Breast milk is a unique source of nutritional and bioactive substances essential to the development of immune and digestive systems of the newborn. Its beneficial effects on development and health are especially important in preterm newborns for whom many studies have demonstrated that breast milk significantly reduces the risk of several diseases including digestive intolerance, ulcerative necrotizing enterocolitis (NEC), sepsis, and food allergy. In addition, breast milk has shown long-term positive effects on cognitive development and metabolism and cardiovascular health in adult. During their hospital stay, preterm infants receive pooled human milk (HM) from different donors provided by human milk bank (HMB). However, HM needs to be treated in order to limit the development of potentially pathogenic agents, whilst retaining its nutritional and immunomodulatory properties. The most common practice performed in HMBs worldwide to treat HM is a low-temperature (62°C) long-time (30 minutes) pasteurization known as “Holder” pasteurization. However, Holder pasteurization performed in HMB completely destroys important milk factors such as the bile salt-stimulated lipase (BSSL), alters milk fat globules structures and reduces both the nutritional value and immunological properties of HM. High hydrostatic pressure (HHP) processing is a recent technology in the food industry that applies a non-thermal high pressure treatment to the product. This new process is one of the most promising methods for food treatment and preservation at room temperature. For HM, HHP is a promising alternative method to Holder pasteurization as several studies have demonstrated that HHP preserves milk nutritional and immunological properties and inactivate microorganisms. Our objectives will be divided into 3 points: 1/ to determine if HHP process improve milk quality in term of sensitive bioactive factors (growth factors, hormones, microRNAs and bacteriostatic properties) compared to Holder pasteurization; 2/ to study experimentally if HHP-treated HM possesses more potent intestinotropic properties than pasteurized HM; 3/ to study in preterm infants, if HHP-treated HM improve the neonatal health, gut microbiome and the early postnatal growth of these infants compared to infants fed with pasteurized HM during 21 days. Our strong consortium implicate recognized scientists (INSERM, Universities, Hospital) specialized in the field of neonatal physiology, a private French partner HPBioTech (AP) that has an international patent for HHP-treated human milk, recognized clinical experts in infant nutrition and recognized experts in the field of gut microbiota. All of these partners have complementary skills to carry out the various tasks to support the present project and have national and international recognition in their respective fields. The clinical study will be performed in the Jeanne de Flandre hospital of the CHRU of Lille. To conclude, providing an alternative to Holder pasteurization with better performance in regard of microbiological safety, nutritional and biological components would be a major step forward including but not limited to the French population of preterm and low birth weight infants. Moreover, our project may have a good economic impact for HMBs as HPP may improve the safety of human milk (microorganism), reduce losses (pasteurization failure) and improve storage and transportation of treated-HM (4°C instead of -20°C). It may also permit to better understand the establishement of gut microbiota associated with breastmilk components.