Development Yeast Strains to Manufacture a Makgeolli and High Shearing Homogenization Process for Makgeolli Manufacturing

Abstract

A variety of nuruk was collected from all around of provinces in Korea, and their microflora profiles were analyzed at the species level. Total 42 nuruk were collected and when viable cell numbers in nuruk were enumerated, average cell numbers of bacteria, fungi, yeast, and lactic acid bacteria from all nuruk were 7.21, 7.91, 3.49, and 4.88 log CFU/10 g, respectively. There were no significant differences in viable cell numbers of bacteria or fungi according to regions collected. Bacillus amyloliquefaciens and B. subtilis were predominant bacterial strains in most nuruk. A significant portion of nuruk, 13 out of 42 nuruk, contained food-borne pathogens such as B. cereus or Cronobacter sakazakii. There were various species of lactic acid bacteria such as Enterococcus faecium and Pediococcus pentosaceus in nuruk. It was unexpectedly found that only 13 nuruk among 42 nuruk contained Aspergillus oryzae, the representative saccharifying fungi in makgeolli, whereas a fungi Lichtheimia corymbifera was widely distributed in nuruk. It was also found that Pichia jadinii was predominant yeast strain in most nuruk, but the representative alcohol fermentation strain, Saccharomyces cerevisiae, was isolated from only 18 out of 42 nuruk. These results suggested that a variety of species of fungi and yeast were distributed in nuruk and involved in the fermentation of makgeolli. In this study, total 64 bacterial species, 39 fugal species, and 15 yeast species were identified from nuruk. Among these strains, 37 bacterial species, 20 fungal species, and 8 yeast species were distributed less than 0.1%. The applicability of Saccharomycopsis fibuligera CJN1020, Pichia jadinii CJN1287 and Saccharomyces cerevisiae CJN1514 isolated from Korean nuruk to manufacture makgeolli was investigated. These yeasts were all suitable for the manufacture of both white rice makgeolli by a steam method and white rice-brown rice-wheat flour (WBW) makgeolli by a complex method. Upon physicochemical evaluation, there was no difference of final ethanol concentration between white rice makgeolli and WBW makgeolli. But it had difference of final ethanol yields according to yeasts species. Final ethanol yields by Saccharomycopsis fibuligera and Pichia jadinii were 16% each and by Saccharomyces cerevisiae was 18%. Upon sensory evaluation, WBW makgeolli samples received higher scores than white rice makgeolli in overall preference. GC/MS analysis revealed that the aromatic compounds of WBW makgeolli were richer than those of white rice makgeolli. These results suggest that the complex method is suitable for manufacturing makgeolli using brown rice and wheat flour. High shearing homogenization (HSH), as an alternative of Holder pasteurization, was applied to inactivate the yeast levels in the fermented rice wine (FRW). The storage stability of FRW is very important because the fermentation of rice wine during distribution is still progressed. Holder pasteurization traditionally used might loss nutrients and quality of FRW. In HSH, the applied pressure at 25000 psi with 5 circulations of treatment reduced over 4 log cycles of yeast. In addition, the effects of HSH and thermal treatment on the inactivation of yeast and volatile components in the FRW were compared. The D-values of yeast in FRW were 28 min at 50 °C and 4.18 min at 65 °C. The HSH at 25000 psi with 5 circulations were equivalent to the thermal treatment at 80 °C for 3 min. Total 34 volatile components were identified, including 8 alcohols, 18 esters, 2 acids, 1 carbonyls, 3 hydrocarbons, 2 miscellaneous. Volatile components having fruit aroma were found more in the samples with HSH, while components having fatty and oily characters were more detected in the samples with thermal treatments. We studied the effect of high shearing process (HSP) on the flow behavior of a colloidal dispersion obtained from the coarse filtered rice fermentation. The translucency, a key major characteristic of the dispersion, is kinetically changed due to the settling of particles. To delay the phase separation of particles, HSP was applied to the colloidal dispersion. The applied pressure of HSP was varied from 7000 psi to 25000 psi, and for 7000 psi and 25000 psi the process was repeated. The mean particle sizes were dropped from 129.69 μm to about 5.24 μm when HSP was applied. In addition to the particle size, viscosity, volume fraction, settling velocity, turbidity and ζ-potential were measured to understand the flow behavior of the dispersion. The viscosity and the volume fraction were inversely proportional to the particle size. The settling velocities were reduced by applying HSP from ~4 x 10-2 m/s to ~3 x 10-7 m/s. The phase separation from solid particles in the dispersion was significantly delayed by applying HSP.