Optimized Ultraviolet-C Processing Inactivates Pathogenic and Spoilage-Associated Bacteria while Preserving Bioactive Proteins, Vitamins, and Lipids in Human Milk

Abstract

Holder pasteurization (HoP) enhances donor human milk microbiological safety but damages many bioactive milk proteins. Though ultraviolet-C irradiation (UV-C) can enhance safety while better preserving some milk proteins, it has not been optimized for dose or effect on a larger array of bioactive proteins. We determined the minimal UV-C parameters that provide >5-log reductions of relevant bacteria in human milk and how these treatments affect an array of bioactive proteins, vitamin E, and lipid oxidation. Treatment at 6000 and 12 000 J/L of UV-C resulted in >5-log reductions of all vegetative bacteria and bacterial spores, respectively. Both dosages improved retention of immunoglobulin A (IgA), IgG, IgM, lactoferrin, cathepsin D, and elastase and activities of bile-salt-stimulated lipase and lysozyme compared with HoP. These UV-C doses caused minor reductions in α-tocopherol but not γ-tocopherol and no increases in lipid oxidation products. UV-C treatment is a promising approach for donor human milk processing.

Keywords: antibody; bactericidal; breast milk; milk bank; mother’s milk; preterm infant health.

Figure 1:

Microbial inactivation (log CFU/mL) of vegetative bacteria in human milk treated with Ultraviolet-C (UV-C: 500-7000 J/L). A) Cronobacter sakazakii ATCC BAA-894, B) Enterococcus faecium ATCC 8459, C) Listeria monocytogenes ATCC 35152, and D) Staphylococcus aureus (138-CPS and 146-CPS). Cell densities of each bacterium were measured in both raw and processed samples. Data are represented as the mean ± standard error (n = 4 independent replicates). * indicates that the 95% confidence interval was above the 5-log reduction target.

Figure 2:

Bacterial spore inactivation (log spores/mL) in human milk treated with ultraviolet-C (UV-C: 1,000–18,000 J/L). A) Bacillus cereus spores cocktail (ATCC 33019, ATCC 49064 and ATCC 33018), B) Bacillus subtilis spore cocktail (NRRL B-354 and NRRLB-356) and C) Paenibacillus spp. spore cocktail (P. macerans NRRL B-14029 and P. polymyxa NRRL B-510). Data represented as the mean ± standard error (n = 4 independent replicates). * indicates that the 95% confidence interval was above the 5-log reduction target.

Figure 3.

Immunoglobulins (A: IgA, B: IgG, C: IgM) in raw, UV-C (1,000–18,000 J/L) and HoP-treated donor milk. UV-C treatments are labeled on the x-axis in J/L. Experiments were performed in triplicate, and results were expressed as mean ± standard deviation. The black bar represents the raw milk. The orange bar represents the HoP-treated milk. Blue bars indicate UV-C treatments that resulted in a significantly reduced level of detectable antibody compared with raw milk (one-sided t-test; P < 0.05). * indicates donor milk treated with UV-C with significantly higher retention of antibodies compared with HoP (one-sided t-test; P < 0.05).

Figure 4.

Elastase (A), cathepsin D (B) and lactoferrin (C) in raw, UV-C (1,000–18,000 J/L) and HoP-treated donor milk. UV-C treatments are labeled on the x-axis in J/L. Experiments were performed in triplicate, and results were expressed as mean ± standard deviation. The black bar represents the raw milk. The orange bar represents the HoP-treated milk. Blue bars indicate UV-C treatments that resulted in a significantly reduced level of detectable each protein compared with raw milk (one-sided t-test; P < 0.05). *indicates donor milk treated with UV-C with significantly higher retention of each protein compared with HoP (one-sided t-test; P < 0.05).

Figure 5.

Osteopontin (A), vascular endothelial growth factor (VEGF) (B) and lysozyme (C) in raw, UV-C (1,000–18,000 J/L) and HoP-treated donor milk. UV-C treatments are labeled on the x-axis in J/L. Experiments were performed in triplicate, and results were expressed as mean ± standard deviation. The black bar represents the raw milk. The orange bar represents the HoP-treated milk. Blue bars indicate UV-C treatments that resulted in a significantly reduced level of detectable antibody compared with raw milk (one-sided t-test; P < 0.05). * indicates donor milk treated with UV-C with significantly higher retention of antibodies compared with HoP (one-sided t-test; P < 0.05).

Figure 6.

Lysozyme activity (A) and bile salt-stimulated lipase (BSSL) activity (B) in raw, UV-C (1,000–18,000 J/L) and HoP-treated donor milk. UV-C treatments are labeled on the x-axis in J/L. Experiments were performed in triplicate, and results were expressed as mean ± standard deviation. The black bar represents the raw milk. The orange bar represents the HoP-treated milk. White bars represent UV-C treatments. * indicates donor milk treated with UV-C with significantly higher retention of antibodies compared with HoP (one-sided t-test; P < 0.05).

Figure 7.

(A) a-tocopherol and g-tocopherol concentrations in raw, UV-C treated (at dosages of 6,000 J/L and 12,000 J/L) and HoP-treated human donor milk. Experiments were performed in triplicate, and results were expressed as mean ± standard deviation. The white bar represents the a-tocopherol concentration. The black bar represents the g-tocopherol concentration. Different letters represent significant difference among the samples within the same tocopherol isoform (a, b, c for a-tocopherol; no significant difference was observed for g-tocopherol) (Tukey’s multiple comparison tests; P < 0.05). (B) Malondialdehyde concentrations in raw, UV-C treated (at dosages of 6,000 J/L and 12,000 J/L) and HoP-treated human donor milk. Experiments were performed in triplicate, and results were expressed as mean ± standard deviation. No significant difference was observed among the samples (Tukey’s multiple comparison tests; P < 0.05).