Effect of cold storage on vitamins C and E and fatty acids in human milk
Introduction
Human breast milk is regarded as the most important nutrient for neonates, especially preterm infants (Lindemann, Foshaugen, & Lindemann, 2004). The early use of breast milk for preterm infants has resulted in a reduced incidence of necrotising enterocolitis, faster tolerance of enteral feeding and thus a reduced need for parenteral nutrition.
If the mother does not produce sufficient milk, frozen milk from a bank should be made available to all ill neonates until the mother’s own production is established (Lindemann et al., 2004). Of equal value, however, is the practice of mothers collecting their own milk for later feeding (Ogundele, 2002). Possible influences on the stability of milk properties include temperature and storage. Current recommendations for storing human milk in neonatal units and at home vary: for refrigerator storage, from 24–48 h (Biancuzzo, 1999) to 3–5 days (Lawrence & Lawrence, 1999)–even up to 8 days (La Leche League International, 1998); for freezer storage at −18 °C, from 3 to 12 months (Biancuzzo, 1999, La Leche League International, 1998, Lawrence and Lawrence, 1999). In human milk banks, donor milk can be either stored at 4 °C in a refrigerator from 24 h (Baumer, 2004) up to 8 days (HMBANA, 2006), frozen at −20 °C from 3 months (Baumer, 2004) up to 12 months (HMBANA, 2006); or frozen at −70 °C for even longer periods (Baumer, 2004, HMBANA, 2006).
Vitamins E (specifically α-and γ-tocopherols) and C are crucial for anti-oxidant activity and immunomodulation (Jensen, 1995). Preterm infants have reduced antioxidant capacity and are often exposed to oxidative stress caused by infection, oxygen, mechanical ventilation, intravenous nutrition, and blood transfusions (Hanna et al., 2004). Preterm infants who ingest human milk rapidly increase their antioxidant concentrations (Sommerburg et al., 2000, Van Zoeren-Grobben et al., 1993).
Long-chain polyunsaturated fatty acids (LC-PUFAs), specifically arachidonic acid (C20:4n−6, AA) and docosahexaenoic acid (C22:6n−3, DHA), are of major importance during the perinatal period, during which the brain and retina are developing. They therefore have an influence upon visual acuity and learning abilities (Innis, 2004).
The usual cold storage conditions of human milk cited in the literature are as follows: refrigeration at temperatures between 4 and 6 °C for 48–72 h (Igumbor et al., 2000, Lawrence, 2001, Ogundele, 2002) and under freezing conditions at temperatures between −20 °C and 70 °C for 15–90 days (Bitman et al., 1983, Buss et al., 2001, Lawrence, 2001, Ogundele, 2002). These periods are used to minimise bacterial growth rather than preserve any nutritional properties. However, storage can result in the loss of nutrients sensitive to oxidation, such as vitamins C and E, since both are sensitive to light, oxygen and temperature (Miquel, Alegrı´a, Barberá, Farré, & Clemente, 2004). Loss of LC-PUFAs can also occur as they contain a large number of double bonds.
Nevertheless, there is scant historical data addressing how vitamins C and E and fatty acids change during cold storage. Therefore, we investigated potential differences in the concentrations of antioxidant vitamins C and E, as well as in the percentage of fatty acids, between fresh and stored milk at three different cold temperatures: refrigeration (4 °C) and frozen at −20 °C or −80 °C. Thus, the objective of our study was to adopt recommendations on the cold storage of human milk, based on the stability of vitamins C and E and fatty acids in human milk stored at these temperatures.
Section snippets
Sample collection
Identical volumes (50 ml) of mature human milk samples (term) were collected from both breasts by means of a Chicco manual breast pump (Chicco®, Italy), following the manufacturer’s instructions, from ten healthy mothers (age 20–35 years) at the department’s Extraction Unit. Human milk was collected into sterile, opaque bottles in the morning, at first expression. Milk samples from five mothers were directly pooled, obtaining two pools that were divided into 10 aliquots each. Fresh samples were
Effect of storage on total vitamin C concentration
Table 1 shows the concentration of total vitamin C in pooled human milk before and after storage at 4 °C for 96 h, as well as at −20 °C and −80 °C for 12 months.
When calculating total vitamin C levels it is important to measure both ascorbic and dehydroascorbic acid levels. Ascorbic acid is the principal biologically active form of vitamin C. However, dehydroascorbic acid also exhibits biological activity since the human body can easily convert it into ascorbic acid (Packer & Fuchs, 1997).
After 3 h
Discussion
The effect of storage on the various components of human milk has been studied extensively. However, most of these studies have focused on bacteriological and immunological effects (Igumbor et al., 2000, Lawrence, 2001, Ogundele, 2002), devoting scant attention to its effect on vitamins C and E and fatty acid levels.
The main findings of our study revealed a decrease in the total vitamin C concentration in human milk stored at both the refrigeration and freezing temperatures recommended by
Conclusions
In conclusion, fatty acid percentages did not decrease at the recommended refrigeration, freezing or ultrafreezing temperatures. The same was observed for vitamin E content in human milk stored at both freezing and ultrafreezing temperatures. On the contrary, the extent of vitamin C loss during storage was considerable. Thus, we recommend a change in some human milk storage practices, specifically, it should be stored up to 3 h in a refrigerator, up to 5 months in a freezer or up to 8 months in
Acknowledgements
This study was financed by the CeRTA (Centre de Referència en Tecnologia dels Aliments, Generalitat de Catalunya) and the CIBER (Centro de Investigación Biomédica en Red) for the research project CB06/020079. Meritxell Romeu Nadal acknowledges financial support from Generalitat de Catalunya. We also thank the “Federació Catalana de Grups de Suport a la Lactància Materna” for providing human milk and Robin Rycroft for revising the English manuscript.
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