activity and its potency may vary depending on the stage of lactation and the serological status of the mother. This biological property could partially neutralize CMV particles excreted in the milk of CMV IgG-positive mothers thus reducing the risk of transmitting infectious viruses to the infant.

Effects of glycomacropeptide in human milk and formula milk on proliferation of bifidobacterium infantis in vitro

Objective To explore the effects of glycomacropeptide (GMP) in human milk and formula milk on proliferation of bifidobacterium infantis and their dose-response relationship. Methods Casein was isolated from the milk of 30 healthy postpartum women from Guangzhou Women and Children's Medical Center in September 2014, and hydrolyzed by rennet to obtain GMP, which was then purified by ultrafiltration and ion exchange chromatography. Human milk GMP and cow milk GMP (0, 250, 500, 1 000,1 500, 2 000 and 3 000 mg/L) were added to bifidobacterium infantis liquid medium, and cultured under anaerobic conditions. Concentration of bacteria was measured by turbidimetric microplate assay (detection of OD600 nm value of medium). Difference of proliferative activities of bifidobacterium infantis in human milk GMP and cow milk GMP was compared with independent samples t-test. Results Purified human milk GMP concentration was 1 712.20 mg/L, with a purity of 80.3%. Increasing the cow milk GMP initial concentration in the culture medium at 250-2 000 mg/L could increase the concentration and proliferation rate of bifidobacteria infantis. When cultured at 36 h with GMP of various concentrations, the proliferation of bifidobacteria infantis maintained at a logarithmic phase. Therefore, 36 h was chosen as the test time point to compare the proliferation of bifidobacterium infantis. At 36 h, when GMP in the medium was 1 000, 1 500, 2 000 and 3 000 mg/L, concentrations of bifidobacteria infantis in human milk GMP were 2.255±0.036, 2.583±0.088, 2.877±0.080 and 3.219±0.081, respectively, which were significantly higher than those in cow milk GMP (2.115±0.053, 2.312±0.064, 2.542±0.090 and 2.894±0.076; t=4.867, 5.569, 6.192 and 6.516; all P<0.01). Conclusions Both human milk GMP and cow milk GMP can promote the proliferation of bifidobacterium infantis in vitro, and the proliferative activity in human milk is greater than in cow milk at the same concentration of GMP. Key words: Milk, Human; Infant formula; Caseins; Peptide fragments; Bifidobacterium

Effect of high pressure and heat treatments on IgA immunoreactivity and lysozyme activity in human milk

Human milk from donor mothers is processed in human milk banks using low-temperature long-time pasteurization to ensure microbial safety. However, this treatment can degrade relevant bioactive components. High-pressure processing of food is a nonthermal treatment that exerts an antimicrobial effect maintaining the nutritional quality of foods. In this study, the effect of high pressure and heat treatments of human milk on denaturation of immunoglobulin A (IgA) and lysozyme activity was determined. Immunoreactive IgA was measured using a sandwich ELISA and lysozyme activity by a Micrococcus lysodeikticus turbidimetric assay. The retention kinetic of IgA in human milk treated by high pressure was studied. The experimental data obtained in the range of 350–650 MPa were well described by the Weibull model. The shape parameter (β) was not affected by the pressure, whereas the scale parameter (α) was affected by the pressure and its behavior was described by an Eyring-type equation. The estimated activation volume (ΔV a) was −25.67 ± 5.32 ml mol−1, and the constant reaction rate at the reference pressure (K p) was 0.022 ± 0.005 min−1. Kinetic parameters obtained allow estimating the pressure-induced denaturation of IgA on the basis of pressure and holding times. A substantial activation of lysozyme activity was obtained after treatment at pressures of 400, 450 and 500 MPa for 30 min. Treatment of human milk at 65 °C for 30 min maintained 43 % of IgA immunoreactivity, whereas lysozyme activity was not affected.

Very stable high molecular mass multiprotein complex with DNase and amylase activities in human milk.

For breastfed infants, human milk is more than a source of nutrients; it furnishes a wide array of proteins, peptides, antibodies, and other components promoting neonatal growth and protecting infants from viral and bacterial infection. It has been proposed that most biological processes are performed by protein complexes. Therefore, identification and characterization of human milk components including protein complexes is important for understanding the function of milk. Using gel filtration, we have purified a stable high molecular mass (~1000 kDa) multiprotein complex (SPC) from 15 preparations of human milk. Light scattering and gel filtration showed that the SPC was stable in the presence of high concentrations of NaCl and MgCl2 but dissociated efficiently under the conditions that destroy immunocomplexes (2 M MgCl2 , 0.5 M NaCl, and 10 mM DTT). Such a stable complex is unlikely to be a casual associate of different proteins. The relative content of the individual SPCs varied from 6% to 25% of the total milk protein. According to electrophoretic and mass spectrometry analysis, all 15 SPCs contained lactoferrin (LF) and α-lactalbumin as major proteins, whereas human milk albumin and β-casein were present in moderate or minor amounts; a different content of IgGs and sIgAs was observed. All SPCs efficiently hydrolyzed Plasmid supercoiled DNA and maltoheptaose. Some freshly prepared SPC preparations contained not only intact LF but also small amounts of its fragments, which appeared in all SPCs during their prolonged storage; the fragments, similar to intact LF, possessed DNase and amylase activities. LF is found in human epithelial secretions, barrier body fluids, and in the secondary granules of leukocytes. LF is a protein of the acute phase response and nonspecific defense against different types of microbial and viral infections. Therefore, LF complexes with other proteins may be important for its functions not only in human milk.

Detection of cow’s milk proteins and minor components in human milk using proteomics techniques

Cow’s milk proteins (CMPs) are the best characterized food allergens. The aim of this study was to investigate cow’s milk allergens in human colostrum of term and preterm newborns’ mothers, and other minor protein components by proteomics techniques, more sensitive than other techniques used in the past. Sixty-two term and 11 preterm colostrum samples were collected, subjected to a treatment able to increase the concentration of the most diluted proteins and simultaneously to reduce the concentration of the proteins present at high concentration (Proteominer Treatment), and subsequently subjected to the steps of proteomic techniques. The most relevant finding in this study was the detection of the intact bovine alpha-S1-casein in human colostrum, then bovine alpha-1-casein could be considered the cow’s milk allergen that is readily secreted in human milk and could be a cause of sensitization to cow’s milk in exclusively breastfed predisposed infants. Another interesting result was the detection, at very low concentrations, of proteins previously not described in human milk (galectin-7, the different isoforms of the 14-3-3 protein and the serum amyloid P-component), probably involved in the regulation of the normal cell growth, in the pro-apoptotic function and in the regulation of tissue homeostasis. Further investigations are needed to understand if these families of proteins have specific biological activity in human milk.

Arginase Activity in Human Milk During the First Month of Lactation

Arginase (L-arginine amidinohydrolase, EC 3.5.3.1) is the key enzyme in urea synthesis, hydrolyzing L-arginine into L-ornithine and urea. Arginase modulates levels of nitric oxide, creatine, and creatinine, likely by regulating intracellular L-arginine availability. The objective of the present study was to determine the arginase activity and concentration of urea and creatinine in colostrum and mature human milk obtained from nursing mothers. Our longitudinal biochemical analyses show that arginase activities and urea concentrations were the highest at the first day of lactation (colostrum). The decreasing enzyme activity and urea start at the second day, remaining at this level until the end of the first month of lactation (30th day). The concentration of creatinine in human colostrum and mature milk did not significantly change. The alteration of arginase activity between colostrum and mature milk may be a consequence of the transfer of arginase from the blood of the breast mother mammary glands into the colostrum and mature milk. The concentration of nutrients in colostrum and mature milk undergo alterations, probably to satisfy the requirements of the nursing infant for arginine, essential amino acids for human body growth, and normal physiology.

Comparison of the activity of human and bovine milk on two cell lines

The activity of human milk on cell growth has been evaluated on two cell lines, MDCK and Caco-2. The proportion of human milk samples that reduced by half the growth of MDCK cells was of 36%. This inhibitory activity was associated with casein and not the whey fraction. Great variability was found in the degree of inhibitory activity depending on the milk sample. The susceptibility of Caco-2 cells to milk inhibitory activity was lower than that of MDCK. Bovine milk did not have any effect on cell growth, either as skimmed milk or as whey or casein. Morphology of cells incubated with active human casein showed abnormal features, such as chromatin condensation, reduced cellular volume and apoptotic bodies, and also fragmented DNA, which are all features of apoptosis.

Antioxidant and Radical Scavenging Activity of Human Colostrum, Transitional and Mature Milk

Human milk from healthy women contains numerous nutrients such as antioxidants which are necessary for newborns. The aim of this study was to evaluate the changes of total antioxidant capacity (TAC) and free radical scavenging activity in human milk during the first six month period of lactation and also its relationship to maternal plasma. A total of 505 milk samples (colostrum, transitional and mature milks) collected from 115 healthy women with full term newborns. Blood plasma was obtained from 58 women at 3 months postpartum. The TAC of samples were measured by Ferric Reducing/Antioxidant Power assay and free radical scavenging activity were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals. TAC was obviously higher in colostrums than transitional and mature milks. Similar results were observed for DPPH radical scavenging activity of the samples. There was a high significant correlation between the results of these two methods. The relationship between the antioxidant content of human milk and maternal plasma was also significant. These data suggest that using colostrum, with high antioxidant potential during the first days of life is vital; moreover, reduction in total TAC during the course of lactation may needs more attention about nutritional status.

Chitotriosidase activity in human milk from mothers of premature and full-term infants during the first month of lactation

Objective The objectives of the present study were to measure the activity of chitotriosidase (ChT) in human milk, to record changes in enzyme activity over time and to determine whether there are differences in activity between the milk of mothers of full-term (FT) and premature (PT) infants. Patients and methods Three samples were collected from each of 28 mothers (26.9 ± 4.3 years of age; mean ± SD) of FT infants (gestational age, 39.1 ± 0.9 weeks; birth weight, 3384.8 ± 369.8 g.; median, 3485 g) and 28 mothers (26.6 ± 3.6 years of age) of healthy PT infants (gestational age, 30.5 ± 3.1 weeks; birth weight, 1400 ± 492.9 g.; median, 1285 g). Samples were collected at 3, 7 and 28th days after delivery. ChT activity was estimated using the fluorimetric method. ChT activities were calculated and expressed as nanomoles per milliliter per hour. Results ChT activity was higher in the PT group than in the FT group at day 3 [170.2 (14.0–294.8) vs. 81.7 (6.9–306.3) nmol/mL/h], day 7 [31.6 (0.0–166.7) vs. 17.2 (0.0–214.1) nmol/mL/h] and day 28 [5.5 (0.0–64.9) vs. 3.4 (0.0–51.6) nmol/mL/h]. Conclusion The higher ChT activity in milk of mothers of PT infants than those of FT infants suggests the presence of activated macrophages as its main source. ChT is well known to play a role in defense against fungi and have the ability to degrade both colloidal chitin and chitin in the cell wall of Candida albicans. Thus, our findings may indicate that infants have a natural advantage for protection from fungus infections when they are fed by their mothers' milk.

Effects of High-Pressure Processing on Immunoglobulin A and Lysozyme Activity in Human Milk

Banked human milk, processed using low-temperature/long-time or Holder pasteurization, inactivates pathogenic microorganisms but degrades important biochemical components. High-pressure processing kinetics favor inactivation of microorganisms with retention of biochemical activity and nutritional quality of foods. The effects of high-pressure processing (400 MPa) and low-temperature/long-time pasteurization (62.5°C, 30 minutes) on total immunoglobulin A and lysozyme activity in human milk were investigated. Indirect modified enzyme-linked immunosorbent and a Micrococcus lysodeikticus turbidimetric assay were performed to measure immunoglobulin A immunoactivity and lysozyme activity, respectively. Pressure-treated samples retained significantly higher ( P &lt; .05) levels of immunoglobulin A and lysozyme activity compared to samples treated with low-temperature/ long-time pasteurization. These data suggest that high-pressure processing is a potential alternative to thermal pasteurization of human milk that can give greater retention of some bioactive components. Further research is needed to determine whether high-pressure processing can inactivate pathogens of concern in donor human milk. J Hum Lact. 23(3):253-261.

Bactericidal activity of human milk: stability during storage

Human milk provides infants with defensive factors against many illnesses. This study aims to analyse global bactericidal activity in fresh human milk and evaluate its stability in relation to milk manipulation and its possible alteration following refrigeration. Nineteen milk samples (mature milk) from 19 healthy women are analysed. Viability testing involving a strain of Escherichia coli NCTC 9111, serovar O111:K58(B4):H– was used to determine the bactericidal effect of human milk. Degree of bacteriolysis is calculated as the difference between E. coli counts in controls and in milk samples, expressed as a percentage of the control sample counts. An evaluation of the effect of refrigeration at 4–6˚C after 24, 48 and 72 hours, and at –20˚C for seven days on bactericidal capacity is made. Bactericidal activity was detected in all milk samples analysed (77.33±15.14%). This activity persisted after refrigeration for 48 hours and after freezing for 10 days, but showed a significant decrease after refrigeration for 72 hours. In conclusion, maternal milk has bactericidal capacity, providing defence and protection against infection for newborn infants. This property can be altered during the storage of milk. Consequently, if storage in excess of 48 hours is required, freezing is preferable to refrigeration.

Human Milk Inactivates Pathogens Individually, Additively, and Synergistically

Breast-feeding can reduce the incidence and the severity of gastrointestinal and respiratory infections in the suckling neonate by providing additional protective factors to the infant's mucosal surfaces. Human milk provides protection against a broad array of infectious agents through redundancy. Protective factors in milk can target multiple early steps in pathogen replication and target each step with more than one antimicrobial compound. The antimicrobial activity in human milk results from protective factors working not only individually but also additively and synergistically. Lipid-dependent antimicrobial activity in milk results from the additive activity of all antimicrobial lipids and not necessarily the concentration of one particular lipid. Antimicrobial milk lipids and peptides can work synergistically to decrease both the concentrations of individual compounds required for protection and, as importantly, greatly reduce the time needed for pathogen inactivation. The more rapidly pathogens are inactivated the less likely they are to establish an infection. The total antimicrobial protection provided by human milk appears to be far more than can be elucidated by examining protective factors individually.

Determination of glutathione peroxidase activity in human milk

An analytical method for determining glutathione peroxidase (GPx) (EC 1.11.1.9) activity in whole blood has been adapted to human milk samples. The values obtained for precision (relative standard deviation: 8.4%), linearity and accuracy (recovery: 90.4%) indicate the adequacy of the method for the mentioned purpose. The method was applied to 11 human milk samples obtained in the range from 6 to 135 days post partum. The resulting GPx activities (83.3 +/- 23.6 U/L) did not correlate to the selenium content of the samples, though a reciprocal correlation was found between the duration of lactation and milk GPx activity.

Advances in the modulation of the microbial ecology of the gut in early infancy.

It is now generally accepted that the microbiota of the human gut may influence health and well-being. Lactic acid bacteria are the most important microorganisms associated with these beneficial effects and the elevated bifidobacterial count may be one of the greatest advantages that breastfed infants have over infants fed with milk formulas. Several studies relative to the selective growth stimulation of bifidobacteria, both in vitro and in vivo, are reported in this review. Over the years, diverse human milk components have been identified as the specific factors able to modulate the growth of bifidobacteria. Even if there is a certain agreement that the bifidogenic activity of human milk may be based not on single growth substances, but on a complex set of interacting factors, the present state of knowledge indicates that the use of non-digestible but fermentable carbohydrates may be an easy and reliable method to influence the growth of lactic acid bacteria. In this context, some of the characteristics of the major physiological effects of inulin-type fructans, of galacto-oligosaccharides, but also of lactoferrin, a milk whey protein fraction with purported bifidogenic activity, are briefly examined.