Acid/base balance in fortified donor human milk: An experimental study

Background: Our goal was to quantify the pH and total acidity of human milk fortified with human milk fortifiers (HMFs), powder infant formulas, and protein additives. Methods: Commercial liquid HMFs and powder infant formulas were added to pasteurized pooled donor human milk in triplicate and stirred. The pH of unfortified and fortified human milk at 22, 24, 26, 27, 28, and 30 kcal/ounce (624, 680, 737, 765, 794, and 850 kcal/g, respectively) was determined using a pH meter. Phenolphthalein acidity at 24 and 30 kcal/ounce (680 and 850 kcal/g, respectively) was determined using diluted sodium hydroxide. Results: The pH of unfortified human milk increased within the first hour (6.52 ± 0.06 vs 6.62 ± 0.05, P < 0.0001). Changes in pH largely correlated with caloric density; however, directional changes varied considerably between HMFs and powder infant formulas. Two liquid HMFs demonstrated modest reductions in pH with increasing caloric density whereas one liquid HMF alkalinized human milk with increasing caloric density (analysis of variance P < 0.0001). Phenolphthalein acidity was significantly higher for five HMFs and lower for one HMF at 30 kcal/ounce (850 kcal/g) but not 24 kcal/ounce (680 kcal/g). Powder infant formulas generally increased pH with increasing caloric density (analysis of variance P < 0.0001), but no differences in phenolphthalein acidity were noted. Conclusion: Changes in acid/base balancefor fortified human milk are variable and may be a consideration when selecting a fortifying agent for human milk.