Effective inactivation of Saccharomyces cerevisiae in minimally processed Makgeolli using low-pressure homogenization-based pasteurization

Abstract

In order to address the limitations associated with the inefficient pasteurization platform used to make Makgeolli, such as the presence of turbid colloidal dispersions in suspension, commercially available Makgeolli was minimally processed using a low-pressure homogenization-based pasteurization (LHBP) process. This continuous process demonstrates that promptly reducing the exposure time to excessive heat using either large molecules or insoluble particles can dramatically improve internal quality and decrease irreversible damage. Specifically, optimal homogenization increased concomitantly with physical parameters such as colloidal stability (65.0% of maximum and below 25-μm particles) following two repetitions at 25.0 MPa. However, biochemical parameters such as microbial population, acidity, and the presence of fermentable sugars rarely affected Makgeolli quality. Remarkably, there was a 4.5-log reduction in the number of Saccharomyces cerevisiae target cells at 53.5°C for 70 sec in optimally homogenized Makgeolli. This value was higher than the 37.7% measured from traditionally pasteurized Makgeolli. In contrast to the analytical similarity among homogenized Makgeollis, our objective quality evaluation demonstrated significant differences between pasteurized (or unpasteurized) Makgeolli and LHBP-treated Makgeolli. Low-pressure homogenization-based pasteurization, Makgeolli, minimal processing-preservation, Saccharomyces cerevisiae, suspension stability.

Keywords: Low-pressure homogenization-based pasteurization; Makgeolli; Minimal processing-preservation; Saccharomyces cerevisiae; Suspension stability.

Figure 1

Real-time changes of suspension stability in minimally processed Makgeolli samples under various homogenization conditions during the storage period. All points shown are the mean values of triplicate experiments.

Figure 2

Conserved photomicrographs of Makgeolli suspension pretreated by homogenization. (A) Supernatant liquid after sedimentation (100× magnified). (B) Untreated (100× magnified). (C) Homogenized at 15.0 MPa (100× magnified). (D) Homogenized at 25.0 MPa (100× magnified). (E) Homogenized at 35.0 MPa (100× magnified). (F) Homogenized twice at 15.0 MPa (100× magnified). (G) Homogenized twice at 25.0 MPa (100× magnified). (H) Homogenized twice at 35.0 MPa (100× magnified).

Figure 3

Size distribution patterns of insoluble microparticles changed in homogenization-treated Makgeolli suspensions containing 7% ethanol.

Figure 4

Fluidic changes of apparent viscosity in Makgeolli suspension with insoluble particles under the various homogenization conditions. All points shown are the mean ± standard deviation of observations that were analyzed in triplicate.

Figure 5

Identification of Makgeolli yeasts by biomolecular techniques. (A) RAPD amplification patterns for yeast strains obtained with primer OPA-18. (Lane a) 1 kb marker. (Lane b) Reference strain, S. cerevisiae ATCC 9080. (Lane c) Yeast strain in homogenized Makgeolli (Lane d) Yeast strain in LHBP-treated Makgeolli. (B) Carbon source utilization tests for yeast identification in processed Makgeolli.

Figure 6

Effect of LHBP treatment on inactivation of S. cerevisiae strains. Makgeolli samples were applied to the LHBP program based on optimal condition (i.e., homogenized twice at 25.0 MPa). After the LHBP process, the number of target colonies was converted to logarithm (base 10) of colony forming units per gram (log CFU/g). All data shown are the mean values of triplicate observations.