Frozen Milk Samples Research Articles

Major Carotenoids in Mature human Milk: Longitudinal and Diurnal Patterns

The present study was undertaken to quantitate the major carotenoids in human milk, monitoring their variance among fore, mid, and hind mature milk samples; during morning, midday, and evening, and among different weeks of lactation. Twenty-three mothers, 6 weeks to 16 weeks postpartum, participated in the study. Reversed-phase high performance liquid chromatography (RP-HPLC) was used to identify and quantitate the major carotenoids found in human milk, including lutein/zeaxanthin, beta cryptoxanthin, lycopene, alpha carotene, and beta carotene. To determine the validity of analyzing carotenoids in frozen milk, freshly expressed and subsequently frozen milk samples were analyzed for four mothers. Freezing did not alter carotenoid concentrations. Wide variations in carotenoid concentrations existed within and between the mothers. Major carotenoid totals ranged from 29 nM to 493 nM. Complete breast expressions at three periods within a day and at specified weekly intervals allowed the accurate determination of diurnal as well as longitudinal carotenoid concentrations. Diurnal evaluation of carotenoid concentrations suggested a peak at midday and highest longitudinal concentrations were at 10 to 12 weeks. Neither of these trends was statistically significant. The analysis of fore, mid, and hind milk carotenoid concentrations demonstrated that hind milk was significantly higher than fore or mid milk ( P < 0.05).

Lipolytic Activity During Storage of Human Milk: Accumulation of Free Fatty Acids

Lipolysis was quantitated during storage of fluid and freezedried human whole and skim milks. Fatty acid accumulation was faster in whole fluid milk stored for 1 week at 4°C than in frozen (−20°C) samples stored for 180 d. The rapid accumulation of fatty acids during 24 h of storage at 4°C was enhanced in previously frozen milk samples. While freeze-dried whole milk showed no lipolysis when stored at −20°C, accumulation of free fatty acids was rapid in samples stored at room temperature. Fluid and freeze-dried skim milk samples exhibited no appreciable lipolysis.

Effect of freezing on distribution of trace elements and minerals in human and cow's milk

Freezing is a common method for preserving human milk during storage and transport prior to its use for feeding to infants or for research purposes. Freezing milk samples may change the trace element and mineral distribution among their binding compounds, potentially affecting the bioavailability of these elements. In this study fresh human and cow's milk samples were fractionated and the distribution of these elements among fractions determined before and after freezing. Overall, very little effect of freezing was found on mineral distribution in human milk. Similarly, freezing did not have a strong effect on cow's milk; minor changes were observed for iron, copper, zinc and calcium in a few fractions. Thus, it is unlikely that freezing will affect the bioavability of iron, zinc, calcium and magnesium from human milk and cow's milk.

Effect of Freezing Milk Samples on Abnormal Milk Test Results

Milk samples were frozen at −20, −78, and −196C and stored for 3, 7, 14, and 28 days at −20C. Results of Electronic Somatic Cell Counts, Direct Microscopic Somatic Cell Counts, Wisconsin Mastitis Test, as well as the Catalase Test were compared with similar values before freezing. Test scores from all milks, except those tested by the Catalase procedure, were significantly reduced.