The total IgA, IgG, IgM and lactoferrin concentrations in human milk from 89 donors were studied at three lactational stages: early transitional (3 to 8 d postpartum), transitional (10 to 14 d postpartum) and mature (30 to 47 d postpartum). The effects of processing and storage on these components in composite samples of mature human milk were determined. There were no significant diurnal variations in any of the four protective factors at either the transitional or mature stages. Concentrations of total IgA, IgM and lactoferrin decreased significantly as time postpartum increased, whereas the IgG content showed no significant changes. The total IgA, IgM and lactoferrin levels were significantly decreased by all heat treatments (62.5°C for 30 min, 72°C for 15 s, 88°C for 5 s, and 100°C for 5 min). Heating at 62.5°C for 30 min did not affect the IgG content; however, the other heat treatments significantly reduced IgG concentration. At the times and temperatures selected for this study, the two lower temperature treatments were less detrimental to the protective factors than the higher temperature treatments.

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