• Michael Pitino

Exploring New Pasteurization Techniques to Optimize Processing of Donor Human Milk

Can replacing 100-year-old ‘technology’ to pasteurize donor human milk propel milk banking operations into the 21st century? The (high) pressure is on to improve the health outcomes of vulnerable preterm infants.
 

Human milk from an infant’s parent is the best nutrition to ensure maximal growth and development. Following preterm birth, it is common for some parents to have difficulty producing a sufficient volume of milk required to meet their infant’s nutritional needs. As an alternative to formula feeding, pasteurized donor human milk can be provided to supplement feeds for preterm infants. In Ontario and across North America, donor human milk is pasteurized using the Holder method (62.5°C, 30 min) to ensure any potential bacteria or viruses are destroyed. While required to ensure the product is safe for infant consumption, heating donor human milk degrades some important bioactive components. Despite this, providing donor human milk has been shown to help prevent necrotizing enterocolitis, a serious life-threatening bowel disease.


Given recent advances in processing technologies available, our research is currently exploring a novel technique that could be used to process human milk without heating. This technique is known as high-pressure processing or HPP.


PhD Student Michael Pitino standing in front of High-Pressure Processing Equipment
PhD Student Michael Pitino with the High-Pressure Processing Equipment. Photo credit: Michael Pitino
 
HPP uses pressures up to 5000-times higher than air pressure, equivalent to the weight of 3 African elephants on a strawberry!
 

Our previous work suggests that HPP processing, compared to traditional Holder pasteurization, can reduce bacteria in milk to an acceptable level. At the same time, HPP preserves nutrients and bioactive components, many of which support growth and might help fend off infection better. While this has the potential to maximize the impact of donor human milk, it is unclear whether this new technique could inactivate viruses which could be present.


What did we do?

Can high-pressure processing inactivate viruses in human milk?


To determine whether HPP could inactivate viruses in milk, we conducted experiments where we artificially injected concentrated virus into human milk samples. We chose to challenge our pasteurization techniques using human cytomegalovirus, a common virus found in human milk, and hepatitis A virus, a generally more difficult virus to inactivate. After inoculation with these viruses, we treated the samples with HPP or the Holder method. We then quantified any infectious virus using specialized culture-based techniques to differentiate between live and dead viruses.


Petri dishes of human milk samples being tested for infectious human cytomegalovirus after different pasteurization techniques
Testing milk samples for infectious human cytomegalovirus after different pasteurization techniques. Photo credit: Michael Pitino

Does high-pressure processing impact the natural ability of human milk to inactivate viruses?


We also investigated whether the processing method (HPP or Holder method) could impact human milk’s natural ability to inactivate viruses. Different proteins and specialized sugars in human milk can neutralize viruses before they can infect cells. Therefore, to complement our first set of experiments, we first pasteurized milk by HPP or the Holder method and then injected the samples with concentrated virus (cytomegalovirus and hepatitis A virus). After injection, we tested the milk for infectious viruses using the same culture-based techniques after 30 min.


What did we find?

We found that the novel HPP method was just as effective as the Holder method to inactivate viruses in milk, rendering the milk safe for infant consumption. HPP was superior to Holder in inactivating hepatitis A virus, the more difficult virus to destroy. Both HPP and Holder pasteurization also reduced bacteria to levels that meet the quality standard used at the milk bank, all while maintaining critical immune-related proteins. Interestingly, while we found that processing did not affect the natural ability of milk to inactivate viruses, milk processed by Holder, but not HPP, had significantly lower activity than unprocessed milk!


What does this mean?

HPP processing is a promising alternative for treating donor human milk. It preserves more important nutrients and bioactive components while reducing viruses (and bacteria) in milk. We also demonstrated that this method does not negatively impact milk’s natural ability to inactivate viruses.


What’s next?

Before implementing this technology clinically at the milk bank, larger-scale testing is required. We need to investigate whether HPP can inactivate other viruses, including HIV. Since HPP minimally affects the composition and bioactivity of milk, we are also beginning preclinical investigations. These investigations will help us understand if HPP processing impacts infant digestion and whether this could positively impact an infant’s immune development and growth!

 

You can read the studies published in Innovative Food Science and Emerging Technology (https://doi.org/10.1016/j.ifset.2021.102891) and Frontiers in Nutrition, Food Chemistry

(https:// doi.org/10.3389/fnut.2022.918814)