Beyond Holder: better preservation, harder decisions

Alternative processing methods for donor human milk are the focus here, but the real subject is the decision a milk bank must make when a method preserves more of one biological property than the standard process. The useful judgment is not to select a universal winner. It is to ask whether a method controls the relevant microbial hazards, preserves a defined component or activity, has evidence that applies to vulnerable recipients, and can operate without reducing safe access.

The alternatives look attractive because Holder pasteurization changes selected proteins, enzymes and vitamins. Yet the problem is not solved by removing heat from the process. Non-thermal methods still need safety evidence, testing and reliable operations. A treatment can be promising in a laboratory and unsuitable for a bank if its viral performance is uncertain, its equipment is unavailable or its cost reduces the supply of donor milk.

What the alternatives preserve—and what remains unproven

HTST is the closest comparison because it remains a heat treatment while changing the exposure pattern. The evidence summarized by WHO and the Frontiers review suggests that its shorter exposure can preserve some heat-sensitive components better than longer thermal treatments. Folate and vitamin C show better retention than with Holder pasteurization in the WHO synthesis, and the Frontiers review reports better preservation of immunoglobulins and lysozyme in the cited comparisons. This is a meaningful shift in the biological trade-off: reducing the time available for heat-related structural change may retain more selected functions.

But HTST is not a clean escape from the trade-off. The Frontiers review reports that some components, including IgA and lactoferrin, still decrease across thermal treatments. The method also has to demonstrate microbial performance under the conditions used by a particular bank. A small randomized comparison of Holder-treated and HTST-treated donor milk found no difference in nosocomial sepsis or additional secondary outcomes, but that finding does not establish that the methods are identical or that every clinical outcome has been settled. It shows why better molecular retention and better clinical outcomes must remain separate claims.

HPP, or high-pressure processing, offers the strongest alternative signal in the sources because it targets microorganisms without relying on the same thermal load. WHO reports that HPP reduced bacterial loads below detectable levels in most of the reviewed studies and that non-thermal processing generally preserved nutrients and bioactive components better than Holder pasteurization. The Frontiers review associates HPP with better retention of immunological proteins, stable HMO concentration and profile in a cited study, and no significant increase in Maillard products in a Holder-versus-HPP comparison. A dynamic digestion study also found better preservation of key protein structure and release of essential amino acids after HPP than after Holder treatment.

That collection of findings makes HPP scientifically important, not clinically proven. The studies are few and heterogeneous, and the evidence does not establish a common infant outcome. WHO’s standards say that alternative technologies are not supported well enough for broad recommendation, even while describing HPP as a method that may produce microbiologically safe milk comparable to heat-treated milk. The distinction is deliberate: a preservation signal can justify more research without yet justifying a change in every milk bank’s practice.

To trust an HPP result, a bank would need to know more than the pressure listed in a paper. It would need evidence that the treatment works with the milk’s starting composition, the containers and the batch sizes it actually handles. It would need a way to verify microbial performance after processing and to preserve the cold chain afterward.