Antioxidant properties of milk from mothers of pre-term and full-term infants compared to infant formula

Langdon, Matthew D. (2000) Antioxidant properties of milk from mothers of pre-term and full-term infants compared to infant formula. Masters thesis, Memorial University of Newfoundland.

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Abstract

Early feeding of low birth weight (LBW) infants with their own mothers' milk has been shown to decrease the incidence of oxygen radical related disease states. Milk from mothers of pre-term (PT) and full-term (FT) infants may exhibit antioxidant and free radical scavenging ability not provided by humanized formulas. This study investigated the ability of milk from weeks 1, 2 and 12 of lactation (17 PT and 28 FT mothers) to resist oxidative stress by free radical attack as compared to formula. The hypoxanthine/xanthine oxidase (HX/XO) system was utilized to generate the radicals and subsequent oxygen consumption was measured. The samples were also tested for catalase (CAT) activity, and for malondialdehyde (MDA) levels by HPLC following stress. As well, normal (3 mg/L) and high (12 mg/L) iron formulas were tested for their ability to resist oxidative damage with and without the presence of added antioxidant enzymes CAT, superoxide dismutase (SOD) and glutathione peroxidase (GSHPx). There was no difference (p > 0.05) between the PT and FT groups with respect to oxygen consumption (nmoles O₂/min) at any stage of lactation. The means ± SEM of O₂ consumption reported for the groups respectively following HX/XO stress, were for week one, 7.97 ± 0.56 and 6.68 ± 0.88; for week two, 4.62 ± 0.42 and 5.17 ± 0.36; and for week twelve, 4.08 ± 0.39 and 4.80 ± 0.49. There was also no difference in MDA levels or CAT activity between groups. This indicates that PT milk has similar antioxidant capability as FT milk. A correlation (r²= .443, p < 0.05) existed between O₂ consumption and MDA levels, and a negative correlation (r²= -0.30, p < 0.01) between the amount of oxygen consumed, and the activity of CAT for all weeks, demonstrating a possible protective role of this enzyme in human milk (HM). A difference (p < 0.001) was reported in total O₂ consumption (nmoles) over time between the HM (44.75 ± 1.66) and both the normal (98.88 ± 3.11)and high-iron (168.94 ± 9.47) formulas. Addition of CAT, SOD and GSHPx together was shown to increase (p < 0.01) the antioxidant capacity of the normal and high-iron formula by decreasing the oxygen consumption to 66.11 ± 6.48 and 104.81 ± 8.65 respectively. Furthermore, the addition of Fe to HM resulted in an increase in O₂ consumption compared to HM controls providing an indication of iron as a free radical generator in infant formula. There was no catalase activity detected in the formula and upon pasteurization of the HM to inactivate the enzymes, antioxidant capability was not compromised.

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