Influence of processing conditions on reducing γ-aminobutyric acid content during fortified milk production

• Whey proteins than casein or lactose has the ability to react with γ-aminobutyric acid.
• Heating or homogenization promotes γ-aminobutyric acid loss.
• γ-Aminobutyric acid concentration determines its loss rate.

The work studied the effects of processing conditions on the γ-aminobutyric acid (GABA) loss during fortified milk production. Bovine milk or their proteins/lactose fractions (0.66% whey protein and 2.6% casein or 4.9% lactose, w/v) containing 0.05–1.0% added γ-aminobutyric acid (w/w, based on bulk milk or these fractions) were subjected to a simulated milk technological process as following the sequential preheating (25–60 °C), homogenization (0–20 MPa), and pasteurization (62 °C/30 min, 72 °C/15 s, 95 °C/5 min, and 138 °C/2 s) or their unit processes to treat GABA. The resulting samples were characterized through GABA and lactose concentrations under various processing conditions. The amine and carboxyl groups and the structural characteristics of the resulting protein (lactose) were also examined through their concentrations (for lactose) and mass/spectral analyses, respectively. The results showed that the increase in temperature significantly promoted a reduction in GABA content. Whey protein fractions than caseins were primarily responsible for inducing GABA, whereas lactose had no remarkable effect on it. The rationale for GABA reduction is potential reactions with milk proteins/lactose, which preliminarily confirmed by the measurement of protein modification and lactose mass spectrometry.