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Changes in the physicochemical properties of ready-to-feed liquid infant formula (LIF) stored at different temperatures (10, 20, 30, and 40°C) for 6 mon, focusing on 5-hydroxymethylfurfural (HMF) content, color, pH, fat globule size distribution, and rheological properties were determined. The HMF content increased with storage time, and LIF stored at 40°C had a higher HMF content than that of LIF stored at 10°C. The lightness (L*) decreased while redness (a*) and yellowness (b*) increased with increasing HMF content. The fat globule size and pH of LIF stored at 10°C did not change. However, in the case of LIF stored at 30°C and 40°C, the fat globule size increased and the pH decreased during storage for 6 mon. LIF stored at 40°C had a higher apparent viscosity (ηa,10) than that of LIF stored at 10°C, and the shear-thinning behavior of LIF stored at higher temperature was stronger than that of LIF stored at low temperature. The physicochemical changes of LIF during storage were accelerated by Maillard reaction (MR) at higher storage temperatures. Therefore, even if LIF is aseptically manufactured, we recommend that sterilized LIF should be stored at low temperature in order to minimize quality changes during storage.

Daily consumption of F-MRP enhanced NK cell function, which was positively associated with ΔIL-12. Moreover, ΔIL-12 was positively correlated with Δpre-albumin.

We investigated the effects of a pulsed electric field (PEF) treatment on microbial inactivation and the physical properties of low-fat milk. Milk inoculated with Escherichia coli, Saccharomyces cerevisiae, or Lactobacillus brevis was supplied to a pilot-scale PEF treatment system at a flow rate of 30 L/h. Pulses with an electric field strength of 10 kV/cm and a pulse width of 30 μs were applied to the milk with total pulse energies of 50-250 kJ/L achieved by varying the pulse frequency. The inactivation curves of the test microorganisms were biphasic with an initial lag phase (or shoulder) followed by a phase of rapid inactivation. PEF treatments with a total pulse energy of 200 kJ/L resulted in a 4.5-log reduction in E. coli, a 4.4-log reduction in L. brevis, and a 6.0-log reduction in S. cerevisiae. Total pulse energies of 200 and 250 kJ/L resulted in greater than 5-log reductions in microbial counts in stored PEF-treated milk, and the growth of surviving microorganisms was slow during storage for 15 d at 4℃. PEF treatment did not change milk physical properties such as pH, color, or particle-size distribution (p<0.05). These results indicate that a relatively low electric-field strength of 10 kV/cm can be used to pasteurize low-fat milk.

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