The impact of heat treatment of bovine milk on gastric emptying and nutrient appearance in peripheral circulation in healthy females: a randomized controlled trial comparing pasteurized and ultra-high temperature milk.

BACKGROUND: Heat treatments of dairy, including pasteurization and ultra-high temperature (UHT) processing, alter milk macromolecular structures, and ultimately affect digestion. In vitro, animal, and human studies show faster nutrient release or circulating appearance after consuming UHT milk (UHT-M) compared to pasteurized milk (PAST-M), with a faster gastric emptying (GE) rate proposed as a possible mechanism.

OBJECTIVES: To investigate the impact of milk heat treatment on GE as a mechanism of faster nutrient appearance in blood. We hypothesized that GE and circulating nutrient delivery following consumption would be faster for UHT-M than PAST-M.

METHODS: In this double-blind randomized controlled cross-over trial, healthy female (n=20; 27.3 ± 1.4 years, mean ± SD) habitual dairy consumers, consumed 500mL of either homogenized bovine UHT-M or PAST-M (1340 versus 1320 kJ). Gastric content volume (GCV) emptying half-time (T50 ) was assessed over 3 h by magnetic resonance imaging Subjective digestive symptoms, plasma amino acid, lipid and B vitamin concentrations, and gastric myoelectrical activity were measured over 5 h.

RESULTS: Although GCV T50 did not differ (102 ± 7 min versus 89 ± 8 min, mean ± SEM, UHT-M and PAST-M, respectively; p=0.051), GCV T25 was 31% longer following UHT-M versus PAST-M (42±2 versus 32±4 min, p=0.004). While GCV remained larger for a longer duration following UHT-M (treatment × time interaction, p=0.002), plasma essential amino acid AUC was greater following UHT-M than PAST-M (55324 ± 3809 versus 36598 ± 5673 μmol·min·L-1 , p=0.006). Heat treatment did not impact gastric myoelectrical activity, plasma appetite hormone markers or subjective appetite scores.

CONCLUSIONS: Contrary to expectations, gastric emptying was slower with UHT-M, yet, as anticipated, aminoacidaemia was greater. The larger GCV following UHT-M suggests that gastric volume may poorly predict circulating nutrient appearance from complex food matrices. Dairy heat treatment may be an effective tool to modify nutrient release by impacting digestion kinetics.

CLINICAL TRIAL REGISTRY: www.anzctr.org.au (ACTRN12620000172909).